[Federal Register Volume 89, Number 169 (Friday, August 30, 2024)]
[Proposed Rules]
[Pages 70698-71073]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-14824]
Vol. 89
Friday,
No. 169
August 30, 2024
Part II
Department of Labor
-----------------------------------------------------------------------
Occupational Safety and Health Administration
-----------------------------------------------------------------------
29 CFR Part 1910, 1915, 1917, et al.
Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings;
Proposed Rule
Federal Register / Vol. 89, No. 169 / Friday, August 30, 2024 /
Proposed Rules
-----------------------------------------------------------------------
DEPARTMENT OF LABOR
Occupational Safety and Health Administration
29 CFR Part 1910, 1915, 1917, 1918, 1926, and 1928
[Docket No. OSHA-2021-0009]
RIN 1218-AD39
Heat Injury and Illness Prevention in Outdoor and Indoor Work
Settings
AGENCY: Occupational Safety and Health Administration (OSHA), Labor.
ACTION: Notice of proposed rulemaking (NPRM); request for comments.
-----------------------------------------------------------------------
SUMMARY: OSHA is proposing to issue a new standard, titled Heat Injury
and Illness Prevention in Outdoor and Indoor Work Settings. The
standard would apply to all employers conducting outdoor and indoor
work in all general industry, construction, maritime, and agriculture
sectors where OSHA has jurisdiction, with some exceptions. It would be
a programmatic standard that would require employers to create a plan
to evaluate and control heat hazards in their workplace. It would more
clearly set forth employer obligations and the measures necessary to
effectively protect employees from hazardous heat. OSHA requests
comments on all aspects of the proposed rule.
DATES: Comments to this NPRM (including requests for a hearing) and
other information must be submitted by December 30, 2024.
Informal public hearing: OSHA will schedule an informal public
hearing on the proposed rule if requested during the comment period. If
a hearing is requested, the location and date of the hearing,
procedures for interested parties to notify the agency of their
intention to participate, and procedures for participants to submit
their testimony and documentary evidence will be announced in the
Federal Register.
ADDRESSES:
Written comments: You may submit comments and attachments,
identified by Docket No. OSHA-2021-0009, electronically at https://www.regulations.gov, which is the Federal e-Rulemaking Portal. Follow
the instructions online for making electronic submissions. After
accessing ``all documents and comments'' in the docket (Docket No.
OSHA-2021-0009), check the ``proposed rule'' box in the column headed
``Document Type,'' find the document posted on the date of publication
of this document, and click the ``Comment Now'' link. When uploading
multiple attachments to regulations.gov, please number all of your
attachments because regulations.gov will not automatically number the
attachments. This will be very useful in identifying all attachments.
For example, Attachment 1--title of your document, Attachment 2--title
of your document, Attachment 3--title of your document. For assistance
with commenting and uploading documents, please see the Frequently
Asked Questions on regulations.gov.
Instructions: All submissions must include the agency's name and
the docket number for this rulemaking (Docket No. OSHA-2021-0009). All
comments, including any personal information you provide, are placed in
the public docket without change and may be made available online at
https://www.regulations.gov. Therefore, OSHA cautions commenters about
submitting information they do not want made available to the public,
or submitting materials that contain personal information (either about
themselves or others), such as Social Security Numbers and birthdates.
Docket citations: This Federal Register document references
material in Docket No. OSHA-2021-0009, which is the docket for this
rulemaking.
Citations to documents: The docket referenced most frequently in
this document is the docket for this rulemaking, docket number OSHA-
2021-0009, cited as Document ID OSHA-2021-0009. Documents in the docket
get an individual document identification number, for example ``OSHA-
2021-0009-0047.'' Because this is the most frequently cited docket, the
citation is shortened to indicate only the document number. The example
is cited in the NPRM as ``Document ID 0047.''
Documents cited in this NPRM are available in the rulemaking docket
(Docket ID OSHA-2021-0009). They are available to read and download by
searching the docket number or document ID number at https://www.regulations.gov. Each docket index lists all documents in that
docket, including public comments, supporting materials, meeting
transcripts, and other documents. However, some documents (e.g.,
copyrighted material) in the dockets are not available to read or
download from that website. All documents in the dockets are available
for inspection at the OSHA Docket Office. This information can be used
to search for a supporting document in the docket at
www.regulations.gov. Contact the OSHA Docket Office at (202) 693-2350
(TTY number: 877-889-5627) for assistance in locating docket
submissions.
FOR FURTHER INFORMATION CONTACT:
For press inquiries: Contact Frank Meilinger, Director, OSHA Office
of Communications, Occupational Safety and Health Administration;
telephone: (202) 693-1999; email: meilinger.francis2@dol.gov.
General information and technical inquiries: Contact Stephen
Schayer, Director, Office of Physical Hazards and Others, OSHA
Directorate of Standards and Guidance; telephone: (202) 693-1950;
email: osha.dsg@dol.gov.
Copies of this Federal Register notice: Electronic copies are
available at https://www.regulations.gov. This Federal Register notice,
as well as news releases and other relevant information, also are
available at OSHA's web page at https://www.osha.gov.
The docket is available at https://www.regulations.gov, the Federal
eRulemaking Portal. A ``100-word summary'' is also available on https://www.regulations.gov. For additional information on submitting items
to, or accessing items in, the docket, please refer to the ADDRESSES
section of this NPRM. Most exhibits are available at https://www.regulations.gov; some exhibits (e.g., copyrighted material) are not
available to download from that web page. However, all materials in the
dockets are available for inspection and copying at the OSHA Docket
Office.
SUPPLEMENTARY INFORMATION:
Table of Contents
I. Executive Summary
II. Pertinent Legal Authority
A. Introduction
B. Significant Risk
C. Feasibility
D. High Degree of Employee Protection
III. Background
A. Introduction
B. Need for Proposal
C. Events Leading to Proposal
D. Other Standards
IV. Health Effects
A. Introduction
B. General Mechanisms of Heat-Related Health Effects
C. Identifying Cases of Heat-Related Health Effects
D. Heat-Related Deaths
E. Heat Stroke
F. Heat Exhaustion
G. Heat Syncope
H. Rhabdomyolysis
I. Hyponatremia
J. Heat Cramps
K. Heat Rash
L. Heat Edema
M. Kidney Health Effects
N. Other Health Effects
O. Factors That Affect Risk for Heat-Related Health Effects
P. Heat-Related Injuries
V. Risk Assessment
A. Risk Assessment
B. Basis for Initial and High Heat Triggers
C. Risk Reduction
VI. Significance of Risk
A. Material Harm
B. Significant Risk
C. Preliminary Conclusions
VII. Explanation of Proposed Requirements
A. Paragraph (a) Scope and Application
B. Paragraph (b) Definitions
C. Paragraph (c) Heat Injury and Illness Prevention Plan
D. Paragraph (d) Identifying Heat Hazards
E. Paragraph (e) Requirements at or Above the Initial Heat
Trigger
F. Paragraph (f) Requirements at or Above the High Heat Trigger
G. Paragraph (g) Heat Illness and Emergency Response and
Planning
H. Paragraph (h) Training
I. Paragraph (i) Recordkeeping
J. Paragraph (j) Requirements Implemented at no Cost to
Employees
K. Paragraph (k) Dates
L. Paragraph (l) Severability
VIII. Preliminary Economic Analysis and Initial Regulatory
Flexibility Analysis
A. Market Failure and Need for Regulation
B. Profile of Affected Industries
C. Costs of Compliance
D. Economic Feasibility
E. Benefits
F. Initial Regulatory Flexibility Analysis
G. Distributional Analysis
H. Appendix A. Description of the Cost Savings Approach
I. Appendix B. Review of Literature on Effects of Heat Exposure
on Non-Health Outcomes
J. Appendix C. Heat Exposure Methodology Used in Distributional
Analysis
K. Appendix D. Definitions of Core Industry Categories Used in
Cost Analysis
IX. Technological Feasibility
X. Additional Requirements
A. Unfunded Mandates Reform Act, 2 U.S.C. 1501 et seq.
B. Consultation and Coordination With Indian Tribal Governments/
Executive Order 13175
C. Consultation With the Advisory Committee on Construction
Safety and Health
D. Environmental Impacts
E. Consensus Standards
F. Incorporation by Reference
G. Protection of Children From Environmental Health Risks and
Safety Risks
H. Federalism
I. Requirements for States With OSHA-Approved State Plans
J. OMB Review Under the Paperwork Reduction Act of 1995
XI. Authority and Signature
I. Executive Summary
Heat is the leading cause of death among all weather-related
phenomena in the United States. Excessive heat in the workplace can
cause a number of adverse health effects, including heat stroke and
even death, if not treated properly. Yet, there is currently no Federal
OSHA standard that regulates heat stress hazards in the workplace.
Although several governmental and non-governmental organizations have
published regulations and guidance to help protect workers from heat
hazards, OSHA believes that a mandatory Federal standard specific to
heat-related injury and illness prevention is necessary to address the
hazards posed by occupational heat exposure. OSHA has preliminarily
determined that this proposed rule would substantially reduce the risk
posed by occupational exposure to hazardous heat by clearly setting
forth employer obligations and the measures necessary to effectively
protect exposed workers.
OSHA is proposing this standard pursuant to the Occupational Safety
and Health Act of 1970, 29 U.S.C. 651 et seq. (OSH Act or Act). The Act
authorizes the agency to issue safety or health standards that are
``reasonably necessary or appropriate'' to provide safe or healthful
employment and places of employment (29 U.S.C. 652(8)). A standard is
reasonably necessary or appropriate when a significant risk of material
harm exists in the workplace and the standard would substantially
reduce or eliminate that workplace risk. Applicable legal requirements
are more fully discussed in Section II., Pertinent Legal Authority.
Workers in both outdoor and indoor work settings without adequate
climate controls are at risk of hazardous heat exposure. Certain heat-
generating processes, machinery, and equipment (e.g., hot tar ovens,
furnaces) can also cause heat hazards when cooling measures are not in
place. Based on the best available evidence, as discussed in this
preamble, OSHA has preliminarily determined that exposure to hazardous
heat in the workplace poses a significant risk of serious injury and
illness. This finding of a significant risk of material harm is based
on the health consequences associated with exposure to heat (see
Section IV., Health Effects) as well as the risk assessment (see
Section V., Risk Assessment and Section VI., Significance of Risk). In
Section V.C., Risk Reduction, OSHA demonstrates the efficacy of the
controls relied on in this proposed rule to reduce the risk of heat-
related injury and illness in the workplace. Employees working in
workplaces without these controls are at higher risk of severe health
outcomes from exposure to hazardous heat.
On October 27, 2021, OSHA published in the Federal Register an
advance notice of proposed rulemaking (ANPRM) for Heat Injury and
Illness Prevention in Outdoor and Indoor Work Settings (86 FR 59309).
The ANPRM outlined key issues and challenges in occupational heat-
related injury and illness prevention and aimed to collect evidence,
data, and information critical to informing how OSHA proceeds in the
rulemaking process. The ANPRM included background information on
injuries, illnesses, and fatalities due to heat, underreporting, scope,
geographic region, and inequality in exposures and outcomes. The ANPRM
also covered existing heat injury and illness prevention efforts
including OSHA's efforts, the National Institute for Occupational
Safety and Health (NIOSH) criteria documents, State standards, and
other standards.
OSHA received 965 unique public comments, which largely supported
the need for continued rulemaking. The agency then worked with the
National Advisory Committee on Occupational Safety and Health (NACOSH)
to assemble a Heat Injury and Illness Prevention Work Group. The Work
Group was tasked with evaluating stakeholder input to the ANPRM and
developing recommendations on potential elements of a proposed heat
injury and illness prevention standard. The Work Group presented its
recommendations on potential elements of a proposed heat injury and
illness prevention standard for consideration by the full NACOSH
committee. On May 31, 2023, NACOSH amended the report to ask OSHA to
include a model written plan and then unanimously voted to submit the
Work Group's recommendations to the Secretary of Labor.
In accordance with the requirements of the Small Business
Regulatory Enforcement Fairness Act (SBREFA), OSHA next convened a
Small Business Advocacy Review (SBAR) Panel in August 2023. The Panel,
comprised of members from the Small Business Administration's (SBA)
Office of Advocacy, OSHA, and OMB's Office of Information and
Regulatory Affairs, heard comments directly from Small Entity
Representatives (SERs) on the potential impacts of a heat-specific
standard. The Panel received advice and recommendations from the SERs
and reported its findings and recommendations to OSHA. OSHA has taken
the SER's comments and the Panel's findings and recommendations into
consideration in the development of this proposed rule (see Section
VIII.F., Initial Regulatory Flexibility Analysis).
In accordance with 29 CFR parts 1911 and 1912, OSHA also consulted
with and considered feedback from the Advisory Committee on
Construction
Safety and Health (ACCSH). On April 24, 2024, the Committee unanimously
passed a motion recommending that OSHA proceed expeditiously with
proposing a standard on heat injury and illness prevention. In
addition, in accordance with Executive Order 13175, Consultation and
Coordination with Indian Tribal Governments, 65 FR 67249 (Nov. 6,
2000), OSHA held a listening session on May 15, 2024, with Tribal
representatives regarding this Heat Injury and Illness Prevention in
Outdoor and Indoor Work Settings rulemaking and provided an opportunity
for the representatives to offer feedback.
The proposed rule is a programmatic standard that requires
employers to create a heat injury and illness prevention plan to
evaluate and control heat hazards in their workplace. It establishes
requirements for identifying heat hazards, implementing engineering and
work practice control measures at or above two heat trigger levels
(i.e., an initial heat trigger and a high heat trigger), developing and
implementing a heat illness and emergency response plan, providing
training to employees and supervisors, and retaining records. The
proposed rule would apply to all employers conducting outdoor and
indoor work in all general industry, construction, maritime, and
agriculture sectors, with some exceptions (see Section VII.A.,
Paragraph (a) Scope and Application). Throughout this document, OSHA
seeks input on alternatives and potential exclusions.
Organizations affected by heat hazards vary significantly in size
and workplace activities. Accordingly, many of the provisions of the
proposed standard provide flexibility for affected employers to choose
the control measures most suited to their workplace. The flexible
nature of the proposed rule may be particularly beneficial to small
organizations with limited resources.
Additionally, to determine whether the proposed rule is feasible
for affected employers, and in accordance with Executive Orders 12866
and 13563, the Regulatory Flexibility Act (RFA), and the Unfunded
Mandates Reform Act (2 U.S.C 1501 et seq.), OSHA has prepared a
Preliminary Economic Analysis (PEA), including an Initial Regulatory
Flexibility Analysis (see Section VIII., Preliminary Economic Analysis
and Initial Regulatory Flexibility Analysis). Supporting materials
prepared by OSHA are available in the public docket for this
rulemaking, Document ID OSHA-2021-0009, through regulations.gov.
II. Pertinent Legal Authority
A. Introduction
In the Occupational Safety and Health Act, 29 U.S.C. 651 et seq.,
Congress authorized the Secretary of Labor (``the Secretary'') ``to set
mandatory occupational safety and health standards applicable to
businesses affecting interstate commerce'' (29 U.S.C. 651(b)(3); see
Nat'l Fed'n of Indep. Bus. v. Dep't of Labor, 595 U.S. 109, 117 (2022)
(per curiam); see also 29 U.S.C. 654(a)(2) (requiring employers to
comply with OSHA standards)). Section 6(b) of the Act authorizes the
promulgation, modification or revocation of occupational safety or
health standards pursuant to detailed notice and comment procedures (29
U.S.C. 655(b)).
Section 3(8) of the Act defines a safety or health standard as a
standard which requires conditions, or the adoption or use of one or
more practices, means, methods, operations, or processes ``reasonably
necessary or appropriate'' to provide safe or healthful employment and
places of employment (29 U.S.C. 652(8)). A standard is reasonably
necessary or appropriate within the meaning of section 3(8) when a
significant risk of material harm exists in the workplace and the
standard would substantially reduce or eliminate that workplace risk
(see Indus. Union Dep't, AFL-CIO v. Am. Petroleum Inst., 448 U.S. 607
(1980) (``Benzene'')). OSHA's authority extends to, for example,
removing workers from environments where workplace hazards exist (see,
e.g., United Steelworkers of America v. Marshall, 647 F.2d 1189, 1228-
38 (D.C. Cir. 1981); 29 CFR 1910.1028(i)(8); 29 CFR 1910.1024(l); cf.
Whirlpool Corp. v. Marshall, 445 U.S. 1, 12 (1980) (upholding
regulation allowing employees to refuse dangerous work in certain
circumstances because ``[t]he Act does not wait for an employee to die
or become injured.'').
In addition to the requirement that each standard address a
significant risk, standards must also be technologically feasible (see
UAW v. OSHA, 37 F.3d 665, 668 (D.C. Cir. 1994)). A standard is
technologically feasible when the protective measures it requires
already exist, when available technology can bring the protective
measures into existence, or when that technology is reasonably likely
to develop (see Am. Iron and Steel Inst. v. OSHA, 939 F.2d 975, 980
(D.C. Cir. 1991)).
Finally, a standard must be economically feasible (see Forging
Indus. Ass'n v. Secretary of Labor, 773 F.2d 1436, 1453 (4th Cir.
1985)). A standard is economically feasible if industry can absorb or
pass on the costs of compliance without threatening its long-term
profitability or competitive structure (see American Textile Mfrs.
Inst., Inc., 452 U.S. 490, 530 n.55 (``Cotton Dust'')). Each of these
requirements is discussed further below.
B. Significant Risk
As noted above, OSHA's workplace safety and health standards must
address a significant risk of material harm that exists in the
workplace (see Benzene, 448 U.S. at 614-15). The agency's risk
assessments are based on the best available evidence, and its final
conclusions are made only after considering all information in the
rulemaking record. Reviewing courts have upheld the Secretary's
significant risk determinations where supported by substantial evidence
and ``a reasoned explanation for [their] policy assumptions and
conclusions'' (Bldg & Constr. Trades Dep't v. Brock, 838 F.2d 1258,
1266 (D.C. Cir. 1988) (``Asbestos II'')).
The Supreme Court in Benzene explained that ``[i]t is the agency's
responsibility to determine, in the first instance, what it considers
to be a `significant' risk'' (Benzene, 448 U.S. at 655). The Court
declined to ``express any opinion on the . . . difficult question of
what factual determinations would warrant a conclusion that significant
risks are present which make promulgation of a new standard reasonably
necessary or appropriate'' (Benzene, 448 U.S. at 659). The Court
stated, however, that the substantial evidence standard applicable to
OSHA's significant risk determination (see 29 U.S.C. 655(b)(f)) does
not require the agency ``to support its finding that a significant risk
exists with anything approaching scientific certainty'' (Benzene, 448
U.S. at 656). Rather, OSHA may rely on ``a body of reputable scientific
thought'' to which ``conservative assumptions in interpreting the
data'' may be applied, ``risking error on the side of overprotection''
(Benzene, 448 U.S. at 656). The D.C. Circuit has further explained that
OSHA may thus act with a pronounced bias towards worker safety in
making its risk determinations (Asbestos II, 838 F.2d at 1266). The
Supreme Court also recognized that the determination of what
constitutes ``significant risk'' is ``not a mathematical straitjacket''
and will be ``based largely on policy considerations'' (Benzene, 448
U.S. at 655 & n.62).
Once OSHA makes its significant risk finding, the standard it
promulgates must be ``reasonably necessary or appropriate'' to reduce
or eliminate that
risk (29 U.S.C. 652(8)). In choosing among regulatory alternatives,
however, ``[t]he determination that [one standard] is appropriate, as
opposed to a marginally [more or less protective] standard, is a
technical decision entrusted to the expertise of the agency'' (Nat'l
Mining Ass'n v. Mine Safety and Health Admin., 116 F.3d 520, 528 (D.C.
Cir. 1997) (analyzing a Mine Safety and Health Administration standard
under the Benzene significant risk standard)).
C. Feasibility
The statutory mandate to consider the feasibility of the standard
encompasses both technological and economic feasibility; OSHA has
performed these analyses primarily on an industry-by-industry basis
(United Steelworkers of Am., AFL-CIO-CLC v. Marshall, 647 F.2d 1189,
1264, 1301 (D.C. Cir. 1980) (``Lead I'')). The agency has also used
application groups, defined by common tasks, as the structure for its
feasibility analyses (Pub. Citizen Health Research Grp. v. OSHA, 557
F.3d 165, 177-79 (3d Cir. 2009)). The Supreme Court has broadly defined
feasible as ``capable of being done'' (Cotton Dust, 452 U.S. at 509-
10).
I. Technological Feasibility
A standard is technologically feasible if the protective measures
it requires already exist, can be brought into existence with available
technology, or can be created with technology that can reasonably be
expected to be developed (Lead I, 647 F.2d at 1272; Amer. Iron & Steel
Inst. v. OSHA, 939 F.2d 975, 980 (D.C. Cir. 1991) (``Lead II'')).
Courts have also interpreted technological feasibility to mean that a
typical firm in each affected industry or application group will
reasonably be able to implement the requirements of the standard in
most operations most of the time (see Public Citizen v. OSHA, 557 F.3d
165, 170-71 (3d Cir. 2009); Lead I, 647 F.2d at 1272; Lead II, 939 F.2d
at 990)). OSHA's standards may be ``technology forcing,'' so long as
the agency gives an industry a reasonable amount of time to develop new
technologies to comply with the standard. Thus, OSHA is not bound by
the ``technological status quo'' (Lead I, 647 F.2d at 1264).
II. Economic Feasibility
In addition to technological feasibility, OSHA is required to
demonstrate that its standards are economically feasible. A reviewing
court will examine the cost of compliance with an OSHA standard ``in
relation to the financial health and profitability of the industry and
the likely effect of such costs on unit consumer prices'' (Lead I, 647
F.2d at 1265 (citation omitted)). As articulated by the D.C. Circuit in
Lead I, ``OSHA must construct a reasonable estimate of compliance costs
and demonstrate a reasonable likelihood that these costs will not
threaten the existence or competitive structure of an industry, even if
it does portend disaster for some marginal firms'' (Lead I, 647 F.2d at
1272). A reasonable estimate entails assessing ``the likely range of
costs and the likely effects of those costs on the industry'' (Lead I,
647 F.2d at 1266). As with OSHA's consideration of scientific data and
control technology, however, the estimates need not be precise (Cotton
Dust, 452 U.S. at 528-29 & n.54), as long as they are adequately
explained.
OSHA standards satisfy the economic feasibility criterion even if
they impose significant costs on regulated industries so long as they
do not cause massive economic dislocations within a particular industry
or imperil the very existence of the industry (Lead II, 939 F.2d at
980; see also Lead I, 647 F.2d at 1272; Asbestos I, 499 F.2d. at 478).
As with its other legal findings, OSHA ``is not required to prove
economic feasibility with certainty, but is required to use the best
available evidence and to support its conclusions with substantial
evidence'' (Lead II, 939 F.2d at 980-81 (citing Lead I, 647 F.2d at
1267)).
In addition to determining economic feasibility, OSHA estimates the
costs and benefits of its proposed and final rules to ensure compliance
with other requirements such as those in Executive Orders 12866 and
13563.
D. High Degree of Employee Protection
Safety standards must provide a high degree of employee protection
to be consistent with the purpose of the Act (see Control of Hazardous
Energy Sources (Lockout/Tagout) Final Rule, Supplemental Statement of
Reasons, 58 FR 16612, 16614-15 (March 30, 1993)). OSHA has
preliminarily determined that this proposed standard is a safety
standard because the health effects associated with exposure to
occupational heat are generally acute. As explained in Section IV.,
Health Effects, the proposed standard aims to address the numerous
acute health effects of occupational exposure to hazardous heat. These
include, among other things, heat stroke, heat exhaustion, heat
syncope, and physical injuries (e.g., falls) due to fatigue or other
heat-related impairments. These harms occur after relatively short-term
exposures to hazardous heat and are typically apparent at the time of
the exposure or shortly thereafter. Consequently, the link between
these harms and heat exposures is also often apparent and they do not
implicate the concerns about latent, hidden harms that underly health
standards (see Benzene, 448 U.S. at 649 n. 54; UAW v. OSHA, 938 F.2d
1310, 1313 (D.C. Cir. 1991) (``Lockout/Tagout I''); National Grain &
Feed Ass'n v. OSHA, 866 F.2d 717, 733 (5th Cir. 1989) (``Grain
Dust'')).
Finally, although OSHA acknowledges that there is growing evidence
occupational exposure to hazardous heat may lead to some chronic
adverse health outcomes like chronic kidney disease, much of the
science in this area is still developing (see Section IV., Health
Effects). In any event, the agency expects that addressing the acute
hazards posed by heat would also protect workers from potential chronic
health outcomes by reducing workers' overall heat strain.
III. Background
A. Introduction
The Occupational Safety and Health Administration (OSHA) is
proposing a new standard to protect outdoor and indoor workers from
hazardous heat in the workplace. OSHA promulgates and enforces
occupational safety and health standards under authority granted by the
Occupational Safety and Health (OSH) Act of 1970 (29 U.S.C. 651 et
seq.).
In the absence of a Federal occupational heat standard, five States
have issued heat injury and illness prevention regulations to protect
employees exposed to heat hazards in the workplace: Minnesota (Minn. R.
5205.0110 (1997)); California (Cal. Code of Regs. tit. 8, section 3395
(2005)); Oregon (Or. Admin. R. 437-002-0156 (2022); Or. Admin. R. 437-
004-1131 (2022)); Colorado (7 Colo. Code Regs. section 1103-15 (2022));
and Washington (Wash. Admin. Code sections 296-62-095 through 296-62-
09560; 296-307-097 through 296-307-09760 (2023)). Although Minnesota
was the first State to adopt a standard covering employees exposed to
indoor environmental heat conditions, California was the first State to
adopt a standard covering employees exposed to outdoor environmental
heat conditions. Washington, Oregon, and Colorado have since enacted
similar regulations to California's, requiring employers to implement
controls and monitor for signs and symptoms of heat-related injury or
illness, among other requirements. In 2023, California proposed a new
standard that would cover indoor work environments (California, 2023).
In 2024, Maryland
published a proposed standard that would cover both outdoor and indoor
work environments (Maryland, 2024).
Workers in many industries are at risk for heat-related injury and
illness stemming from hazardous heat exposure (see Section V.A., Risk
Assessment). While the general population may be able to avoid and
limit prolonged heat exposure, workers across a wide range of indoor
and outdoor settings often are required to work through shifts with
prolonged heat exposure. Some workplaces have heat generation from
industrial processes and expose workers to sources of radiant heat,
such as ovens and furnaces. Additionally, employers may not take
adequate steps to protect their employees from exposure to hazardous
heat (e.g., not providing rest breaks in cool areas). Many work
operations also require the use of personal protective equipment (PPE)
that can reduce the worker's heat tolerance because it can decrease the
body's ability to cool down. Workers may also face pressure, or
incentivization through pay structures, to push through and continue
working despite high heat exposure, which can increase the risk of
heat-related injury and illness (Billikopf and Norton, 1992; Johansson
et al., 2010; Spector et al., 2015; Pan et al., 2021).
OSHA uses several terms related to excessive heat exposure
throughout this proposal. Heat stress is the combined load of heat that
a person experiences from sources of heat (i.e., metabolic heat and the
environment) and heat retention (e.g., from clothing or personal
protective equipment). Heat strain refers to the body's response to
heat stress (American Conference of Governmental Industrial Hygienists
(ACGIH), 2023). Heat-related illness means adverse clinical health
outcomes that occur due to heat exposure, such as heat exhaustion or
heat stroke. Heat-related injury means an injury linked to heat
exposure, such as a fall or cut. OSHA sometimes refers to these
collectively as ``heat-related injuries and illnesses.''
B. Need for Proposal
Occupational heat exposure affects millions of workers in the
United States. Each year, thousands of workers experience heat-related
injuries and illnesses, and some of these cases result in fatalities
(BLS, 2023b; BLS, 2024c). OSHA has relied on the General Duty Clause of
the OSH Act (discussed further below), as well as enforcement emphasis
programs and hazard alerts and other guidance, to protect workers and
inform employers of their legal obligations. However, a standard
specific to heat-related injury and illness prevention would more
clearly set forth enforceable employer obligations and the measures
necessary to effectively protect employees from hazardous heat.
Workers in both outdoor and indoor work settings without adequate
climate controls are at risk of hazardous heat exposure. In addition to
weather-related heat, certain heat-generating processes, machinery, and
equipment (e.g., hot tar ovens, furnaces) can cause hazardous heat
exposure when cooling measures are not in place. An evaluation of 66
heat-related illness enforcement investigations from 2011-2016 found
heat-related injuries and illnesses, including fatalities, occurring in
both outdoor (n=34) and indoor (n=29) work environments (Tustin et al.,
2018a). Excessive heat exacerbates existing health conditions like
asthma, diabetes, kidney failure, and heart disease, and can cause heat
stroke and death if not treated properly and promptly. Some groups may
be more likely to experience adverse health effects from heat, such as
pregnant workers (NIOSH, 2024), while others are disproportionately
exposed to hazardous levels of heat, such as workers of color in
essential jobs, who are more often employed in work settings with a
high risk of hazardous heat exposure (Gubernot et al., 2015).
The Bureau of Labor Statistics (BLS), in its Census of Fatal
Occupational Injuries, documented 1,042 U.S. worker deaths due to
occupational exposure to environmental heat from 1992-2022, with an
average of 34 fatalities per year during that period (BLS, 2024c). In
2022 alone, BLS reported 43 work-related deaths due to environmental
heat exposure (BLS, 2024c). The BLS Annual Survey of Occupational
Injuries and Illnesses (SOII) estimates 33,890 work-related heat
injuries and illnesses involving days away from work from 2011-2020,
which is an average of 3,389 injuries and illnesses occurring each year
during this period (BLS, 2023b).
Workers across hundreds of industries are at risk for hazardous
heat exposure and resulting heat-related injuries and illnesses. From
January 1, 2017, to December 31, 2022, 1,054 heat-related injuries,
illnesses, and fatalities were reported to and investigated by OSHA,
including 625 heat-related hospitalizations and 211 heat-related
fatalities, as well as 218 heat-related injuries and illnesses that did
not result in hospitalization. During this time, hospitalizations
occurred most frequently in construction, manufacturing, and postal and
delivery service. Fatalities were most frequently reported in
construction, landscaping, agriculture, manufacturing, and postal and
delivery service (as identified by 2-digit NAICS codes).
However, as explained in Section V.A., Risk Assessment, these
statistics likely do not capture the true magnitude and prevalence of
heat-related injuries, illnesses, and fatalities. Recent studies
demonstrate significant undercounting of occupational injuries and
illnesses by both the BLS SOII and OSHA's enforcement data. One reason
for this undercounting is that the BLS SOII only reports the number of
heat-related injuries and illnesses involving days away from work and
thus does not capture the full picture of heat-related injuries and
illnesses. An examination of workers' compensation claims in
California, which include more than only cases involving days away from
work, identified 3 to 6 times the number of annual heat-related illness
and injury cases than reported by BLS SOII (Heinzerling et al., 2020).
In addition, evidence has shown significant underreporting as employers
and employees are disincentivized from reporting injuries and illnesses
due to several factors, including potential increases in workers'
compensation costs or impacts on the employer's reputation, or an
employee's fear of retaliation or lack of awareness of their right to
speak out about workplace conditions (BLS, 2020b).
Heat-related injuries and illnesses may present unique challenges
to surveillance efforts. As the nature of heat-related symptoms (e.g.,
headache, fatigue) vary, some cases may be attributed to other
illnesses rather than heat (as discussed in Section IV., Health
Effects). Furthermore, heat is not always identified as a contributing
factor to fatality, as heat exposure may exacerbate existing medical
conditions and medical professionals may not witness the symptoms and
events preceding death (Luber et al., 2006).
Finally, exposure to heat can interfere with routine occupational
tasks and impact workers' psychomotor and mental performance, which can
lead to workplace injuries. Particularly, heat can impair performance
of job tasks related to complex cognitive function (Hancock and
Vasmatzidis, 2003; Piil et al., 2017) and reduce decision making
abilities (Ramsey et al., 1983; Xiang et al., 2014a) and productivity
(Foster et al., 2021). A growing body of evidence has demonstrated that
heat-induced impairments may result in significant occupational
injuries that are not currently factored into official statistics for
heat-related cases (Spector et al., 2016; Calkins et al., 2019;
Dillender, 2021; Park et al., 2021). See Section V.A., Risk Assessment,
for further
discussion on underreporting of heat-related injuries, illnesses, and
fatalities.
While a significant percentage of heat-related incidents are
unreported, OSHA's investigations of reported heat-related fatalities
point to many gaps in employee protections. OSHA has identified the
following circumstances in its review of 211 heat-related fatality
investigations from 2017-2022: employees left alone by employers after
symptoms started; employers not providing adequate medical attention to
employees with symptoms; employers preventing employees from taking
rest breaks; employers not providing water on-site; employers not
providing on-site access to shade; employers not providing cooling
measures on-site; and employers not having programs to acclimatize
employees to hot work environments (https://www.osha.gov/fatalities).
OSHA has relied on multiple mechanisms to protect employees from
hazardous heat, however, OSHA's efforts to prevent the aforementioned
circumstances have been met with challenges without a heat-specific
standard (as discussed in Section III.C.III., OSHA's Heat-Related
Enforcement).
Many U.S. States run their own OSHA-approved State Plans (e.g.,
State heat standards, voluntary consensus standards) (see Section
III.D., Other Standards), however OSHA has preliminarily determined
that this standard is still needed to protect workers from the
persistent and serious hazards posed by occupational heat exposure. As
explained in Section VI., Significance of Risk, OSHA has preliminarily
determined that a significant risk of material harm from occupational
exposure to hazardous heat exists, and issuance of this standard would
substantially reduce that risk. Therefore, to more clearly set forth
employer obligations and the measures necessary to more effectively
protect employees from hazardous heat, and reduce the number and
frequency of occupational injuries, illness, and fatalities caused by
exposure to hazardous heat, OSHA is proposing a Federal standard for
Heat Injury and Illness Prevention for Outdoor and Indoor Work
Settings.
C. Events Leading to the Proposal
I. History of Heat as a Recognized Occupational Hazard
Heat exposure has long been recognized as an occupational hazard.
For example, in the United States, the occupational hazards associated
with the construction of the Hoover Dam between 1931 and 1935 brought
attention to the effects of heat on worker health. The Bureau of
Reclamation reported that 14 dam workers and two others residing in the
work area died from ``heat prostration'' in 1931 (Bureau of
Reclamation, 2015). According to a local newspaper, temperatures at the
dam site that summer reached 140 [deg]F in the sun and 120 [deg]F in
the shade (Turk, 2018; Rogers, 2012). In response to the extreme heat
of the summer and other unsafe working conditions, the Industrial
Workers of the World convinced Hoover Dam workers to strike over safety
concerns (Turk, 2018; Rogers, 2012). Six Companies, the conglomerate of
companies hired by the Bureau of Reclamation to construct most of the
dam, was forced to make concessions, including protections against HRI
such as providing potable water in dormitories, bringing ice water to
workers at their work sites, and adding first aid stations closer to
the job site (Rogers, 2012). The heat-related deaths that occurred
during 1931 also prompted Harvard University researchers from the
Harvard Fatigue Laboratory to travel to the Hoover Dam and study the
relationship between hot, dry temperatures, physical performance, and
heart rate (Turk, 2018).
Heat-related illnesses were identified as a major concern for the
U.S. military in the 1940s and 1950s. Between 1942 and 1944, 198
soldiers died of heat stroke at U.S.-based training camps, 157 of which
did not have a known history of cardiac diseases or other conditions
that may predispose them to heat illness (Schickele, 1947, p. 236).
This led to investigations of the environmental conditions at the time
of these deaths, and eventually to the development of wet bulb globe
temperature (WBGT) to measure heat stress (Yaglou and Minard, 1957;
Minard, 1961; Department of the Army, 2022; Department of the Navy,
2023).
Research on the effects of occupational heat exposure continued in
the 1960s, as researchers conducted trials examining the physiological
effects of work at various temperatures (e.g., Lind, 1963). Findings
from these trials would eventually underpin the American Conference of
Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV),
as well as the National Institute of Occupational Safety and Health
(NIOSH) Recommended Exposure Limit (REL) (Dukes-Dobos and Henschel,
1973). ACGIH first proposed guidelines for a TLV in 1971, which were
later adopted in 1974.
Heat was recognized as a preventable workplace hazard in the
legislative history of the OSH Act. Senator Edmund Muskie submitted a
letter in support of the OSH Act into the Congressional record on
behalf of ``a distinguished group of citizens, including a former
Secretary of Labor and several noted scientists.'' (Senate Debate on S.
2193, Nov. 16, 1970), reprinted in Legislative History of the
Occupational Safety and Health Act of 1970, pp. 513-14 (1971)
(Committee Print) (``Leg. Hist.''). The letter states, ``Most
industrial diseases and accidents are preventable. Modern technological
and medical sciences are capable of solving the problems of noise,
dust, heat, fumes, and toxic substances in the plants. However,
existing legislation in this area does not begin to meet the problems''
(Leg. Hist., pp. 513-14).
In 1972, just two years after promulgation of the OSH Act, NIOSH
first recommended a potential OSHA heat standard in its Criteria for a
Recommended Standard (NIOSH, 1972). This criteria document, issued
under the authority of section 20(a) of the OSH Act, recommended an
OSHA standard based on a critical review of scientific and technical
information. In response, an OSHA Standards Advisory Committee on Heat
Stress was appointed in 1973 and presented recommendations for a
standard for work in hot environments in 1974. At the time, 12 of 15
members of the advisory committee agreed that occupational heat stress
warranted a standard (Ramsey, 1975).
NIOSH's criteria document for a recommended standard has since been
updated in 1986 (NIOSH, 1986) and again in 2016 (NIOSH, 2016). The 2016
criteria document recommends various provisions to protect workers from
heat stress, including rest breaks, hydration, shade, acclimatization
plans, and worker training (NIOSH, 2016). The 2016 criteria document
also recommends that no worker be ``exposed to combinations of
metabolic and environmental heat greater than'' the recommended alert
limit (RAL) for unacclimatized workers or the recommended exposure
limit (REL) for acclimatized workers). The document recommends that
environmental heat be assessed with measurements of WBGT (NIOSH, 2016).
A detailed report of the history of heat as a recognized
occupational hazard is available in the docket (ERG, 2024a). The report
summarizes historical documentation of occupational heat-related
illness beginning in ancient times and from the eighteenth century
through the regulatory interest in the twentieth century.
II. OSHA's Heat Injury and Illness Prevention Efforts
In 2011, OSHA issued a memorandum to inform regional administrators
and State Plan designees of inspection guidance for heat-related
illnesses (OSHA, 2011). That same year, OSHA launched the Heat Illness
Prevention Campaign (https://www.osha.gov/heat) to build awareness of
prevention strategies and tools for employers and workers to reduce
occupational heat-related illness. In its original form, the Campaign
delivered a message of ``Water. Rest. Shade.'' The agency updated
Campaign materials in 2021 to recognize both indoor and outdoor heat
hazards, as well as the importance of protecting new and returning
workers from hazardous heat with an acclimatization period.
In addition, OSHA maintains on its website a Heat Topics page on
workplace heat exposure (https://www.osha.gov/heat-exposure/), which
provides additional information and resources. The page provides
information on planning and supervision in hot work environments,
identification of heat-related illness and first aid, information on
prevention such as training, calculating heat stress and controls,
personal risk factors, descriptions of other heat standards and case
study examples of situations where workers developed heat-related
illness. OSHA and NIOSH also co-developed a Heat Safety Tool Smartphone
App for both Android and iPhone devices (see www.osha.gov/heat/heat-app). The app provides outdoor, location-specific temperature,
humidity, and heat index (HI) readings. Measurements for indoor work
sites must be collected and manually entered into the app by the user
for accurate calculations. The app also provides relevant information
on identifying signs and symptoms of heat-related illness and steps to
prevent heat-related injuries and illnesses. Despite the strengths and
reach of the Campaign, Heat Topics page, and Heat Safety Tool App,
these guidance and communication materials are not legally enforceable
requirements.
III. OSHA's Heat-Related Enforcement
Without a specific standard governing hazardous heat conditions at
workplaces, the agency currently enforces section 5(a)(1) (the General
Duty Clause) of the OSH Act against employers that expose their workers
to this recognized hazard. Section 5(a)(1) states that employers have a
general duty to furnish to each of their employees ``employment and a
place of employment which are free from recognized hazards that are
causing or are likely to cause death or serious physical harm'' to
employees (29 U.S.C. 654(a)(1)). To prove a violation of the General
Duty Clause, OSHA must establish--in each individual case--that: (1)
the employer failed to keep the workplace free of a hazard to which its
employees were exposed; (2) the hazard was recognized; (3) the hazard
was causing or likely to cause death or serious injury; and (4) a
feasible means to eliminate or materially reduce the hazard existed
(see, e.g., A.H. Sturgill Roofing, Inc., 2019 O.S.H. Dec. (CCH) ]
[thinsp]33712, 2019 WL 1099857 (No. 13-0224, 2019)).
OSHA has relied on the General Duty Clause to cite employers for
heat-related hazards for decades (see, e.g., Duriron Co., 11 BNA OSHC
1405, 1983 WL 23869 (No. 77-2847, 1983), aff'd, 750 F.2d 28 (6th Cir.
1984)). According to available OSHA enforcement data, between 1986 and
2023, Federal OSHA issued at least 348 hazardous heat-related citations
under the General Duty Clause. Of these citations, 85 were issued
between 1986-2000 (OSHA, 2024b). Citations were identified using
multiple queries of OSHA enforcement data and then manually reviewed to
ensure the inclusion of only citations due to heat exposure and no
other exposures (e.g., burns or explosions). Several keywords were
utilized to filter the data for inclusion (e.g., ``heat,'' ``heat
stress,'' ``heat illness,'' ``WBGT'') and exclusion (e.g.,
``explosion,'' ``flash,'' ``electrical burn,'' ``fire''). Due to
limitations of the data set on which OSHA relied, OSHA did not have
access to violation text descriptions of citations issued before the
mid-1980s and thus did not determine how many are related to heat
exposure prior to this time period. Additionally, over half of the
citations from 1986-1989 are missing violation text descriptions, which
likely resulted in an undercount of heat-related citations.
OSHA has used its general inspection authority (29 U.S.C. 657) to
target heat-related injuries and illnesses in various Regional Emphasis
Programs (REPs). OSHA enforcement emphasis programs focus the agency's
resources on particular hazards or high-hazard industries (see Marshall
v. Barlow's, Inc., 436 U.S. 307, 321 (1978) (affirming OSHA's use of an
administrative plan containing specific neutral criteria to focus
inspections)). OSHA's Region VI regional office, located in Dallas, TX,
has a heat-related special REP (OSHA, 2019). This region covers Texas,
New Mexico, Oklahoma, Arkansas, and Louisiana. OSHA's Region IX
regional office, located in San Francisco, CA, also has a heat-related
REP (OSHA, 2022). This region covers American Samoa, Arizona,
California, Guam, Hawaii, Nevada, and the Northern Mariana Islands.
These REPs allow field staff to conduct heat illness inspections of
outdoor work activities on days when the high temperature is forecasted
to be above 80 [deg]F.
On September 1, 2021, OSHA issued updated Inspection Guidance for
Heat-Related Hazards, which established a new enforcement initiative to
protect employees from heat-related injuries and illnesses while
working in hazardous hot indoor and outdoor environments (OSHA, 2021).
The guidance provided that days when the heat index exceeds 80 [deg]F
would be considered heat priority days. It announced that enforcement
efforts would be increased on heat priority days for a variety of
indoor and outdoor industries, with the aim of identifying and
mitigating potential hazards and preventing heat-illnesses before they
occur.
In April 2022, OSHA launched a National Emphasis Program (NEP) to
protect employees from heat-related hazards and resulting injuries and
illnesses in outdoor and indoor workplaces. The NEP expanded the
agency's ongoing heat-related injury and illness prevention initiatives
and campaign by setting forth a targeted enforcement component and
reiterating its compliance assistance and outreach efforts. The NEP
targets specific industries expected to have the highest exposures to
heat-related hazards and resulting illnesses and deaths. This approach
is intended to encourage early interventions by employers to prevent
illnesses and deaths among workers during high heat conditions (CPL 03-
00-024). As of June 26, 2024, OSHA has conducted 5,038 Heat NEP Federal
inspections. More than 1,229 of these were initiated by complaints and
117 were due to the occurrence of a fatality or catastrophe. As a
result of these inspections, OSHA issued 56 General Duty Clause
citations and 736 Hazard Alert Letters (HALs). Inspections occurred
across various industries (as identified by 2-digit NAICS codes)
including construction, which had the highest number of inspections, as
well as manufacturing, maritime, agriculture, transportation,
warehousing, food services, waste management, and remediation services.
On July 27, 2023, OSHA issued a heat hazard alert to remind
employers of their obligation to protect workers against heat injury
and illness in outdoor and indoor workplaces. The alert highlights what
employers can and
should be doing to protect employees. It also serves to remind
employees of their rights, including protections against retaliation.
In addition, the alert highlights steps OSHA is currently taking to
protect workers and directs employers, employees, and the public to
OSHA resources, including guidance and fact sheets on heat.
OSHA's efforts to protect employees from hazardous heat conditions
using the General Duty Clause, although important, have limitations
leaving many workers vulnerable to heat-related hazards. For example,
the Commission has struggled to determine exactly what conditions
create a recognized heat hazard under the General Duty Clause, and has
therefore suggested the necessity of a standard (see, A.H. Sturgill
Roofing, Inc., 2019 OSHD (CCH) ] [thinsp]33712, 2019 WL 1099857, at *2-
5 and n.8 (No. 13-0224, 2019) (``The Secretary's failure to establish
the existence of an excessive heat hazard here illustrates the
difficulty in addressing this issue in the absence of an OSHA
standard.''); U.S. Postal Service, 2023 OSHD (CCH) ] 33908, 2023 WL
2263313, at *3 n.7 (Nos. 16-1713, 16-1872, 17-0023,17-0279, 2023)
(noting Commissioner Laihow's opinion that ``A myriad of factors, such
as the geographical area where the work is being performed and the
nature of the tasks involved, can impact'' whether excessive heat is
present, and indicating that a standard is therefore necessary to
define the hazard).
Under the General Duty Clause, OSHA cannot require abatement before
proving in an enforcement proceeding that specific workplace conditions
are hazardous; whereas a standard would establish the existence of the
hazard at the rulemaking stage, thus allowing OSHA to identify and
require specific abatement measures without having to prove the
existence of a hazard in each case (see Sanderson Farms, Inc. v. Perez,
811 F.3d 730, 735 (5th Cir. 2016) (``Since OSHA is required to
determine that there is a hazard before issuing a standard, the
Secretary is not ordinarily required to prove the existence of a hazard
each time a standard is enforced.'')). Given OSHA's burden under the
General Duty Clause, it is currently difficult for OSHA to ensure
necessary abatement before employee lives and health are unnecessarily
endangered. Further, under the General Duty Clause OSHA must largely
rely on expert witness testimony to prove both the existence of a
hazard and the availability of feasible abatement measures that will
materially reduce or eliminate the hazard in each individual case (see,
e.g., Industrial Glass, 15 BNA OSHC 1594, 1992 WL 88787, at *4-7 (No.
88-348, 1992)).
Moreover, as OSHA has noted in similar contexts, standards have the
advantage of providing greater clarity to employers and employees of
the measures required to protect employees and are developed with the
benefit of information gathered in the notice and comment process (see
86 FR 32376, 32418 (Jun. 21, 2021) (COVID-19 Healthcare ETS); 56 FR
64004, 64007 (Dec. 6, 1991) (Bloodborne Pathogens Standard)).
OSHA currently has other existing standards that, while applicable
to some issues related to hazardous heat, have not proven to be
adequate in protecting workers from exposure to hazardous heat. For
example, OSHA's Recordkeeping standard (29 CFR 1904.7) requires
employers to record and report injuries and illnesses that meet
recording criteria. Additionally, the agency's Sanitation standards (29
CFR 1910.141, 1915.88, 1917.127, 1926.51, and 1928.110) require
employers to provide potable water readily accessible to workers. While
these standards require that drinking water be made available in
``sufficient amounts,'' they do not specify quantities, and employers
are not required to encourage workers to frequently hydrate on hot
days.
OSHA's Safety Training and Education standard (29 CFR 1926.21)
requires employers in the construction industry to train employees in
the recognition, avoidance, and prevention of unsafe conditions in
their workplaces. OSHA's PPE standards (29 CFR 1910.132, 1915.152,
1917.95, and 1926.28) require employers to conduct a hazard assessment
to determine the appropriate PPE to be used to protect employees from
the hazards identified in the assessment. However, hazardous heat is
not specifically identified as a hazard for which workers need training
or PPE, complicating the application of these requirements to hazardous
heat.
IV. Rulemaking Activities Leading to This Proposal
OSHA has received multiple petitions to promulgate a heat injury
and illness prevention standard, including in 2018 from Public Citizen,
on behalf of approximately 130 organizations (Public Citizen et al.,
2018). OSHA has also been urged by members of Congress to initiate
rulemaking for a Federal heat standard, as well as by the Attorneys
General of several States in 2023.
On October 27, 2021, OSHA published an advance notice of proposed
rulemaking (ANPRM) for Heat Injury and Illness Prevention in Outdoor
and Indoor Work Settings in the Federal Register (86 FR 59309)
(referred to as ``the ANPRM'' hereafter). The ANPRM outlined key issues
and challenges in occupational heat-related injury and illness
prevention and aimed to collect evidence, data, and information
critical to informing how OSHA proceeds in the rulemaking process. The
ANPRM included background information on injuries, illnesses, and
fatalities due to heat, underreporting, scope, geographic region, and
inequality in exposures and outcomes. The ANPRM also covered existing
heat injury and illness prevention efforts, including OSHA's efforts,
the NIOSH criteria documents, State standards, and other standards. The
initial public comment period was extended and closed on January 26,
2022. In response to the ANPRM, OSHA received 965 unique comments. The
comments covered several topics, including the scope of a standard,
heat stress thresholds for workers across various industries, heat
acclimatization planning, and heat exposure monitoring, as well as the
nature, types, and effectiveness of controls that may be required as
part of a standard.
Following the publication of the ANPRM, OSHA presented topics from
the ANPRM and updates on the heat rulemaking to several stakeholders,
including several trade associations, the Office of Advocacy of the
Small Business Administration's (SBA's Office of Advocacy) Labor Safety
Roundtable (November 19, 2021), and NIOSH National Occupational
Research Agenda (NORA) councils, including the Construction Sector
Council (November 17, 2021), Landscaping Safety Workgroup (January 12,
2022), and Oil and Gas Extraction Sector (April 7, 2022).
On May 3, 2022, OSHA held a virtual public stakeholder meeting on
the agency's ``Initiatives to Protect Workers from Heat-Related
Hazards.'' A total of over 1,300 people attended the virtual meeting,
and the recorded video has been viewed over 3,500 times (see
www.youtube.com/watch?v=Ud29WsnsOw8) as of June 2024. The six-hour
meeting provided stakeholders an opportunity to learn about and comment
on efforts OSHA is taking to protect workers from heat-related hazards
and ways the public can participate in the agency's rulemaking process.
OSHA also established a Heat Injury and Illness Prevention Work
Group of the National Advisory Committee on Occupational Safety and
Health (NACOSH) to support the agency's rulemaking and outreach
efforts. The Work Group was tasked with reviewing
and developing recommendations on OSHA's heat illness prevention
guidance materials, evaluating stakeholder input, and developing
recommendations on potential elements of any proposed heat injury and
illness prevention standard. On May 31, 2023, the Work Group presented
its recommendations on potential elements of a proposed heat injury and
illness prevention standard for consideration by the full NACOSH
committee. The Work Group recommended that any proposed heat injury and
illness prevention standard include: a written exposure control plan/
heat illness prevention plan; training; environmental monitoring;
workplace control measures; acclimatization; worker participation; and
emergency response (Document ID OSHA-2023-0003-0007). After
deliberations, NACOSH amended the report to ask OSHA to include a model
written plan and then submitted its recommendations to the Secretary of
Labor (Document ID OSHA-2023-0003-0012).
As an initial rulemaking step, OSHA convened a Small Business
Advocacy Review Panel (SBAR Panel) on August 25, 2023, in accordance
with the Regulatory Flexibility Act (RFA) (5 U.S.C. 601 et seq.), as
amended by the Small Business Regulatory Enforcement Act (SBREFA) of
1996. This SBAR Panel consisted of members from OSHA, SBA's Office of
Advocacy, and the Office of Information and Regulatory Affairs (OIRA)
in the White House Office of Management and Budget (OMB). The SBAR
Panel identifies individual representatives of affected small entities,
termed small entity representatives (SERs), which includes small
businesses, small local government entities, and non-profits. This
process enabled OSHA, with the assistance of SBA's Office of Advocacy
and OIRA, to obtain advice and recommendations from SERs about the
potential impacts of the regulatory options outlined in the regulatory
framework and about additional options or alternatives to the
regulatory framework that may alleviate those impacts while still
meeting the objectives and requirements of the OSH Act.
The SBAR Panel hosted six online meetings on September 9, 12, 13,
14, 18, and 19, 2023, with participation from a total of 82 SERs from a
wide range of industries. A final report containing the findings,
advice, and recommendations of the SBAR Panel was submitted to the
Assistant Secretary of Labor for Occupational Safety and Health on
November 3, 2023, to help inform the agency's decision making with
respect to this rulemaking (Document ID OSHA-2021-0009-1059).
In accordance with 29 CFR parts 1911 and 1912, OSHA presented to
the Advisory Committee on Construction Safety and Health (ACCSH) on its
framework for a proposed rule for heat injury and illness prevention in
outdoor and indoor work settings on April 24, 2024. The Committee then
passed unanimously a motion recommending that OSHA proceed
expeditiously with proposing a standard on heat injury and illness
prevention. The Committee also recommended that OSHA consider the
feedback and questions discussed by Committee members during the
meeting in formulating the proposed rule (see the minutes from the
meeting, Docket No. 2024-0002). OSHA has considered the Committee's
feedback in the development of this proposal.
In accordance with Executive Order 13175, Consultation and
Coordination with Indian Tribal Governments, 65 FR 67249 (Nov. 6,
2000), OSHA held a listening session with Tribal representatives
regarding this Heat Injury and Illness Prevention in Outdoor and Indoor
Work Settings rulemaking on May 15, 2024. OSHA provided an overview of
the rulemaking effort and sought comment on what, if any, tribal
implications would result from the rulemaking. A summary of the meeting
and list of attendees can be viewed in the docket (DOL, 2024a).
D. Other Standards
Various other organizations have also either identified the need
for standards to prevent occupational heat-related injury and illness
or published their own standards. In 2024, the American National
Standards Institute/American Society of Safety Professionals A10
Committee (ANSI/ASSP) published a consensus standard on heat stress
management in construction and demolition operations. The International
Organization for Standardization (ISO) also has a standard for
evaluating heat stress: ISO 7243: Ergonomics of the thermal
environments--Assessment of heat stress using the WBGT (wet bulb globe
temperature) index (ISO, 2017). ISO 7243 uses WBGT values, along with
metabolic rate, to assess hot environments, similar to ACGIH and NIOSH
recommendations. Additional ISO standards address predicting sweat rate
and core temperature (ISO 7933), and determining metabolic rate (ISO
8996), physiological strain (ISO 9886), and thermal characteristics for
clothing (ISO 9920). In 2021, the American Society for Testing and
Materials (ASTM) finalized its Standard Guide for Managing Heat Stress
and Heat Strain in Foundries (E3279-21) which establishes ``best
practices for recognizing and managing occupational heat stress and
heat strain in foundry environments.'' The standard outlines employer
responsibilities and recommends elements for a ``Heat Stress and Heat
Strain Management Program'' (ASTM, 2021).
ACGIH has identified TLVs for heat stress (ACGIH, 2023). The TLVs
utilize WBGT and take into consideration metabolic rate or workload
categories. Additionally, ACGIH provides clothing adjustment factors
which are added to the measured WBGT for certain types of work clothing
to account for the impaired thermal regulation.
The U.S. Armed Forces has developed extensive heat-related illness
prevention and management strategies. The Warrior Heat and Exertion
Related Events Collaborative is a tri-service group of military leaders
focused on clinical, educational, and research efforts related to
exercise and exertional heat-related illnesses and medical emergencies
(HPRC, 2023). The U.S. Army has a Heat Center at Fort Benning which
focuses on management, research, and prevention of heat-related illness
and death (Galer, 2019). In 2023, the U.S. Army updated its Training
and Doctrine Command (TRADOC) Regulation 350-29 addressing heat and
cold casualties. The regulation includes requirements for rest and
water consumption according to specific WBGT levels and work intensity
(Department of the Army, 2023). The U.S. Navy has developed
Physiological Heat Exposure Limit curves that are based on metabolic
and environmental heat loads and represent the maximum allowable heat
exposure limits, which were most recently updated in 2023. The Navy
monitors WBGT and has guidelines based on these measurements, with
physical training diminishing as WBGTs increase and all nonessential
outdoor activity stopped when WBGTs exceed 90 [deg]F (Department of the
Navy, 2023). The U.S. Marine Corps follows the Navy's guidelines for
implementation of the Marine Corps Heat Injury Prevention Program
(Commandant of the Marine Corps, 2002). In 2022, the U.S. Army and U.S.
Air Force issued an update to their technical heat stress bulletin,
which outlines measures to prevent indoor and outdoor heat-related
illness in soldiers. The bulletin includes recommended acclimatization
planning, work-rest cycles, fluid and electrolyte replacement, and
limitations on work based on WBGT (Department of the Army, 2022).
As of April 2024, five States have promulgated heat standards
requiring employers in various industries and workplace settings to
implement protections to reduce the risk of heat-related injuries and
illnesses for their employees: California, Minnesota, Oregon,
Washington, and Colorado. In addition, Maryland and California are
currently engaged in rulemaking. State standards differ in the scope of
coverage (see tables III-1 and 2). For example, Minnesota's standard
covers only indoor workplaces. California and Washington standards
cover only outdoor workplaces, although California's proposal would
include coverage of indoor workplaces. Oregon's rule covers both indoor
and outdoor workplaces. State rules also differ in the methods used for
triggering protections against hazardous heat. Minnesota's standard
considers the type of work being performed (light, moderate, or heavy)
and provides WBGT trigger levels based on the type of work activity.
California's heat-illness prevention protections go into effect at an
ambient temperature of 80 [deg]F. Washington's rule also relies on
ambient temperature readings combined with considerations for the
breathability of workers' clothing. Oregon's rule uses a heat index 80
[deg]F as a trigger.
California, Washington, Colorado, and Oregon all have additional
protections that are triggered by high heat. However, they differ as to
the trigger for these additional protections. In California, high heat
protections are triggered at an ambient temperature reading of 95
[deg]F (and only apply in certain industries). In Washington, high heat
protections are triggered at an ambient temperature reading of 90
[deg]F. In Colorado, additional protections are triggered at an ambient
temperature reading of 95 [deg]F or by other factors such as unhealthy
air quality, length of workday, heaviness of clothing or gear, and
acclimatization status. These additional protections only apply to the
agricultural industry. Finally, in Oregon, high heat protections are
triggered at a heat index of 90 [deg]F.
All the State standards require training for employees and
supervisors. All the State standards, except for Minnesota, require
employers to provide at least one quart of water per hour for each
employee, require some form of emergency response plan, include
provisions related to acclimatization for workers, and require access
to shaded break areas. Washington and Oregon require that employers
provide training in a language that the workers understand. Similarly,
California's standard requires that employers create a written heat-
illness prevention plan in English as well as in whatever other
language is understood by the majority of workers at a given workplace.
California also requires close monitoring of new employees for the
first fourteen days and monitoring of all employees during a heat wave.
Table III-1 below provides an overview of the provisions included in
the existing and proposed State standards on heat injury and illness
prevention. Table III-2 provides an overview of the additional
provisions required when the high heat trigger is met or exceeded.
Table III-1--Initial Heat Triggers and Provisions in State Heat Standards
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Shade or
Threshold Provision of cool-down Rest breaks Emergency Acclimatization Training Heat illness prevention Observation/
water means if needed response plan supervision
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
General
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
California: Outdoor................... 80 [deg]F (Ambient) \1\.. ................ ............
Washington: Outdoor................... 80 [deg]F (Ambient), All (accident ............
other clothing; 52 prevention).
[deg]F, Non-breathable
clothes.
Colorado: Agriculture................. 80 [deg]F (Ambient)...... ........................
California (proposal): Indoor......... 82 [deg]F (Ambient)...... ................ ............
Maryland (proposal): Indoor & Outdoor. 80 [deg]F (Heat Index)... ............ ................ ............
Minnesota: \2\ Indoor................. 86 [deg]F (WBGT), Light ............ ............ ............ ............ ............... ........................ ............
work; 80 [deg]F,
Moderate work; 77
[deg]F, Heavy work.
Oregon: Indoor & Outdoor.............. 80 [deg]F (Heat Index)... ............ ................ ............
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Some provisions, including water, emergency response, training, and heat illness prevention plan, apply to covered employers regardless of the temperature threshold.
\2\ Minnesota uses a 2-hour time-weighted average permissible exposure limit rather than a trigger.
Table III-2--High Heat Triggers and Additional Provisions in State Heat Standards
----------------------------------------------------------------------------------------------------------------
Assessment
Threshold Work-rest Observation/ Pre-shift and control
schedule supervision meetings measures \1\
----------------------------------------------------------------------------------------------------------------
Additional High Heat Provisions
----------------------------------------------------------------------------------------------------------------
California: Outdoor \2\....... 95 [deg]F (only ........ ............
(Ambient). agriculture).
Washington: Outdoor........... 90 [deg]F ........ ........ ............ ............
(Ambient).
Colorado: Agriculture......... 95 [deg]F ........ covered in ............
(Ambient) or general
other condition provisions
\3\. above.
California (proposal): Indoor. 87 [deg]F ................ ................ ............
(Ambient or
Heat Index) or
other
conditions \4\.
Maryland (proposal): Indoor & 90 [deg]F (Heat ........ ........ ............ ............
Outdoor. Index).
Oregon: Indoor & Outdoor...... 90 [deg]F (Heat ........ ........ ............ ............
Index).
----------------------------------------------------------------------------------------------------------------
\1\ Assessment and control measures include measuring temperature and heat index, identifying and evaluating all
other environmental risk factors for heat illness, and using specified control measures to minimize the risk
of heat illness.
\2\ High heat procedures apply in agriculture; construction; landscaping; oil and gas extraction; transportation
or delivery of agricultural products, construction materials or other heavy materials, except for employment
that consists of operating an air-conditioned vehicle and does not include loading or unloading.
\3\ Other conditions include unhealthy air quality, shifts over 12 hours, heavy clothing or gear required, or
the employee is new or returning from absence.
\4\ Other conditions include wearing clothing that restricts heat removal, or working in a high radiant heat
area, when the ambient temperature is at or above 82 [deg]F.
IV. Health Effects
A. Introduction
I. Health Effects of Occupational Heat Exposure
Exposure to workplace heat can be seriously detrimental to workers'
health and safety and, in some cases, can be fatal. Workplace heat
contributes to heat stress, which is a person's total heat load (NIOSH,
2016) from the following sources combined: (1) heat from the
environment, including heat generated by equipment or machinery; (2)
metabolic heat generated through body movement, which is proportional
to one's relative level of exertion (Sawka et al., 1993; Astrand 1960);
and (3) heat retained due to clothing or personal protective equipment
(PPE), which is highly dependent on the breathability of the clothing
and PPE worn (Bernard et al., 2017). Heat is routinely an occupation-
specific risk because, for example, workers may experience greater heat
stress than non-workers, particularly when they are required to work
through shifts with prolonged heat exposure, complete tasks that
require physical exertion, and/or their employers do not take adequate
steps to protect them from exposure to hazardous heat. In addition,
many work operations require the use of PPE. PPE can increase heat
stress and can reduce workers' heat tolerance by decreasing the body's
ability to cool down. Workers may also face pressure, or
incentivization through pay structures (e.g., piece-rate, bonuses), to
work through hazardous heat. Pressure to produce results and be seen as
a good worker can have a direct impact on worker self-care choices that
impact health (Wadsworth et al., 2019). Pay structures and production
quotas intended to motivate workers may also compromise worker safety
(Iglesias-Rios et al., 2023). These pressures can increase their risk
of heat-related injury and illness (Billikopf and Norton, 1992;
Johansson et al., 2010; Spector et al., 2015; Pan et al., 2021). The
body's response to heat stress is called heat strain (NIOSH, 2016). As
the heat stress a person experiences increases, the body attempts to
cool itself by releasing heat into the surrounding environment. If the
body begins to acquire heat faster than it can release it, the body
will store heat. As stored heat accumulates, the body can show signs of
excessive heat strain, such as increased core temperature and heart
rate, as well as symptoms of heat strain, such as sweating, dizziness,
or nausea.
Two large meta-analyses (n=2,409 and n=11,582) \1\ have confirmed
that occupational heat exposure is associated with both signs and
symptoms of heat strain (Ioannou et al., 2022; Flouris et al., 2018).
In one, the authors found a high prevalence of heat strain (35%) among
workers in hot conditions, defined by the authors as WBGT greater than
26 [deg]C (78.8 [deg]F); they also found that workers in hot conditions
were four times more likely to experience signs and symptoms of heat
strain than workers in more moderate conditions (Flouris et al., 2018).
---------------------------------------------------------------------------
\1\ In the Health Effects section, OSHA refers to statistics
that were reported by authors when describing results from their
research studies. These include the sample size (n), the odds ratio
(OR), the confidence interval (CI), and the p-value (p). These
statistics provide information about effect size, error, and
statistical significance.
---------------------------------------------------------------------------
II. Literature Review for Health Effects Section
OSHA conducted a non-systematic review of the medical and
scientific literature to identify evidence on the relationship between
heat exposure and illnesses and death. OSHA's literature review focused
on meta-analyses, systematic reviews, and studies cited in NIOSH's
Criteria for a Recommended Standard: Occupational Exposure to Heat and
Hot Environments, published in 2016. OSHA separately searched for
additional meta-analyses and systematic reviews that were not cited in
the NIOSH Criteria document, including those that were published after
the document was released (i.e., 2016 and on).
OSHA also reviewed sentinel epidemiological evidence including
observational, experimental, and randomized controlled studies. OSHA
primarily reviewed epidemiological studies focusing on worker
populations, athletes, and military members, but also included studies
in non-worker populations where appropriate. For example, when there
was limited occupation-specific research or data for some heat-related
health effects, OSHA sometimes considered general population studies as
they relate to understanding physiological mechanisms of heat-related
illness, severity of an illness, and prognosis. In addition to the
evidence of heat-related illnesses and deaths, OSHA reviewed a large
body of evidence that evaluated the association of occupational heat
exposure with workplace injuries such as falls, collisions, and other
accidents. OSHA also reviewed evidence regarding individual factors
such as age, medication use, and certain medical conditions that may
affect one's risk for heat-related health effects.
III. Summary
The best available evidence in the scientific and medical
literature, as summarized in this Health Effects section, demonstrates
that occupational heat exposure can result in death; illnesses,
including heat stroke, heat exhaustion, heat syncope, rhabdomyolysis,
heat cramps, hyponatremia, heat edema, and heat rash; and heat-related
injuries, including falls, collisions, and other workplace accidents.
B. General Mechanisms of Heat-Related Health Effects
This section briefly describes the mechanisms of heat-related
health effects, i.e., how the body's physiological responses to heat
exposure can lead to the heat-related health effects identified in
OSHA's literature review. More detailed information about the
mechanisms underpinning each specific heat-related health effect is
described in the relevant subsections that follow.
As explained above, occupational heat exposure contributes to heat
stress. The resulting bodily responses are collectively referred to as
heat strain (Cramer and Jay, 2016). The bodily responses included in
heat strain serve to decrease stored heat by increasing heat loss to
the environment to maintain a stable body temperature (NIOSH, 2016).
When the brain recognizes that the body is storing heat, it activates
the autonomic nervous system to initiate cooling (Kellogg et al., 1995;
Wyss et al., 1974). Blood is shunted towards the skin and vasodilation
begins, meaning that the blood vessels near the skin's surface become
wider, thereby increasing blood flow near the surface of the skin
(Kamijo et al., 2005; Hough and Ballantyne, 1899). The autonomic
nervous system also triggers the body's sweat response, in which sweat
glands release water to wet the skin (Roddie et al., 1957; Grant and
Holling, 1938). These processes allow the body to cool in four ways:
(1) radiation, i.e., when heat is released directly into the
surrounding air; (2) convection, i.e., when there is air movement that
moves heat away from the body; (3) evaporation, i.e., when sweat on the
skin diffuses into surrounding air (as clothing/PPE permits) and (4)
conduction, i.e., when heat is directly transferred through contact
with a cooler surface (e.g., wearing an ice-containing vest (Cramer and
Jay, 2016; Leon and Kenefick, 2012)).
Importantly, the extent of heat release through radiation,
convection, and evaporation depends on environmental conditions such as
the speed of air flow, temperature, and relative humidity (Clifford et
al., 1959; Brebner et al., 1958). For example, when relative humidity
is high, sweat is less likely to evaporate off the skin, which
significantly reduces the cooling effect of evaporation. Additionally,
when sweat remains on the skin and irritates the sweat glands, it can
cause a condition known as heat rash, whereby itchy red clusters of
pimples or blisters develop on the skin (DiBeneditto and Worobec, 1985;
Sulzberger and Griffin, 1968).
While the purpose of the sweat response is to cool the body, in
doing so, it can deplete the body's stores of water and electrolytes
(e.g., sodium [Na], potassium [K], chloride [Cl], calcium [Ca], and
magnesium [Mg]) that are essential for normal bodily function
(Shirreffs and Maughan, 1997). The condition resulting from abnormally
low sodium levels is known as hyponatremia. When stores of electrolytes
are depleted, painful muscle spasms known as heat cramps can occur
(Kamijo and Nose, 2006). Additionally, depletion of the body's stored
water causes dehydration, which is known to reduce the body's
circulating blood volume (Trangmar and Gonzalez-Alonso, 2017; Dill and
Costill, 1974).
During vasodilation that happens as the body attempts to cool,
blood can pool in areas of the body that are most subject to gravity,
and fluid can seep from blood vessels causing noticeable swelling under
the skin (known as heat edema). Upright standing would further
encourage blood to pool in the legs, and thus, the heart has an even
lower blood volume available for circulation (Smit et al., 1999). A
large reduction in circulating blood volume will lead to (1) a
continued rise in core body temperature, and (2) reduced blood flow to
the brain, muscles, and organs. A rise in core body temperature and
reduced blood flow to the brain can cause neurological disturbances,
such as loss of consciousness, which are characteristic of heat stroke
and heat syncope (Wilson et al., 2006; Van Lieshout et al., 2003). A
rise in core body temperature and reduced blood flow to muscles can
also cause extreme muscle fatigue (to the point of collapse) and muscle
cell damage during exertion, which are characteristic of heat
exhaustion and rhabdomyolysis, respectively (Torres et al., 2015; Nybo
et al., 2014). Finally, a rise in core body temperature and reduced
blood flow to organs can damage multiple vital organs (such as the
heart, liver, and kidneys), which is often observed in heat stroke
(Crandall et al., 2008; O'Donnell and Clowes, 1972). Heat stroke and
rhabdomyolysis can lead to death if not treated properly and promptly.
C. Identifying Cases of Heat-Related Health Effects
In its review of the scientific and medical literature on the
health effects of occupational heat exposure, OSHA found several
studies that relied upon coding systems, in which medical providers or
other public health professionals identify fatalities and non-fatal
cases of various illnesses and injuries, including heat-related
illnesses and injuries (HRIs). The medical and scientific communities
use data from these coding systems to study the incidence and
prevalence of illnesses and injuries, including HRIs. In both this
Health Effects section and Section V., Risk Assessment, OSHA relied on
several studies that make use of data from these coding systems. A
brief summary of each of the major coding systems is provided below.
I. International Statistical Classification of Diseases and Related
Health Problems (ICD) Codes
The International Statistical Classification of Diseases and
Related Health Problems (ICD) System is under the purview of the World
Health Organization (WHO), an international agency that, as the leading
authority on health and disease, regularly publishes evidence-based
guidelines to advance clinical practice and public health policy. The
ICD System harmonizes the diagnosis of disease across many countries,
and ICD codes are used routinely in the U.S. healthcare system by
medical personnel to record diagnoses in patients' medical records, as
well as to identify cause of death. These codes are utilized as part of
a standardized system for recording diagnoses, as well as organizing
and collecting data into public health surveillance systems. Each ICD
code is a series of letters and/or numbers that corresponds to a highly
specific medical diagnosis. Healthcare providers may record multiple
ICD codes if an individual presents with multiple diagnoses. The ICD
system has multiple codes that medical personnel can use when
diagnosing HRIs.
The ICD system was first developed in the 18th century and was
adopted under the purview of the World Health Organization (WHO) in
1948 (Hirsch et al., 2016). Since then, the ICD system has been revised
11 times--ICD-11 was released in 2022. However, because the ICD-11
system has not yet been implemented in the United States, many of the
epidemiological studies cited throughout this Health Effects section
used the ICD-9 and ICD-10 systems to survey heat-related deaths and
HRIs. Table IV-1 provides a list of heat-related ICD-9 and ICD-10
codes.
Table IV--1--ICD-9 and ICD-10 Codes for Heat-Related Health Effects *
------------------------------------------------------------------------
ICD-9 code ICD-10 code equivalent
------------------------------------------------------------------------
992 Effects of heat and light.......... T67 Effects of heat and light.
992.0 Heatstroke and sunstroke......... T67.0 Heatstroke and sunstroke.
992.1 Heat syncope..................... T67.1 Heat syncope.
992.2 Heat cramps...................... T67.2 Heat cramp.
992.3 Heat exhaustion, anhydrotic...... T67.3 Heat exhaustion,
anhydrotic.
992.4 Heat exhaustion due to salt T67.4 Heat exhaustion due to
depletion. salt depletion.
992.5 Heat exhaustion, unspecified..... T67.5 Heat exhaustion,
unspecified.
992.6 Heat fatigue, transient.......... T67.6 Heat fatigue, transient.
992.7 Heat edema....................... T67.7 Heat edema.
992.8 Other effects of heat and light.. T67.8 Other effects of heat and
light.
992.9 Effects of heat and light, T67.9 Effects of heat and
unspecified. light, unspecified.
E900 Accident caused by excessive heat. NA.
E900.0 Accident caused by excessive X30 Exposure to excessive
heat due to weather conditions. natural heat.
E900.1 Accidents due to excessive heat W92 Exposure to excessive heat
of man-made origin. of man-made origin.
E900.9 Accidents due to excessive heat X30 Exposure to excessive
of unspecified origin. natural heat.
------------------------------------------------------------------------
Note: The above heat-related codes exclude X32 Exposure to sunlight and
W89 Exposure to man-made radiation, among others.
* These ICD codes are specific to heat as indicated by the names of the
codes. There are additional codes that can be associated with
diagnosed heat illness but may not be specific to heat-related illness
which are not included here but may be included in text where relevant
(e.g., M62.82 for rhabdomyolysis and E87.1 for hypo-osmolality and
hyponatremia).
Various surveillance systems exist to track documentation of ICD
codes. For example, the CDC leverages ICD-10 codes to collect nearly
real-time data on heat-related deaths and HRIs through the National
Syndromic Surveillance System (NSSP). The CDC also uses ICD-10 codes to
collect annual data on heat-related deaths and HRIs, then reports these
data via the National Vital Statistics System (NVSS) and National
Center for Health Statistics (NCHS). Additionally, all branches of the
U.S. Armed Forces (i.e., Army, Navy, Air Force, and Marine Corps) use
ICD-10 codes to document HRIs among service members in the Defense
Medical Surveillance System (DMSS). The US Army also uses ICD-10 codes
to document HRIs in the Total Army Injury and Health Outcomes Database
(TAIHOD) (Bell et al., 2004).
II. Occupational Illness and Injury Classification System (OIICS) Codes
The U.S. Bureau of Labor Statistics (BLS) is a Federal agency,
housed in the Department of Labor, that collects and analyzes data on
the U.S. economy and workforce. In 1992, BLS developed the Occupational
Illness and Injury Classification System (OIICS) to harmonize reporting
of injuries and illnesses that affect U.S. workers. The OIICS is
similar to the ICD system. Each OIICS code is a series of numbers that
specifies a diagnosis (referred to as the nature of an illness or
injury, or a ``nature code'') and event(s) leading to an illness or
injury (referred to as an ``event code''). OIICS was updated in 2010
(Version 2.0), and again in 2022 (Version 3.0); Version 3.0 is the most
up to date version (https://www.bls.gov/iif/definitions/occupational-injuries-and-illnesses-classification-manual.htm; BLS, 2023e). The
OIICS system has multiple codes that can be used when identifying
occupational HRIs. Table IV-2 provides a list of heat-related OIICS
codes (nature and event codes).
Table IV--2--OIICS Codes (Version 3.0) for Heat-Related Health Effects
[dagger]
------------------------------------------------------------------------
-------------------------------------------------------------------------
Nature Codes:
172 Effects of heat and light.
1720 Effects of heat--unspecified.
1721 Heat stroke, syncope.
1722 Heat exhaustion, fatigue.
1729 Effects of heat--not elsewhere classified.
2893 Prickly heat, heat rash, and other disorders of the sweat
glands including ``miliaria rubra''.
Event Codes:
53 Exposure to temperature extremes.
530 Exposure to temperature extremes--unspecified.
531 Exposure to environmental heat.
5310 Exposure to environmental heat--unspecified.
5311 Exposure to environmental heat--indoor.
5312 Exposure to environmental heat--outdoor.
------------------------------------------------------------------------
[dagger] Some of the data OSHA relies on uses older versions of OIICS
codes (Versions 1 and 2) but the major categories for heat-related
incidents did not change significantly between versions.
Through a combination of survey staff and a specialized automated
coding system, BLS applies OIICS codes to data collected through their
worker safety and health surveillance systems, the Census of Fatal
Occupational Injuries (CFOI) and the Survey of Occupational Injuries
and Illnesses (SOII), to identify and document occupational heat-
related deaths and occupational HRIs, respectively. Researchers have
also relied on this system for identifying occupational HRIs (e.g.,
Spector et al., 2016). However, BLS data does not currently specify
discrete codes for all HRIs described in this health effects section.
The CFOI is a cooperative program between the Federal Government and
the States that relies on various administrative records, including
death certificates, to accurately produce counts of fatal work injuries
(BLS, 2012). The CFOI examines all cases marked ``At work'' on the
death certificate, and the CFOI database relies on the death
certificate (among other sources) to ascertain the cause(s) of death.
Further details about BLS reporting using OIICS codes, as well as rates
of HRIs, can be found in Section V., Risk Assessment.
III. Limitations
A limitation to relying on these coding systems to identify heat-
related fatalities and HRIs is underreporting. Numerous studies have
found that HRIs are likely vastly underreported (see Section V., Risk
Assessment). Reasons for the likely underreporting include
underreporting of illness and injuries by workers to their employers
(Kyung et al., 2023), underreporting of injuries and illnesses by
employers to BLS and OSHA (Wuellner and Phipps, 2018; Fagan and
Hodgson, 2017), underutilization of workers' compensation insurance
(Fan et al., 2006; Bonauto et al., 2010), influence of structural
factors and work culture on workers perceptions about seeking help
(Wadsworth et al., 2019; Iglesias-Rios, 2023), and difficulties with
determining heat-related causes of death (e.g., Luber et al., 2006;
Pradhan et al., 2019). As a result, there are likely many heat-related
fatalities and cases of HRIs that are not
captured in these coding systems. For a more detailed discussion of
underreporting, see Section V., Risk Assessment.
IV. Summary
As demonstrated by these coding systems, in which medical providers
or other public health professionals assign one or more codes to
identify a heat-related fatality or HRI, it is well accepted in the
medical and scientific communities that heat exposure, including
occupational heat exposure, can result in death and HRIs. Indeed, in
its review of the best available scientific and medical literature on
the health effects of occupational heat exposure, OSHA identified
several studies that relied upon data from these coding systems to
determine the incidence or prevalence of heat-related deaths and HRIs
in workers. OSHA relies on these studies in both this Health Effects
section and Section V., Risk Assessment, of this preamble to the
proposed rule.
D. Heat-Related Deaths
I. Introduction
Heat is the deadliest weather phenomenon in the United States (NWS,
2022). Heat as a cause of death is widely recognized in the medical and
scientific communities. Studies investigating relationships between
heat and mortality have long demonstrated positive associations between
heat exposure and increased all-cause mortality (e.g., Weinberger et
al., 2020; Basu and Samet, 2002; Whitman et al., 1997). As explained
below, the connection between heat exposure, the body's physiological
responses, and death (i.e., heat-related death mechanisms) is clearly
established. Exposure to occupational heat can be fatal. According to
BLS's CFOI, occupational heat exposure has killed 1,042 U.S. workers
between 1992-2022 (BLS, 2024c).
II. Physiological Mechanisms
Death caused by exposure to heat can occur in occupational settings
if the worker's body is not able to adequately cool in response to heat
exposure or if treatment for symptoms of heat-related illness is not
provided promptly. Nearly all body systems can be negatively affected
by heat exposure. Mora et al. (2017) systematically reviewed
mechanistic studies on heat-related deaths and identified five harmful
physiological mechanisms triggered by heat exposure that can lead to
death: ischemia (inadequate blood flow), heat cytotoxicity (damage to
and breakdown of cells), inflammatory response (inflammation that
disrupts cell and organ function), disseminated intravascular
coagulation (widespread dysfunction of blood clotting mechanisms), and
rhabdomyolysis (breakdown of muscle tissue). These mechanisms, with the
exception of rhabdomyolysis, are associated with the development of
heat stroke. Rhabdomyolysis, which is a potentially fatal illness
resulting from the breakdown of muscle tissue, can also occur in
conjunction with or in the absence of heat stroke. For a more detailed
discussion on rhabdomyolysis, see Section IV.H., Rhabdomyolysis. Mora
et al. (2017) also identified seven vital organs that can be critically
impacted by heat exposure--the brain, heart, kidneys, lungs, pancreas,
intestines, and liver. Across the five identified mechanisms and seven
vital organs, Mora et al. (2017) found medical evidence for twenty-
seven pathways whereby physiological mechanisms triggered by heat
exposure could lead to organ failure and fatality.
The most common cause of heat-related occupational deaths is heat
stroke. Heat stroke is a potentially fatal dysregulation of multiple
physiological processes and organ systems resulting in widespread organ
damage. Heat stroke is typically marked by significant elevation in
core body temperature and cognitive impairment due to central nervous
system damage. The physiological mechanisms involved in the development
and progression of heat stroke are discussed in more detail in Section
IV.E., Heat Stroke.
III. Determining Heat as a Cause of Death
The identification of deaths caused by heat exposure can take place
in a few different ways. Healthcare professionals may identify heat-
related deaths in medical settings. For example, a heat-related death
may be identified if an individual experiencing heat stroke presents to
an emergency room and then later dies. The heat-related nature of the
death should be documented by the healthcare professional in the chief
complaint field during medical history taking and selection of relevant
ICD diagnosis codes. The ICD system allows for identification of heat
as either an underlying cause of death or a significant contributing
condition. The ICD-10 instruction manual defines underlying cause as
``(a) the disease or injury which initiated the train of morbid events
leading directly to death, or (b) the circumstances of the accident or
violence which produced the fatal injury'' (WHO, 2016, p. 31). A
significant contributing condition is defined as a condition that
``contributed to the fatal outcome, but was not related to the disease
or condition directly causing death'' (WHO, 2004, p. 24).
Medical examiners or coroners can also identify heat as a cause of
death or significant condition contributing to death during death
investigations, which should be noted on the deceased individual's
death certificate. The National Association of Medical Examiners
(NAME), a professional organization for medical examiners, forensic
pathologists, and medicolegal affiliates and administrators, defines
``heat-related death'' as ``a death in which exposure to high ambient
temperature either caused the death or significantly contributed to
it'' (Donoghue et al., 1997). This definition was developed in an
effort to standardize the way in which heat-related deaths were
identified and documented on death certificates. According to the NAME
definition, cause is ascertained based on circumstances of the death,
investigative reports of high environmental temperature (e.g., a known
heat wave), or a pre-death temperature >=105 [deg]F. Cause is also
indicated in cases where the person may have a lower body temperature
due to attempted cooling measures, but where the individual had a
history of mental status changes and specific toxicological findings of
elevated muscle and liver enzymes. Heat may be designated as a
``significant contributing condition'' if: (1) ``antemortem body
temperature cannot be established but the environmental temperature at
the time of collapse was high''; and/or (2) heat stress exacerbated a
pre-existing disease, in which case heat and the pre-existing disease
would be listed as the cause and significant contributing condition,
respectively, or vice versa. Importantly, Donoghue et al. note ``The
diagnosis of heat-related death is based principally on investigative
information; autopsy findings are nonspecific.'' (Donoghue et al.,
1997). While this definition is the official definition of this
professional organization, other definitions or processes for
determining whether or not a death is heat-related may be used.
Additionally, there are processes in place to identify and document
deaths that are work-related. Death certificates include a field that
can be checked for ``injury at work'' (Russell and Conroy, 1991).
Further, work-related fatalities due to heat are identified and
documented through the CFOI (for more details, see Section IV.C.,
Overview of ICD and OIICS Codes for Heat-Related Health Effects).
IV. Occupational Heat-Related Deaths
Occupational heat exposure has led to worker fatalities in both
indoor and outdoor work settings and across a variety of industries,
occupations, and job tasks (Petitti et al., 2013; Arbury et al., 2014;
Gubernot et al., 2015; NIOSH, 2016; Harduar Morano and Watkins, 2017).
BLS's CFOI identified 1,042 U.S. worker deaths due to heat exposure
between 1992 and 2022, with an average of 34 fatalities per year during
that period (BLS, 2024c). Between 2011 and 2022, BLS reports 479 worker
deaths (BLS, 2024c). During the latest three years for which BLS
reports data (2020-2022), there was an average of 45 work-related
deaths due to exposure to environmental heat per year (BLS, 2024c).
However, for the reasons explained in Section V., Risk Assessment,
these statistics likely do not capture the true magnitude and
prevalence of heat-related fatalities because of underreporting.
There are numerous case studies documenting the circumstances under
which occupational heat exposure led to death among workers. For
example, in three NIOSH Fatality Assessment and Control Evaluations
(FACE) investigations of worker fatalities, workers died of heat stroke
after not receiving prompt treatment upon symptom onset (NIOSH, 2004;
NIOSH, 2007; NIOSH, 2015). Another case report of a farmworker who died
due to heat stroke indicates that confusion the worker experienced as a
result of heat exposure may have played a role in his ability to seek
help (Luginbuhl et al., 2008). Additional case reports show workers
have collapsed and later died while working alone, such as in mail
delivery (Shaikh, 2023), and that worker distress has been interpreted
as drug use as opposed to symptoms of heat illness (Alsharif, 2023).
V. Summary
OSHA's review of the scientific and medical literature indicates
that occupational heat exposure can and does cause death. The
physiological mechanisms by which heat exposure can result in death are
clearly established in the literature, and heat exposure being a cause
of death is widely recognized in the medical and scientific
communities. Indeed, occupational surveillance data demonstrates that
numerous work-related deaths from occupational heat exposure occur
every year.
E. Heat Stroke
I. Introduction
Among HRIs, the most serious and deadly illness from occupational
heat exposure is heat stroke. NIOSH (2016) defines heat stroke as ``an
acute medical emergency caused by exposure to heat from an excessive
rise in body temperature [above 41.1 [deg]C (106 [deg]F)] and failure
of the [body's] temperature-regulating mechanism.'' When this happens,
an individual's central nervous system is affected, which can result in
a sudden and sustained loss of consciousness preceded by symptoms
including vertigo, nausea, headache, cerebral dysfunction, bizarre
behavior, and excessive body temperature (NIOSH 2016).
Because progression of symptoms varies and involves central nervous
system function, it may be difficult for individuals, or those they are
with, to know when they are experiencing serious heat illness or to
understand that they need urgent medical care (Alsharif, 2023). If not
treated promptly, early symptoms of heat stroke may progress to
seizures, coma, and death (Bouchama et al., 2022). Thus, heat stroke is
often referred to as a life-threatening form of hyperthermia (i.e.,
elevated core body temperature) because it can cause damage to multiple
organs such as the liver and kidneys. Of note, the term ``stroke'' in
``heat stroke'' is a misnomer in that it does not involve a blockage or
hemorrhage of blood flow to the brain.
There are two types of heat stroke: classic heat stroke (CHS) and
exertional heat stroke (EHS). CHS can occur without any activity or
physical exertion, whereas EHS occurs as a result of physical activity.
CHS typically occurs in environmental conditions where ambient
temperature and humidity are high and is most often reported during
heat waves (Bouchama et al., 2022). It is most likely to affect young
children and the elderly (Laitano et al., 2019). Studies have found
that EHS can occur with any amount of physical exertion, even within
the first 60 minutes of exertion (Epstein and Yanovich, 2019; Garcia et
al., 2022). Additionally, EHS can occur in healthy individuals who
would otherwise be considered low risk performing physical activity,
regardless of hot or cool environmental conditions (Periard et al.,
2022; Epstein et al., 1999).
Cases of heat stroke can be identified in a few ways. Medical
personnel who make a formal diagnosis of heat stroke record the
corresponding ICD code in the patient's medical record. Medical
examiners also identify heat stroke as a cause of death or significant
condition contributing to death and note it on the deceased
individual's death certificate.
II. Physiological Mechanisms
Heat stroke happens when the body is under severe heat stress and
is unable to dissipate excessive heat to keep the body temperature at
37 [deg]C (98.6 [deg]F), resulting in an elevated core body temperature
(Epstein and Yanovich, 2019). The hallmark characteristics of heat
stroke are: (1) central nervous system (CNS) dysfunction, including
encephalopathy (i.e., brain dysfunction manifesting as irrational
behavior, confusion, coma, or convulsions); and (2) damage to multiple
organs, including the kidneys, liver, heart, pancreas, gastrointestinal
tract, as well as the circulatory system. There are three accepted
mechanisms through which heat exposure can cause CNS dysfunction and/or
multi-organ damage (Bouchama et al., 2022; Garcia et al., 2022; Iba et
al., 2022). All three mechanisms share a common origin: heat exposure
contributes to excessive heat stress, which results in hyperthermia.
One mechanism of heat stroke is reduced cerebral blood velocity
(CBV) (an indicator of blood flow to the brain) that results in
orthostatic intolerance (i.e., the inability to remain upright without
symptoms) (Wilson et al., 2006). As individuals experience whole body
heating, CBV is reduced and cerebral vascular resistance (the ratio of
carbon dioxide stimulus to cerebral blood flow) increases. These
changes ultimately contribute to reduced cerebral perfusion (flow of
blood from the circulatory system to cerebral tissue) and blood flow,
as well as orthostatic intolerance (Wilson et al., 2006).
Another mechanism is damage to the vascular endothelium.
Hyperthermia can damage or kill cells in the lining of blood vessels,
known as the vascular endothelium. The body responds to vascular
endothelium damage through a process called disseminated intravascular
coagulation (DIC). DIC is characterized by two processes: (1) tiny
clots form in the tissues of multiple organs, and (2) bleeding occurs
at the sites of those tiny clots. DIC is extremely damaging and results
in injury to organs (Bouchama and Knochel, 2002). Namely, DIC limits
the delivery of oxygen and nutrients to several organs including the
brain, heart, kidneys, and liver. Thus, DIC can result in both CNS
dysfunction and multi-organ damage. Additionally, damage to the
vascular endothelium makes it more permeable and creates an imbalance
in the substances that control blood clotting,
which promotes abnormal and increased blood clotting (Bouchama and
Knochel, 2002; Wang et al., 2022).
A third mechanism is damage to the cells in the lining of the gut,
known as the gut epithelium. Hyperthermia can alter the cell membranes'
permeability (Roti Roti et al., 2008), or directly cause cells to die
(Bynum et al., 1978). In either case, cells in the gut epithelium will
leak endotoxins into the blood, a process known as endotoxemia. When
these endotoxins circulate throughout the body, the immune system
aggressively responds by activating cells to fight infection and
inflammation, known as systemic inflammatory response syndrome (SIRS)
(Leon and Helwig, 2010). The presence of endotoxins, as well as the
body's aggressive immune response, can cause serious multi-organ damage
(Epstein and Yanovich, 2019; Wang et al., 2022). In particular, the
liver is usually one of the first organs to be damaged and is often
what causes a heat stroke death (Wang et al., 2022).
III. Occupational Heat Stroke
Heat stroke is life-threatening and can severely impair workers'
safety and health (Lucas et al., 2014). A study of work-related HRIs in
Florida using hospital data reported that, during the warm seasons from
May through October between 2005 through 2012, heat stroke was the
primary diagnosis in 91% (21 of 23) of deaths. In total, they reported
160 cases of work-related heat stroke (Harduar Morano and Watkins,
2017). Analyses of heat stroke among military members indicate that
roughly 73% of EHS patients require hospitalization for at least two
days (Carter et al., 2007).
IV. Treatment and Recovery
Heat stroke is a serious medical emergency that requires immediate
rest, cooling, and usually hospitalization. Prognosis for heat stroke
is highly dependent on how quickly heat stroke is recognized and how
quickly an affected worker can be cooled. When an affected person can
be diagnosed early and cooled rapidly, the prognosis is generally good.
For example, rapid cooling within one hour of presentation of symptoms
of CHS was found to reduce the mortality rate from 33% to 15% (Vicario
et al., 1986). For EHS, cooling the body below 104 [deg]F within 30
minutes of collapse is associated with very good outcomes (Casa et al.,
2012; Casa et al., 2015). The authors also reported that they were
unaware of any cases of fatalities among EHS victims where it was
recorded that the body was cooled below 104 [deg]F within 30 minutes of
collapse (Casa et al., 2012).
Comparably, others have found that the risk of morbidity and
mortality from heat stroke increases as treatment is delayed (Demartini
et al., 2015; Schlader et al., 2022). Schlader et al. (2022) found that
a delay in cooling can result in tissue damage, multi-organ
dysfunction, and eventually death. Similarly, Zeller et al. (2011)
found in their retrospective cohort study that patients who did not
receive early or immediate cooling had worse outcomes, such as more
severe forms of disease or death, although their study design does not
allow for conclusions regarding causality (Zeller et al., 2011).
Khogali and Weiner's (1980) case study report on 18 cases of heat
stroke found that 72% of the patients took between 30-90 minutes to
cool, whereas the other 28% were resistant to cooling, taking two to
five hours to reach 38 [deg]C (100.4 [deg]F). This means that there is
variation in how individuals respond to heat stroke treatment and that
some individuals will respond quicker to treatment than others. Prompt
treatment is likely even more critical for the individuals who take
longer to cool.
Data from the general population also demonstrate the serious
nature of heat stroke. One analysis of nationwide data estimated that
nearly 55% of emergency department visits for heat stroke required
hospitalization and roughly 3.5% of patients died in the emergency
department or at the hospital (Wu et al., 2014). This study also found
that heat stroke medical emergencies are more severe than other non-
heat-related emergencies, with a 2.6-fold increase in admission rate
and a 4.8-fold increase in case fatality compared to those other
conditions (Wu et al., 2014).
Complete recovery for individuals who are affected by heat stroke
may require time away from work. Some research suggests the length of
recovery time and the need for time away from work is based on how long
a person was at or above the critical core body temperature of 41
[deg]C (105.8 [deg]F), and how long it takes for biomarkers in blood to
normalize (McDermott et al., 2007). Relevant biomarkers include those
for acute liver dysfunction, myolysis (the breakdown of muscle tissue),
and other organ system biomarkers (Ward et al., 2020; Schlader et al.,
2022).
Guidelines for military personnel and athletes suggest that it may
be weeks or months before a worker who has suffered heat stroke can
safely return to work or perform the same level of work they did before
suffering heat stroke. U.S. military members have clear return-to-work
protocols post-heat stroke where members are assigned grades of
functional capacity in six areas: physical capacity or stamina, upper
extremities, lower extremities, hearing and ears, eyes, and psychiatric
functioning (O'Connor et al., 2007). For example, when a soldier/airman
experiences heat stroke, they automatically receive a reduced function
capacity grade status in physical capacity. This also results in an
automatic referral to a medical examination board. Soldiers and airmen
are not cleared to return to duty until their laboratory results
normalize, and even then, their status remains a trial of duty. If the
individual has not exhibited any heat intolerance after three months,
they are returned to a normal work schedule. However, maximal exertion
and significant heat exposure remains prohibited for these individuals.
If a military member experiences any heat intolerance during the period
of restriction, or subsequent resumption to normal duty, a referral to
the physical examination board for a hearing regarding their health
status is required (O'Connor et al., 2007).
The U.S. Navy has its own set of guidelines, which does not
distinguish between heat exhaustion and heat stroke, but uses
laboratory tests, especially liver function tests, to determine when
sailors are allowed to return to duty. For those who have suffered heat
stroke, full return to duty is usually not granted until somewhere
between two days to three weeks later (O'Connor et al., 2007).
In 2023, the American College of Sports Medicine (ACSM) published
their consensus statement which provides evidence-based strategies to
reduce and eliminate HRIs, including a return to activity protocol for
athletes recovering from EHS (Roberts et al., 2023). Of note, ACSM
names athletes (whether elite, recreational, or tactical) and
occupational laborers as groups who are active and regularly perform
exertional activities that could lead to EHS. Specifically, ACSM
recommendations include refraining from exercise for at least seven
days following release from the initial medical care for EHS treatment.
Once all laboratory results and vital signs have normalized, ACSM
recommends an individual can exercise in cool environments and
gradually increase duration, intensity, and heat exposure over a two to
four-week period to initiate environmental acclimatization (Roberts et
al., 2023). If the affected athlete does not return to pre-EHS activity
levels within four to six weeks, further medical evaluation is needed.
ACSM recommends a full return to
activity between two to four weeks after the individual has
demonstrated exercise acclimatization and heat tolerance with no
abnormal symptoms or test results during the re-acclimatization period
(Roberts et al., 2023). Similarly, the National Athletic Trainer's
Association proposes that individuals who experience EHS should
complete a 7 to 21-day rest period, be asymptomatic, have normal blood-
work values, and obtain a physician's clearance prior to beginning a
gradual return to activity (Casa et al., 2015).
In the military setting it is accepted that returning to work too
early and/or without adequate work restrictions can result in
incomplete recovery from heat stroke, which may necessitate a prolonged
restricted work status (McDermott et al., 2007). About 10-20% of people
who have had heat stroke have been shown to experience heat intolerance
roughly two months after having the heat stroke (Binkley et al., 2002).
In some instances, this has lasted for five years and has increased the
risk for another heat stroke (Binkley et al., 2002; McDermott et al.,
2007). Similarly, a case study report of EHS cases amongst the U.S.
Army found that in one of the ten cases examined, the person was heat
intolerant for 11.5 months post-EHS (Armstrong et al., 1989).
Only a limited number of studies have focused on the long-term
effects of heat stroke. This includes research by Wallace et al.
(2007), whose retrospective review of military service members found
that those who suffered an EHS event earlier in life were more likely
to die due to cardiovascular disease and ischemic heart disease.
Similarly, Wang et al. (2019) report that prior exertional heat illness
was associated with a higher prevalence of acute ischemic stroke, acute
myocardial infarction, and an almost three-fold higher prevalence of
chronic kidney disease. Other research in mice support these claims and
indicate that epigenetic effects post-EHS result in immunosuppression
and an altered heat shock protein response as well as development of
metabolic disorders that could negatively impact long-term
cardiovascular health (Murray et al., 2020; Laitano et al., 2020).
V. Summary
OSHA's review of the scientific and medical literature indicates
that occupational heat exposure can cause heat stroke, a medical
emergency. The physiological mechanisms by which heat exposure can
result in heat stroke are well-established in the literature, and heat
exposure as a cause of heat stroke is well-recognized in the medical
and scientific communities. The best available research demonstrates
that heat stroke must be treated as soon as possible and that prolonged
time between experiencing heat stroke and seeking treatment increases
the likelihood of death and may result in long-term health effects.
F. Heat Exhaustion
I. Introduction
NIOSH defines heat exhaustion as ``[a] heat-related illness
characterized by elevation of core body temperature above 38 [deg]C
(100.4 [deg]F) and abnormal performance of one or more organ systems,
without injury to the central nervous system'' (NIOSH, 2016). Heat
exhaustion can progress to heat stroke if not treated properly and
promptly, and may require time away from work for a full recovery.
Signs and symptoms of heat exhaustion typically include profuse
sweating, changes in mental status, dizziness, nausea, headache,
irritability, weakness, decreased urine output and elevated core body
temperature up to 40 [deg]C (104 [deg]F) (NIOSH, 2016; Kenny et al.,
2018). Collapse may or may not occur. Significant injury to the central
nervous system, and significant inflammatory response do not occur
during heat exhaustion. However, there appears to be a fine line
between heat exhaustion and heat stroke. Kenny et al. 2018 state that
it can be difficult to clinically differentiate between heat exhaustion
and early heat stroke. NIOSH also states that heat exhaustion ``may
signal impending heat stroke'' (NIOSH, 2016). Armstrong et al. (2007)
recommend that rectal temperature be taken to distinguish between heat
exhaustion and heat stroke.
II. Physiological Mechanisms
Heat exhaustion occurs when heat stress results in elevated body
temperature between 98.6 [deg]F and 104 [deg]F (37 [deg]C and 40
[deg]C) and physiological changes occur (Kenny et al., 2018). Under
these significant heat stress conditions, heavy sweating occurs, tissue
perfusion is reduced, and inflammatory mediators are released.
Electrolyte imbalances can occur due to fluid and electrolyte losses
through sweating paired with inadequate replenishment. Voluntary and
involuntary dehydration can exacerbate this process (Hendrie et al.,
1997; Brake and Bates, 2003). ``Voluntary dehydration,'' as used by
Brake and Bates, refers to the circumstance where a dehydrated worker
does not adequately rehydrate, despite the availability of water. Upon
review of several studies, Kenny et al. (2018) report that dehydration
among workers is common, even when water is readily available. There is
also evidence that even when water intake increases, as sweat rate and
dehydration increase, intake may not be adequate to fully replace
losses (Hendrie et al., 1997).
Brake and Bates (2003) summarized various hypothesized reasons for
voluntary and involuntary dehydration. One hypothesized reason for
voluntary dehydration is a delayed or decreased thirst response (Brake
and Bates, 2003). Other reasons include mechanisms that affect fluid
retention, such as the dependence of fluid retention on solutes such as
sodium, which may be in imbalance under heat stress (Brake and Bates,
2003). Lack of adequate hydration could also be due to workplace
pressures or concerns about sanitation (Rao, 2007; Iglesias-Rios,
2023).
The combination of heat stress, upright posture, and low vascular
fluid volume (hypovolemia) can further dysregulate the circulatory
system and affect clotting mechanisms (Kenny et al., 2018). Heat stress
reduces blood flow to the abdominal organs, kidneys, muscles, and brain
and increases blood flow to the skin to aid in cooling. These changes
in the circulatory system and blood flow to the brain can potentially
lead to dizziness or faintness upon standing (orthostatic intolerance),
or collapse. Other factors that affect the development of heat
exhaustion include individual health status, preparedness (such as
acclimatization level), individual characteristics, knowledge, access
to fluids, environmental factors, personal protective equipment use and
work pacing and intensity (Kenny, 2018).
III. Occupational Heat Exhaustion
Heat exhaustion is one of the more common heat-related illnesses
(Armstrong et al., 2007; Harduar Morano and Watkins, 2017; Lewandowski
and Shaman, 2022). In their study of heat-illness hospitalizations in
Florida during May to October from 2005-2012, Harduar Morano and
Watkins (2017) reported that there were 2,659 cases of work-related
heat exhaustion that resulted in emergency department visits or
hospitalization, versus 181 cases of work-related heat stroke that
resulted in emergency department visits, hospitalization, or death.
Similar results have been reported in studies of heat-related illness
among the United States Armed Forces and miners showing the frequency
of heat exhaustion (Dickinson, 1994; Armed Forces Health Surveillance
Division, 2022b;
Lewandowski and Shaman, 2022; Donoghue et al., 2000; Donoghue, 2004).
While in some studies heat exhaustion is not specifically diagnosed,
several qualitative studies describe self-reported symptoms in workers
that may be indicative of heat exhaustion (e.g., Mirabelli et al.,
2010; Fleischer et al., 2013; Kearney et al., 2016; Mutic et al.,
2018). These symptoms included headache, nausea, vomiting, feeling
faint, and heavy sweating.
IV. Treatment and Recovery
Heat exhaustion may require treatment beyond basic first aid to
prevent progression to heat stroke (Kenny et al., 2018). In cases where
the degree of severity of heat illness is unclear, the individual
should be treated as if they have heat stroke (Armstrong, 1989). For a
worker experiencing heat exhaustion, NIOSH recommends the following
steps to ensure the worker receives proper and adequate treatment:
``Take worker to a clinic or emergency room for medical evaluation and
treatment; If medical care is unavailable, call 911; Someone should
stay with worker until help arrives; Remove worker from hot area and
give liquids to drink; Remove unnecessary clothing, including shoes and
socks; Cool the worker with cold compresses or have the worker wash
head, face, and neck with cold water; Encourage frequent sips of cool
water'' (NIOSH, 2016).
Complete recovery from heat exhaustion may require a restricted
work status (or limited work duties). Donoghue et al. (2000) reported
that following heat exhaustion, 29% (22 of 77) of miners included in
the study required a restricted work status for at least one shift. The
military has specific protocols for return to duty following heat
exhaustion. For example, the U.S. Army and Air Force follow the
protocol outlines in AR 40-501 (O'Connor et al., 2007). Three instances
of heat exhaustion in less than 24 months can result in referral to a
Medical Evaluation Board before a full return to service. Some military
units have additional or more specific guidelines. For example, one
military unit, at Womack Army Medical Center in North Carolina, has
guidelines that allow individuals who are considered to have mild
illness, fully recovered in the emergency room, and have no abnormal
laboratory findings to return to light duty the following day and
limited duty the day after that. However, they also indicate that some
effects of heat illness may be subtle or delayed and recommend
individuals avoid strenuous exercise for several days and remain under
observation (O'Connor et al., 2007).
V. Summary
The scientific and medical literature presented here clearly
demonstrate that heat exhaustion is a recognized health effect of
occupational heat exposure. The best available evidence on the
symptoms, treatment, and recovery of heat exhaustion demonstrates that
heat exhaustion can progress to heat stroke, a medical emergency, if
not treated promptly and that heat exhaustion may require time away
from work for a full recovery.
G. Heat Syncope
I. Introduction
Occupational heat exposure can result in heat syncope. Syncope is
the medical term for ``fainting,'' and heat syncope is defined as
``fainting, dizziness, or light-headedness after standing or suddenly
rising from a sitting/lying position'' due to heat exposure (NIOSH,
2023a). Heat syncope may sometimes be referred to as ``exercise-
associated collapse'' (EAC), but heat syncope can happen without
significant levels of exertion (Asplund et al., 2011; Pearson et al.,
2014). As explained below, heat syncope is an acknowledged and
documented health effect of occupational heat exposure.
II. Physiological Mechanisms
There are two mechanisms for how heat exposure can cause heat
syncope (Schlader et al., 2016; Jimenez et al., 1999). One mechanism
for heat syncope is reduced blood flow to the brain. Elevated core
temperature induces vasodilation, sweating, and may result in blood
pooling in certain areas of the body (see Section IV.B., General
Mechanisms of Heat-Related Health Effects). Thus, there is a lower
circulating blood volume, which can reduce blood flow to the brain and
cause loss of consciousness (Wilson et al., 2006; Van Lieshout et al.,
2003).
A second mechanism for heat syncope is reduced cerebral blood
velocity (CBV) (indicative of reduced blood flow to the brain) that
results in orthostatic intolerance (the inability to remain upright
without symptoms) during a heat stress episode (Wilson et al., 2006).
As individuals experience whole body heating, CBV is reduced and
cerebral vascular resistance (the ratio of carbon dioxide stimulus to
cerebral blood flow) increases. These changes ultimately contribute to
reduced cerebral perfusion and blood flow, as well as orthostatic
intolerance (Wilson et al., 2006). The orthostatic response to heat
stress during ``rest'' (i.e., standing/sitting) is essentially
equivalent to the orthostatic response to heat stress after exercise if
skin temperature is similarly elevated (Pearson et al., 2014). While
core temperature is not always elevated in cases of heat syncope, skin
temperature typically is (Department of the Army, 2022; Noakes et al.,
2008).
Differentiating between heat syncope, heat exhaustion, and heat
stroke is a critical step in proper diagnosis (Santelli et al., 2014;
Coris et al., 2004). As stated above, heat syncope always involves loss
of consciousness, but it does not require elevated core body
temperature (Santelli et al., 2014; Holtzhausen et al., 1994).
Conversely, heat exhaustion and stroke do not require loss of
consciousness. Though central nervous system (CNS) disturbances are
possible in heat stroke and heat stroke is always characterized by
significantly elevated core temperature. Further, recovery of mental
status is faster in heat syncope than in exhaustion and heat stroke,
since cooling may not be required for treatment of heat syncope (Howe
and Boden, 2007).
III. Occupational Heat Syncope
Workers have experienced heat syncope when exposed to heat. A
survey-based study in southern Georgia found that 4% of 405 farmworkers
experienced fainting within the previous week (Fleischer et al., 2013).
Another survey-based study in North Carolina asked 281 farmworkers if
they had ever experienced heat-related illness and found that 3% of
workers had fainted (Mirabelli et al., 2010). While these cases were
not formally diagnosed as heat syncope, Fleischer reported temperatures
ranging from 34-40 [deg]C (94-104 [deg]F) and a heat index of 37-42
[deg]C (100-108 [deg]F) at the time workers fainted, and Mirabelli
described the working conditions at the time of fainting as being in
``extreme heat.''
IV. Treatment and Recovery
NIOSH recommends treating heat syncope by having the worker sit
down in a cool environment and hydrate with either water, juice, or a
sports drink (NIOSH, 2016). The Department of the Army recommends that
``victims of heat/parade syncope will recover rapidly once they sit or
lay supine, though complete recovery of stable blood pressure and heart
rate (resolution of orthostasis or ability to stand without fainting)
in some individuals may take 1 to 2 hours'' (Department of the Army,
2022). Treatment recommendations for athletes consist of moving the
athlete to a cool area and laying them supine with elevated legs to
assist in venous return,
possibly with oral or intravenous rehydration (Peterkin et al., 2016;
Howe and Boden, 2007; Seto et al., 2005; Lugo-Amador et al., 2004).
An episode of heat syncope may require time away from work for a
thorough evaluation to ascertain one's risk for recurrent/future
episodes of heat syncope. No studies have evaluated recurring episodes
of syncope among workers specifically, but a study found that, for the
general population, 1-year syncope recurrence (any type) was 14% in
working-age people (18-65 years) (Barbic et al., 2019). The U.S. Army
has a requirement to ``obtain a complete history to rule out other
causes of syncope, including an exertional heat illness or other
medical diagnosis (for example, cardiac disorder)'' (Department of the
Army, 2022). Recommendations for athletes include thorough evaluation
``for injury resulting from a fall, and all cardiac, neurologic, or
other potentially serious causes for syncope'' (Howe and Boden, 2007;
Lugo-Amador et al., 2004; Binkley et al., 2002). Indeed, if an injury
(e.g., fall, collision) is sustained because of heat syncope, treatment
beyond first aid (including hospitalization) may be necessary.
Supporting this point, more general syncope has been linked to
occupational accidents requiring hospitalizations (Nume et al., 2017).
V. Summary
The scientific and medical literature presented in this section
demonstrate that heat syncope is a recognized health effect of
occupational heat exposure. Studies suggest that heat syncope may
require time away from work for further evaluation. Additionally, heat
syncope can lead to injuries (e.g., injury from a fall), some of which
may require hospitalization.
H. Rhabdomyolysis
I. Introduction
Rhabdomyolysis is a life-threatening illness that can affect
workers exposed to occupational heat. NIOSH defines rhabdomyolysis as
``a medical condition associated with heat stress and prolonged
physical exertion, resulting in the rapid breakdown of muscle and the
rupture and necrosis of the affected muscles'' (NIOSH, 2016). This
definition is specific to exertional rhabdomyolysis. Another form of
rhabdomyolysis, called traumatic rhabdomyolysis, is caused by direct
muscle trauma (e.g., from a fall or crush injury). Workers can
experience such injuries, and consequently suffer from traumatic
rhabdomyolysis, because of occupational heat exposure (see Section
IV.P., Heat-Related Injuries). However, this section will focus only on
exertional rhabdomyolysis. Unless otherwise specified, all references
to rhabdomyolysis are shorthand for exertional rhabdomyolysis.
Signs and symptoms of rhabdomyolysis include myalgia (muscle pain),
muscle weakness, muscle tenderness, muscle swelling, and/or dark-
colored urine (Armed Forces Health Surveillance Division, 2023b; Dantas
et al., 2022; O'Connor et al., 2008; Cervellin et al., 2010). Notably,
the onset of these symptoms may be delayed by 24-72 hours (Kim et al.,
2016). Rhabdomyolysis commonly affects individuals who are exposed to
heat during physical exertion. For example, the Centers for Disease
Control and Prevention (CDC) investigated an incident in which an
entire cohort of 50 police trainees were diagnosed with rhabdomyolysis
after the first 3 days of a 14-week training program; the trainees had
engaged in heavy physical exertion outdoors with limited access to
water. The CDC concluded that adequate hydration is particularly
important when the HI approaches 80 [deg]F (Goodman et al., 1990).
Rhabdomyolysis has long been recognized as a heat-related illness
by NIOSH, the U.S. Armed Forces, and national athletic organizations
such as the American College of Sports Medicine (Armstrong et al.,
2007). Specifically, NIOSH lists rhabdomyolysis as an ``acute heat
disorder'' in its Criteria for a Recommended Standard (2016) and
provides detailed recommendations for recognition and treatment of
rhabdomyolysis. NIOSH also conducted case studies and retrospective
analyses to identify cases of rhabdomyolysis among workers exposed to
heat, including firefighter cadets and instructors, as well as park
rangers (Eisenberg et al., 2019; Eisenberg J et al., 2015; Eisenberg
and Methner, 2014).
Similarly, the U.S. Armed Forces developed a case definition that
specifies rhabdomyolysis can be heat-related (Armed Forces Health
Surveillance Board, 2017), and this definition is applied in their
annual surveillance reports of HRIs. From 2018 to 2022, most
rhabdomyolysis cases (75.9%) occurred during warmer months (i.e., May
to October) (Armed Forces Health Surveillance Division, 2023b). In a
retrospective study of hospital admissions for rhabdomyolysis in
military members (2010-2013), 60.1% (193 out of 321) cases were deemed
to be associated with exertion and exposure to heat (Oh et al., 2022).
Many studies have also found that rhabdomyolysis often coincides
with exertional heat stroke and other HRIs such as heat exhaustion,
heat cramps, hyponatremia, and dehydration. The frequent co-occurrence
of rhabdomyolysis and other HRIs has been reported among workers,
including police and firefighters (Eisenberg et al., 2019; Goodman et
al., 1990), workers included in OSHA enforcement investigations (Tustin
et al., 2018a), military members (Oh et al., 2022; Carter et al.,
2005), athletes (Thompson et al., 2018), and in the general population
(Thongprayoon et al., 2020).
II. Physiological Mechanisms
Studies have identified two interrelated mechanisms through which
heat exposure, combined with exertion, can cause rhabdomyolysis. Both
mechanisms share a common origin: occupational heat exposure and
exertion both contribute to excessive heat stress, which in turn causes
an elevated core temperature. Both mechanisms also share a common
outcome: the breakdown and death of muscle tissue, which is the
hallmark characteristic of rhabdomyolysis. The first mechanism is
thermal injury to muscle cells. When the body's core temperature is
elevated, it creates a toxic environment that can directly injure or
kill muscle cells. The temperature at which this occurs, known as the
thermal maximum, is estimated to be about 107.6 [deg]F (42 [deg]C)
(Bynum et al., 1978). At the thermal maximum, the structural components
of the cells' membranes are liquified and the membrane breaks down.
Proteins in the cells' mitochondria, which are key to energy
production, change shape and no longer function properly. Calcium,
which is normally maintained at a low level inside muscle cells, will
rush into the cells and activate inflammatory processes that accelerate
the death of those cells (Torres et al., 2015; Khan, 2009).
The second mechanism is lack of oxygen to muscle cells. When the
body attempts to cool itself, it can lose high volumes of sweat. Sweat
loss can deplete the body's stores of water and electrolytes, leading
to low blood volume (see Section IV.B., General Mechanisms of Heat-
Related Health Effects). Low blood volume, and low potassium in the
blood (known as hypokalemia), can both contribute to muscle cell death.
An adequate supply of blood is necessary to deliver oxygen to muscles,
and an adequate supply of potassium is needed to support vasodilation
(to support increased blood flow to the muscles during exertion). When
neither blood volume nor
potassium are sufficient, the muscle cells do not receive enough oxygen
(known as ischemia). When this occurs, the muscle cells produce less
energy and eventually will die if exertion continues (Knochel and
Schlein, 1972).
III. Occupational Rhabdomyolysis
While OSHA is not aware of surveillance data on the incidence of
rhabdomyolysis in the worker population in the United States, there are
surveillance data on the incidence of rhabdomyolysis among active
military members in the Army, Navy, Air Force, and Marine Corps. These
data have been reported for the U.S. Army from 2004 to 2006 (Hill et
al., 2012) and for all military branches from 2008 through 2022 (Armed
Forces Health Surveillance Division, 2023b; Armed Forces Health
Surveillance Division, 2018; U.S. Armed Forces, 2013). These
surveillance data and the studies described above by NIOSH and others
indicate that workers performing strenuous tasks in the heat are at
risk of developing rhabdomyolysis. The U.S. Armed Forces has
successfully identified many cases of heat-related rhabdomyolysis by
searching medical records for the presence of either the ICD-10 code
for rhabdomyolysis and/or the ICD-10 code for myoglobinuria, along with
any other heat-related codes (table IV-1) (Armed Forces Health
Surveillance Division, 2023b; Oh et al., 2022).
IV. Treatment and Recovery
Rhabdomyolysis is a serious heat-related illness that can cause
life-threatening complications. Many cases of rhabdomyolysis may
require hospitalization. For example, A CDC investigation into a police
training program in Massachusetts found that 26% of police trainees (13
out of 50) were hospitalized for rhabdomyolysis only three days into
their training (Goodman et al., 1990). The mean length of
hospitalization was 6 days, with a range of 1 to 20 days (Goodman et
al., 1990). Similarly, a military surveillance study identified 473
rhabdomyolysis cases among military members in 2022, with 35.3% of
cases (167 out of 473) requiring hospitalization (Armed Forces Health
Surveillance Division, 2023b). In a retrospective study of 193 military
trainees hospitalized for rhabdomyolysis, the mean length of
hospitalization was 2.6 days, with a range of 0 to 25 days (Oh et al.,
2022).
The focus of treatment for rhabdomyolysis during hospitalization is
to reduce levels of creatine kinase (CK) and myoglobin in the blood, as
well as correct electrolyte imbalances, through aggressive
administration of intravenous fluids (generally normal saline)
(O'Connor et al., 2020; Luetmer et al., 2020; Manspeaker et al., 2016;
Torres et al., 2015). Monitoring is used to repeatedly measure CK
levels until a peak concentration is reached (often within 1-3 days),
and then to ensure that CK levels are consistently trending downwards
before discharge from the hospital (Kodadek et al., 2022; Oh et al.,
2022).
Complications of rhabdomyolysis are also possible. When muscle
cells die, they release several electrolytes and proteins into the
bloodstream that can cause severe health complications. For example,
the release of potassium from muscle cells can cause hyperkalemia (high
level of potassium in the blood), which then leads to heart arrhythmias
(abnormal heart rhythms) (Mora et al., 2017; Sauret et al., 2002).
Also, the release of myoglobin into the bloodstream can be toxic for
the kidneys. When blood is filtered by nephrons (functional units of
the kidneys) to produce urine, the presence of even small amounts of
myoglobin can obstruct and damage the nephrons (Mora et al., 2017;
Sauret et al., 2002). In some cases, these complications from
rhabdomyolysis can be life-threatening (Wesdock and Donoghue, 2019) and
in fact fatalities have been reported (Gardner and Kark, 1994; Goodman
et al., 1990). A more detailed discussion of how rhabdomyolysis can
cause acute kidney injury or other kidney damage can be found in
Section IV.M., Kidney Health Effects.
Guidelines for return to work among workers diagnosed with
rhabdomyolysis are limited. In the U.S. military, soldiers deemed to be
at low risk for recurrence of rhabdomyolysis are restricted to light,
indoor duty and encouraged to rehydrate for at least 72 hours to allow
for normalization of CK levels. If CK levels do not normalize, they
must continue indoor, light duty; if CK levels do normalize, they can
proceed to light, outdoor duty for at least 1 week and must show no
return of clinical symptoms before they can gradually return to full
duty. In contrast, soldiers deemed to be at high risk for recurrence of
rhabdomyolysis must undergo additional diagnostic tests, with
consultation from experts, and can be given an individualized,
restricted exercise program while they await clearance for full return
to duty (O'Connor et al., 2020; O'Connor et al., 2008). These
guidelines have been adopted by the Armed Forces and restated in their
surveillance reports of rhabdomyolysis (Armed Forces Health
Surveillance Division, 2023b).
V. Summary
The available scientific literature indicates that rhabdomyolysis
can result from physical exertion in the heat. Based on plausible
mechanistic data, studies by NIOSH and others, and surveillance data
indicating incidence of rhabdomyolysis among active military members,
OSHA preliminarily determines that workers performing strenuous tasks
in the heat are at risk of rhabdomyolysis.
I. Hyponatremia
I. Introduction
Workers in hot environments may experience hyponatremia, a
condition that occurs when the level of sodium in the blood falls below
normal levels (<135 milliequivalents per liter (mEq/L)) (NIOSH, 2016).
Hyponatremia is often caused by drinking too much water or hypotonic
fluids, such as sports drinks, over a prolonged period of time. Without
sodium replacement, the high water intake can result in losses of
sodium in the blood as more sodium is lost due to increased sweating
from heat exposure and urination (Korey Stringer Institute (KSI),
n.d.). Mild forms of hyponatremia may not produce any signs or
symptoms, or may present with symptoms including muscle weakness and/or
twitching, dizziness, lightheadedness, headache, nausea and/or
vomiting, weight gain, and swelling of the hands or feet (KSI, n.d.;
NIOSH, 2016). In severe cases, hyponatremia may cause altered mental
status, seizures, cerebral edema, pulmonary edema, and coma, which may
be fatal (KSI, n.d.; NIOSH, 2016; Rosner and Kirven, 2007). NIOSH and
the U.S. Army classify hyponatremia as a heat-related illness (NIOSH,
2016; Department of the Army, 2022).
II. Physiological Mechanisms
When exposed to heat, the autonomic nervous system triggers the
body's sweat response, in which sweat glands release water to wet the
skin (Roddie et al., 1957; Grant and Holling, 1938). The purpose of the
sweat response is to cool the body. However, in doing so, it can
deplete the body's stores of water and electrolytes (e.g., sodium,
potassium, chloride, calcium, and magnesium) that are essential for
normal bodily function (Shirreffs and Maughan, 1997). As the body's
store of sodium is lessening and high quantities of water are consumed,
hyponatremia may develop as sodium in the blood becomes diluted (<135
mEq/L). In some cases, this dilution may cause an osmotic
disequilibrium--an imbalance in the amount of sodium inside and outside
the cell resulting in
cellular swelling--which can lead to the serious and fatal health
outcomes discussed above.
III. Occupational Hyponatremia
Surveillance of hyponatremia among workers is limited. However, a
recent case study demonstrates the potential severity and life-
threatening nature of hyponatremia. After a seven-day planned absence
from work, a 34-year-old male process control operator in an aluminum
smelter pot room was hospitalized due to a variety of HRI symptoms
including hyponatremia, with serum (the liquid portion of blood
collected without clotting factors) sodium level of 114 millimoles per
liter (mmol/L) (reference range: 136-145 mmol/L) (Wesdock and Donoghue,
2019). After 13 days in the hospital, the patient was discharged with a
diagnosis of ``severe hyponatremia likely triggered by heat exposure''
(Wesdock and Donoghue, 2019). The patient was still out of work 32
weeks after the incident. While no temperature data for the pot room
were available, an exposure assessment used outdoor temperatures that
day and pot room temperatures from the literature to estimate that the
WBGT could have been as high as 33 [deg]C, which the authors state
exceeds the ACGIH TLV for light work for acclimatized workers (Wesdock
and Donoghue, 2019).
The relationship of heat exposure and hyponatremia was examined
among male dockyard workers in Dubai, United Arab Emirates (Holmes et
al., 2011). This population performed long periods of manual work in
the heat and consumed a diet low in sodium. A first round of plasma
(i.e., the liquid part of blood collected that contains water,
nutrients and clotting factors) samples were taken at the end of the
summer (n=44), with a second round taken at the end of the winter among
volunteers still willing to participate (n=38). In the summer, 55% of
participants were found to be hyponatremic (<135 millimolar (mM)),
whereas only 8% were hyponatremic in the winter. Although ambient
temperature conditions were not reported, the authors indicate that
hyponatremia was highest during the summer because of sodium losses
through sweat and inadequate sodium replacement (Holmes et al., 2011).
Hyponatremia among the military population has been well documented
by the Annual Armed Forces Health Surveillance Division, which releases
annual reports on exertional hyponatremia among active duty component
services members, each with surveillance data for the previous 15 years
(e.g., Armed Forces Health Surveillance Division, 2023a; Armed Forces
Health Surveillance Division, 2022a; Armed Forces Health Surveillance
Division, 2021; Armed Forces Health Surveillance Division, 2020). Cases
come from the Defense Medical Surveillance System and include both
ambulatory medical visits and hospitalizations in both military and
civilian facilities. During the period of 2004 through 2022, the number
of cases of hyponatremia among U.S. Armed Forces peaked in 2010 with
180 cases. The lowest number during that time period was 2013, when 72
cases were reported. During the last 15 years in which data were
reported (2007-2022), 1,690 cases of hyponatremia occurred. Of these
1,690 cases, 86.8% (1,467) were diagnosed and treated during an
ambulatory care visit (Armed Forces Health Surveillance Division,
2023a). As the diagnostic code for hyponatremia may include cases that
are not heat-related, these data may be overestimates. However, such
overestimation is reduced in this study as the authors controlled for
many other related diagnoses (e.g., kidney diseases, endocrine
disorders, alcohol/illicit drug abuse), which can cause hyponatremia.
IV. Treatment and Recovery
Treatment and recovery for hyponatremia can vary depending on
severity and symptoms. Workers presenting with mild symptoms should
increase salt intake by consuming salty foods or oral hypertonic saline
and restrict fluid until symptoms resolve or sodium levels return to
within normal limits (KSI, n.d.). Medical attention may be required in
severe cases, which may be life-threating, and may be sought to address
symptoms and personal risk factors (e.g., history of heart conditions,
on a low sodium diet) (NIOSH, 2016).
V. Summary
The available evidence in the scientific literature indicates that
hyponatremia can result from occupational heat exposure. The evidence
on treatment and recovery demonstrates that hyponatremia can require
medical attention and, in some cases, may be life-threatening.
J. Heat Cramps
I. Introduction
Workers exposed to environmental or radiant heat can experience
sudden muscle cramps known as ``heat cramps.'' NIOSH defines heat
cramps as ``a heat-related illness characterized by spastic
contractions of the voluntary muscles (mainly arms, hands, legs, and
feet), usually associated with restricted salt intake and profuse
sweating without significant body dehydration'' (NIOSH, 2016). Someone
can experience heat cramps even if they are frequently hydrating with
water, but they are not replenishing electrolytes. Heat cramps are
recognized as a ``heat-related illness'' by numerous organizations,
including NIOSH, U.S. Army, U.S. Navy, National Athletic Trainers'
Association (NATA), American College of Sports Medicine (ACSM), and
World Medicine (formerly known as IAAF).
II. Physiological Mechanisms
It is recognized in the medical and scientific communities that
heat cramps result from heat exposure. However, the exact physiological
mechanism is not known. In an early study of heat cramps, investigators
included the following as the diagnostic criteria for heat cramps:
exposure to high temperatures at work; painful muscle cramps; rapid
loss of salt in the sweat that is not replaced (which may cause
hyponatremia); diminished concentration of chloride in the blood and in
the body tissues (also known as hypochloremia); and rapid amelioration
of symptoms after appropriate treatment (Talbott and Michelsen, 1933).
The following mechanism has been proposed for the development of
heat cramps: profuse sweating can deplete electrolyte stores (e.g.,
sodium (Na), potassium (K), calcium (Ca)), which exacerbates muscle
fatigue and can cause heat cramps (Bergeron, 2003; Horswill et al.,
2009; Schallig et al., 2017; Derrick, 1934). The U.S. Army further
posits that ``intracellular calcium is increased via a reduction in the
sodium concentration gradient across the cell membrane. The increased
intracellular calcium accumulation then stimulates actin-myosin
interactions (that is, filaments propelling muscle filaments) causing
the muscle contractions'' (Department of the Army, 2022). Heat cramps
are sometimes referred to, more broadly, as exercise-associated muscle
cramps (EAMCs) (Bergeron et al., 2008). However, heat cramps are
distinct in that they only occur in hot conditions, which exacerbate
electrolyte depletion, and may or may not be associated with exercise.
III. Occupational Heat Cramps
Surveillance data and survey study data demonstrate that workers
exposed to environmental or radiant heat frequently experience heat
cramps in the United States. In a study of heat-related illness
hospitalizations and deaths for the U.S. Army from 1980-
2002, 8% of heat-related illness hospitalizations recorded were due to
heat cramps (Carter et al., 2005). Similarly, in studies of self-
reported heat-related illness, workers frequently cite heat cramps as a
common symptom of heat exposure. Specifically, in several studies of
self-reported heat-related symptoms among farmworkers in multiple
States, participants reported experiencing sudden muscle cramps in the
prior week in Georgia (33.7% of 405 respondents) (Fleischer et al.,
2013), North Carolina (35.7% of 158 respondents) (Kearney et al.,
2016), and Florida (30% of 198 respondents) (Mutic et al., 2018). In
another study of self-reported symptoms among 60 migrant farmworkers in
Georgia, heat-related muscle cramps were reported by 25% of
participants, the second most frequently reported HRI symptom (Smith et
al., 2021). In a study examining exertional heat illness and
corresponding wet bulb globe temperatures in football players at five
southeastern U.S. colleges from August to October 2003, the authors
found that the highest incidences of exertional heat illness (EHI)
occurred in August (88%, EHI rate= 8.95/1000 athlete-exposures (Aes))
and consisted of 70% heat cramps (6.13/1000 Aes) (Cooper et al., 2016).
IV. Treatment and Recovery
Treatment for heat cramps includes electrolyte-containing fluid
replacement (also known as isotonic fluid replacement), stretching, and
massage (Gauer and Meyers, 2019; Peterkin et al., 2016). In some cases,
sodium replacement may be a treatment for heat cramps (Talbott and
Michelsen, 1933; Sandor, 1997; Jansen et al., 2002). In severe cases,
it is recommended that magnesium levels of the patient are obtained and
if necessary, magnesium replacement through IV therapy is provided
(O'Brien et al., 2012). The ACSM recommends rest, prolonged stretching
in targeted muscle groups, oral sodium chloride ingestion in fluids or
foods, or intravenous normal saline fluids in severe cases (ACSM,
2007). NIOSH recommends that medical attention is needed if the worker
has heart problems, is on a low sodium diet, or if cramps do not
subside within 1 hour (NIOSH, 2016). If treated early and effectively,
individuals may return to activity after heat cramps have subsided
(Bergeron, 2007; Savioli et al., 2022; Gauer and Meyers, 2019).
However, severe heat cramps may require an emergency department visit
or hospitalization (Harduar Morano and Waller, 2017; Carter et al.,
2005). While most cases of heat cramps do not require restricted work
status or time away from work, guidelines for military personnel
suggest some cases may require light workload the next day and limited
workload the following day, with observation of the affected patient
because some additional deficits may be delayed or subtle (O'Connor et
al., 2007). In addition, guidelines for military personnel advise that
strenuous exercise be avoided for several days in some cases of heat
cramps (O'Connor et al., 2007). Severe heat cramps may also elicit
soreness for several days which can lead to a longer recovery period
(Casa et al., 2015).
V. Summary
OSHA's review of the scientific and medical literature indicates
that heat cramps are a recognized health effect of occupational heat
exposure. Indeed, several studies of self-reported symptoms of HRI
among farmworkers in multiple States have indicated that heat cramps
are quite common. The best available evidence on treatment and recovery
indicates that heat cramps can, in some cases, require medical
attention and may require time away from work or an adjusted workload.
K. Heat Rash
I. Introduction
Workers in hot environments may experience heat rash. Heat rash is
defined by NIOSH as ``a skin irritation caused by excessive sweating
during hot, humid weather'' (NIOSH, 2022). NIOSH, the U.S. Army, and
the U.S. Navy classify heat rash as a heat-related illness (NIOSH,
2016; Department of the Army, 2022; Department of the Navy, 2023). Also
known as miliaria rubra or prickly heat, workers with heat rash develop
red clusters of pimples or small blisters, which can produce itchy or
prickly sensations that become more irritating as sweating persists in
the affected area. Heat rash can last for several days and tends to
form in areas where clothing is restrictive and rubs against the skin,
most commonly on the neck, upper chest, groin, under the breasts, and
in elbow creases (OSHA, 2011; NIOSH, 2022; OSHA, 2024a). If left
untreated, heat rash can become infected, and more severe cases can
lead to high fevers and heat exhaustion (Wenzel and Horn, 1998). In
some cases, heat rash can lead to hypohidrosis (i.e., the reduced
ability to sweat) in the affected area, even weeks after the heat rash
is no longer visible, which impairs thermoregulation and can cause
predisposition for heat stress (Sulzberger and Griffin, 1969; Pandolf
et al., 1980; DiBeneditto and Worobec, 1985). This can impair an
employee's ability to work and prevent resumption of normal work
activities in hot environments to allow for the area to heal, which in
some cases can take 3-4 weeks for heat intolerance to subside (Pandolf
et al., 1980).
II. Physiological Mechanisms
The development of heat rash has been studied for centuries
(Renbourn, 1958). While working in hot environments with a high
relative humidity, the body's ability to cool itself is greatly
reduced, as sweat is less likely to evaporate from the skin (Sulzberger
and Griffin, 1969; DiBeneditto and Worobec, 1985). Heat rash occurs
when sweat remains on the skin and causes a blockage of sweat (eccrine)
glands and ducts (Wenzel and Horn, 1998). Since the sweat ducts are
blocked, sweat secretions can leak and accumulate beneath the skin,
causing an inflammatory response and resulting in clusters of red bumps
or pimples (Dibeneditto and Worobec, 1985). If left untreated, heat
rash may become infected (Holzle and Kligman, 1978). Depending on the
level of blockage, this can manifest as various types of miliaria, with
miliaria rubra being the most common form of heat rash (Wenzel and
Horn, 1998).
III. Occupational Heat Rash
Surveillance of heat rash in worker populations is limited.
However, farmworkers have reported cases of skin rash or skin bumps
while working in summer months (Bethel and Harger, 2014; Kearney et
al., 2016; Luque et al., 2020). From these studies, the percentage of
participants surveyed or interviewed that report experiencing skin rash
or skin bumps in the previous week were 10% (n=100, Beth and Harger,
2014), 12.1% (n=158, Kearney et al., 2016) and 5% (n=101, Luque et al.,
2020). Although these studies do not purport a diagnosis, presentation
of skin rash or skin bumps while working in hot environments with
reported average high temperatures ranging to the mid-90s [deg]F
indicates respondents may have developed heat rash.
Similar findings with diagnosis of heat rash or related symptoms
have been recorded outside of the U.S. among workers in the following
professions: 17% of indoor electronics store employees in air-
conditioned (4%) and non-air-conditioned (13%) areas in Singapore
(n=52, Koh, 1995); 2% of underground miners at a site in Australia
(n=1,252, Donoghue and Sinclair, 2000); 34% of maize farmers in Nigeria
(n=396, Sadiq et al., 2019); 68% of sugarcane cutters and 23% of
sugarcane factory workers in Thailand (n=183, Boonruksa et al., 2020);
41% of sugarcane farmers in Thailand (n=200, Kiatkitroj et al., 2021);
17% of autorickshaw drivers (n=78), 23% of outdoor street vendors
(n=75), 16% of street sweepers (n=75) in India (n=228, Barthwal et al.,
2022); and 13% of underground and open pit miners across Australia
(n=515, Taggart et al., 2024). Although these studies illustrate the
prevalence of heat rash in various worker populations, OSHA notes that
differences in study methodologies and the populations studied mean
that the results of these studies are not necessarily directly
comparable to each other or to similar industries or worker populations
in the United States.
The type of clothing worn may also contribute to formation of heat
rash while working in higher temperatures. Heat rash was formally
diagnosed among U.S. military personnel wearing flame resistant army
combat uniforms in hot and arid environments (102.2 [deg]F to 122
[deg]F (39 [deg]C to 50 [deg]C), 5% to 25% relative humidity) (Carter
et al., 2011). In this case series, 18 patients with heat rash
presented with moderate to severe skin irritation, which was worsened
by reactions to chemical additives not removed from the laundering
process and increased heat retention from sweat-soaked clothing, as
well as the friction from the fabric and the occlusive effect of the
clothing, which allowed sweat to accumulate on the skin despite the
lower humidity (Carter et al., 2011). This study calls attention to the
effect of clothing on the development of heat rash and factors that may
influence its severity.
IV. Treatment and Recovery
Although most cases of heat rash can be self-treated without
seeking medical attention, symptoms typically last for several days
(Wenzel and Horn, 1998). It is important that heat rash is kept dry and
cool to avoid possible infection. Workers experiencing heat rash should
move to a cooler and less humid work environment and avoid tight-
fitting clothing, when possible (NIOSH, 2022). The affected area should
be kept dry, and ointments and creams, especially if oil-based, should
not be used (NIOSH, 2022). However, powder may be used for relief.
V. Summary
The available evidence in the scientific literature indicates that
heat rash can result from occupational heat exposure. Although heat
rash usually resolves on its own without medical attention, symptoms
often persist for several days and more severe cases can impair an
employee's ability to work and lead to infection if left untreated.
L. Heat Edema
I. Introduction
Workers in hot environments may experience heat edema. Heat edema
is the swelling of soft tissues, typically in the lower extremities
(feet, ankles, and legs) and hands, and may be accompanied by facial
flushing (Gauer and Meyers, 2019). Surveillance systems and the U.S.
Army classify heat edema as a heat-related illness (Department of the
Army, 2022). Workers who are sitting or standing for prolonged periods
may be at higher risk for heat edema (Barrow and Clark, 1998). Workers
who are not fully acclimatized to the work site may be more prone to
developing heat edema as the body adjusts to hotter temperatures (Howe
and Boden, 2007).
II. Physiological Mechanism
When exposed to heat, the body increases blood flow and induces
vasodilation to cool itself and thermoregulate. This means, as blood is
shunted towards the skin and vasodilation begins, the blood vessels
near the skin's surface become wider (Hough and Ballantyne, 1899;
Kamijo et al., 2005). However, blood can pool in areas of the body that
are most subject to gravity (e.g., legs), and fluid can seep from blood
vessels causing noticeable swelling under the skin--this is known as
heat edema (Gauer and Meyers, 2019).
III. Occupational Heat Edema
Surveillance of heat edema is limited. Many studies include heat
edema as one of many HRIs that contributed to an aggregate measure of
HRI in worker, military, or general populations, but very few were
found to quantify heat edema alone.
Multiple studies outside of the U.S. have examined HRIs among farm
and factory workers in the sugarcane industry through surveys and
interviews (Crowe et al., 2015; Boonruksa et al., 2020; Kiatkitroj et
al., 2021; Debela et al., 2023). Respondents in the studies were asked
if they experienced swelling of the feet or hands (with varying degrees
of frequency) during periods of heat exposure, which could indicate
presentation of heat edema. In different samples of sugarcane workers
in two provinces of Thailand, two studies found incidence of swelling
of the hands and feet. Among sugarcane cutters, 16.7% self-reported
ever experiencing swelling of the hands or feet and 5.6% self-reported
experiencing these symptoms (mean 30.6 [deg]C WBGT) (n=90, Boonruksa et
al., 2020). In another province, 10.5% self-reported swelling of the
hands/feet while working one summer (n=200, Kiatkitroj et al., 2021).
While comparing HRI symptoms among sugarcane harvesters and non-
harvesters in Costa Rica, 15.1% of harvesters (n=106) and 7.9% of non-
harvesters (n=63) self-reported having ever experienced swelling of
hands/feet (p=0.173) (n=169, Crowe et al., 2015). While 7.5% of
harvesters, who worked outdoors in the field, self-reported
experiencing this symptom at least once per week, no non-harvesters
self-reported swelling with this level of frequency (p=0.026) (Crowe et
al., 2015). The sample of non-harvesters included both workers that
were intermediately exposed to heat (e.g., in the processing plant or
machinery shop) and workers not exposed to heat (e.g., in offices).
In a sample of sugarcane factory workers (n=1,524) in Ethiopia,
72.4% (1,104) were considered exposed to heat defined as conditions
exceeding the ACGIH's TLV (Debela et al., 2023). Of the total sample
(including workers considered exposed to heat and not), 78% (1,189)
self-reported having experienced swelling of hands and feet at least
once per week, which was the most commonly reported HRI symptom (Debela
et al., 2023). Although these studies do not purport a diagnosis,
presentation of swelling of the hands and feet while working in hot
environments suggests respondents may have developed heat edema.
IV. Treatment and Recovery
Although most cases of heat edema can be self-treated without
seeking medical attention, symptoms can last for days and reoccurrence
is less likely if individuals are properly acclimatized (Howe and
Boden, 2007; Department of the Army, 2023). It is important that the
affected individual moves out of the heat and elevates the swollen
area. Diuretics are not typically recommended for treatment (Howe and
Boden, 2007; Gauer and Meyers, 2019; CDC, 2024a).
V. Summary
The available evidence in the scientific literature indicates that
heat edema can result from occupational heat exposure, causing swelling
of the lower extremities (feet, ankles, and legs) and hands. It may be
difficult to move swollen body parts, thereby impeding an employee's
ability to perform their job. The need for medical attention can
typically be avoided if the condition is properly treated.
M. Kidney Health Effects
I. Introduction
The kidneys perform many functions in the body, including filtering
toxins out of the blood and balancing the body's water and electrolyte
levels (NIDDK, 2018). Working in the heat places a lot of demand on the
kidneys to conserve water and regulate electrolytes, like sodium, lost
through sweat. A growing body of experimental and observational
literature suggests that intense heat strain can cause damage to the
kidneys in the form of acute kidney injury (AKI), even independent of
conditions like heat stroke and rhabdomyolysis. An epidemic of chronic
kidney disease in Central America and other regions around the world
has placed additional attention on the potential of recurrent heat
stress-related AKI to cause chronic kidney disease (CKD) over time
(Johnson et al., 2019; Schlader et al., 2019). Working in the heat has
also been associated with the development of kidney stones among
workers outside the U.S., likely a result of decreased urine volume
leading to increased concentration of minerals in the urine that
crystallize into stones.
Each kidney is comprised of hundreds of thousands of functional
units called nephrons. Each nephron has multiple parts, including the
glomerulus (a cluster of blood vessels that conduct the initial
filtering of large molecules) and the tubules (tubes that reabsorb
needed water and minerals and secrete waste products). The fluid that
remains after traveling through the glomeruli and tubules becomes urine
and is eliminated from the body (NIDDK, 2018).
This section will discuss three kidney-related health effects
associated with heat exposure: kidney stones, AKI, and CKD.
II. Kidney Stones
A. Introduction
Kidney stones are hard objects that form in the kidney from the
accumulation of minerals. They range in size from a grain of sand to a
pea (NIDDK, 2017a). Symptoms include sharp pain in the back, side,
lower abdomen, or groin; pink, red, or brown blood in the urine; a
constant need to urinate; pain while urinating; inability to urinate or
only able to urinate a small amount; and cloudy or foul-smelling urine
(NIDDK, 2017b). Nausea, vomiting, fever, and chills are also possible,
and symptoms may be brief, prolonged, or come in waves (NIDDK, 2017b).
In rare cases or when medical care is delayed, kidney stones can lead
to complications including severe pain, urinary tract infections (UTI),
and loss of kidney function (NIDDK, 2017a). Risk factors for kidney
stones include being male, a family history of kidney stones, having
previously had kidney stones, not drinking enough liquids, other
medical conditions (e.g., chronic inflammation of the bowel, digestive
problems, hyperparathyroidism, recurrent UTIs), drinking sugary
beverages, and working in the heat, especially if unacclimatized
(NIDDK, 2017a; Maline and Goldfarb, 2024). NIOSH has also cautioned
workers that experiencing chronic dehydration can increase the risk of
developing kidney stones (NIOSH, 2017a).
B. Physiological Mechanisms
Kidney stones form when concentrations of minerals are high enough
to the point of forming crystals, which then aggregate into a stone in
either the renal tubular or interstitial fluid (Ratkalkar and Kleinman,
2011). Reduced urine volume, altered urine pH, diet, genetics, or many
other factors may cause this concentration of minerals (Ratkalker and
Kleinman, 2011). Heat exposure has the potential to cause kidney stones
through heat-induced sweating and dehydration. Loss of extracellular
fluid increases osmolality (i.e., increased concentration of solutes,
like sodium and glucose) which leads to increased secretion of
vasopressin, an antidiuretic hormone. Vasopressin signals to the
kidneys to conserve water by reducing urine volume, leading to
increased concentration of relatively insoluble salts, like calcium
oxalate, in the urine. These salts can eventually form crystals which
can develop into stones (Fakheri and Goldfarb, 2011).
C. Occupational Heat Exposure and Kidney Stones
Epidemiological studies conducted outside the U.S. have documented
the association between working in heat and developing kidney stones.
One of the earliest publications on occupational heat and kidney stones
was a small study of beach lifeguards in Israel (Better et al., 1980).
Eleven of 45 randomly selected lifeguards (24%) were found to have had
kidney stones, which Better et al. noted was approximately 20 times the
incidence rate of the general Israeli population at the time. The
authors attributed this finding to low urine output due to dehydration,
hyperuricemia (elevated levels of uric acid in the blood), and
absorptive hypercalciuria (elevated levels of calcium in the urine),
among other factors. In 1992, Pin et al. compared outdoor workers
exposed to hot environmental conditions to indoor workers exposed to
cooler conditions (Pin et al., 1992). This study of 406 men in Taiwan
included quarry, postal, and hospital engineering support workers. The
prevalence of kidney stones was found to be significantly higher in the
outdoor workers than the indoor workers (5.2% versus 0.85%, p<0.05).
The authors posited that chronic dehydration from working outdoors in a
tropical environment might explain the higher prevalence of kidney
stones among outdoor workers (Pin et al., 1992).
Several studies have also considered occupational exposure to
indoor heat sources. Borghi et al. studied machinists who had been
working in the blast furnaces of a glass plant in Parma, Italy for five
or more years, excluding those who had kidney stones before working at
the plant (Borghi et al., 1993). The prevalence of kidney stones was
significantly higher among machinists exposed to heat (n=236) than
among those working in cooler temperatures (n=165) (8.5% vs. 2.4%,
p=0.03) (Borghi et al., 1993). An analysis of risk factors revealed
that workers in the heat lost substantially more water to sweat and
that their urine had higher concentrations of uric acid, higher
specific gravity, and lower pH than workers in normal temperatures
(Borghi et al., 1993).
In a large study in Brazil, the prevalence of at least one episode
of kidney stones was 8.0% among the 1,289 workers in hot areas, which
was significantly higher than the 1.75% prevalence found among the
9,037 people working in room temperature conditions (p<0.001) (Atan et
al., 2005). An analysis of a subset of workers demonstrated that
workers in hot temperatures had significantly less citrate in their
urine (p=0.03) and lower urinary volume (p=0.01) compared to room-
temperature workers.
Venugopal et al. studied 340 steel workers in southern India
engaged in moderate to heavy labor with three or more years of heat
exposure (Venugopal et al., 2020). Of the 340 participants, 91 workers
without other risk factors for kidney disease, but who had reported a
symptom of kidney or urethral issues, underwent renal ultrasounds,
which revealed that 27% had kidney stones. 84% of the participants with
kidney stones were occupationally exposed to heat, as defined as
working in conditions above the ACGIH TLV. Having five or more years of
heat exposure was significantly associated with risk of kidney stones,
while
controlling for smoking (OR: 3.6, 95% CI: 1.2, 10.7).
Most recently, Lu et al. studied 1,681 steel workers in Taiwan, 12%
of whom had kidney stones, compared to the age-adjusted prevalence
among men in Taiwan of 9% (Lu et al., 2022). Heat exposure was found to
be positively associated with prevalence of stones, particularly among
workers <=35 years old (OR: 2.7, 95% CI: 1.2, 6.0) (Lu et al., 2022).
Overall, the peer-reviewed literature supports occupational heat
exposure as a risk factor for kidney stones, in both indoor and outdoor
environments, across multiple countries, and in several industries.
D. Treatment and Recovery
Treatment of kidney stones depends on their size, location, and
type. Someone with a small kidney stone may be able to pass it by
drinking plenty of water and taking pain medications as prescribed by a
doctor (NIDDK, 2017c). Larger kidney stones can block the urinary
tract, cause intense pain, and may require medical intervention such as
shock wave lithotripsy, cystoscopy, ureteroscopy, or percutaneous
nephrolithotomy to remove or break up the stone (NIDDK, 2017c).
Percutaneous nephrolithotomy, whereby kidney stones are removed through
a surgical incision in the skin, requires several days of
hospitalization, but the other interventions typically do not require
an overnight hospital stay (NIDDK, 2017c). One study found that among
working aged adults, approximately one third of people treated for
kidney stones miss work and that they miss, on average, 19 hours of
work per person (Saigal et al., 2005). With monitoring or treatment,
people typically recover from kidney stones. However, over the long
term, individuals who develop kidney stones are at increased risk of
chronic kidney disease and end-stage renal disease, particularly if
kidney stones are recurrent (Uribarri, 2020).
E. Summary
The available peer-reviewed scientific literature demonstrates
occupational heat exposure as a risk factor for kidney stones, in both
indoor and outdoor environments. Kidney stones may require medical
treatment and in some cases hospitalization. Finally, individuals who
develop kidney stones are at increased risk of other kidney diseases.
III. Acute Kidney Injury
A. Introduction
Acute kidney injury (AKI) can affect workers exposed to
occupational heat. AKI is an abrupt decline in kidney function in a
short period (e.g., a few days). As normally functioning kidneys filter
blood and maintain fluid balance in the body, AKI events can disrupt
this fluid balance, which can impact major organs like the heart. AKI
can also have metabolic consequences, like a build-up of too much
potassium in the blood (hyperkalemia) (Goyal et al., 2023). AKI is not
always accompanied by symptoms and is typically diagnosed with blood
and/or urine tests (e.g., increase in serum creatinine). While damage
to the kidneys is one potential consequence of heat stroke (such as in
the context of multi-organ failure, as mentioned in Section IV.E., Heat
Stroke), this section is focused on AKI that is not necessarily
preceded by clinical heat stroke.
B. Physiological Mechanisms
There are three categories of AKI used to distinguish the location
of the cause(s) of AKI--prerenal, intrarenal, and postrenal (Goyal et
al., 2023). Prerenal AKI represents a reduction in blood volume being
delivered to the kidneys (i.e., renal hypoperfusion). This can be the
result of heat-induced sweating that leads to reduced circulating blood
volume. Prerenal AKI that is reversed (e.g., dehydration is quickly
reversed) is typically not associated with impairment to the kidney
glomeruli or tubules, however prolonged exposure can lead to direct
injury to renal cells through ischemia (inadequate blood and oxygen
supply to cells). Intrarenal AKI is when the function of the glomeruli,
tubules, or interstitium are affected, such as in the case of
nephrotoxic exposures (e.g., heavy metals) or prolonged ischemia.
Rhabdomyolysis, which was previously discussed in Section IV.H.,
Rhabdomyolysis, is one potential cause of necrosis of tubular cells
resulting from myoglobin precipitation and direct iron toxicity (Sauret
et al., 2002, Patel et al., 2009). Postrenal AKI is when there is an
obstruction to the flow of urine, such as kidney stones, pelvic masses,
or prostate enlargement. Postrenal AKI is less relevant to a discussion
of heat-related health effects, apart from kidney stones, which is
discussed in Section IV.M.II., Kidney Stones.
Researchers have written specifically about potential mechanisms
leading from occupational heat exposure to AKI (Roncal-Jim[eacute]nez
et al., 2015; Johnson et al., 2019; Schlader et al., 2019; Hansson et
al., 2020), often in the context of chronic kidney disease. As
previously discussed in Section IV.B., General Mechanisms of Heat-
Related Health Effects, working in the heat can lead to increases in
core temperature and reductions in circulating blood volume.
Researchers hypothesize that elevated core temperature could directly
injure renal tissue or that injury could be mediated through
subclinical (mild and asymptomatic) rhabdomyolysis or increases in
intestinal permeability that can cause inflammation. Reductions in
blood volume could inflame or injure the kidneys through reduced renal
blood flow that leads to ischemia and/or local reductions in adenosine
triphosphate (ATP) availability. Reduced blood flow and increased blood
osmolality also trigger physiologic pathways (e.g., renin-angiotensin-
aldosterone system, polyol-fructokinase pathway) which are energy-
intensive and may lead to oxidative stress and inflammation. Other
mechanistic pathways under investigation include urate crystal-induced
injury (Roncal-Jim[eacute]nez et al., 2015) and increased reabsorption
of nephrotoxicants (Johnson et al., 2019).
C. Identifying Cases of Acute Kidney Injury
Serum creatinine levels are used in clinical settings to estimate
kidney function (glomerular filtration rate, or GFR), as it is
typically produced in the body at a relatively stable rate and is
removed from circulation by the kidneys. Multiple criteria exist for
defining AKI based on increases in serum creatinine over hours or days,
such as the KDIGO criteria published by a non-profit organization that
produces recommendations on kidney disease (KDIGO, 2012). There are
multiple factors that could affect the reliability of using serum
creatinine to estimate GFR, including the increased production of
creatinine during exercise. As a result of the limitations of serum
creatinine, there is growing use of alternative biomarkers to identify
cases of AKI, which may be more reliable and specific to AKI, such as
neutrophil gelatinase-associated lipocalin, or NGAL.
D. Experimental Evidence
Researchers have documented an association between heat strain and
biomarkers of AKI in controlled experimental conditions. In 2013,
Junglee et al. documented elevations in urine and plasma NGAL and
reductions in urine flow rate in participants after a heat stress trial
that induced elevations in core temperature and reductions in body mass
(an indication of hydration status) (Junglee et al., 2013). These
increases in NGAL were higher in an experimental group that underwent a
muscle damaging, downhill (-10% gradient) run (compared to a non-
muscle damaging run on a 1% gradient) prior to the heat stress trial,
providing support for the argument that subclinical rhabdomyolysis may
be a pathway from heat stress to kidney injury. Schlader et al.
conducted a trial in which participants wearing firefighting gear
completed two separate exercise trials in hot conditions of different
durations. The longer duration trial was intended to induce higher
levels of heat strain, while the shorter duration was intended to
induce lower levels (Schlader et al., 2017). The researchers found that
the longer trial was associated with elevated core temperature and
reduced blood volume, as well as increases in serum creatinine and
plasma NGAL, suggesting the magnitude of kidney injury may be
proportional to the magnitude of heat strain. McDermott et al. tested
longer durations of exercise in the heat (5.7 1.2 hours)
and similarly found elevations in serum creatinine and serum NGAL from
before the trial to after (McDermott et al., 2018). To determine
whether it is elevated core temperature or reduced blood volume that
primarily drives heat-induced AKI, Chapman et al. conducted four trials
in which subjects exercised for two hours in the same conditions, but
received different interventions (water, cooling, water plus cooling,
and no intervention) (Chapman et al., 2020). The group with no
intervention had the highest levels of urinary AKI biomarkers in the
recovery period, whereas the water and cooling groups each experienced
reductions in AKI biomarker levels relative to the control group. The
researchers concluded that limiting hyperthermia and/or dehydration
reduces the risk of AKI.
The relationship between AKI and hyperthermia and/or dehydration
has also been demonstrated in animal models (Hope and Tyssebotn 1983;
Miyamoto 1994; Roncal-Jim[eacute]nez et al., 2014; Sato et al., 2019).
E. Cases of Occupational Heat-Related AKI
In addition to experimental evidence, heat-related AKI has also
been observed in ``real world'' conditions going back to the 1960s. In
1967, Schrier et al. documented evidence of military recruits
developing AKI (referred to as ``acute renal failure'') following
training exercises in the heat (Schrier et al., 1967). It was soon
after reported that AKI cases linked to exercise in the heat
represented a sizeable portion (approximately 10%) of all AKI cases
treated at Walter Reed General Hospital in the early 1960s (Schrier et
al., 1970).
More recently, serum creatinine-defined AKI has been observed in
agricultural workers in both Florida and California. Among a cohort of
field workers from the Central Valley of California, Moyce et al.
report a post-work shift incidence of AKI of 12.3% (35 of 283 workers)
(Moyce et al., 2017). Workers with heat strain, characterized by
increased core temperature and heart rate, were significantly more
likely to have AKI (OR: 1.34, 95% CI: 1.04, 1.74). Among a cohort of
agricultural workers in Florida, Mix et al. found that heat index
(based on nearest weather monitor) was positively associated with the
risk of AKI--47% increase in the odds of AKI for every 5 [deg]F
increase in heat index. The authors reported an incidence of AKI of 33%
(i.e., 33% of workers had AKI on at least one day of monitoring) in
this study (Mix et al., 2018).
OSHA researchers have also identified cases of heat-related AKI
among workers in the agency's own databases: the Severe Injury Reports
(SIR) database and case files from consultations by the Office of
Occupational Medicine and Nursing (OOMN) (Shi et al., 2022). Shi et al.
identified 22 cases of heat-related AKI between 2010 and 2020 in the
OOMN consultation records (based on serum creatine elevations meeting
the KDIGO requirements) after excluding cases related to severe
hyperthermia, multi-organ failure, or death. Using inclusion criteria
of a heat-related OIICS code (172*) and a mention of AKI in the
narrative, they also identified 57 cases of probable heat-related AKI
between 2015 and 2020 in the SIR database.
Studies conducted among workers outside the U.S. have also reported
a relationship between working in the heat and acute elevations in
serum creatinine or increased risk of AKI (Garc[iacute]a-Trabanino et
al., 2015; Wegman et al., 2018; Nerbass et al., 2019; Sorensen et al.,
2019).
There are a few limitations to these observational studies, such as
the use of serum creatinine to characterize AKI, as described above. An
additional limitation is the inability to determine from these studies
whether the AKI observed is due to prerenal or intrarenal causes. As
discussed in Physiological Mechanisms, prerenal AKI may be due to
reductions in renal blood flow (which would be expected in cases of
dehydration) and is not necessarily indicative of clinically
significant structural injury. Another limitation may be the use of
serum creatinine measures taken over relatively short spans of time,
which may be too short to see true reductions in GFR (Waikar and
Bonventre, 2009). However, there are a growing number of studies that
find a relationship between short-term fluctuations in serum creatinine
and longer-term declines in kidney function among outdoor workers (see
discussion in Section IV.M.IV., Chronic Kidney Disease).
F. Treatment and Recovery
There is a spectrum of severity for AKI. For example, some
individuals may not know they are experiencing AKI without a serum or
urine test. There is also a spectrum of time and medical treatment
needed for recovery, dependent on whether the AKI is quickly reversed
or sustained for longer periods of time. In Schlader et al. 2017,
researchers noted that the biomarkers of AKI for participants in their
trial returned to baseline the following day. However, intrarenal
causes of AKI may require longer periods of time for recovery and may
potentially require the need for medication or dialysis (Goyal et al.,
2023). AKI can be severe, which can be the case when resulting from
heat stroke, where it may represent irreversible damage to the kidneys
and can be fatal (Roberts et al., 2008; King et al., 2015; Wu et al.,
2021). Recurrent AKI may also lead to chronic kidney disease (as
discussed in Section IV.M.IV., Chronic Kidney Disease).
G. Summary
The available peer-reviewed scientific literature, both
experimental and observational studies, suggests that occupational heat
exposure causes AKI among workers. However, there are limitations in
the case definitions used to define AKI in observational settings.
IV. Chronic Kidney Disease
A. Introduction
Chronic kidney disease (CKD) is a progressive disease characterized
by a gradual decline in kidney function over months to years. It is
typically asymptomatic or mildly symptomatic until later stages of the
disease, when symptoms such as edema, weight loss, nausea, and vomiting
can occur (NIDDK 2017d). People with CKD can be at a greater risk for
other health conditions, like AKI, heart attacks, hypertension, and
stroke. The diagnosis typically requires multiple blood and urine tests
taken over time (NIDDK 2016). Typical risk factors for CKD include
hypertension and diabetes.
Epidemics of CKD in Central America and other pockets of the world,
such as India and Sri Lanka, that appear to be afflicting mostly young,
outdoor workers with no history of hypertension or diabetes have raised
questions about
whether working in hot conditions can cause the development of CKD
(Johnson et al., 2019). Researchers have been investigating this
question and the cause of the epidemic over the past 20 years,
including other potential exposures, such as heavy metals,
agrichemicals, silica, and infectious agents (Crowe et al., 2020).
B. Physiological Mechanisms
Researchers have proposed that working in the heat could lead to
the development of CKD through repetitive AKI events (see discussion of
heat-related mechanisms in Section IV.M.III., Acute Kidney Injury).
However, some researchers acknowledge the possibility that the
unexplained CKD cases observed in Central America and elsewhere may
instead represent a chronic disease process that begins earlier in life
which places workers at increased risk of AKI (Johnson et al., 2019;
Schlader et al., 2019). Additionally, as discussed above in Section
IV.M.III., Acute Kidney Injury, some occupational cases of AKI could be
transient, the result of prerenal causes, and possibly unrelated to the
development of CKD.
Independent of the epidemic of unexplained CKD, frequent and/or
severe AKI has been identified as a risk factor for developing CKD
(Ishani et al., 2009; Coca et al., 2012; Chawla et al., 2014; Hsu and
Hsu 2016; Heung et al., 2016). The relationship between heat-related
AKI and risk of developing CKD is untested in the experimental
literature because of the ethical implications (Schlader et al., 2019;
Hansson et al., 2020).
As discussed in Section IV.E., Heat Stroke, there is also evidence
that experiencing heat stroke may increase an individual's risk of
developing CKD (Wang et al., 2019; Tseng et al., 2020).
C. Identifying Cases of Chronic Kidney Disease
As discussed previously in the context of AKI, serum creatinine is
commonly used to estimate glomerular filtration rate (GFR), the
indicator of kidney function. When measures of serum creatinine (and
therefore estimates of GFR) are taken over periods of months to years,
medical professionals can determine if an individual's kidney function
is declining. CKD is typically diagnosed when the estimated GFR is
below a rate of 60 mL/min/1.73m\2\ for at least 3 months, although
there are other indicators, like a high albumin-to-creatinine ratio.
There are various stages of CKD; the final stage is called end-stage
renal disease (ESRD) and represents a point at which the kidneys can no
longer function on their own and require dialysis or transplant.
D. Observational Evidence
There is a growing body of evidence that suggests that heat-exposed
workers who experience AKI (or short-term fluctuations in serum
creatinine) are at greater risk of experiencing declines in kidney
function over a period of months to years. For instance, sugarcane
workers in Nicaragua who experienced cross-shift increases (i.e.,
increase from pre-shift to post-shift) in serum creatinine at the
beginning of the harvest season were more likely to experience declines
in estimate GFR nine weeks later (Wesseling et al., 2016). Another
study conducted among Nicaraguan sugarcane workers found that
approximately one third of workers who experienced AKI during the
harvest season had newly decreased kidney function (greater than 30%
decline) and a measure of estimated GFR of less than 60 mL/min/1.73m2
one year later (Kupferman et al., 2018). In an analysis among
Guatemalan sugarcane workers, Dally et al. found that workers with
severe fluctuations in serum creatinine over a period of 6 workdays had
greater declines in estimated GFR (-20% on average) (Dally et al.,
2020). In a separate study conducted in Northwest Mexico, researchers
observed declines in estimated GFR among migrant and seasonal farm
workers from March to July that were not observed in a reference group
of office workers in the same region (L[oacute]pez-G[aacute]lvez et
al., 2021).
Further support for the hypothesis that working in the heat may
lead to declines in GFR and increased risk of CKD comes from
intervention studies in Central America, in which workers were given
water-rest-shade interventions and observed longitudinally for kidney
outcomes. In these studies, implementation of the heat stress controls
was associated with reductions in the declines in kidney function and
reduced rates of kidney injury (Glaser et al., 2020; Wegman et al.,
2018).
While much of the literature is focused on Central American
workers, OSHA did identify one paper conducted among a cohort of U.S.
firefighters. Pinkerton et al. (2022) found lower than expected rates
of ESRD in the cohort (relative to the general U.S. population) despite
high levels of occupational exposure to heat. However, as the authors
point out, this may be due to the healthy worker effect (i.e., a
phenomenon in occupational epidemiology by which workers appear to be
healthier than the general population due to individuals with health
conditions leaving the workforce) (Pinkerton et al., 2022). The authors
also examined associations between proxies for heat exposure and risk
of developing ESRD and found non-significant associations between the
number of exposed days and all-cause ESRD, systemic ESRD, and
hypertensive ESRD. Very few of the ESRD cases identified in this cohort
were due to interstitial nephritis (which would be most consistent with
the CKD cases observed in Central America), limiting the authors'
ability to examine associations between those cases and exposure.
There may be differences between the heat-exposed worker
populations in Central America and the U.S. that could limit the
ability to extrapolate findings from that region, such as differences
in other potentially nephrotoxic exposures (e.g., agrichemicals,
infectious agents). There is also evidence that children in regions
with epidemics of unexplained CKD have signs of kidney injury (Leibler
et al., 2021). Unfortunately, surveillance of CKD in the U.S. (namely
the U.S. Renal Data System) may be missing cases among susceptible
workers, such as migrant agricultural workers, limiting the ability to
detect a potential epidemic of heat-related CKD in this country.
In addition to the general lack of studies conducted among U.S.
workers, there may be other limitations with these observational
studies, such as limited data on longer-term follow-up (i.e., years
instead of months) and the potential for reverse causality (i.e.,
undetected CKD is causing AKI).
E. Treatment and Recovery
Often kidney disease gets worse over time and function continues to
decline as scarring occurs (NIDDK 2017d). As discussed above, late-
stage CKD (or ESRD) requires dialysis or a kidney transplant for an
individual to survive. Kidney failure is permanent. Having even early-
stage CKD may impair workers' urine concentrating ability, which could
increase their heat strain and risk of HRIs while working (Petropoulos
et al., 2023).
F. Summary
There is growing evidence suggesting that heat stress and
dehydration may be contributing to an epidemic of CKD among workers in
Central America and other parts of the world, although the cause is
still being investigated by researchers. There is currently limited
information as to whether this type of CKD is affecting U.S. workers
and if so, to what extent. Experiencing heat stroke has been identified
in the literature as a risk factor for developing CKD.
N. Other Health Effects
I. Introduction
In addition to the health effects discussed in the previous sub-
sections, heat exposures have also been linked to reproductive health
effects. Additionally, health effects have been associated with prior
episodes of heat illness.
II. Reproductive and Developmental Health Effects
There is mixed evidence that heat affects reproductive and
developmental health outcomes. NIOSH reported two mechanisms by which
heat may affect reproductive and developmental health: infertility
(e.g., such as through damaged sperm) and teratogenicity (harm to the
developing fetus, e.g., spontaneous abortion or birth defects) (NIOSH,
2016). NIOSH concluded that while human data about reproductive risks
at exposure limits (see NIOSH, 2016, table 5-1, p. 70) were limited,
results of research and animal experiments support the conclusion heat-
related infertility and teratogenicity are possible (NIOSH, 2016, p.
91).
More recent evidence, although also limited, continues to provide
support of a reproductive risk to people who are pregnant and
developmental risk to their children. Numerous epidemiological studies
have reported that heat exposure during pregnancy is associated with
poor outcomes, such as pre-term labor and birth and low-birth weight
babies (e.g., Kuehn and McCormick, 2017; Basu et al., 2018; Chersich et
al., 2020; Rekha et al., 2023). While most studies assess this
relationship in the general population of pregnant women and do not
specifically address occupational exposures, Rekha et al. show that
occupational exposures to heat were associated with adverse pregnancy
and fetal outcomes, as well as adverse outcomes during birth in a
cohort of pregnant women in Tamil Nadu, India (Rekha et al., 2023).
Although the mechanisms for these outcomes are unclear, a study of
pregnant women conducting agricultural work or similar activities for
their homes in The Gambia reported an association between heat exposure
and fetal strain (through measures of fetal heart rate and umbilical
artery resistance) (Bonell et al., 2022). Further, a recent
longitudinal prospective cohort study in Germany found that heat
exposure was associated with vascular changes in the uterine artery.
This study reports that changes of increased placental perfusion and
decreased peripheral resistance in the uterine artery indicate blood
redistribution to the fetus during the body's response to heat stress.
They also report increased maternal cardiovascular strain. This data
may support a mechanistic role for uterine and placental blood flow
changes during heat exposures in resultant birth outcomes, such as pre-
term birth (Yuzen et al., 2023; Bonell et al., 2022).
There is evidence that occupational heat exposures can affect male
reproductive health (e.g., Mieusset and Bujan, 1995). Some research
studies report associations between occupational heat exposure and time
to conceive (e.g., Rachootin and Olsen, 1983; Thonneau et al., 1997),
sperm velocity (Figa-Talamanca et al., 1992), and measures of semen
quality such as sperm abnormalities (Rachootin and Olsen, 1983; Bonde,
1992; Figa-Talamanca et al., 1992; De Fleurian et al., 2009). Effects
of heat on sperm have also been demonstrated in experiments in animal
models (Waites, 1991). Cao et al. report that in their study of heat
stress in mice, heat stress reduced sperm count and motility (Cao et
al., 2023). In this study, the heat exposed mice were exposed to
38[deg]C (100.4 [deg]F) temperatures for 2 hours per day for two weeks.
When the mice were not being exposed to heat, they were kept at
25[deg]C (77 [deg]F). Control mice were kept at 25[deg]C for the
duration of the study. Their study results indicate that reduced sperm
quality may be a result of disrupted testicular microbial environment
and disruption in retinol metabolism that occurs during heat stress.
Although, the authors note that the heat exposure does not accurately
mimic real world heat exposures in humans.
While it is accepted that heat impairs spermatogenesis, or
development of sperm (e.g., MacLeod and Hotchkiss, 1941; Mieusset et
al., 1987; Thonneau et al., 1997), some studies of occupational heat
exposure find no relationship between heat and semen quality (Eisenberg
ML et al., 2015). Another study found observable but not statistically
significant associations between heat and semen quality (Jurewicz et
al., 2014). Many studies of the effects of occupational heat exposure
on reproductive outcomes are cross-sectional in nature and measure
exposures through occupation categories or self-report answers on
questionnaires (e.g., Figa-Talamanca et al., 1992; Thonneau et al.,
1997; Jurewicz et al., 2014). These methods can be susceptible to
recall bias and misclassification errors, which can reduce accuracy in
characterizing the association between occupational heat exposures and
reproductive health outcomes, and they are also unable to determine
causality on their own. Additional research that quantifies
occupational heat exposures directly (e.g., through measures of heat
strain or on-site temperatures) would help to clarify the impacts of
occupational heat exposures on male reproductive outcomes.
III. Health Effects Associated With Prior Episodes of Heat Illness
A limited number of studies have focused on a variety of long-term
effects following a prior episode of heat illness. This includes
research by Wallace et al., also reviewed by NIOSH in the 2016 Criteria
for a Recommended Standard Occupational Exposure to Heat and Hot
Environments, whose retrospective case control study of military
members found that those who experienced an exertional heat illness
event earlier in life were more likely to die due to cardiovascular or
ischemic heart disease (Wallace et al., 2007). Similarly, Wang et al.
reports that, in their retrospective cohort study in Taiwan, prior heat
stroke was associated with a higher incidence of acute ischemic stroke,
acute myocardial infarction, and an almost three-fold higher incidence
of chronic kidney disease compared to patients who had other forms of
heat illness or compared to the control group that had no prior heat
illness, over the study's 14 year follow-up period (Wang et al., 2019).
They also found significantly higher incidence of cardiovascular
events, cardiovascular disease, and chronic kidney disease among
individuals in the study who had other forms of heat illness (heat
syncope, heat cramps, heat exhaustion, heat fatigue, heat edema and
other unspecified effects) compared to the control group that had no
prior heat illness. In a long-term follow-up study of military
personnel who had experienced exertional heat illness, Phinney et al.
reported a transient and small but observable increase in the rate of
subsequent hospitalizations and decreased retention in the military
(Phinney et al., 2001). While these studies suggest a relationship
between episodes of serious heat illness and subsequent health effects,
this body of research is small and subject to some limitations. The
cross-sectional nature of some of these studies does not allow for
determination of causality on their own. Additionally, given the
retrospective nature of some of these studies it is possible that
important confounding variables were not adjusted for in analyses,
including occupation in some cases.
IV. Summary
The description of evidence presented here demonstrates that there
is some evidence to support a link between occupational heat exposures
and adverse reproductive health outcomes. There is also limited
evidence that prior episodes of heat illness may affect health outcomes
later in life such as increased risk of cardiovascular disease and
kidney diseases. This evidence of reproductive and developmental health
effects and health effects associated with prior episodes of heat
illness, while suggestive, is still nascent and requires further
investigation.
O. Factors That Affect Risk for Heat-Related Health Effects
I. Introduction
This section discusses individual risk factors for heat-related
injury and illness. The purpose of this discussion is to summarize the
factors that may exacerbate the risk of workplace heat-related hazards
and to provide information to better inform workers and employers about
those hazards. However, exposure to workplace heat contributes to heat
stress for all workers and can be detrimental to workers' health and
safety regardless of individual risk factors. OSHA is not suggesting
that application of the proposed standard would depend on an employer's
knowledge or analysis of these factors for their individual workers.
Nor do these individual risk factors detract from the causal link
between occupational exposure to heat and adverse safety and health
outcomes or an employer's obligation to address that occupational risk
(see Reich v. Arcadian Corp., 110 F.3d 1192, 1198 (5th Cir. 1997)
(Congress intended the Act to protect all employees, ``regardless of
their individual susceptibilities''); Pepperidge Farm, Inc., 17 O.S.H.
Cas. (BNA) ] 1993 (O.S.H.R.C. Apr. 26, 1997) (that non-workplace
factors may render some workers more susceptible to causal factors does
not preclude finding the existence of an occupational hazard); see also
Bldg. & Const. Trades Dep't, AFL-CIO v. Brock, 838 F.2d 1258, 1265
(D.C. Cir. 1988) (holding that OSHA did not err in including smokers in
its analysis of the significant risk posed by occupational exposure to
asbestos, despite the ``synergistic effects'' of smoking and
asbestos)). Many factors can influence an individual's risk of
developing heat-related health effects. These factors include variation
in genetics and physiology, demographic factors, certain co-occurring
health conditions or illnesses, acclimatization status, certain
medications and substances, and structural factors (e.g., economic,
environmental, political and institutional factors) that lead to
disproportionate exposures and outcomes. Although there is a lack of
evidence that explores the full extent to which these factors interact
to affect heat-related health effects, or how various risk factors
compare in their impacts, there is evidence that each of these factors
can affect risk of heat-related health effects. This section focuses on
factors that relate to an individual's health status. For an in-depth
discussion on acclimatization as a risk factor, see Section V., Risk
Assessment, and for an in-depth discussion on demographic factors and
structural factors that affect risk of heat-related illness, see
Section VIII.I., Distributional Analysis.
II. Risk Factors
There are a number of factors that can impact an individual's
response to heat stress and lead to variation in heat stress response
between individuals. These include variation in genotype (Heled et al.,
2004), gene expression (Murray et al., 2022), body mass and differences
in thermoregulation between the biological sexes (Notley et al., 2017),
differences in thermoregulation as people age (e.g., Pandolf 1997,
Kenny et al., 2010; Kenny et al., 2017), and pregnancy (Wells, 2002;
NIOSH, 2016). Normal variation across individuals in genetics,
physiology, and body mass results in variation in how individuals
respond to heat stress. There is some evidence that, at least in some
specific populations, variation in genotype (i.e., genetic makeup) can
affect heat storage and heat strain (Heled et al., 2004; Gardner et
al., 2020). Normal variation in body mass can also correspond to
variation in thermoregulation between individuals (e.g., Havenith et
al., 1998). Results from Havenith et al.'s experimental study of heat
stress under different climate and exercise types indicates that one
reason for this effect may be due to the relationship between size and
surface area of the skin which plays an important role in cooling
capacity (Havenith et al., 1998). A more detailed discussion of the
relationship between obesity and heat stress response can be found
below.
There is some evidence that biological sex could be considered a
risk factor for heat-related illness, although the evidence is mixed.
Some studies find differences in heat stress response between males and
females (e.g., Gagnon et al., 2008; Gagnon and Kenny, 2011; Gagnon and
Kenny, 2012). These differences may be due to differences in body mass
(Notley et al., 2017), lower sweat output in females or differences in
metabolic heat production (Gagnon et al., 2008; Gagnon and Kenny,
2012). However, recent experimental data assessing differences in
thermoeffector responses (autonomic responses that affect
thermoregulation, such as skin blood flow and sweat rate) between males
and females exposed to exercise show that differences between the sexes
in heat stress response are mostly explained by differences in
morphology (body shape and size and the resultant mass-surface ratios)
(Notley et al., 2017). Although, Notley et al.'s (2017) experiment only
involved heat environments where enough heat could be lost so that the
body does not continue to gain heat (compensable heat stress), so it is
unclear if an increased effect due to biological sex would occur in
conditions where heat gain is expected, such as in occupational
settings where environmental heat or environmental heat and exertion
exceed the body's ability to cool.
Healthy aging processes can also make individuals more susceptible
to heat-related illness. Aging may impact thermoregulation through
reduced cardiovascular capacity (Minson et al., 1998; Lucas et al.,
2015), reduced cutaneous vasodilation (the widening of blood vessels at
the skin to aid heat loss), sweat rate, altered sensory function
(Dufour and Candas, 2007; Wong and Hollowed, 2017), and changes in
fluid balance and thirst sensation (Pandolf, 1997). Observational
evidence tends to show that elderly individuals, particularly those
with co-existing chronic or acute diseases, are at highest risk for
morbidity or mortality related to heat exposures, and that risk
increases with age (e.g., Semenza et al., 1999; Fouillet et al., 2006;
Knowlton et al., 2008). However, experimental evidence shows that,
under certain conditions, when individuals are matched for fitness
level and body build and composition, middle-aged individuals can
compensate for heat exposures similarly to younger adults (Lind et al.,
1970; Pandolf, 1997, Kenny et al., 2017). Conversely, observational
studies of occupational populations often find that younger workers
experience greater rates of heat-related illness than do older workers
(e.g., Harduar Morano et al., 2015; Hesketh et al., 2020; Heinzerling
et al., 2020). While it is unclear why younger workers appear to have
greater rates of heat-related illness in epidemiological data,
Heinzerling et al. (2020) suggest that this could be a result of a
greater number of younger workers being
employed in high-risk occupations. Further, younger workers have less
work experience, meaning that younger workers are less familiar with
the heat risks associated with their jobs, how their body responds to
heat, and/or how to respond if they experience symptoms of heat-related
illness.
Health status is another factor that plays a role in how someone
responds to heat stress (e.g., Semenza et al., 1999; Knowlton et al.,
2008; NIOSH, 2016; Vaidyanathan et al., 2019, 2020). Conditions such as
cardiovascular disease and diabetes can affect risk of heat-related
illness (e.g., Kenny et al., 2016; Kenny et al., 2018). The
cardiovascular system plays an integral role in thermoregulation and
heat stress response (Costrini et al., 1979; Lucas et al., 2015; Wong
and Hollowed, 2017; Kenny et al., 2018). Cardiovascular diseases can
affect the heart and blood vessels, increasing cardiovascular strain
and decreasing cardiovascular function and thermoregulatory capacity
(Kenny et al., 2010) and, as a result, increase risk of heat-related
illness during heat stress (Kenny et al., 2010; Semenza et al., 1999).
For example, people with hypertension (i.e., high blood pressure) may
be at increased risk of heat-related illness due to changes in skin
blood flow that can impair heat dissipation during heat stress (Kenny
et al., 2010). Further, many individuals with hypertension and
cardiovascular diseases may take prescription medications that reduce
thermoregulatory functions, through mechanisms like reduced blood flow
to the skin, which can increase sensitivity to heat (Wee et al., 2023).
Studies estimate that a substantial percentage of the population, and
therefore the population of workers, have the type of health status
(i.e., having a chronic condition such as cardiovascular diseases)
(Boersma et al., 2020; Watson et al., 2022) that could affect their
response to heat stress. For example, Watson et al. (2022) estimate
that of the 46,781 surveyed adults between the ages of 18 and 34 who
reported being employed, 26.1% have obesity, 11% have high blood
pressure, and 9.7% have high cholesterol. Additionally, 19.4% were
estimated to have depression, which is sometimes treated with
medications that can affect thermoregulation.
Diabetes and obesity are other factors that may affect risk of
developing heat-related illness (Kenny et al., 2016). Both diabetes and
obesity may affect thermoregulation by reducing a person's ability to
dissipate heat through changes in skin blood flow and sweat response
(Kenny et al., 2016). While some evidence shows that individuals with
well-controlled diabetes may be able to maintain normal
thermoregulatory capacity (Kenny et al., 2016), some evidence indicates
that individuals with poorly controlled diabetes (Kenny et al., 2016)
or older individuals with Type 2 diabetes (Notley et al., 2021) may
experience decreased heat tolerance. Obesity has also been identified
as a risk factor for exertional heat illness in the military (e.g.,
Bedno et al., 2014; Nelson et al., 2018b; Alele et al., 2020). Gardner
et al. (1996) reported increasing risk of exertional heat illness among
male Marine Corps recruits as BMI increased. Additionally, a smaller
body mass to surface area ratio can reduce capacity for heat loss since
surface area is relatively smaller in relationship to mass (Bar-Or et
al., 1969; Kenny et al., 2016). Differences in tissue properties
between adipose (fat) tissue and other body tissues may indicate that a
higher body fat mass can lead to greater rises in core temperature for
a given amount of heat storage in the body (Kenny et al., 2016).
Beyond chronic health conditions, prior episodes of significant
heat-related illness and recent or concurrent acute illness or
infection may also affect an individual's response to heat stress and
increase the risk of heat-related illness (e.g., Carter et al., 2007;
Nelson et al., 2018a; Nelson et al., 2018b; Alele et al., 2020).
Reviews of research and case studies of heat-related illness indicate
that acute illnesses that may affect risk of heat-related illness
include upper respiratory infections and gastrointestinal infections
(Casa et al., 2012; Alele et al., 2020). However, statistical evidence
is limited (Alele et al., 2020). Leon and Kenefick (2012) discuss
results from a study of four marine recruits who presented with
exertional heat illness and who also had an acute illness separate from
heat-related illness. The recruits' blood tests showed elevated levels
of immune-related substances which Leon and Kenefick identify as being
substances that are both mediators of viral infection symptoms and
substances associated with exertional heat illness. Leon and Kenefick
interpret this observation, along with evidence from a study on rats
that showed that bacteria exposure exacerbated inflammation and organ
dysfunction due to heat stress, to suggest that pre-existing
inflammatory states, such as those that occur with acute viral illness,
compromise the ability to thermoregulate appropriately (Carter et al.,
2007; Leon and Kenefick, 2012) (see also Bouchama and Knochel, 2002).
Several studies in military populations also show that a prior heat
illness may increase risk of a future episode of heat illness (Nelson
et al., 2018b; Alele et al., 2020). Assessments of heat and epigenetics
(the study of how the environment and behavior affects genes) suggest
that the complex physiological responses to heat impact genetic
mechanisms that could play a role in increasing susceptibility to
future heat illness following an episode of heat illness (Sonna et al.,
2004; Murray et al., 2022).
Certain medications can also affect thermoregulation and risk of
heat-related illness. Medications that may decrease thermoregulatory
capability include medications that treat cardiovascular diseases,
diabetes, neuropsychiatric diseases, neurological diseases, and cancer
(Wee et al., 2023). Some of these medications affect thermoregulation
by directly affecting the region of the brain that controls
thermoregulation or through other central nervous system effects (e.g.,
antipsychotics, dopaminergics, opioids, amphetamines) (Cuddy, 2004;
Stollberger et al., 2009; Musselman and Saely, 2013; Gessel and Lin,
2020; Wee et al., 2023). Other medications affect thermoregulation
through effects on heat dissipation that occur due to changes in sweat
response and/or blood flow to the skin (e.g., anticholinergics,
antihypertensives, antiplatelets, some antidepressants and
antihistamines, aspirin) (see, e.g., Freund et al., 1987; Cuddy, 2004;
Stollberger et al., 2009; Wee et al., 2023; CDC, 2024b). There are also
medications that may affect ability to perceive heat and exertion
(e.g., dopaminergics) (Wee et al., 2023). Some medications can affect
electrolyte balances (e.g., diuretics, beta-blockers, calcium channel
blockers, and antacids) (CDC, 2024b). When accompanied by dehydration,
some medications also pose a toxicity risk (e.g., apixaban, lithium,
carbamazepine) (CDC, 2024b). Finally, some medications can affect fluid
volume, kidney function, hydration status, thirst perception, or
cardiac output (e.g., diuretics, ACE inhibitors, some anti-diabetics,
beta-blockers, non-steroidal anti-inflammatories (NSAIDs), tricyclic
antidepressants, laxatives, and antihistamines) (Stollberger et al.,
2009; Wee et al., 2023; CDC, 2024b). The NIOSH Criteria for a
Recommended Standard for Occupational Exposure to Heat and Hot
Environments (table 4-2), the Department of the Army's Technical
Bulletin 507 (table 4-2), and CDC's Heat and Medications--Guidance for
Clinicians contain additional information about classes of
medications and the proposed mechanisms for how they affect
thermoregulation (NIOSH, 2016; Department of the Army, 2022; CDC,
2024b).
Medications that can affect how individuals respond to heat are
used by a significant portion of the U.S. population. Survey data from
the National Health and Nutrition Examination Survey from 2015-2016
showed that 60% of adults aged 40-79 used a prescription medication
within the last thirty days and approximately 22% of adults in that
same age range took five or more prescription medications (Hales et
al., 2019). Many of the medications reported by survey respondents are
medications that can affect an individual's response to heat (e.g.,
commonly used blood pressure and diabetes medications).
Amphetamines (whether prescription or illicit), methamphetamines,
and cocaine can also affect thermoregulation and increase risk of heat-
related illness (NIOSH, 2016; Department of the Army, 2022). These
substances can affect the central nervous system's thermoregulatory
functions, stimulate heat generation, and reduce heat dissipation
through vasoconstriction (Cuddy, 2004). The synergy between the
hyperthermia induced by these substances, physical activity, and heat
exposure can increase risk of heat-related illness (Kiyatkin and
Sharma, 2009). Analyses of occupational heat-related fatalities find
amphetamines and methamphetamines to be an important risk factor
(Tustin et al., 2018a, Karasick et al., 2020; Lin et al., 2023). In Lin
et al.'s 2023 review of heat-related hospitalizations and fatalities
documented through NIOSH Fatalities in Oil and Gas Database (2014-2019)
and OSHA's Severe Injury Report Database (2015-2021), 50% of identified
fatalities occurred in workers that had tested positive for
amphetamines or methamphetamines after they died. However, small sample
sizes, sampling strategies, and incomplete data have so far limited the
ability of studies to fully characterize the association between these
substances and risk of heat-related illness or fatality. Poor data
quality or limited data has also limited current studies from
concluding if and when amphetamine-like substances are from
prescription or non-prescription use.
Alcohol and caffeine use may also affect risk of heat-related
illness through effects on hydration status and heat tolerance (NIOSH,
2016; Tustin, 2018; Department of the Army, 2022). There have been
cases of fatalities due to occupational heat exposure in individuals
with a history of ``alcohol abuse or high-risk drinking'' (Tustin et
al., 2018a, p. e385). Both alcohol and caffeine may affect how someone
responds to heat stress due to their ability to cause loss of fluids
and subsequently dehydration, and alcohol also affects central nervous
system function (NIOSH, 2016). In the case of caffeine, it appears that
moderate consumption associated with normally caffeinated beverages
(e.g., one cup of coffee, tea, soda) may not interfere with
thermoregulation in a way that negatively affects response to heat
stress (NIOSH, 2016; Kazman et al., 2020; Department of the Army,
2022). However, heavily caffeinated beverages, such as energy drinks,
have been linked to negative health outcomes (Costantino et al., 2023)
and could potentially exacerbate heat stress through diuretic (salt and
water loss) mechanisms and cardiovascular strain (NIOSH, 2016).
Overall, there is a lack of robust data that quantify the specific
amounts of alcohol or caffeine that are problematic for heat stress
response. However, experts generally advise against drinking alcohol or
caffeinated beverages before or during work or exercise in the heat
(NIOSH, 2016; Department of the Army, 2022; CDC, 2022).
III. Summary
The evidence presented in this section demonstrates that there are
numerous factors that can affect risk of heat-related illness (e.g.,
genetics, age, body mass, some chronic conditions, prescription
medications and drugs). Because prevalence data show that a majority of
working-age adults live with or experience at least one risk factor,
these factors should be considered an important component of
understanding how individuals can be at increased risk for heat-related
illness. OSHA acknowledges, however, that for most of the described
risk factors, the evidence is not robust enough to determine the full
picture of how the factor impacts risk of heat-related illness or to
establish the degree to which the risk factor contributes to overall
risk of developing heat-related illness. There is also a lack of
evidence evaluating the way in which multiple risk factors combine to
affect risk of heat-related health outcomes.
P. Heat-Related Injuries
I. Introduction
In addition to heat-related illnesses, heat exposure can lead to a
range of occupational heat-related injuries. A heat-related injury
means an injury, such as a fall or cut, that is linked to heat
exposure. A heat-related injury may occur as a result of a heat-related
illness, such as a fracture following heat syncope. The association
between heat exposure and heat-related injury among workers has been
well documented over the last decade (Tawatsupa et al., 2013; Xiang et
al., 2014b; Adam-Poupart et al., 2015; Spector et al., 2016; McInnes et
al., 2017; Calkins et al., 2019; Dillender, 2021; Dally et al., 2020;
Park et al., 2021; Negrusa et al., 2024). In particular, analyses of
workers' compensation claim data has demonstrated the increased risk of
occupational traumatic injury with increasing heat exposure (Xiang et
al., 2014b; Adam-Poupart et al., 2015; Spector et al., 2016; McInnes et
al., 2017; Calkins et al., 2019; Dillender, 2021; Park et al., 2021;
Negrusa et al., 2024). These types of heat-related injuries can cause
hospitalizations, extended time out of work, and reduced productivity.
In some instances, a heat-related injury may be fatal, like in the
event of accidents such as a slip, trip, or fall. In 1972, NIOSH
identified occupational heat exposure as contributing to workplace
injuries, and discussed how accidents and injuries were outcomes that
could be prevented by a heat stress standard (NIOSH, 1972).
Specifically, NIOSH highlighted how reduced physical and psychological
performance, fatigue, accuracy of response, psychomotor performance,
sweaty palms, and impaired vision may result in a workplace heat-
related injury.
Since multiple types of injuries can be heat-related (e.g., strain,
fracture, crushing) and the mechanisms underlying those injuries vary
(e.g., impaired speed and reaction time, impaired vision, impaired
dexterity), the identification and classification of heat-related
injuries varies on a case-by-case basis. Although there are no ICD or
OIICS codes specific to diagnosing heat-related injuries, medical
professionals and occupational health professionals can combine a heat-
related illness code with other injury related codes to indicate an
injury is heat-related. An injury specifically attributed to heat would
be expected to be assigned both a heat-related OIICS or ICD code and an
injury OIICS or ICD code. Numerous researchers have used ICD and OIICS
code to conduct studies on heat-related injuries (Dillender, 2021;
Garzon-Villalba et al., 2016; Morabito et al., 2006; Spector et al.,
2016).
This section first presents the epidemiological evidence of
increasing occupational injuries during periods of hotter temperatures,
followed by a discussion of mechanisms that can lead to heat-related
injuries.
II. Occupational Heat-Related Injuries
A multitude of studies have identified an association between heat
exposure and occupational injury in the U.S. (Knapik et al., 2002;
Fogleman et al., 2005; Garzon-Villalba et al., 2016; Spector et al.,
2016; Calkins et al., 2019; Dillender, 2021; Park et al., 2021; Negrusa
et al., 2024). These analyses primarily rely on workers' compensation
claim data and meteorological data and are often case-crossover or
observational time-series in design.
In two studies of outdoor agricultural workers (Spector et al.,
2016) and outdoor construction workers (Calkins et al., 2019) in
Washington State, traumatic injury claims were significantly associated
with heat exposure. Among outdoor agricultural workers (n=12,213
claims), Spector et al. (2016) found a statistically significant
increased risk of traumatic injuries at a daily maximum humidex (the
apparent, or ``feels like,'' temperature calculated from air
temperature and dew point, similar to heat index) above 25 [deg]C (77
[deg]F). Among outdoor construction workers (n=63,720 claims), Calkins
et al. (2019) found an almost linear statistically significant
association between traumatic injury risk and humidex. Both studies
reported that injuries most commonly resulted from falls or bodily
reaction and exertion, which may include sudden occurrences of strains,
sprains, fractures, or loss of balance, among others (Spector et al.,
2016; Calkins et al., 2019).
Using workers' compensation claim data from Texas, Dillender (2021)
found that hotter temperatures resulted in larger percent increases in
traumatic injuries among two similar sets of injury types, ``open
wounds, crushing injuries, and factures'' and ``sprains, strains,
bruises, and muscle issues.'' Park et al. (2021) examined over 11
million workers' compensation records in California and estimated that
approximately 20,000 additional injuries per year between 2001 and 2018
were related to hotter temperatures. In comparison to a day with
temperatures in the 60s [deg]F, the risk of occupational heat-related
injury increased by 5-7% (p<0.05) and 10-15% (p<0.05) on days with high
temperatures between 85-90 [deg]F and above 100 [deg]F, respectively
(Park et al., 2021).
In these case-crossover studies, cases serve as their own controls,
allowing for variables such as age, sex, race, and ethnicity, as well
as other known and unknown time-invariant confounders to be controlled.
However, there are still some limitations to these studies, such as the
potential for time-varying confounders (e.g., air pollutants like ozone
and sleep duration influenced by nighttime temperatures).
Studies conducted among workers outside the U.S. have also reported
a relationship between working in the heat and increased risk of
injuries (Morabito et al., 2006; Tawatsupa et al., 2013; Adam-Poupart
et al., 2015; McInnes et al., 2017; Martinez-Solanas et al., 2018).
Analyses from Dally et al. (2020), found an increase in injury risk
with increasing average daily mean WBGT above 30 [deg]C (86 [deg]F)
among sugarcane harvesters in Guatemala; although this result was not
statistically significant, this may have been due to small sample and
event size.
III. Mechanisms
Heat exposure can impair workers' psychomotor and mental
performance, which can interfere with routine occupational tasks.
Consequently, the risk of work-related injuries, including slips,
trips, and falls, as well as cuts and other traumatic injuries, is
exacerbated when job tasks are performed in hot environments. As
summarized in the prior health effects sections of this preamble, heat
can impair a variety of physiological systems and produce a range of
symptoms. Changes in the cardiorespiratory, locomotor, and nervous
systems due to heat exposure can induce various bodily responses such
as fatigue, which may lead to injury (Ross et al., 2016). Changes from
elevated skin and core body temperatures, which may result in increased
sweating and dehydration, can cause decrements in physical, visuomotor,
psychomotor, and cognitive performance (Grandjean and Grandjean, 2007;
Lieberman, 2007). Even experiencing a high level of heat sensation may
contribute to discomfort and distress, causing distraction and other
behavioral changes that can result in accidents and injuries (Simmons
et al., 2008). An explanation of how heat exposure can impair
psychomotor and mental performance, and consequently lead to
occupational heat-related injuries is provided below.
A. Impaired Psychomotor Performance
Heat exposure can impair psychomotor function (i.e., the connection
between mental and muscle functions) which may cause heat-related
injuries. Impaired psychomotor function from heat exposure can take
multiple forms, including impaired movement, strength, or coordination
(fatigue); impaired postural stability and balance; and impaired
accuracy, speed, and reaction time. Each of these impairments to
psychomotor performance are discussed in turn below.
I. Impaired Movement, Strength, or Coordination (Fatigue)
Heat exposure can hamper psychomotor performance by impairing
workers' movement, strength, or coordination and causing fatigue.
Fatigue has been described as having a lack of energy or a feeling of
weariness or tiredness (NIOSH, 2023b). Effects from heat strain on the
cardiorespiratory and locomotor systems can cause both central and
peripheral fatigue due to increased heat storage at the brain and
muscle levels, along with other physiological mechanisms (Ross et al.,
2016). As an individual's metabolic rate increases in hot environments,
blood pH level may become more acidic and cause muscle fatigue from
increased muscle glycogen degradation, lactate accumulation, and
elevated carbohydrate metabolism (Varghese et al., 2018). These changes
have been shown to compromise performance.
Numerous studies demonstrate the relationship between heat exposure
and fatigue. In a cross-sectional survey of 256 occupational health and
safety professionals in Australia, fatigue was the most reported
incident in workers during higher temperatures (Varghese et al., 2020).
Among two groups of 55 steel plant workers who completed a
questionnaire assessing fatigue, the group of workers exposed to hotter
environments (30-33.2 [deg]C (80-91.76 [deg]F) WBGT) were significantly
more likely to report symptoms of fatigue in comparison to workers in
cooler environments (25.4-28.7 [deg]C (77.7-83.6 [deg]F) WBGT) (Chen et
al., 2003). This study highlights how fatigue symptoms increase with
rising heat exposure levels (Chen et al., 2003).
Moreover, in a review of 55 studies on workplace heat exposure,
core temperature elevation and dehydration have been shown to have
numerous negative behavioral effects including fatigue, lethargy, and
impaired coordination, which may lead to injury (Xiang et al., 2014a).
These 55 articles included ecological (22%), cross-sectional (64%), and
cohort (5%) studies, as well as epidemiological experiments (9%). From
one study included in the review, 42% of construction workers surveyed
reported it was ``easy to get fatigued'' while working in the summer
(Inaba and Mirbod, 2007). In another review of heat stress risks in the
construction industry, Rowlinson et al. (2014) also discussed the
association of high temperatures and
level of fatigue, which has been considered one of the critical factors
leading to construction accidents (Garrett and Teizer, 2009; Chan,
2011). In a case study of 15 workers who experienced fatigue-related
accidents, fatigue was shown to trigger other safety risks, such as not
following proper safety procedures or becoming distracted, which can
induce injury (Chan, 2011).
II. Impaired Postural Stability and Balance
Heat exposure has also been shown to impair postural stability and
balance as increases in metabolic heat can impact workers' gross motor
capacity (i.e., the ability to move the body with appropriate
sequencing and timing to perform bodily movements with refined
control), including postural balance. As individuals become dehydrated,
they may experience negative neuromuscular effects. Distefano et al.
(2013) demonstrated the detrimental impact of dehydration during task
performance in hot conditions, where subjects experienced decreased
neuromuscular control as characterized by poorer postural stability.
The authors found that neuromuscular control was impaired while
participants were hypohydrated (defined as uncompensated loss of body
water) and hyperthermic. Additionally, when an individual is
experiencing high-intensity exertion in hot environments and is already
dehydrated, this can result in further dilution of blood sodium. When
blood sodium is diluted, water may be forced from the extracellular
compartment into the intracellular compartment, which could lead to
pulmonary congestion, brain swelling, and heat stroke (Distefano et
al., 2013). At this stage, neurons begin degenerating in the cerebellum
and cerebral cortex, and this process coupled with the rise in body
temperature, impairs central nervous system functionality (Sawka et
al., 2011; Nybo, 2007; Distefano et al., 2013).
Research also indicates that performing exertional activities in a
hot environment may impair balance. To better understand lower
extremity biomechanics, Distefano et al. (2013) used an assessment tool
to measure gross movement errors, such as medial knee displacement, hip
or knee rotation, and limited sagittal plane (front to back) motion.
The authors found that after performing the exercise protocol,
participants demonstrated poorer movement technique when they were
hypohydrated in a hot environment compared with when they were
hypohydrated in a temperate environment or in a hot environment but
euhydrated (state of optimal total body water content) (Distefano et
al., 2013). These findings suggest that working in hot temperatures
while dehydrated may increase risk for injury due to impaired balance
(Distefano et al., 2013).
III. Impaired Performance in Accuracy, Speed, and Reaction Time
The compromising effects of heat strain on psychomotor function
have long been established, but the level of performance deterioration
is dependent on the severity of heat strain and the complexity of the
task (Taylor et al., 2016; Hancock, 1986; Ramsey, 1995; Pilcher et al.,
2002; Hancock and Vasmatzidis, 2003). Some research has found that when
high skin and core temperatures increase cardiovascular strain, heat
exposure results in faster reaction times where individuals respond
more quickly, but less accurately when in the heat (Simmons et al.,
2008). Other research, such as Mazloumi et al. (2014), found that heat
stress conditions impair selective attention (the ability to select and
focus on a particular task while simultaneously ignoring other stimuli)
and reaction time. In their study of 70 workers in Iran, where half of
the workers experienced heat stress and half worked in air-
conditioning, the authors found impaired psychomotor function among the
exposed workers indicated through an increase in the duration of a task
and response time as well as an increase in the number of errors
(Mazloumi et al., 2014).
Additional studies examine the impacts of high skin and core
temperatures on psychomotor function contributing to more mistakes
(Allan and Gibson, 1979; Gibson and Allan, 1979; Gibson et al., 1980).
In one study of foundry workers, response time, reaction time, and
number of errors were reported to be adversely affected when workers
were exposed to WBGTs of 31-35 [deg]C (87.8-95 [deg]F) compared to
unexposed workers in a WBGT of 17 [deg]C (62.6 [deg]F) (Mazlomi et al.,
2017). A meta-analysis review of 23 studies supports these conclusions,
finding that under hot conditions, performance on mathematical-related
tasks and reaction time tasks can be negatively impacted at 32.2 [deg]C
(89.9 [deg]F) with a roughly 15% average decrement in performance
(Pilcher et al., 2002).
Pyschomotor performance is an important factor when considering job
tasks that require precision and concentration to prevent injuries. In
a study observing steel plant workers, it was found that electrical arc
melting workers who were exposed to hotter environments (30-33.2 [deg]C
WBGT) experienced a significant decrease in their attention span and
slower response time compared to the continuous cast workers, who
worked in cooler environments (25.4-28.7 [deg]C WBGT) (Chen et al.,
2003). A decline in psychomotor function could also negatively affect
speed of response, reasoning ability, associative learning, mental
alertness, and visual perception, which has been reported as a key
cause of fatal accidents (Rowlinson et al., 2014).
B. Impaired Mental Performance
The effects of heat exposure on mental performance can also play a
significant role in increasing workplace accidents and injuries and
compromise workplace safety. Heat exposure can result in impaired
cognition or cognitive performance; impaired visual motor tracking; and
impaired decision-making or judgment, which can lead to unsafe
behaviors (like the removal of required PPE). Each of these are
discussed in turn below.
I. Impaired Cognition or Cognitive Performance
Declines in cognitive function from heat are correlated with an
elevated risk of injury. Evidence indicates a statistically significant
increase in unsafe behaviors above 23 [deg]C WBGT and an increased risk
of accidents (Ramsey et al., 1983). When an individual experiences
hyperthermia, even if it is mild and only occurring for a short period,
the central nervous system is vulnerable to damage (Hancock and
Vasmatzidis, 2003). This can acutely affect memory, attention, and
ability to process information (Walter and Carraretto, 2016). When
hyperthermia triggers cerebral damage, these cerebral injuries can be
characterized into three broad areas. The first area includes cellular
effects (where cells are damaged as temperatures continue to rise and
normal cell function is disrupted and cell replication is no longer
possible). The second area includes local effects (like inflammatory
changes and vascular damage), and the third area includes systemic
changes (like changes in cerebral blood flow (Walter and Carraretto,
2016). These negative effects are typically seen when core body
temperatures reach 40 [deg]C (104 [deg]F), although some changes can
begin at temperatures of 38 [deg]C (100.4 [deg]F) (Walter and
Carraretto, 2016). These physiological changes also negatively impact
cognitive performance.
Heat exposure has been shown to affect cognitive performance
differentially, based on type of cognitive task (Yeoman et al., 2022).
The more complex a task, especially if it requires motor accuracy, the
more likely an individual's cognitive ability to perform the task will
decline because of heat stress (Hancock and Vasmatzidis, 2003). Some
research indicates a decrease in cognitive performance for tasks
requiring more perceptual motor skills will be observed in the 30-33
[deg]C (80-91.4 [deg]F) range, well before the physiological system
reaches its tolerance limit (Ramsey and Kwon, 1992; Hancock and
Vasmatzidis, 2003; Piil et al., 2017). Ramsey and Kwon (1992) have
summarized over 150 studies looking at task exposure time and task type
and found statistically significant performance decrements at the 30-33
[deg]C (80-91.4 [deg]F) range. The decrements at this range occurred
regardless of duration of exposure (from short exposures under 30
minutes and longer exposures up to 8 hours) (Ramsey and Kwon, 1992).
Furthermore, in a case study of nine male volunteers, results indicate
that highly motivated subjects were strongly affected by heat load
within the first two hours of exposure, and that these subjects'
performance was significantly impaired when assigned complex tasks
requiring a significant amount of reasoning and judgment (Epstein et
al., 1980). The authors found that performance began to decrease when
workers were exposed to temperatures above 27 [deg]C (80.6 [deg]F).
Moreover, in a review of fifteen laboratory experiments assessing
the effects of high ambient temperature on mental performance, one
study found that mental performance declines were statistically
significant at exposure durations of four consecutive hours in 87
[deg]F (30.55 [deg]C) temperatures (Wing, 1965). Similarly, in a study
of the effects of hot-humid and hot-dry environments on mental
functioning, 25 participants were exposed to a variety of temperatures
in humid and dry conditions, while performing physical exercises with
bouts of rest, to assess mental alertness, associative learning,
reasoning ability and dual-performance efficiency (Sharma et al.,
1983). The authors found that all the psychological functions tested
were adversely affected under heat stress, and that a significant drop
in various psychological functions was seen at temperatures of 32.2
[deg]C (89.9 [deg]F) and 33.3 [deg]C (91.9 [deg]F) in hot-humid and
hot-dry conditions, respectively. Moreover, the authors suggest that,
for heat-acclimatized subjects who continuously work for four hours,
that the temperature should not exceed 31.1 [deg]C (87.9 [deg]F) in hot
and humid conditions, and 32.2 [deg]C (89.9 [deg]F) for workers in hot
desert conditions (Sharma et al., 1983).
II. Impaired Visual-Motor Tracking
Hyperthermia and dehydration, a common symptom of heat exposure,
have been found to impair visual-motor tracking (i.e., the eyes'
ability to focus on and follow an object), increasing the risk of
workplace injury. In a review of studies on hydration and cognition,
the authors indicate that a 2% or more loss of body weight due to
dehydration from heat and exercise can result in significant reduction
in visual-motor tracking (Lieberman, 2007). In an experimental study
assessing performance in complex motor tasks in hyperthermic humans
(Piil et al., 2017), the authors found that visual-motor tracking
performance was reduced following exercise-induced hyperthermia.
Participants were exposed to hot (40 [deg]C (104 [deg]F)) and control
(20 [deg]C (68 [deg]F)) conditions. At baseline, and after exercise,
participants completed simple and complex motor tasks, which included
visual tracking assessment. The authors concluded that visual-motor
tracking is impaired by hyperthermia, and especially so when multiple
tasks are combined (Piil et al., 2017).
III. Impaired Decision-Making or Judgment
Heat exposure has been found to affect decision-making or judgment
amongst workers, increasing the risk of injury. In a review of
ecological, cross-sectional, and cohort studies, as well as
epidemiological experiments, Xiang, et al. indicate that core
temperature elevation and dehydration impair judgment and concentration
(Xiang, et al., 2014a). In a study analyzing over 17,000 observations
of unsafe behavioral acts (e.g. mishandling tools, equipment, or
materials) in two industrial facilities with varying temperature
conditions, authors found that unsafe behavioral acts decreased within
the zone of preferred temperature (approximately 17 [deg]C (62.6
[deg]F) to 23 [deg]C (73.4 [deg]F), WBGT) and increased outside of this
zone (when the temperature was equal to or less than 17 [deg]C WBGT or
equal to or greater than 23 [deg]C WBGT) (Ramsey et al., 1983). This
study indicates that the risk of unsafe behavioral acts may increase
when the temperature increases.
C. Other Factors Contributing to Heat-Related Injury
In addition to psychomotor and mental impairments that can result
from heat exposure, other mechanisms may also contribute to heat-
related injuries. The purpose of this section is to summarize some
additional factors that may exacerbate the risk of workplace heat-
related injuries and to provide information to better inform workers
and employers about those hazards.
PPE is another factor that plays a role in increasing
susceptibility to a heat-related injury given that some PPE insolates
the body and reduces evaporative cooling capacity. For instance,
research among firefighters finds that a self-contained breathing
apparatus can lead to heat buildup and can impact postural stability
and balance (Hur et al., 2015; Hur et al., 2013; Games et al., 2020;
Mani et al., 2013; Ross, 2016). Other examples of PPE that may result
in heat stress, and therefore increase the risk of heat-related
injuries, include reflective vests that are made of water impermeable
material that block effective heat dissipation and safety helmets with
no ventilation that can raise the temperature inside the helmet. In one
case, the air temperature inside a worker's helmet (57 [deg]C (134.6
[deg]F)) was measured to be over 20 [deg]C hotter than the
environmental temperature (33 [deg]C (91.4 [deg]F)) they were working
in (Rowlinson et al., 2014). The authors found that workers will often
remove helmets in these situations to alleviate heat stress, exposing
them to other workplace hazards (e.g., falling objects) (Rowlinson et
al., 2014). Other research by Karthick et al. (2023) found that in hot
weather conditions, physical health challenges, specifically major
accidents at the job site, minor injuries, physical fatigue, excessive
sweating, and dermatological problems were found to be significant
based on a workers' clothing comfort. The authors highlighted how PPE
can make workers feel uncomfortable, and when combined with extremely
hot weather, it creates fatigue which may increase the number of
workplace injuries and accidents (Karthick et al., 2023).
There is also evidence indicating heat exposure can contribute to
impaired vision, which may lead to workplace injuries. For example,
fogged safety glasses or sweat in eyes due to heat exposure can reduce
workers' visibility, creating additional hazards and increasing risk of
injury (NIOSH, 2016). Individual case studies also report issues with
protective eyewear in hot temperatures, noting the uncomfortable
feeling of the eyewear under heat and in sunlight as well as difficulty
seeing through the glasses (Choudhry and Fang, 2008). In a survey
conducted among occupational health and safety professionals in
Australia, one of the most frequently cited causes of heat-
related injuries was from ``impaired vision due to fogged safety
glasses (39%)'' (Varghese et al., 2020). Injuries resulting from
impaired vision may include manual handling (musculoskeletal injuries),
joint/ligament injuries, hand injuries, wounds or lacerations, burns,
head or neck injuries, motor vehicle accidents, eye injuries, or
fractures (Varghese et al., 2020).
When exposed to heat, workers may also experience impaired
dexterity (or fine motor skills) leading to workplace injuries. For
example, sweaty palms and hands due to heat exposure can reduce
workers' ability to handle tools or other work-related materials,
increasing the risk of injury. Occupational health and safety
professionals have reported losing control of tools as one of the most
common causes for heat-related injuries (Varghese et al., 2020).
Researchers have also found sweaty palms to increase the risk of
workplace injuries (Shulte et al., 2016).
IV. Summary
The scientific and mechanistic data and association studies on
heat-related injuries summarized in this section demonstrate that heat-
related injuries are a recognized health effect of occupational heat
exposure. While the types of heat-related injuries can be broad, the
scientific community recognizes that heat exposure can diminish the
body's senses through various mechanisms like impaired psychomotor
performance (e.g., fatigue, impaired balance, or impaired dexterity),
and impaired mental performance (e.g., impaired cognition or vision)
which can result in various types of injuries. The best available
evidence demonstrates that heat-related injuries can have serious
adverse effects on worker safety and health.
Q. Requests for Comments
OSHA requests information and comments on the following question
and requests that stakeholders provide any relevant data, information,
or additional studies (or citations) supporting their view, and explain
the reasoning for including such studies:
Has OSHA adequately identified and documented the studies
and other information relevant to its conclusions regarding heat-
related health effects, and are there additional studies OSHA should
consider?
V. Risk Assessment
A. Risk Assessment
I. Introduction
In this risk assessment, OSHA relied on surveillance data of
occupational heat-related fatalities and non-fatal injuries and
illnesses reported by the Bureau of Labor Statistics (BLS).
Additionally, OSHA relied on annual incidence estimates derived from
State workers' compensation systems and hospital discharge datasets.
These estimates were calculated and reported in a variety of sources,
such as reports from State health departments, as well as the peer-
reviewed scientific literature. OSHA has preliminarily concluded that
inclusion criteria for HRIs in these data sources (days away from work,
workers' compensation claim, emergency department visit, or inpatient
hospitalization) demonstrate that the HRIs are a material impairment of
health, thus making these data sources relevant to OSHA's determination
of significant risk.
OSHA has previously relied on such injury, illness, and death data
to demonstrate the extent of risk (see, e.g., Fall Protection, 81 FR
82494 (2016); Working Conditions in Shipyards, 76 FR 24576 (2011);
Permit-Required Confined Spaces, 58 FR 4462, 4465 (1993) (finding
significant risk based on available accident data showing that confined
space hazards had caused deaths and injuries); Hazard Communication, 48
FR 53280, 53284-85, 53321 (1983) (finding significant risk of harm from
inadequate chemical hazard communication based on BLS chemical source
injury and illness data)).
Estimating annual incidence among heat-exposed workers (i.e., the
number of annual work-related HRIs divided by the number of heat-
exposed workers) requires being able to accurately estimate the number
of exposed workers and using that number in the denominator.
Unfortunately, there is no published estimate for the number of U.S.
workers exposed to hazardous heat on the job and the majority of the
incidence estimates that OSHA identified used a denominator that would
include both exposed and unexposed workers. This use of a larger
denominator has the effect of diluting the resulting annual incidence
estimates. For instance, BLS estimates and reports annual incidence of
injuries and illnesses involving days away from work that were the
result of ``exposure to environmental heat,'' but in their calculation,
BLS captures the broader U.S. workforce in the denominator, which
includes a large number of unexposed workers (e.g., office workers in
climate-controlled buildings).
Some of the annual incidence estimates that OSHA identified, such
as those based on workers' compensation claims in California and
Washington State, were stratified by sector, industry, or occupation.
OSHA considers these incidence estimates to be helpful in getting to a
more accurate estimate of risk among heat-exposed workers, specifically
the sectors, industries, and occupations where exposure to hazardous
heat on the job is more common. Furthermore, OSHA identified incidence
estimates from cohort data in which the entire cohort was presumed to
be exposed to hazardous heat on the job. These estimates are much
higher than the estimates based on surveillance data. One potential
reason for this difference is that the denominator used in the cohort
studies contains much less unexposed worker-time.
In the following sections (V.A.II., and V.A.III.), OSHA has
summarized the best available incidence data that the agency
identified. Given the limitations with these data, OSHA relied on this
incidence data as a range of possible incidence estimates with the
assumption that many of these estimates represent a lower bound and
that the true incidence is likely higher.
II. Reported Annual Incidence of Nonfatal Occupational Heat-Related
Injuries and Illnesses
A. BLS Survey of Occupational Injuries and Illnesses
The BLS Survey of Occupational Injuries and Illnesses (SOII) is the
primary nationwide source of surveillance data for nonfatal
occupational injuries and illnesses. The scope includes both private
and public (State and local government) sector employees, but excludes
the self-employed, workers on farms with 10 or fewer employees, private
household workers, volunteers, and Federal Government employees. The
data are derived from a two-stage sampling process, during which a
sample of employers are surveyed and report to BLS the number of
injuries and illnesses occurring at their workplace. To reduce the
reporting burden on employers, BLS only requires detailed case
information on a sample of the injuries and illnesses that occurred at
each establishment. BLS uses these survey responses to estimate the
counts and incidence for nonfatal injuries and illnesses across all
workplaces. In estimating annual incidence, BLS uses a denominator of
full-time equivalent (FTE) workers,
which is based on 2,000 hours worked per year (i.e., 40 hours per week
over 50 weeks). Relevant Occupational Injury and Illness Classification
System (OIICS) v2.01 event and nature codes for this proposed standard
include ``Exposure to environmental heat'' (event code-531) and
``Effects of heat and light'' (nature codes beginning in 172-). Codes
beginning with 172- include heat stroke and heat exhaustion (among
other outcomes) but exclude sunburn and loss of consciousness without
reference to heat. For more information about OIICS codes generally,
see Section IV., Health Effects.
Between 2011 and 2020, there were an estimated 33,890 work-related
injuries and illnesses that involved days away from work that were
coded with event code 531, for an annual average of 3,389 such injuries
and illnesses during this period (BLS 2023b). In 2023, BLS reported
biennial rather than annual estimates for work-related injuries and
illnesses that involved days away from work (as well as for the first
time reporting an estimate of injuries and illnesses involving job
restriction or job transfer). The biennial estimate for 2021-2022 for
heat-related cases meeting either of these criteria was 6,550 (5,560
cases involved days away from work; 990 cases involved job transfer or
restriction) (BLS 2023g). The estimated annual heat-related injury and
illness incidence (for cases involving days away from work) calculated
by BLS for all workers covered by SOII from 2011-2020 varied by year
but ranged from 2.0/100,000 workers to 4.0/100,000 workers. The average
estimated annual incidence for the entire time period was 3.0/100,000
workers. However, as stated above, OSHA considers these incidence
estimates to be underestimated for heat-exposed workers because BLS
calculates the incidence rate for the entire U.S. workforce covered by
SOII. Therefore, they are including workers who are not exposed to
hazardous heat. In subsectors and industries where OSHA expects a
greater proportion of workers to be exposed to hazardous heat, the
incidence rate estimates are much higher. For instance, according to
unpublished data from BLS SOII for the period 2011-2020, the crop
production subsector (NAICS code 111) had an annual average incidence
of 14.2/100,000 workers, and the specialty trade contractors subsector
(NAICS code 238) had an annual average of 9.3/100,000 workers. This was
also true of subsectors with primarily indoor workers where OSHA
expects a greater proportion of those workers to be exposed to
hazardous heat, including the primary metal manufacturing subsector
(NAICS code 331), which had an annual average incidence of 13.1/100,000
workers for the period 2011-2020.
B. Workers' Compensation Claims
Workers' compensation claims are an alternative way to quantify
occupational injuries and illnesses, particularly those that involve
outpatient medical treatment, inpatient hospitalization, intensive
care, and/or lost workdays. OSHA identified five papers and a report
from Wisconsin that have evaluated State workers' compensation data and
calculated statewide incidence for heat-related injuries and illnesses.
I. Washington State
The earliest of these, a paper by Bonauto et al., in 2007,
evaluated workers' compensation claims submitted to and accepted by the
Washington State Fund between 1995 and 2005 (Bonauto et al., 2007). The
State Fund is the sole provider of workers' compensation insurance to
Washington employers unless they are self-insured or fall under an
alternative system (e.g., Federal employees) and it covers
approximately two-thirds of the State's workers. Certain workers are
exempt from mandatory coverage, such as self-employed and household
workers. The authors identified heat-related cases using the American
National Standards Institute (ANSI) Z16.2 codes \2\ submitted in the
claims by workers or their physicians, the ICD-9 codes submitted on
bills from healthcare providers and hospitals, and a physician review
of cases that included relevant Z16.2 or ICD-9 codes. The researchers
used all ICD-9 codes beginning in 992 (``Effects of heat and light,''
specifically 992.0-992.9) and the ANSI Z16.2 type code 151 (``Contact
with general heat--atmosphere or environment''). ICD-9 codes were not
available for claims from the self-insured, so the authors restricted
the analysis to State Fund claims only. They also excluded claims in
which the employer's physical location was outside of Washington
(n=12).
---------------------------------------------------------------------------
\2\ The American National Standards Institute, or ANSI, created
a standard for occupational health and safety metrics in 1962
(revised in 1969) referred to as ANSI Z16. The first version of
OIICS was based on the ANSI coding scheme. ANSI revised the Z16
standard in 1995 and adopted the OIICS scheme in that revision.
---------------------------------------------------------------------------
Over the 11-year study period, 480 accepted claims met the authors'
inclusion criteria after physician review, in which they identified and
removed cases where the recorded illness had been miscoded, contained
incorrect data, or represented a burn. Most of the 480 claims (n=442;
92.1%) were medical-only claims, meaning the State Fund only paid for
the medical bills and did not compensate the worker otherwise (e.g.,
wage replacement, disability benefits). The claims included the
employer's NAICS code, which the authors used to stratify cases by
industry sectors and industries. Employers covered under the Washington
State Fund are required to report hours worked by their employees every
quarter (i.e., three-month increments), which the authors used to
estimate denominators for rates assuming 2,000 work hours is 1 FTE.
This means the authors could calculate rates for certain portions of
the year rather than the whole year without needing to divide by the
total number of annual workers (i.e., they could adjust for hours
worked only during the specified portion). The employment reporting by
quarter also allowed for the authors to estimate claim rates for the
third quarter only (July, August, and September), which corresponded to
the time of year with the ``greatest level of exposure to elevated
environmental temperatures'' (Bonauto et al., 2007, p. 5).
The authors reported an average annual claim rate (which can be
thought of similarly to an injury or illness incidence rate) of 3.1
claims/100,000 FTE for the overall workforce covered by the State Fund
during the study period, with annual rates ranging from 1.9 to 5.1/
100,000 FTE. They reported a corresponding average third-quarter claim
rate of 8.6 claims/100,000 FTE for the overall workforce covered by the
State Fund during the study period. In their paper, Bonauto et al.
report annual and third-quarter rates for all sectors and industries
that had more than five claims during the study period. The sectors (2-
digit NAICS) with the highest annual average claim rates were:
1. Construction (12.1/100,000 FTE),
2. Public administration (12.0/100,000 FTE),
3. Agriculture, forestry, fishing, and hunting (5.2/100,000 FTE),
4. Administrative and support and waste management and remediation
services (3.9/100,000 FTE), and
5. Transportation and warehousing (3.5/100,000 FTE).
The corresponding average third-quarter claim rates for these
sectors were more than double the annual averages: 33.8/100,000 FTE,
31.2/100,000 FTE, 12.6/100,000 FTE, 9.9/100,000 FTE, and 10.6/100,000
FTE, respectively. This pattern was also true
for some sectors with a majority of indoor claims. For example,
Manufacturing (3.0/100,000 FTE vs. 7.6/100,000 FTE) and Accommodation
and food services (1.7/100,000 FTE vs. 5.1/100,000 FTE).
The industries (6-digit NAICS) with the highest annual average
claim rates were:
1. Fire protection (80.8/100,000 FTE),
2. Roofing construction (59.0/100,000 FTE),
3. Highway, street and bridge construction (44.8/100,000 FTE),
4. Site preparation construction (35.9/100,000 FTE) (tie), and
5. Poured concrete foundation and structural construction (35.9/
100,000 FTE) (tie).
Similar to the pattern observed among sectors, the corresponding
third-quarter claim rates for the top 5 industries were more than
double the annual averages, except for fire protection--158.8/100,000
FTE, 161.2/100,000, 105.6/100,000 FTE, 106.5/100,000 FTE, and 102.6/
100,000 FTE, respectively. This was also true for restaurants: limited
service restaurants (2.4/100,000 FTE vs. 6.0/100,000 FTE) and full
service restaurants (1.6/100,000 FTE vs. 5.3/100,000 FTE). These
industries have few to no outdoor claims, indicating that even some
industries that involve primarily indoor work are at higher risk in the
summer months.
A follow-up paper to Bonauto et al., 2007, published in 2014,
examined heat-related illnesses among workers in Washington State in
certain agriculture and forestry subsectors between 1995 and 2009
(Spector et al., 2014). The State changed their injury and illness
codes from ANSI to OIICS in July 2005, so for this paper, the
researchers used a combination of ANSI (prior to July 2005), OIICS
(beginning in July 2005), and ICD-9 codes to identify potential heat-
related claims and then reviewed each claim to ensure it was heat-
related. These authors used additional ICD-9 codes that were not
included in the 2007 paper, specifically: prickly heat (705.1),
hyperosmolality and/or hypernatremia (276.0), volume depletion (276.5
and 276.50), dehydration (276.51), hypovolemia (276.52), and acute
renal failure (584 and 584.9). The authors identified 84 accepted
claims meeting their eligibility criteria, the majority of which (n=76;
90%) were medical only claims. Of the 84 claims, 61 (73%) met the
diagnostic code criteria used in the 2007 paper (ICD-9 codes beginning
in 992). The average annual claim rate for the agriculture and forestry
subsectors the authors examined over the 15-year period was 7.0/100,000
FTE and the average third-quarter (July-September) claim rate was 15.7/
100,000 FTE. The majority of claims (61%) were among crop production
and support workers (NAICS 111 or 1151).
A second follow-up paper to Bonauto et al., 2007, was published in
2020 and included all Washington State Fund-covered workers over a more
recent 12-year period, 2006 to 2017 (Hesketh et al., 2020). The authors
used similar methods, except for different screening criteria for
ascertaining cases prior to investigators reviewing each case. To
identify potential heat-related claims, they used OIICS v1.01 event/
exposure code 321, OIICS nature code 072*, OIICS source codes 9362 and
9392 (Sun), and the ICD-9 codes used in Spector et al., 2014. (Note
that these OIICS codes are v1.01 OIICS, which was the coding scheme
used from 1992-2010. BLS updated the coding scheme in 2010, which first
applied to 2011 data.) The State adopted ICD-10 coding in October 2015,
so the following ICD-10 codes were used for claims after that date:
E86* (Volume depletion), T67* (Effects of heat and light), T73.2*
(Exhaustion due to exposure), W92* (Exposure to excessive heat of man-
made origin), X30* (Exposure to excessive natural heat), and Z57.6
(Occupational exposure to extreme temperature). The researchers
excluded claims in which service date for treatment of dehydration or
kidney failure was not within one day of the illness date or claims in
which dehydration or kidney failure were the only identifiers flagged,
as they noted that these cases often did not represent heat-related
illnesses.
The authors reported a total of 918 confirmed heat-related claims,
of which 654 (71%) were accepted claims. Of the accepted claims, 595
(91%) were medical-only claims. Using only accepted claims, they
estimated an average annual claim rate of 3.2 claims/100,000 FTE for
the overall workforce covered by the State Fund during the study period
(Communication with David Bonauto and June Spector, June 2024). Similar
to Bonauto et al., 2007, the authors reported claim rates for all
sectors and industries with more than 11 claims. The sectors (2-digit
NAICS) with the highest annual average accepted claim rates were:
1. Agriculture, forestry, fishing, and hunting (13.0/100,000 FTE),
2. Construction (10.8/100,000 FTE),
3. Public administration (10.3/100,000 FTE),
4. Administrative and support and waste management and remediation
services (4.6/100,000 FTE), and
5. Transportation and Warehousing (3.8/100,000 FTE).
The average third-quarter (July-September) claim rates for some
sectors were more than 10 times greater than the average annual rates.
These third-quarter claim rates were also much higher than those
calculated for 1995-2005 in Bonauto et al., 2007. The sectors with the
highest average third-quarter accepted claim rates were:
1. Public administration (131.3/100,000 FTE),
2. Agriculture, forestry, fishing, and hunting (102.6/100,000 FTE),
3. Construction (70.0/100,000 FTE),
4. Administrative and support and waste management and remediation
services (61.5/100,000 FTE), and
5. Wholesale trade (44.9/100,000 FTE).
The industries (6-digit NAICS) with the highest annual average
accepted claims rates were:
1. Farm labor contractors and crew leaders (77.3/100,000 FTE),
2. Fire protection (60.0/100,000 FTE),
3. Structural steel and precast concrete contractors (54.2/100,000
FTE),
4. Poured concrete foundation and structure contractors (31.6/
100,000 FTE), and
5. Roofing contractors (29.0/100,000 FTE).
The ratio between third-quarter rates and annual rates for all
industries reported in table 3 of the paper ranged from 2.5-13.7, with
the highest average third-quarter accepted claim rates in the following
industries:
1. Farm labor contractors and crew leaders (600.9/100,000 FTE),
2. Fire protection (394.6/100,000 FTE),
3. Administration of conservation programs (282.7/100,000 FTE),
4. Site preparation contractors (232.1/100,000 FTE), and
5. Poured concrete foundation and structure contractors (172.3/
100,000 FTE).
II. California
A group of researchers conducted a similar analysis for the State
of California, using data from the California Workers' Compensation
Information System (WCIS) between 2000 and 2017 (Heinzerling et al.,
2020). Virtually all California employees are required to be covered by
workers' compensation; voluntary, non-compensated workers, owners, and
workers covered under separate programs are excluded. The WCIS contains
all accepted and rejected workers' compensation claims in the State
since 2000 that required medical treatment beyond first aid or more
than
one day of lost work time. The investigators identified heat-related
claims in the system using WCIS-specific nature of injury and cause of
injury codes (e.g., ``temperature extremes''), heat-related illness
keywords (e.g., ``heat stroke''), and certain ICD-9 (992.0-992.9 and
E900.0-E900.9) and ICD-10 (T67.0-T67.9, X30, and W92) codes. They also
manually reviewed all claims that met only the ICD code identification
criteria to ensure the claims were heat-related, as some of the codes
they used to identify claims were not specific to heat-related illness
or injury. In WCIS, the employer's industry is coded using NAICS codes
classified by the claims adjusters. The authors converted the NAICS
codes into the appropriate 2002 census industry codes using the NIOSH
Industry and Occupation Computerized Coding System (NIOCCS). This was
necessary to obtain the corresponding employment denominator estimates
from the NIOSH Employed Labor Force Tool, which relies on data from the
Current Population Survey (CPS), a Census Bureau survey conducted for
BLS. The CPS data provide estimates of all employed and non-
institutionalized civilian workers over the age of 15. To account for
changes in coding schemes implemented in 2002, the investigators
extrapolated 2002-2017 data to estimate denominators for 2000 and 2001.
The authors excluded claims for workers below 16 years of age
(n=104 claims) and institutionalized workers (n=455 claims), as these
workers are excluded from CPS data. They reported a final estimate of
15,996 claims meeting their inclusion criteria, corresponding to an
overall annual claims rate of 6.0/100,000 workers. Industry and
occupation codes were available for 86% and 74% of the included claims,
respectively. The authors reported claim rates for all sectors, but the
sectors with the highest annual claim rates were:
1. Agriculture, forestry, fishing, and hunting (38.6/100,000
workers; 95% CI: 26.9, 40.4),
2. Public administration (35.3/100,000 workers; 95% CI: 34.3,
36.3),
3. Mining (21.3/100,000 workers; 95% CI: 17.6, 25.7),
4. Utilities (11.4/100,000 workers; 95% CI: 10.1, 12.8), and
5. Administrative and support and waste management (8.8/100,000
workers; 95% CI: 8.3, 9.3).
The major occupational groups with the highest annual claim rates
were:
1. Protective services (56.7/100,000 workers; 95% CI: 54.9, 58.7),
2. Farming, fishing, and forestry (35.9/100,000 workers; 95% CI:
34.1, 37.9),
3. Material moving (12.3/100,000 workers; 95% CI: 11.5, 13.1),
4. Construction and extraction (8.9/100,000 workers; 95% CI: 8.4,
9.4), and
5. Building and grounds cleaning and maintenance (6.0/100,000
workers; 95% CI: 5.6, 6.5).
III. Texas
Another study examined workers' compensation claims in an unnamed,
mid-sized Texas city before and after an intervention among a cohort of
604 municipal workers and calculated the incidence of HRI claims from
2009 to 2017 (McCarthy et al., 2019). The municipal departments
included in the study were picked because the job descriptions for
workers within each included work in hot environments with moderate and
heavy physical activity. These departments were Streets and Traffic,
Parks and Recreation, Utilities, and Solid Waste. After removing
worker-time contributed by administrative personnel who were not
exposed to heat on the job, the remaining worker-time represented 329
FTEs per year. Prior to the intervention in 2011, the heat-exposed
workers experienced 17 total HRIs between 2009 and 2010. The authors
reported an average annual rate of HRIs among the heat-exposed workers
during this time of 25.5/1,000 FTEs (McCarthy et al., 2019, Figure 2).
These estimates are much higher than other incidence estimates reported
in this section, possibly because the denominator is solely comprised
of heat-exposed workers. This explanation is supported by evidence of
higher incidences reported in other cohort studies (e.g., approximately
3 HRIs/1,000 National Guard troops involved in flood relief activities
between July 5 and August 18, 1993, calculated from data in Dellinger
et al., 1996). The results of the voluntary intervention are discussed
in Section V.C., Risk Reduction.
IV. Wisconsin
Finally, a report issued by the Wisconsin Occupational Health and
Safety Surveillance Program in 2024 summarized an analysis of heat-
related workers' compensation claims in the State from 2010-2022 (Fall
et al., 2024). The authors analyzed lost work time claims (under
Wisconsin workers' compensation, there must be more than three days of
lost work time to be compensable) reported by both insurance carriers
and self-insured employers and reported rates by industry sector and
industry subsector (rather than overall workforce rates). These do not
include medical-only claims, which were the majority of HRI claims
reported in the Washington State Fund database. The authors reported
cumulative claim rates only. To convert cumulative rates to annual
average rates, OSHA divided the reported rates by 13 (the number of
years' worth of data reported). The sectors with the highest annual
average claim rates were:
1. Administrative and Support and Waste Management and Remediation
Services (2.9/100,000 FTE),
2. Public Administration (2.8/100,000 FTE),
3. Wholesale Trade (1.9/100,000 FTE),
4. Construction (1.4/100,000 FTE), and
5. Transportation and Warehousing (1.1/100,000 FTE).
The major occupational groups with the highest annual average
claims rates were:
1. Protective Service (4.1/100,000 FTE),
2. Transportation and Material Moving (2.6/100,000 FTE),
3. Production (1.6/100,000 FTE),
4. Construction and Extraction (1.5/100,000 FTE), and
5. Building and Grounds Cleaning and Maintenance (1.5/100,000 FTE).
Similarly, the minor occupational groups with the highest annual
average claims rates were:
1. Fire Fighting and Prevention (14.7/100,000 FTE),
2. Material Moving Workers (3.3/100,000 FTE),
3. Metal and Plastic Workers (2.8/100,000 FTE),
4. Motor Vehicle Operations (2.2/100,000 FTE), and
5. Assemblers and Fabricators (2.2/100,000 FTE).
C. Emergency Department (ED) Visits and Inpatient Hospitalizations
Another way to quantify occupational injury and illnesses requiring
medical treatment is to use data reported directly by hospitals to
public health departments or national databases, such as the National
Electronic Injury Surveillance System (NEISS). Data in NEISS are
estimated from a nationally representative probability sample of
hospitals across the country, which report data for every injury-
related ED visit. A paper from 2010 analyzed NEISS data for heat-
related emergency department visits from 2001-2004 (Sanchez et al.,
2010). The authors reported an annual average of 8,376 work-related ED
visits for nonfatal heat injuries and illnesses. OSHA used annual
average employment estimates from NIOSH's Employed Labor Force query
system for 2001-2004 (both total workers and FTEs) to estimate a
nationwide annual average rate of 6.1
visits/100,000 workers and 6.3 visits/100,000 FTEs from this study.
More recent studies estimating the incidence of work-related ED visits
and/or hospitalizations for HRIs within individual or multiple States
are discussed below.
I. Southeast U.S.
A group of public health researchers from nine States in the
Southeast (Florida, Georgia, Kentucky, Louisiana, Mississippi, North
Carolina, South Carolina, Tennessee, and Virginia) used hospital
discharge data reported directly to State health departments to
characterize rates of heat-related inpatient hospitalization and ED
visits among workers from 2007--2011 (Harduar Morano et al., 2015). The
researchers used ICD-9 codes to identify heat-related cases,
specifically 992.0-992.9, E900.0, E900.1, and E900.9. To assess work-
relatedness, they determined whether the expected payer was workers'
compensation or if a work-related external cause of injury code
(sometimes referred to as E-codes) was noted by the physician (e.g.,
E000.0 Civilian activity done for income). They restricted cases only
to those where the patient was at least 16 years old but included both
State residents and non-residents in reported case counts. To calculate
rates, the investigators used CPS data for estimating denominators,
which were age-adjusted using direct standardization and population
weights for the entire U.S. Non-residents were not included in the rate
calculations. The authors noted that hospital discharge data weren't
available for every year in every State and that the missing data were
primarily for discharges following ED visits.
Across the five-year study period, the authors identified 8,315
occupational heat-related ED visits (7,664 of these among residents, or
92%), which corresponded to an overall age-adjusted rate of 6.5 visits/
100,000 workers (95% confidence interval, CI = 6.4, 6.7). While they
reported rates for each State (e.g., 4.8 visits/100,000 workers in
Florida and 17.3 visits/100,000 workers in Louisiana), they cautioned
against directly comparing between States given differences in the data
collection methods, data availability, and use of work-related
variables. They identified 1,051 occupational heat-related inpatient
hospitalizations (930 among residents, or 88%), which corresponded to
an overall age-adjusted rate of 0.61 hospitalizations/100,000 workers
(95% CI = 0.58, 0.66). The average length of stay for State residents
was 2.7 days, which was comparable to non-residents (2.4 days).
II. Florida
The Florida Department of Health published a similar analysis in
2011 using the same methods for the State of Florida for the years
2005--2009 (Florida DOH, 2011). They identified 2,198 occupational
heat-related hospitalizations and ED visits, which corresponded to an
average overall age-adjusted annual rate of 3.7 cases/100,000 workers
(95% CI = 1.9, 5.5) and a crude rate (no age adjustment) of 5.1/100,000
workers (Communication with Laurel Harduar Morano, October 2023). The
majority of these (89.4%) were ED visits. They identified 3 fatalities
in this subset, which they noted corresponds to a case fatality rate of
1.4 fatalities/1,000 cases. They reported a third-quarter (July,
August, and September) rate of 3.2 cases/100,000 workers using a
denominator of total number of workers, whereas using a denominator of
FTEs instead produced a third-quarter rate of 13.0 cases/100,000 FTE
(Communication with Laurel Harduar Morano, October 2023). A 2016 study
conducted a more in-depth analysis of the statewide Florida
hospitalization data and included data for three additional years
(2010, 2011, and 2012) (Harduar Morano et al., 2016). The authors
restricted the data to cases occurring in May-October of each year and
identified a total of 2,979 work-related ED visits and 415 work-related
hospitalizations between 2005-2012. Using total number of workers in
the denominator (calculated from monthly CPS data), these corresponded
to average annual age-adjusted rates of 8.5 ED visits/100,000 workers
and 1.1 hospitalizations/100,000 workers.
III. Louisiana
In March 2023, the Louisiana Department of Health published a
report on heat-related illnesses in the State using ED and
hospitalization data from 2010-2020 (Louisiana DOH 2023). The authors
used workers' compensation as payer and work-related ICD codes to
determine which cases were among workers. They reported an annual
average of 320 work-related ED visits and 20 work-related
hospitalizations for heat-related illness during this period. Using
State employment data from CPS, the authors calculated an overall age-
adjusted rate of 15.1 work-related ED visits/100,000 workers and 0.9
work-related hospitalizations/100,000 workers. In 2024, the Department
of Health released a syndromic surveillance report on ED visits for
HRIs between April 1 and October 31, 2023 (Louisiana DOH 2024). They
identified 1,412 ED visits for HRIs among workers during this time
period.
IV. Multiple States
Since 2013 over 20 States have reported rates of heat-related ED
visits among workers to the Council of State and Territorial
Epidemiologists (CSTE), comprising the organization's Occupational
Health Indicator #24 (see www.cste.org/page/ohindicatorstable). These
data are compiled by the State health departments using workers'
compensation as primary payer and external cause of injury codes to
determine work-relatedness. Rates are calculated using CPS estimates of
total employed persons by State. While multiple States report their
annual rates to CSTE, the organization cautions against directly
comparing these rates between States because ``workers' compensation
eligibility criteria and availability of data from workers'
compensation programs varies among states, prohibiting state-level data
from being directly compared to other states or with national
estimates.''
Additionally, given that these data are not available for every
State, they cannot be combined to produce an accurate national rate.
The State-reported rates are currently available for 2013-2019. During
this period, the annual rates for heat-related ED visits ranged from
0.1 to 18.7 ED visits per 100,000 workers.
V. Maricopa County, Arizona
Arizona is not one of the States to share their ED visit data to
CSTE, but the most populated county in the State--Maricopa County--has
published a Heat Morbidity Report in which they provide case counts for
heat-related hospitalization discharges, including a breakdown of the
``preceding activity type'' (determined by ICD activity E-codes)
(Maricopa County Public Health Department, n.d.). Using the case counts
reported under ``occupational'' activity type and yearly estimates of
the average annual employment for Maricopa County provided by the BLS
Quarterly Census of Employment and Wages, there was an average annual
hospitalization rate among workers of 4.1 cases/100,000 workers (range:
3.1-6.4/100,000) between 2010-2017. Primary payer of workers'
compensation was not used to determine work-relatedness, which means
some occupational cases not involving E-codes may have been missed.
Given that for the majority of cases (77%-83% per year), the preceding
activity was marked as ``unknown'', it's likely that some number of
these were occupational in nature and just not listed as such. This
is supported by the fact that an ``Industrial Site'' was the place of
injury for, on average, 8% of cases, which may also be an
underestimate. It should be noted that the authors only used the
following ICD-9/ICD-10 activity E-codes to determine work-relatedness:
E011/Y93.C Activities involving computer technology and electronic
devices; E012/Y93.D Activities involving arts and handcrafts; and E016/
Y93.H Activities involving exterior property and land maintenance,
building and construction. To OSHA's knowledge, the authors did not use
any other external cause of injury codes, such as E000.0 Civilian
activity done for income, but it is not clear from the report if these
E-codes were not available or were just not used.
D. Indirect Injuries
As discussed in Section IV.P., Heat Related Injuries, one area of
research has used the natural fluctuations in temperatures to conduct
quasi-experimental studies examining the relationship between heat and
workers' compensation claims for traumatic injuries (e.g., Spector et
al., 2016; Calkins et al., 2019; Dillender 2021; Park et al., 2021).
The findings of these papers suggest that there may be many workers'
compensation claims that are heat-related but not coded as such. For
instance, Park, Pankratz, and Behrer (2021) estimated that
approximately 20,000 injuries per year in California between 2001-2018
resulted from hotter temperatures (relative to ``optimal''
temperature). For comparison, for a similar time period (2000-2017),
Heinzerling et al. (2020) only identified an average of 889 HRI
workers' compensation claims per year in California (a 22-fold
difference), suggesting that relying on workers' compensation claims
coded as HRIs alone does not capture the higher incidence of injuries
of other kinds where heat may have played a role. A research report
from the Workers Compensation Research Institute expanded this type of
analysis to 24 States, using a convenience sample of workers'
compensation claims from May-October 2016-2021 (Negrusa et al., 2024).
They found that the number of injuries increased 3.2-6.1% when the
daily maximum temperature was 75 [deg]F or higher relative to a day
with a daily maximum temperature of 65-70 [deg]F. This relationship was
even more pronounced for the construction industry.
E. Worker Self-Reports
Another source of incidence data is surveys of workers exposed to
heat. Multiple papers describe the results of surveys of outdoor
workers, typically agricultural workers, who are asked about heat-
related symptoms experienced over a week-long period while working in
the summer months (Fleischer et al., 2013; Kearney et al., 2016; Mutic
et al., 2018). Commonly reported symptoms in these studies include
heavy sweating (38-66% of surveyed workers), headache (44-58%), muscle
cramps (30-36%), dizziness (14-32%), weakness or fatigue (18%), and
nausea or vomiting (9-17%). Notably, in two of these studies, multiple
workers reported fainting on the job. A study in southern Georgia found
that 4% of 405 farmworkers experienced fainting within the previous
week, during which the heat index ranged from 100-108 [deg]F (Fleischer
et al., 2013). Another study involved asking 281 farmworkers in North
Carolina if they had ever worked in ``extreme heat.'' Of those
answering ``yes'', 3% reported having ever fainted on the job
(Mirabelli et al., 2010). When asked about symptoms over a single
workday, a separate study found that 25% of workers reported cramps,
22% headache, 10% dizziness, and 3% nausea (Smith et al., 2021).
F. Summary of Reported Annual Incidence of Nonfatal Occupational Heat-
Related Injuries and Illnesses
OSHA identified multiple sources that have reported annual
incidence estimates for nonfatal HRIs among workers. These studies and
reports generally reported heat-related incidence across an entire
workforce (either National or State), using the total workforce as the
denominator. This would understate the risk to workers who are actually
exposed to heat on the job since the denominator includes a large
percentage of workers who are not exposed to heat (e.g., office
workers). Evidence in support of this claim comes from studies showing
higher incidence of HRI when populations are stratified by sector,
industry, or occupation, as well as those reporting incidence that
occurred only during the third quarter (July, August, and September).
For instance, in Heinzerling et al., 2020, the authors report an
overall annual incidence of 6.0/100,000 workers whereas they report an
annual incidence of 38.6/100,000 workers for workers in the
agriculture, forestry, fishing, and hunting sector (a greater than 6-
fold difference). OSHA considers these stratified estimates to be more
accurate estimates of the ``true'' incidence of HRIs among heat-exposed
workers.
A summary of the annual incidence estimates for nonfatal
occupational HRIs discussed above can be found in table V-1. In the
same table, OSHA calculated the number of non-fatal HRIs that would be
expected over a working lifetime (assuming a working lifetime is 45
years long) based on those annual incidence estimates (i.e., the annual
incidence multiplied by 45). These estimates represent the total number
of HRIs that may be expected to occur in a cohort of 100,000 workers
all of whom enter the workforce at the same time and all of whom work
for 45 years. Estimates of HRI risk over a working lifetime based on
annual incidence among entire working populations (National or State)
range from 90-180/100,000 for HRIs requiring days away from work, 140-
270/100,000 for HRIs leading to a workers' compensation claim, and 4.5-
842/100,000 for HRIs leading to emergency department visits or
inpatient hospitalizations. Like incidence estimates, these values
understate the risk to workers who are actually exposed to heat on the
job since the denominator includes a large percentage of workers who
are not exposed to heat (e.g., office workers). However, when using
incidence estimates specific to individual sectors, industries, or
occupations, the HRI estimates over a working lifetime are much higher,
ranging from 49.5-114,750/100,000 for HRIs leading to a workers'
compensation claim.
III. Reported Occupational Heat-Related Fatalities
The BLS Census of Fatal Occupational Injuries (CFOI), established
in 1992, is the primary source of surveillance data on work-related
fatalities, including fatalities due to environmental heat exposure,
for the United States. The fatality data in CFOI come from diverse data
sources to identify, verify, and describe work-related fatalities. In
each case, at least two sources (e.g., death certificates, workers'
compensation reports, media reports, and government agency
administrative reports) and an average of four are used to validate
that the fatality was work-related and to verify the event or exposure
leading to death and the nature of injury or illness in each case,
which are then classified with OIICS codes. Heat-related fatalities can
be identified with an event code (``Exposure to environmental heat'')
and/or a nature code (``Effects of heat and light'').
According to BLS's CFOI, occupational heat exposure killed 1,042
U.S. workers between 1992 and 2022 (BLS, 2024c). Between 2011 and 2022,
BLS reports 479 worker deaths, an average of 40 fatalities per year
during that time. During the latest three years
for which BLS reports data (2020-2022), there was an average of 45
work-related deaths due to exposure to environmental heat per year.
Multiple sources have relied on BLS surveillance data to estimate
annual incidence rates of occupational heat-related fatalities.
Gubernot et al. (2015) calculated overall fatality rates and
fatality rates by industry sector using BLS CFOI data from 2000-2010
(Gubernot et al., 2015). The authors focused on the three industry
sectors with the highest rates in preliminary analyses: Agriculture,
Forestry, Fishing and Hunting (NAICS code 11); Construction (NAICS code
23); and Administrative and Support and Waste Management and
Remediation Services (NAICS code 56). All other industry sectors were
combined for comparison as a referent group. The authors used
nationwide worker population data from the CPS to estimate fatality
rates. The CPS data provide estimates of all employed and non-
institutionalized civilian workers over the age of 15.
The authors identified 339 occupational heat-related deaths from
2000-2010, after excluding volunteers and military personnel. They
reported an average annual heat-related fatality rate of 0.022
fatalities per 100,000 workers for the overall workforce.
For the three industry sectors preliminarily identified as having
the highest rates, the authors reported the following average annual
fatality rates:
1. Agriculture, forestry, fishing and hunting (0.306 fatalities per
100,000 workers),
2. Construction (0.113 fatalities per 100,000 workers), and
3. Administrative and Support and Waste Management and Remediation
Services (0.056 fatalities per 100,000 workers).
For all other industry sectors combined, the average annual
fatality rate was substantially smaller (0.009 fatalities per 100,000
workers). The agriculture and construction sectors combined accounted
for 58% of the fatalities during the study period (n=207).
A CDC Morbidity and Mortality Weekly Report (MMWR) from 2008
reported by Luginbuhl et al. investigated heat-related fatalities among
all workers--and agriculture workers in particular--using BLS CFOI data
from 1992-2006 (Luginbuhl et al., 2008). During the study period, the
authors identified 423 deaths related to environmental heat in CFOI
using the OIICS v1.01 event/exposure code 321 (Exposure to
environmental heat) and nature code 072* (Effects of heat and light).
Similar to the approach taken by Gubernot et al., the authors
calculated rates using CPS estimates of the average annual worker
population for denominators.
For the overall workforce, the authors calculated an average annual
incidence of 0.02 fatalities/100,000 workers, which is similar to the
estimate reported by Gubernot et al. for 2000-2010 (0.022/100,000). Of
the 423 fatalities identified, 102 (24%) occurred in the agriculture,
forestry, fishing, and hunting sector (average annual fatality rate of
0.16/100,000 workers) and 68 occurred among workers in crop production
or support activities for crop production (annual fatality rate of
0.39/100,000 workers). The rates for crop workers in North Carolina,
Florida, and California were 2.36/100,000 workers, 0.74/100,000
workers, and 0.49/100,000 workers, respectively. These findings were
later included in a peer-reviewed article (Jackson and Rosenberg 2010).
The editorial note accompanying this MMWR report mentioned, among
other limitations, that CPS estimates used for denominators likely
underestimate the number of crop workers--because of the potential lack
of stable residences among these workers and the seasonal trends in
employment--which would lead to an overestimate of risk for these
workers. This limitation would presumably apply to any rate estimates
calculated with CPS data for this specific population. To OSHA's
knowledge, this is the only reported limitation in the included
articles that would suggest a potential overestimation of incidence.
A third paper analyzed BLS CFOI heat-related fatality data for the
construction sector, estimating fatality rates for various occupations
within the sector using Standard Occupational Classification codes
(Dong et al., 2019). Using the OIICS v2.01 nature code 172* (Effects of
heat and light) to determine heat-relatedness and CPS estimates for
sector-wide and occupation-specific denominators, the authors
identified 82 heat-related construction deaths between 2011-2016 and
estimated an average annual fatality rate for the entire sector (0.15
fatalities/100,000 workers) as well as for specific occupations. The
occupations with the highest fatality rates included cement masons
(1.62/100,000); roofers (1.04/100,000); helpers (1.03/100,000); brick
masons (0.50/100,000); and laborers (0.29/100,000).
Finally, a paper from 2005 by Mirabelli and Richardson identified
heat-related fatalities using medical examiner records from North
Carolina for the period from 1977 to 2001, including 15 years of data
before the creation of CFOI (Mirabelli and Richardson 2005). They
determined that heat was a primary or underlying cause of death based
on ICD-9 codes. The researchers used the decedents' location and
activities reported in the records to determine work-relatedness, and
they excluded cases in which the decedent was <10 years old or those
which involved manufactured sources of heat.
The authors identified 40 occupational heat-related deaths. They
classified 18 of these as farm workers and reported an annual fatality
rate among these farm workers of 1.52 fatalities/100,000 workers. They
reported 10 cases having occurred at a construction site but did not
report a fatality rate for this group of workers. The average annual
fatality rate for the entire State working population was 0.05
fatalities/100,000 workers.
As none of the identified papers reported fatality rates for the
overall workforce for years beyond 2010, OSHA used the heat-related
fatality counts reported by BLS for 2011-2022 (479 worker deaths) and
employment estimates for the same years from CPS to calculate fatality
rates for these years. For the denominator, OSHA used the total number
of workers and average hours worked to estimate total FTEs per year.
The average annual fatality rate during this period was 0.029 deaths/
100,000 FTEs.
A. Summary of Reported Occupational Heat-Related Fatalities
OSHA identified multiple studies that calculated and reported
annual incidence estimates for heat-related fatalities among workers
using data from BLS CFOI or medical examiner records. These studies
reported heat-related fatality rates across an entire workforce (either
National or State), using the total workforce as the denominator. As
mentioned above, this would understate the risk to workers who are
actually exposed to heat on the job since the denominator includes a
large percentage of workers who are not exposed to heat (e.g., office
workers). Evidence in support of this claim comes from studies showing
higher fatality rates when populations are stratified by sector,
industry, or occupation. For instance, in Gubernot et al., 2015, the
authors report an overall annual fatality rate of 0.022/100,000 workers
whereas they report an annual fatality rate of 0.306/100,000 workers
for workers in the agriculture, forestry, fishing, and hunting sector
(a 14-fold difference). OSHA considers these stratified estimates to be
more accurate estimates of the ``true'' incidence of heat-related
fatalities among heat-exposed workers.
Table V-1--Estimated Risk of Experiencing a Heat-Related Injury or Illness Annually and Over a 45-Year Working
Lifetime
----------------------------------------------------------------------------------------------------------------
Expected
number of non-
Average annual fatal HRIs per
Population Source of data rate (per 100,000
100,000 workers over
workers) working
lifetime
----------------------------------------------------------------------------------------------------------------
Rates Based on Entire Working Populations
----------------------------------------------------------------------------------------------------------------
U.S., All Workers.......................... BLS SOII Injuries and Illnesses \1\ 2.0-4.0 90-180
Involving Days Away from Work.
State Working Populations.................. Workers' Compensation Records...... \2\ 3.1-6.0 140-270
State Working Populations.................. Emergency Department Visits and/or \3\ 0.1-18.7 4.5-842
Inpatient Hospitalization.
----------------------------------------------------------------------------------------------------------------
Rates Based on Sector-Specific Groups (2-digit NAICS)
----------------------------------------------------------------------------------------------------------------
Agriculture, forestry, fishing, and hunting Washington State, 1995-2005........ 5.2 234
Washington State, 2006-2017........ 13.0 585
California, 2000-2017.............. 38.6 1,737
Construction............................... Washington State, 1995-2005........ 12.1 545
Washington State, 2006-2017........ 10.8 486
Wisconsin, 2010-2022............... 1.4 63.0
Public Administration...................... Washington State, 1995-2005........ 12 540
Washington State, 2006-2017........ 10.3 464
California, 2000-2017.............. 35.3 1,589
Wisconsin, 2010-2022............... 2.8 126
Administrative and support and waste Washington State, 1995-2005........ 3.9 176
management and remediation services. Washington State, 2006-2017........ 4.6 207
California, 2000-2017.............. 8.8 396
Wisconsin, 2010-2022............... 2.9 131
Transportation and warehousing............. Washington State, 1995-2005........ 3.5 158
Washington State, 2006-2017........ 3.8 171
Wisconsin, 2010-2022............... 1.1 49.5
Utilities.................................. California, 2000-2017.............. 11.4 513
Mining..................................... California, 2000-2017.............. 21.3 959
Wholesale Trade............................ Wisconsin, 2010-2022............... 1.9 85.5
----------------------------------------------------------------------------------------------------------------
Rates Based on Industry-Specific Groups (6-digit NAICS)
----------------------------------------------------------------------------------------------------------------
Farm labor contractors and crew leaders.... Washington State, 2006-2017........ 77.3 3,479
Fire protection............................ Washington State, 1995-2005........ 80.8 3,636
Washington State, 2006-2017........ 60.0 2,700
Structural steel and precast concrete...... Washington State, 2006-2017........ 54.2 2,439
Poured concrete foundation and structural Washington State, 1995-2005........ 35.9 1,616
contractors.
Washington State, 2006-2017........ 31.6 1,422
Roofing contractors........................ Washington State, 1995-2005........ 59.0 2,655
Washington State, 2006-2017........ 29.0 1,305
Highway, street, and bridge construction... Washington State, 1995-2005........ 44.8 2,016
Site preparation construction.............. Washington State, 1995-2005........ 35.9 1,616
----------------------------------------------------------------------------------------------------------------
Rates Based on Major Occupational Groups
----------------------------------------------------------------------------------------------------------------
Protective services........................ California, 2000-2017.............. 56.7 2,552
Wisconsin, 2010-2022............... 4.1 185
Farming, fishing, and forestry............. California, 2000-2017.............. 35.9 1,616
Transportation and Material moving......... California, 2000-2017.............. 12.3 554
Wisconsin, 2010-2022............... 2.6 117
Construction and extraction................ California, 2000-2017.............. 8.9 401
Wisconsin, 2010-2022............... 1.5 67.5
Building and grounds cleaning and California, 2000-2017.............. 6.0 270
maintenance.
Wisconsin, 2010-2022............... 1.5 67.5
Production................................. Wisconsin, 2010-2022............... 1.6 72.0
Municipal workers in departments governing Texas, 2009-2017................... 2,550 114,750
streets and traffic, parks and recreation,
utilities, and solid waste.
----------------------------------------------------------------------------------------------------------------
Rates Based on Minor Occupational Groups
----------------------------------------------------------------------------------------------------------------
Fire Fighting and Prevention............... Wisconsin, 2010-2022............... 14.7 662
Material Moving Workers.................... Wisconsin, 2010-2022............... 3.3 149
Metal and Plastic Workers.................. Wisconsin, 2010-2022............... 2.8 126
Motor Vehicle Operations................... Wisconsin, 2010-2022............... 2.2 99.0
Assemblers and Fabricators................. Wisconsin, 2010-2022............... 2.2 99.0
----------------------------------------------------------------------------------------------------------------
\1\ Ranges reflect varying annual average estimates between 2011-2020.
\2\ Ranges reflect values reported in Heinzerling et al., 2020, Bonauto et al., 2007, and Hesketh et al., 2020.
\3\ Ranges reflect values reported in or derived from Harduar Morano et al., 2015, Florida DOH 2011, Louisiana
DOH 2023, Harduar Morano et al., 2016, CSTE, and Maricopa County Public Health Department.
IV. Limitations and Underreporting
Evidence suggests that existing surveillance data undercount the
total number of heat-related injuries, illnesses, and fatalities, among
workers. The incident rates presented in the previous section are
likely vast underestimates both because they use this surveillance data
as the numerator when calculating incidence rates and because they
overestimate the number of workers exposed to hot work environments
(i.e., the denominator for incidence rates). These sources of
uncertainty are described below.
A. Incidence Estimation
Incidence estimates based on BLS data are likely to underestimate
the true risk to workers who are exposed to specific hazards, like
heat, in part because of difficulties in estimating the population of
exposed workers. The current approach for BLS SOII rate estimates is to
use the population of all workers in the U.S. for the denominator, not
just those exposed to the hazard of interest. For instance, the
denominators used for the risk estimates presented above would include
most office workers who work in climate-controlled buildings and would
therefore not have occupational exposure to the levels of heat stress
that have been associated with adverse outcomes. For 2022, BLS reported
116,435,925 full-time workers in the U.S. However, OSHA estimates the
proposed standard would cover approximately 36 million workers,
approximately one-third of the total full-time workers in the U.S.
Therefore, BLS's use of a larger denominator likely underestimates risk
because it includes workers not exposed to hazardous heat and therefore
less likely to experience an HRI.
The denominators for the annual incidence estimates presented above
also include worker-time for the entire year, even though for many
workers, exposure to potentially harmful levels of heat only occurs
during the hottest months of the year. Including unexposed worker-time
in the denominator has the effect of diluting the incidence estimates,
meaning annual incidence estimates do not accurately represent the risk
to workers when they are actually exposed to hazardous heat. The risk
to workers whose jobs do expose them to harmful levels of heat, on the
days on which those exposures occur, would therefore be expected to be
higher than the estimates published by BLS. In addition, using total
worker populations as a basis for estimating incidence likely will
underestimate the risk to particularly susceptible workers, such as
older workers, workers with pre-existing conditions, and workers not
acclimatized to the heat.
OSHA believes that studies that reported illness rates by sector or
occupation provide evidence showing that the annual average illness
rates reported across the entire workforce underestimate risk for
exposed workers. For example, the Washington State and California
workers' compensation studies found that heat-related illness rates for
sector- or occupation-specific populations were substantially higher
than the rates for the general working population in the State
(Heinzerling et al., 2020; Bonauto et al., 2007; Hesketh et al., 2020).
The sectors and occupations examined included those where exposure to
hot environments was more likely than for the population as a whole
(e.g., Construction and Agriculture, Forestry, Fishing, and Hunting).
Additionally, many of the surveillance papers described above also
reported the month in which the injury, illness, or fatality occurred
and found that most cases were clustered in the hotter, summer months
(e.g., June, July, and August). When researchers in Washington and
Florida restricted their rate estimates to include data only for the
third quarter (July, August, and September), they found rates that were
several-fold higher than annual average illness rates over the whole
population, which include many unexposed worker-days.
B. Undercounting of Cases
The general underreporting and undercounting of occupational
injuries and illnesses has been a topic of multiple government reports
(e.g., Ruser, 2008; Miller, 2008; GAO, 2009; Wiatrowski, 2014). The
authors of the peer-reviewed papers described in sections V.A.II., and
V.A.III., above list underreporting or misclassification of cases as a
limitation in their analyses that would have the effect of
underestimating risk.
I. BLS SOII
Two papers from the early 2000s that linked workers' compensation
records to BLS SOII data found evidence that SOII missed a substantial
amount of workers' compensation claims, depending on the State analyzed
and the assumptions and methodology used (Rosenman et al., 2006; Boden
and Ozonoff, 2008). In response to increased attention around this
topic at the time, BLS funded additional research to examine the extent
of underestimation in SOII and potential reasons (Wiatrowski, 2014).
One of these studies involved linking multiple data sources (i.e., not
just SOII and workers' compensation) for cases of amputation and carpal
tunnel syndrome (Joe et al., 2014). The authors found that the State-
based surveillance systems included 5 times and 10 times more cases
than BLS SOII, respectively.
Another study conducted as part of this broader effort estimated
that approximately 30% of all workers' compensation claims in
Washington between 2003-2011 were not captured in BLS SOII (Wuellner et
al., 2016). This included sectors with higher rates of heat-related
injuries and illnesses, such as Agriculture, Forestry, Fishing, and
Hunting (28% of cases uncaptured) and Construction (28% uncaptured)
(Wuellner et al., 2016, Table III). The rate of underreporting was
particularly high for large construction firms (Wuellner et al., 2016,
Table IV).
In response to the studies on SOII undercount, BLS authors have
argued that differences in the inclusion criteria, scope, and purpose
between BLS SOII and workers' compensation explain some of differences
in the estimates and complicate the interpretations of the linkage-
based studies (Ruser, 2008; Wiatrowski, 2014). SOII estimates OSHA-
recordable injuries and illnesses each year and provides detailed case
and demographic information (e.g., nature of injury) for a specific
subset of the more severe cases (e.g., those involving days away from
work). This scope (OSHA-recordable injuries and illnesses) inherently
limits the ability for SOII to be used to estimate all occupational
injuries and illnesses. Additionally, injuries and illnesses involving
days away from work represent a limited percentage of the total
injuries and illnesses reported to BLS. In 2022, these cases were 42%
of total recordable cases, suggesting the case counts for HRIs in SOII
could be missing up to 58% of all OSHA-recordable HRIs (i.e., those not
involving days away from work) (https://www.bls.gov/iif/latest-numbers.htm).
The injury and illness data that employers report to BLS come from
the employer's OSHA Form 300 Log of Work-Related Injuries and Illnesses
and OSHA Form 301 Injury and Illness Incident Report, so information on
the quality of the data in these forms is relevant for understanding
limitations of SOII. Through the Recordkeeping National Emphasis
Program (NEP) from 2009-2012, OSHA found that almost half (47%) of
establishments inspected by the agency had unrecorded and/or under-
recorded cases, which were more common at establishments that
originally reported low rates (Fagan and Hodgson, 2017). Several
factors contributed to the under-recording and unrecording cases.
First, in conducting thousands of interviews, the authors found that
workers do not always report injuries to their employers because of
fear of retaliation or disciplinary action. Second, some employers used
on-site medical units, which the authors explained could contribute to
underreporting (e.g., if these units were used to provide first aid
when additional medical care, which would have warranted reporting on
OSHA forms, should have been provided).
Employers rely on workers to report injuries and illnesses that may
otherwise be unobserved, but workers have multiple reasons to not do
so. In addition to Fagan and Hodgson 2017, multiple studies have
interviewed or surveyed workers on this topic. A recent systematic
review of 20 studies found that 20-74% of workers--which included
cleaning staff, carpenters, construction workers, and healthcare
workers--did not report injuries or illnesses to management (Kyung et
al., 2023). Some of the researchers asked workers about the barriers to
reporting, which included fear, a lack of knowledge on the reporting
process, and considering the injury to be a part of the job or not
serious.
Finally, employers are disincentivized from reporting injuries and
illnesses on their OSHA logs. Disincentives for reporting include
workers' compensation premiums being tied to injury and illness rates,
competition for contracts involving safety records, and a perception
that reporting will increase the probability of being inspected by OSHA
(GAO, 2009).
In interviews with employers selected to respond to SOII,
researchers found that 42% of them were not maintaining a log (Wuellner
and Phipps, 2018). In the same study, researchers found evidence to
suggest that misunderstandings about the reporting requirements would
likely lead to employers underreporting cases involving days away from
work. A similar study conducted among SOII respondents in Washington
State found that 12% weren't maintaining a log and 90% weren't
complying with some aspect of OSHA's recordkeeping requirements
(Wuellner and Bonauto, 2014).
While the general underreporting articles described here are not
specific to heat, Heinzerling et al. 2020 examined rates of heat-
related injuries and illnesses among workers in California and found
that California's workers' compensation database, WCIS, had 3-6 times
the number of heat-related cases between 2009-2017 than the official
BLS SOII estimates for California for each year in that period
(Heinzerling et al., 2020). Part of the reason for this discrepancy
could be the difference in inclusion criteria between the two datasets,
however, it is still a useful estimate for contextualizing the
potential magnitude of underreporting of heat-related cases when using
only SOII. While outside the U.S., a recent survey of 51 Canadian
health and safety professionals in the mining industry found that 71%
of respondents believed HRIs were underreported (Tetzlaff et al.,
2024).
II. Workers' Compensation
While workers' compensation data may capture injury and illness
cases not included in BLS SOII, the data are not available for the
entire U.S., as insurance coverage and reporting requirements vary
across States, and most States do not have single-payer systems.
Therefore, the majority of claims data are compiled by various insurers
and not within a single database. Even when the data are available for
an entire State, it is generally presumed that not all worker injuries
and illnesses are captured in these data, in part because of
eligibility criteria and in part because of underutilization of
workers' compensation for reimbursement of work-related medical
expenses.
Multiple papers have examined the extent to which and reasons why
workers don't always use workers' compensation insurance to pay for
work-related medical expenses and other reimbursable expenses. Some
reasons workers have reported for not filing workers' compensation
claims include fear, a lack of knowledge, ``too much trouble'' or
effort, and considering the injury to be a part of the job or not
serious (Kyung et al., 2023; Scherzer et al., 2005). Using the
Washington State Behavioral Risk Factor Surveillance System (BRFSS), a
telephone survey, Fan et al. (2006) found that 52% of the respondents
in 2002 reporting a work-related injury or illness filed a workers'
compensation claim. Using similar methodology across 10 States, Bonauto
et al. (2010) found that among respondents who reported a work-related
injury, there was a wide range in the proportion who reported having
their treatment paid for by workers' compensation by State--47% in
Texas to 77% in Kentucky (with a median of 61%). A study from 2013
estimated that 40% of work-related ED visits were paid for by a source
other than workers' compensation (Groenewold and Baron, 2013). Worker
race, geography, and having an illness rather than an injury were all
predictors of whether workers' compensation was the expected payer.
There are a few papers that suggest this phenomenon is occurring
for heat-related outcomes. Harduar Morano et al. 2015 (described above
in Section V.A.II., Reported Annual Incidence of Nonfatal Occupational
Heat-Related Injuries and Illnesses) found that across several
southeastern States, workers' compensation as expected primary payer
alone captured 60% of all emergency department visits and inpatient
hospitalizations, which varied by State (50-80% for emergency
department visits and 38-84% for inpatient hospitalizations) (Harduar
Morano et al., 2015). Similarly, in the 2011 report by the Florida
Department of Health (described above in Section V.A.II., Reported
Annual Incidence of Nonfatal Occupational Heat-Related Injuries and
Illnesses), 83% of claims identified were captured by workers'
compensation as primary payer (Florida DOH, 2011). It should be noted
that these percentages are influenced by the total number of captured
cases and in both sources the authors presume that they did not capture
all relevant cases.
III. Hospital Discharge Data
Hospital discharge data are the only surveillance data presented in
this risk assessment for which work-relatedness is not an inclusion
criterion; therefore, researchers relying on this data need to take an
additional step to assess work-relatedness for each case that
introduces the possibility that work-related cases are not recognized
as such and are thus excluded. Researchers identifying work-related
cases typically use a combination of workers' compensation as the
primary payer or ICD codes for external cause of injury. As discussed
in the previous section, workers' compensation is not always used by
workers, so relying on this variable will lead to undercounting. For
external cause of injury codes (e.g., E900.9 Excessive heat of
unspecified origin), researchers have found that these are not always
present or accurate for work-related injury cases (Hunt et al., 2007),
which isn't unexpected given that they aren't required for
reimbursement. For instance, codes indicating the location of
occurrence were present in 43% of probable work-related injury cases
the authors reviewed (Hunt et al., 2007). Harduar Morano and Watkins
(2017) used external cause of injury codes to identify work-related
emergency department visits and hospitalizations for heat-related
illnesses in Florida. They found that 2.8% of emergency
department visits, 1.2% of hospitalizations, and 0% of deaths were
identified solely by an external cause of injury code for work.
Both workers' compensation claims and hospitalization data are also
affected by the accuracy of diagnostic codes for identifying heat-
related cases. While the use of ICD codes for surveillance of heat-
related deaths, illnesses, and injuries is widely accepted, it is not
infallible, as these codes are designed for billing rather than
surveillance. The use of specific codes is up to the discretion of
healthcare providers, so practices may vary by provider and facility.
Healthcare providers may not always recognize that a patient's symptoms
are heat-related and thus, they may not record a heat-specific ICD
code. For example, a patient who presents to the emergency room after
fainting would likely be diagnosed with ``syncope'' (the medical term
for fainting). If the provider is aware that the patient fainted due to
heat exposure, they should record a heat-specific ICD-10 code, T67.1
Heat syncope. However, if the provider is unaware that the patient
fainted due to heat exposure (or otherwise fails to recognize the
connection between the two), they may record a non-heat-specific ICD-10
code, R55 Syncope and collapse. Researchers suspect underreporting when
ICD codes are used for surveillance of HRIs (Harduar Morano and
Watkins, 2017) and recommend researchers use all possible fields
available (e.g., primary diagnosis, secondary diagnosis, underlying
cause of death, contributing cause of death).
Researchers examining trends in heat-related illnesses using
electronic health records for the Veterans Health Administration
identified a dramatic increase in cases when ICD-10 was adopted,
suggesting that the coding scheme in ICD-9 may have led to systematic
underreporting of heat-related cases, at least for this population
(Osborne et al., 2023). The authors also note that 8.4% of the HRI
cases they identified were captured using unstructured fields (e.g.,
chief complaint, reason for admission) and not ICD codes.
Not all sick and injured workers go to an emergency department or
hospital and those that do are likely to be more severe cases.
Unfortunately, estimating the proportion of injured and sick workers
who do go to the hospital or emergency room is difficult, given a lack
of data on this topic. In a 1998 CDC Morbidity and Mortality Weekly
Report written by NIOSH safety researchers, the authors reported an
analysis of unpublished data from the 1988 National Health Interview
Survey (NHIS) Occupational Health Supplement which found that 34% of
all occupational injuries were first treated in hospital emergency
departments, 34% in doctors' offices/clinics, 14% in work site health
clinics, and 9% in walk-in clinics (NIOSH DSR 1998). 1988 was the last
year that NIOSH asked that question in the NHIS.
Care-seeking for workers experiencing heat-related symptoms
specifically may be low. In a study evaluating post-deployment survey
response data among a subset of the Deepwater Horizon oil spill
responders (U.S. Coast Guard), Erickson et al. found that less than 1%
of respondents reported seeking medical treatment for heat-related
illness, yet 12% reported experiencing any heat-related symptoms
(Erickson et al., 2019).
IV. BLS CFOI
CFOI is well-regarded as the most complete and authoritative source
on fatal workplace injuries. However, the approach used to classify the
event and nature codes by BLS is not immune to misclassification of
heat-related deaths. BLS relies on death certificates, OSHA fatality
reports, news articles, and coroner reports (among other sources) to
determine the primary or contributing causes of death. The criteria for
defining a heat-related death or illness can vary by State, and among
physicians, medical examiners, and coroners. Additionally, individuals
who fill out death certificates are not necessarily equipped to make
these distinctions or confident in their accuracy (Wexelman, 2013).
Depending on State policies, individuals performing this role may be a
medical professional or an elected official with limited or no
medically relevant experience (National Research Council, 2009; CDC,
2023).
Researchers estimating fatality rates attributable to heat in the
overall U.S. population using historical temperature records have
produced much higher counts than approaches solely using death
certificates (Weinberger et al., 2020). While outside the U.S., a
recent study examining causes of death among migrant Nepali workers in
Qatar from 2009-2017 demonstrated that deaths coded as cardiovascular-
related (e.g., ``cardiac arrest'') among these mostly young workers
were unexpectedly common and correlated with higher wet bulb globe
temperatures, suggesting that these deaths may have been heat-related
but not coded as such (Pradhan et al., 2019). Heat-related deaths are
uniquely hard to identify if the medical professional didn't witness
the events preceding the death, particularly because heat can
exacerbate an existing medical condition, acting as a contributing
factor (Luber et al., 2006).
C. Summary
In conclusion, the available evidence indicates that the existing
surveillance data vastly undercount cases of heat-related injuries and
illnesses among workers. OSHA additionally believes that the inclusion
of unexposed worker-time in the denominator for incidence estimates
underestimates the true risk among heat-exposed workers.
V. Requests for Comments
OSHA requests information and comments on the following questions
and requests that stakeholders provide any relevant data, information,
or additional studies (or citations) supporting their view, and explain
the reasoning for including such studies:
Are there additional data or studies OSHA should consider
regarding the annual incidence of HRIs and heat-related fatalities
among workers?
OSHA has identified data from cohort-based and time series
studies that would suggest higher incidence rates than data from
surveillance datasets (e.g., BLS SOII, workers' compensation claims).
Are there other data from cohort-based or time series studies that OSHA
should rely on for determining risk of HRIs to heat-exposed workers?
Are employers aware of occupational HRIs that are not
reported through BLS SOII, workers' compensation claims, or hospital
discharge data? How commonly do HRIs occur that are not recorded on
OSHA 300 logs?
Are there additional data or studies that OSHA should
consider regarding the extent of underreporting and underestimating of
HRIs or heat-related fatalities?
B. Basis for Initial and High Heat Triggers
I. Introduction
In this section, OSHA presents the evidence that forms the basis of
the heat triggers contained in the proposed standard. These triggers
are based on the heat index and wet bulb globe temperature (WBGT). The
WBGT triggers are based on NIOSH exposure limits (i.e., the REL and
RAL), which are supported by empirical evidence dating back to the
1960s and have been found to be highly sensitive in capturing
unsustainable heat exposures.
Although there are no consensus-based heat index exposure limits
for workers, the question of which heat
index values represent a highly sensitive and appropriate screening
threshold for heat stress controls in the workplace has been evaluated
in the peer-reviewed scientific literature. The evidence described
below provides information on the sensitivity of alternative heat index
values, that is, the degree to which a particular heat index value can
be used to screen for potential risk of heat-related injuries and
illnesses (HRIs) and fatalities. OSHA looked at both experimental and
observational evidence, including efforts to derive more accessible and
easily understood heat index-based triggers from WBGT-based exposure
limits, to preliminarily determine appropriate heat index values for
triggering heat stress control measures. Each of these evidence streams
has strengths and limitations in informing this question.
Relevant experimental evidence in the physiology literature is
often conducted in controlled laboratory settings among healthy, young
volunteers, but the conditions may not always mimic conditions
experienced by workers (e.g., workers often experience multiple days in
a row of working in high temperatures). Observational evidence does not
have this limitation because the data are collected among actual
workers in real-world settings. However, observational evidence is
potentially affected by exposure misclassification since exposure
metrics are often derived from local weather stations and rely on
maximum daily values. Experimental data does not have this limitation,
since the laboratory conditions are highly controlled, including the
exposure levels.
OSHA used both streams of evidence to support proposing an initial
heat trigger of 80 [deg]F (heat index) and a high heat trigger of 90
[deg]F (heat index). The observational evidence that OSHA identified
suggests that the vast majority of known occupational heat-related
fatalities occur above the initial heat index trigger, making it a
sensitive trigger for heat-related fatalities. The vast majority of
nonfatal occupational HRIs also occur above this trigger. The
experimental evidence (specifically the WBGT-based exposure limits)
also suggests that when there is high radiant heat, a heat index of 90
[deg]F would be an appropriate time to institute additional controls
(e.g., mandatory rest breaks). This is supported by observational
evidence that shows a rapidly declining sensitivity above a heat index
of 90 [deg]F. OSHA has preliminarily concluded that the experimental
evidence also supports the selection of these triggers as highly
sensitive and therefore protective.
II. Observational Evidence
To determine an appropriate initial heat trigger, OSHA sought to
identify a highly sensitive screening level above which the majority of
fatal and nonfatal HRIs occur. This could presumably be used to
identify the environmental conditions for which engineering and
administrative controls would be most important to prevent HRIs from
occurring. One challenge for determining this trigger level is that
many factors influence an individual's risk of developing an HRI. In
addition to workload, PPE, and acclimatization status, the risk of
developing an HRI is also influenced by workers' abilities to self-pace
at their jobs as well as whether there had been exposure to hot
conditions on the prior day(s). There are also medications and
comorbidities that may increase workers' risk of HRIs (see discussion
in Section IV.O., Factors that Affect Risk for Heat-Related Health
Effects).
The observational studies reviewed by OSHA used retrospective
temperature and humidity data matched to the locations where HRIs and
fatalities occurred over a period of time. Although these studies did
not account specifically for workload, PPE use, acclimatization status,
or other relevant factors, the HRI cases studied included worker
populations where these factors were likely present to varying degrees.
Therefore, OSHA has preliminarily determined that retrospective
observational data collected among workers who have experienced fatal
or nonfatal HRIs on the job is valuable to informing a screening level
that reflects the presence of these multiple risk factors among worker
populations. These studies are summarized in the following sections.
A. Fatalities
In a doctoral dissertation from 2015, Gubernot matched historic
weather data to the heat-related fatalities reported in BLS CFOI
(fatality data described in Section V.A., Risk Assessment) between
2000-2010 (Gubernot, 2015). Gubernot used historic, weather monitor-
based temperature and dew point measurements from the National Climatic
Data Center to recreate the heat index (using daily maximum temperature
and daily average dew point) on the day of each fatality. If there was
not already a monitor in the county where a fatality occurred, then the
next closest weather monitor to that county was used. Of the 327
fatalities identified as being related to ambient heat exposure (i.e.,
cases with secondary heat sources, like ovens, were excluded), 96.3%
occurred on a day with a calculated heat index above 80 [deg]F and
86.9% occurred on a day above 90 [deg]F. Using a higher threshold such
as a heat index of 95 [deg]F would have only captured approximately 71%
of fatalities (estimated from Figure 4-2 of the study). The author also
evaluated how many cases occurred on a day when a National Weather
Service (NWS)-defined excessive heat event (EHE) was declared. In a
directive to field offices, the NWS outlines when offices should issue
excessive heat warnings--when there will be 2 or more days that meet or
exceed a heat index of 105 [deg]F for the Northern U.S. and 110 [deg]F
for the Southern U.S., with temperatures not falling below 75 [deg]F
(although local offices are allowed to use their own criteria) (NWS,
2024a). Gubernot appears to have used a simpler criterion to evaluate
the sensitivity of these EHEs--whether the heat index on the day of the
fatality was at or above 105 [deg]F for northern States and at or above
110 [deg]F for southern States. Only 42 fatalities (12.8%) occurred on
days meeting the EHE definitions, suggesting EHEs are not a sensitive
trigger for occupational heat-related fatalities. During the SBREFA
process, small entity representatives suggested that OSHA consider the
NWS EHE definitions as options for the initial and/or high heat
triggers, but based on these findings (and those reported in other
studies summarized in this section), OSHA has preliminarily determined
that these criteria are not sensitive enough and would not adequately
protect workers.
Some limitations of this analysis include the use of nearest-
monitor exposure assignment, as well as the use of maximum temperature
with average dew point to calculate heat index, both of which may
introduce exposure misclassification. Although the author did not refer
to the latter as a daily maximum heat index, this estimate would most
closely approximate that value, which would suggest that workers were
likely exposed to heat index values below that level during the work
shift leading up to the fatality.
In a meta-analysis published in 2020, Maung and Tustin (both
affiliated with OSHA at the time) conducted a systematic review of
studies, such as the one described above by Gubernot, where researchers
retrospectively assigned heat exposure estimates to occupational heat-
related fatalities (Maung and Tustin, 2020). The purpose of their meta-
analysis was to identify a heat index threshold below which
occupational heat-related fatalities do not occur (i.e., a highly
sensitive
threshold). Maung and Tustin identified 418 heat-related fatalities
among civilian workers across 8 studies. Approximately three quarters
of these civilian fatalities (n=327; 78%) came from Gubernot 2015. The
authors found a heat index threshold of 80 [deg]F to be highly
sensitive for civilian workers--96% of fatalities (402 of 418) occurred
on days with a heat index estimate at or above this level. A heat index
threshold of 90 [deg]F had slightly lower sensitivity--approximately
86% (estimated from table 1 and figure 3 of their study). Similar to
the findings reported in Gubernot 2015, one of the NWS thresholds for
issuing heat advisories (heat index of 105 [deg]F) did not appear to be
a sensitive trigger, missing 68% of civilian worker fatalities.
The limitations for Gubernot 2015 apply to this analysis as well.
These analyses (including the data from Gubernot, 2015) were limited to
outdoor workers, potentially limiting the generalizability of the
findings. This analysis also relied on single values (e.g., daily
maximum heat index) to capture exposure across a work shift. As pointed
out by Maung and Tustin, it is important to consider that exposure
characterizations using daily maximum heat index likely over-estimates
the exposures that workers experience throughout the shift leading to
the fatality. For example, a fatality occurring on a day with a daily
maximum heat index of 90 [deg]F likely involved prolonged exposure to
heat index values in the 80s [deg]F.
In 2019, a group of OSHA researchers published a similar analysis
for both fatal and nonfatal HRIs reported to OSHA in 2016 among outdoor
workers (Morris CE et al., 2019). They identified 17 fatalities in this
subset and used nearest weather station data to estimate daily maximum
heat index on the day of the fatality. All 17 fatalities occurred on a
day with a daily maximum heat index of at least 80 [deg]F (the lowest
was at 88 [deg]F). A daily maximum heat index of 90 [deg]F had a
sensitivity of approximately 94%, while 100 [deg]F had a sensitivity of
approximately 35%. A major limitation with this analysis is its small
sample size (n=17 fatalities).
B. Non-Fatalities
Morris et al., identified 217 nonfatal HRIs among outdoor workers
reported to OSHA in 2016 (Morris CE et al., 2019). They found that 99%
of these cases happened on a day with a daily maximum heat index of at
least 80 [deg]F. There is a steep decline in sensitivity for daily
maximum heat index values in the 90s [deg]F--89% for 90 [deg]F but
approximately 58% for 100 [deg]F (estimated from Figure 5 of the study
which combines fatal and nonfatal cases)--suggesting that many nonfatal
HRIs occur on days when the heat index does not reach 100 [deg]F. One
limitation of this dataset is potential selection bias, because the
dataset only included cases that were reported to OSHA. This study
therefore did not include cases in State Plan States.
A much larger analysis conducted among emergency department (ED)
visits in the Southeastern U.S. was published by Shire et al. (Shire et
al., 2020). The authors identified 5,017 hyperthermia-related ED visits
among workers in 5 southeastern States (Florida, Georgia, Kentucky,
Louisiana, and Tennessee) between May and September in 2010-2012. While
the previously described studies used nearest monitor data, Shire et
al. used data from the North American Land Data Assimilation System
(NLDAS), which incorporates both observation and modeled data to fill
in gaps between locations of monitors, providing data at a higher
geographic resolution (0.125[deg] grid). Since the authors only had ED
visit data at the county level, they used the NLDAS data to compute
population-weighted, county-level estimates of daily maximum heat index
using all the grids within each county. They found that approximately
99% of ED visits occurred on days with a daily maximum heat index of at
least 80 [deg]F and about 95% of cases on days with a maximum heat
index of at least 90 [deg]F. Approximately 54% of cases occurred on
days with a daily maximum heat index of 103 [deg]F or higher. This
further supports the finding from Morris et al. (2019) that sensitivity
declines steeply above a heat index of 90 [deg]F. One limitation of
this analysis is the use of the emergency department location as the
basis for the exposure assignment, which has the potential to introduce
exposure misclassification if workers were working far away from the ED
facility.
In a 2016 doctoral dissertation, Harduar Morano conducted a
retrospective analysis of 3,394 heat-related hospitalizations and ED
visits among Florida workers in May-October between 2005-2012, using
data from the weather monitor nearest to the zip codes where the
hospitalizations and ED visits occurred to characterize heat exposure
(Harduar Morano, 2016). The vast majority of cases occurred on a day
with a daily maximum heat index of at least 80 [deg]F, with
approximately 91% of cases occurring on a day with a maximum heat index
of at least 90 [deg]F (estimated from Figure 6-4). There was also a 13%
increase in the HRI hospitalization and ED visit rate for every 1
[deg]F increase in heat index at values below 99 [deg]F (Figure 6-4,
Lag 0 plot of the study), suggesting that potential triggers in the
mid-to-high 90's would increasingly miss many cases. One limitation of
this analysis and that conducted by Shire et al. is that
hospitalization and ED visit data did not include enough information to
distinguish between indoor vs outdoor workers; it is possible that
indoor workers could have been exposed to conditions not captured by
the weather data (such as working near hot industrial processes).
In addition, four studies of workers' compensation data in
Washington State--three of which were reported in Section V.A., Risk
Assessment--have examined maximum temperature or heat index on the days
of reported HRIs (Bonauto et al., 2007; Spector et al., 2014; Hesketh
et al., 2020; Spector et al., 2023). Hesketh et al., 2020 (an update on
Bonauto et al., 2007) matched weather data to addresses for the HRI
claims in the State's workers' compensation database between 2006 and
2017 (Hesketh et al., 2020). They found that, of the 905 claims for
which they had temperature data, over 75% of HRIs occurred on days with
a maximum temperature of at least 80 [deg]F and approximately 50% of
claims occurred on days with a maximum temperature of at least 90
[deg]F (estimated from Figure 2). They also reported that approximately
75% of claim cases occurred when the hourly maximum temperature was at
least approximately 79 [deg]F. This paper is part of the rationale for
Washington State lowering the trigger level in its heat-specific
standard from 89 [deg]F to 80 [deg]F--the old trigger of 89 [deg]F had
missed 45% of cases in this dataset (Washington Dept. of Labor &
Industries, 2023). A similar study published in 2023 expanded the
dataset used by Hesketh et al. to include HRI claims from 2006 to 2021
(n=1,241) (Spector et al., 2023). The authors used gridded
meteorological data from the PRISM Climate Group at Oregon State
University and geocoded accident location (or business location or
provider location if accident location was unable to be used) to
determine the maximum temperature on the day of the event. They found
that 76% of HRI claims occurred on a day with a maximum temperature of
at least 80 [deg]F (this increased to 79% when restricted to cases that
were ``definitely'' or ``probably'' outdoors). A major limitation of
these studies is the use of ambient temperature, limiting the ability
to compare findings to other papers that relied on the heat index. In
Spector et al. 2014, the authors calculated the daily maximum heat
index for each county with an HRI in their dataset on the date of
injury (Spector et al., 2014). They obtained the county of injury and,
when not available, imputed the location of the injury rather than
using the employer address, which is assumed to be more accurate for
characterizing exposure. In their analysis of 45 agriculture and
forestry worker HRI claims between 1995-2009 that had corresponding
weather data, Spector et al. found that 75% of HRI claims occurred on
days when the maximum heat index was at least 90 [deg]F, whereas only
50% occurred on days when it was at least 99 [deg]F and 25% for 106
[deg]F.
C. Summary
In summary, researchers have identified a heat index of 80 [deg]F
as a highly sensitive trigger for heat-related fatalities (capturing
96-100% of fatalities) and nonfatalities (99-100%) among workers
(excluding results from Washington State). When looking at ambient
temperature, researchers in Washington found that 75-76% of HRI claims
occurred on a day with a maximum ambient temperature of 80 [deg]F or
greater. Multiple studies additionally identified a rapidly declining
sensitivity above a heat index of 90 [deg]F, suggesting that additional
protective measures (e.g., observation for signs and symptoms of HRIs)
are needed once the heat index reaches approximately 90 [deg]F.
One of the common limitations of the analyses presented in this
section is the use of a single reading (e.g., daily maximum heat index)
to capture each affected worker's exposure on the day of the event. In
reality, conditions fluctuate throughout the day, so relying on maximum
measures would likely overestimate heat exposure across the workday.
The use of nearest monitor weather data is also likely to lead to
exposure misclassification. The inclusion of indoor workers in some of
the studies is also a limitation, since the exposure for those workers
could be very different (e.g., if there is process heat). In Spector et
al. 2023, the authors noted an increase in the percent of cases
occurring on days with a maximum temperature of 80 [deg]F when
restricting to cases that definitely or probably occurred outdoors. In
all these studies, researchers can only examine conditions for the
cases that were captured in the surveillance systems. There could be a
bias such that cases occurring on hotter days were more likely to have
been coded as heat-related and included in these databases. Failure to
ascertain HRI cases occurring at lower heat indices could have skewed
the findings upwards, making it appear that hotter thresholds were more
sensitive than they actually were. Finally, the use of heat index (or
ambient temperature) ignores the impacts of air movement as well as
radiant heat, which can substantially increase the heat stress a worker
is exposed to and increase the risk of an HRI.
III. Experimental Evidence
NIOSH has published exposure limits based on WBGT in its Criteria
for a Recommended Standard going back multiple decades.\3\ These
exposure limits--the REL and RAL--account for the contributions of wind
velocity and solar irradiance, in addition to ambient temperature and
humidity. (ACGIH has published similar exposure limits--the TLV and
AL.) In addition to WBGT, NIOSH and ACGIH heat stress guidelines
require the user to account for metabolic heat production (through the
estimation of workload) and the contributions of PPE and clothing. The
user adds an adjustment factor to the measured WBGT to account for the
specific clothing or PPE worn (specifically those ensembles that impair
heat loss) and uses a formula based on workload to estimate the
exposure limit. They then compare the measured (or adjusted, if using a
clothing adjustment factor) WBGT to the calculated exposure limit to
determine if the limit is exceeded. Work-rest schedules with increasing
time spent on break can further increase the exposure limit.
---------------------------------------------------------------------------
\3\ NIOSH plays an important role in carrying out the purpose of
the OSH Act, including developing and establishing recommended
occupational safety and health standards (29 U.S.C. 671).
---------------------------------------------------------------------------
These exposure limits and guidelines are based in empirical
evidence, such as laboratory-based trials conducted in the 1960s and
1970s. This basis for WBGT exposure limits is described in detail by
both NIOSH and ACGIH (NIOSH, 2016; ACGIH, 2017). These exposure limits
have been tested and found to be highly sensitive (100%) in modern
laboratory conditions in capturing unsustainable heat exposures (i.e.,
when a steady increase in core temperature is observed) (Garzon-
Villalba et al., 2017). Among workers in real-world settings, these
WBGT-based exposure limits have been found to be highly sensitive for
fatal outcomes (100% in one study; 92-100% in another) and, although
slightly less so, still sensitive for nonfatal outcomes (73% in one
study; 88-97% in another); however, these studies are limited by their
small sample size and retrospective characterization of workload,
acclimatization status, and clothing/PPE use (which are required for
accurately estimating WBGT-based exposure limits) (Tustin et al.,
2018b; Morris CE et al., 2019).
Two papers have attempted to apply the concepts of the WBGT-based
exposure limits to the more easily accessible and understood heat index
metric. Based on the relationship between WBGT and heat index, Bernard
and Iheanacho developed a screening tool that reflects heat stress risk
based on heat index and workload category--light (180 W), moderate (300
W), and heavy (415 W)--using assumptions about radiant heat but
ignoring the contributions of wind and clothing (Bernard and Iheanacho,
2015). To do this, they created a model predicting WBGT from the heat
index. From this model, WBGT estimates were produced within a 1 [deg]C
range for heat index values of 100 [deg]F or more but the model was
less accurate at heat index values below 100 [deg]F. Using their
reported screening table, which allows the user to adjust for low vs
high radiant heat, an acclimatized worker performing a heavy (415 W)
workload in high radiant heat outdoors would be above the WBGT-based
exposure limit and in need of a break at a heat index of 90 [deg]F. The
same worker, if unacclimatized, would be above the exposure limit at a
heat index of 80 [deg]F. These findings support the provision of 15-
minute breaks at a heat index of 90 [deg]F in OSHA's proposed standard,
as well as the provision requiring these breaks for unacclimatized
workers at a heat index of 80 [deg]F (unless the employer is following
the gradual acclimatization schedule and providing breaks if needed).
The authors noted that high radiant heat indoors could require even
greater adjustments to the heat index. As further evidence for the need
to adjust these values for radiant heat exposure, Morris et al. (2019)
reported that for the days on which HRIs occurred in their dataset,
cloud cover was often minimal suggesting there was exposure to high
radiant heat when the HRIs occurred.
More recently, Garz[oacute]n-Villalba et al. used an experimental
approach to derive workload-based HI heat stress thresholds
(Garz[oacute]n-Villalba et al., 2019). The researchers used data from
two progressive heat stress studies of 29 acclimatized individuals.
Participants were assigned different work rates and wore different
clothing throughout the trials, serving as their own controls. Once
thermal equilibrium was established, the ambient temperature was
increased in five-minute intervals while holding relative humidity
constant. The critical condition defined for each subject was the
condition at which there was a transition from a stable core body
temperature to an increasing core body temperature (i.e., the point at
which heat exposure became unsustainable). Using the results from these
trials, the authors established an equation deriving a heat index
exposure limit (equivalent to the TLV or REL) at different metabolic
rates for a worker wearing woven clothing:
HI benchmark ([deg]C) = 49-0.026 M
Where M is workload in Watts.
Garz[oacute]n-Villalba et al. assessed the effectiveness of the
proposed heat index thresholds for predicting unsustainable heat stress
by using receiver operating characteristic curves and area-under-the-
curve (AUC) values to determine predictive power (this technique is
commonly used to evaluate the predictive power of diagnostic tests).
The AUC value for the proposed heat index thresholds with subjects
wearing woven clothing was 0.86, which is similar to that of the WBGT-
based thresholds, based on the authors' prior analysis (Garz[oacute]n-
Villalba et al., 2017). This result showed that the heat index
thresholds derived by Garz[oacute]n-Villalba et al. (2019) would
reasonably identify unsustainable heat exposure conditions.
Compared to the heat index thresholds proposed by Bernard and
Iheanacho (2015), the heat index thresholds proposed by Garz[oacute]n-
Villalba et al. are the same at low metabolic rates (111 [deg]F for 180
W) but higher at higher metabolic rates: 105.8 [deg]F versus 100 [deg]F
at 300 W and 100.4 [deg]F versus 95 [deg]F at 415 W (Note: these values
are unadjusted for radiant heat). This is likely because the ACGIH
WBGT-based exposure limits, upon which Bernard and Iheanacho based
their heat index thresholds, are intentionally more conservative at
higher metabolic rates, whereas Garz[oacute]n-Villalba used a less
conservative linear model to derive their heat index thresholds
(Garz[oacute]n-Villalba et al., 2019). When adding an adjustment for
full sunshine provided by the authors, the proposed heat index-based
exposure limit derived from the Garz[oacute]n-Villalba et al. (2019)
equation for a worker performing a very heavy workload (450 W) is 92.8
[deg]F.
Thus, laboratory-derived heat index thresholds for unsustainable
heat exposure are higher than heat index thresholds shown in
observational studies to be sensitive for predicting the occurrence of
HRIs. There are several reasons that may explain why values determined
to be sensitive in laboratory settings are higher than those reported
among workers in real-world settings. For one, volunteers in laboratory
studies are often young, healthy, and euhydrated (i.e., beginning the
trial adequately hydrated). They are also not exposed to consecutive
days of heat exposure for eight-hour or longer work shifts. Working in
hot conditions on the prior day has been demonstrated in the literature
to be a risk factor for HRIs, even among acclimatized individuals
(Garz[oacute]n-Villalba et al., 2016; Wallace et al., 2005). Therefore,
the use of volunteers and exposure conditions in laboratory-based
trials may not always provide good proxies for workers and the
environments in which they work. There is also significant inter-
individual variability in heat stress tolerance, which may mean trial
studies with few participants might not capture the full range of heat
susceptibilities faced by workers.
In summary, long-established and empirically validated occupational
exposure limits exist for WBGT. In observational studies, WBGT exposure
limits have been found to be highly sensitive for detecting fatal HRIs
among workers and, although slightly less so, still sensitive for
nonfatal outcomes (although these studies are limited by small sample
size and retrospective work characterization). Research efforts to
crosswalk the WBGT-based exposure limits to the more accessible heat
index metric have demonstrated that a heat index of 90-92.8 [deg]F
would represent an appropriate trigger for controls such as mandatory
rest breaks for acclimatized workers performing heavy or very heavy
workloads in high radiant heat conditions (Bernard and Iheanacho, 2015;
Garz[oacute]n-Villalba et al., 2019). For unacclimatized workers
performing heavy workloads in high radiant heat conditions, a heat
index trigger of 80 [deg]F would be in line with the WBGT-based
exposure limits (Bernard and Iheanacho, 2015). Although these two
studies suggest that higher triggers could reasonably be applied to
workers performing lighter workloads, the assumptions used may not
always apply to workers (e.g., no exposure to working in the heat the
prior day, healthy, euhydrated). This may explain, at least in part,
the discrepancy in findings between the observational and experimental
studies discussed in this section.
IV. State Standards and Non-Governmental Recommendations
In their heat-specific standards, summarized in the table below,
States use various initial and high heat triggers, some of which depend
on the clothing or gear worn by workers. OSHA's proposed triggers are
generally in line with those used by these States.
OSHA is proposing using the same initial heat trigger (heat index
of 80 [deg]F) as Oregon's existing standard and Maryland's proposed
standard (Or. Admin. R. 437-002-0156 (2022); Or. Admin. R. 437-004-1131
(2022); Code of Maryland Regulations 09.12.32: Heat Stress Standards
(2024)). California and Colorado use an ambient temperature trigger of
80 [deg]F for outdoor work sites and agricultural sites, respectively,
as does the Washington standard for workers wearing breathable clothing
(Cal. Code of Regulations (CCR), tit. 8, section 3395 (2015); 7 Colo.
Code Regs. section 1103-15 (2022); Wash. Admin. Code sections 296-62-
095 through 296-62-09560; 296-307-097 through 296-307-09760 (2023)).
California's proposed indoor standard uses an ambient temperature
trigger of 82 [deg]F (CCR, tit. 8, section 3396 (2023)).
The high heat trigger that OSHA is proposing (heat index of 90
[deg]F) is the same as Oregon's existing standard and Maryland's
proposed standard. California and Colorado use an ambient temperature
high heat trigger of 95 [deg]F, while the Washington standard uses 90
[deg]F. The California indoor proposal uses an ambient temperature or
heat index trigger of 87 [deg]F to impose additional requirements.
Table V-2--Summary of Triggers Used in Various Heat-Specific Standards at the State Level
----------------------------------------------------------------------------------------------------------------
State Setting Initial heat trigger High heat trigger
----------------------------------------------------------------------------------------------------------------
California........................... Outdoor................ 80 [deg]F (Ambient).... 95 [deg]F (Ambient).
Washington........................... Outdoor................ 80 [deg]F (Ambient) 90 [deg]F (Ambient).
(all other clothing)
52 [deg]F (non-
breathable clothes)..
California (proposal)................ Indoor................. 82 [deg]F (Ambient).... 87 [deg]F (Ambient or
Heat Index), except
for certain clothing
or in high radiant
heat (82 [deg]F).
Oregon............................... Indoor/Outdoor......... 80 [deg]F (Heat Index). 90 [deg]F (Heat Index).
Maryland (proposal).................. Indoor/Outdoor......... 80 [deg]F (Heat Index). 90 [deg]F (Heat Index).
Colorado............................. Indoor/Outdoor 80 [deg]F (Ambient).... 95 [deg]F (Ambient) or
Agriculture only. other conditions.
----------------------------------------------------------------------------------------------------------------
Note: There are different provisions required at each trigger by each State.
In the Heat Stress and Strain chapter of their most recent TLV
booklet, ACGIH recommends establishing a heat stress management plan
when heat stress is suspected (ACGIH, 2023). One criterion they provide
for determining when heat stress may be present is whether the heat
index or air temperature is 80 [deg]F. In comments received from small
entity representatives during the SBREFA process and a public commenter
during the ACCSH meeting on April 24, 2024, OSHA heard feedback that
the agency should consider different triggers that vary by geography.
Neither the ACGIH TLV/REL nor NIOSH REL/RAL vary by geography; these
formulas are used globally. Additionally, California regulators, in
their existing outdoor heat standard and their proposed indoor heat
standard, use single State-wide triggers, despite the State
experiencing a wide range of microclimates (e.g., both desert and
coastal areas exist in the State). Such microclimates would make it
difficult to identify appropriate geographically specific triggers, as
factors like elevation and humidity can vary widely even within a
specific State or region. OSHA has also heard from stakeholders who
suggested that the triggers in a proposed rule should be presented
simply, which would be challenging if there were multiple triggers for
different parts of the country.
V. Summary
In conclusion, OSHA preliminarily finds that the experimental and
observational evidence support that heat index triggers of 80 [deg]F
and 90 [deg]F are highly sensitive and therefore highly protective of
workers. These triggers are also generally in-line with current and
proposed triggers in State heat-specific standards. Therefore, OSHA is
proposing an initial heat trigger of heat index of 80 [deg]F and a high
heat trigger of heat index of 90 [deg]F. OSHA is also proposing to
permit employers to use the WBGT-based NIOSH RAL and REL, which are
supported by empirical evidence and have been found to be highly
sensitive in capturing unsustainable heat exposure.
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether OSHA has adequately identified, documented, and
correctly interpreted all studies and other information relevant to its
conclusion about sensitive heat triggers;
Whether there are additional observational studies or data
that use more robust exposure metrics (e.g., more than daily maximum
heat index) to retrospectively assess occupational heat exposure on the
day of heat-related fatalities and nonfatal HRIs;
Whether OSHA should consider other values for the initial
and/or high heat trigger and if so, what evidence exists to support
those other values;
The appropriateness of using heat index to define the
initial and high heat triggers;
Whether OSHA should explicitly incorporate radiant heat
into the initial and/or high heat triggers, and if so, how;
Whether OSHA should explicitly incorporate clothing
adjustment factors into the initial and/or high heat triggers, and if
so, how;
Whether OSHA should use different triggers for different
parts of the country, and if so, how;
The appropriateness of applying the same triggers to
employers who conduct on-site measurements as opposed to employers who
use forecast data; and
Whether OSHA should consider an additional trigger
specific to heat waves or sudden increases in temperature and, if so,
whether there are definitions of heat waves that are simple and easy-
to-apply.
C. Risk Reduction
I. Introduction
OSHA identified and reviewed dozens of studies evaluating the
effectiveness of various controls designed to reduce the risk of heat-
related injuries and illnesses (HRIs). The studies captured include
observational and experimental studies that examined the effect of
either a single control or the combined effect of multiple controls.
These studies were conducted among civilian workers, athletes, military
personnel, and volunteers. Observational studies conducted outside the
U.S. were included if OSHA determined the work tasks to be comparable
to those of U.S.-based workers. OSHA also examined systematic review
articles that summarized the literature on various individual controls.
OSHA acknowledges that observational studies evaluating the
effectiveness of multi-pronged interventions or programs in reducing
HRI incidence in ``real-world'' occupational settings are the most
relevant for assessing the reduction in risk of the proposed rule.
However, OSHA identified very few of these studies in the literature
review and determined there to be some limitations in extrapolating
their findings to the proposed rule. Therefore, OSHA also examined
studies looking at the effectiveness of single interventions, many of
which were experimental in design.
One limitation of the experimental studies--often conducted in
laboratory settings--is that they were not conducted in ``real-world''
occupational settings. However, some of these studies were designed to
simulate actual work tasks and work environments, which increases the
generalizability for occupational settings (i.e., the extent that the
study results can be applied to employees exposed in the workplace).
Additionally, one advantage of experimental studies is that they can be
conducted under controlled conditions and are thus able to better
measure endpoints of interest and control for confounding variables.
Experimental studies are also sometimes able to examine situations in
which subjects experience high levels of heat strain because the close
physiological monitoring of subjects allows the study to be stopped
before the subject is at risk of heat stroke or death.
Although many of these studies evaluated measures of heat strain
(e.g., core body temperature, heart rate) rather than instances of
HRIs, OSHA believes that these metrics are important for understanding
risk of HRIs. As discussed in Section IV., Health Effects, these
metrics are intermediary endpoints on the path to HRIs (e.g., heat
stroke, heat exhaustion). The controls required in the proposed
standard are effective in that they reduce or slow the
accumulation of heat in the body, which in turn reduces the risk of
HRIs.
OSHA also examined and summarized systematic review articles that
reviewed and discussed the experimental literature. These articles were
written by prominent heat safety experts (in either an occupational or
athletic context) and were typically conducted using a consensus-type
approach. OSHA also looked outside the peer-reviewed literature for
consensus statements, reports, recommendations, and requirements from
governmental bodies and non-governmental organizations.
Despite the limitations noted above, the studies, review articles,
and non-peer reviewed sources presented in this section represent the
best available evidence OSHA has identified regarding the effectiveness
of controls designed to reduce the risk of HRIs. The following summary
of OSHA's findings demonstrates that the requirements of the proposed
rule will be effective in reducing the risk of HRIs among workers.
II. Evidence on the Effectiveness of Individual Control Measures
A. Systematic Reviews and Consensus Statements
Several publications have summarized the literature on the efficacy
of controls to reduce the risk of HRI in the form of review articles or
consensus statements. For example, Morris et al. (2020) assessed
systematic reviews, meta-analyses, and original studies on heat-related
intervention strategies published in English prior to November 6, 2019,
that included studies conducted at ambient temperatures over 28 [deg]C
or among hypohydrated (i.e., fluid intake is less than water lost
through sweat) participants, used healthy adult participants, and
reported physiological outcomes (e.g., change in heart rate, core
temperature, thermal comfort) and/or physical or cognitive performance
outcomes. Most of the captured articles were from the exercise
literature, but 9 of the 36 systematic reviews (i.e., a detailed and
comprehensive reviews of relevant scientific studies and other
evidence) mentioned occupational exposure in various professions, such
as military personnel, firefighters, and emergency responders. A second
search identified 7 original studies that were not covered in the
systematic reviews. Based on their systematic review, the study authors
identified the following effective interventions: environmental
conditioning (e.g., fans, shade, air-conditioning); optimal clothing
(e.g., hats; loose fitting, light/brightly colored/reflective,
breathable, clothing; ventilation patches in PPE; cooling garments/
PPE); physiological adaptation (e.g., acclimatization, improving
physical fitness); pacing (e.g., reduced work intensity, breaks);
hydration and nutrition (e.g., hydration, electrolytes); and personal
cooling options (e.g., cold water ingestion, water immersion). They
also noted that ``a generally under investigated, yet likely effective
. . . intervention is to utilize pre-planned breaks in combination with
the cooling interventions mentioned above.'' Morris et al. (2020) also
noted that ``maintaining hydration is important for maintaining
cognitive and physical performance'' (Morris et al., 2020).
Morrissey et al. (2021b) assembled 51 experts with experience in
physiology, occupational health, and HRIs to review and summarize
current data and gaps in knowledge for eight heat safety topics to
develop consensus recommendations. The experts created a list of 40
heat safety recommendations within those eight topics that employers
could implement at their work site to protect workers and to avoid
productivity losses associated with occupational heat stress. These
recommendations for each of the eight topics included:
(1) Hydration: e.g., access and availability to cool, potable
water; training on hydration; addressing availability of fluids during
rest breaks in the prevention plan;
(2) Environmental monitoring: e.g., measurements as close to the
work site as possible; consideration of environmental conditions (e.g.,
temperature, humidity, wind speed, radiance), work demands, PPE, and
worker acclimatization status in assessing heat stress; including
environment-based work modifications (e.g., number of rest breaks) in a
prevention plan;
(3) Emergency procedures and plans: e.g., availability of an
emergency plan for each work site; identification of personnel to
create, manage, and implement the plan; making available, rehearsing,
and reviewing the plan annually;
(4) Body cooling: e.g., availability of rest/cooling/hydration
areas made accessible to workers as needed; cooling during rest breaks
(e.g., immersion, shade, hydration, PPE removal); use of fans (at
temperatures below 40 [deg]C (104 [deg]F)) or air-conditioners; use of
portable cooling strategies (e.g., ice, water, ice towels) in areas
without electricity; use of cooling strategies before, during, and
after work; cooling PPE used under other PPE when PPE can't be removed;
(5) Acclimatization: e.g., creation and implementation of a 5-7 day
acclimatization plan; plans for both new and returning workers that are
tailored to factors such as environmental conditions and PPE; training
on benefits of acclimatization;
(6) Textiles/PPE: e.g., use of clothing/PPE that is thin,
lightweight, promotes heat dissipation, that fits properly, and
adequately protects against hazards; PPE with ventilated openings;
removal of PPE/extra layers during rest periods;
(7) Physiological monitoring: (e.g., checking heart rate/body
temperature); and
(8) Heat hygiene: e.g., annual training on heat related illness,
prevention, first aid, and emergency response in language and manner
that is easily understood; designated personnel or ``buddy approach to
monitor for symptoms''; communication strategies to inform employees of
heat mitigation strategies before the work shift, healthcare worker
using examination results (if examinations are required or recommended)
to educate employees.
Racinais et al. (2015) presented consensus recommendations to
reduce physiological heat strain and optimize sports performance in hot
conditions that were developed in roundtable discussions by a panel of
experts. While recommendations were focused on athletes, the study
authors noted that current knowledge on heat stress is mainly available
from military and occupational research, with information from sport
sciences available only more recently. The study authors recommended
three main interventions. The first recommendation, considered to be
most important by study authors, was acclimatization, involving
repeated training in heat for at least 60 minutes a day over a 1-2 week
period. The authors explained that acclimatization attenuates the
physiological strain of heat by improving cardiovascular stability and
electrolyte balance through an increase in sweat rate, skin blood flow,
and plasma volume. The second recommendation was drinking sufficient
fluids to maintain adequate hydration before and after exercise. Study
authors explain that sweating during exercise can lead to dehydration
which, if not mitigated by fluid intake, has the potential to
exacerbate cardiovascular strain and reduce the capacity to exercise in
the heat. The third recommendation was cooling methods to reduce heat
storage and physiological strain (e.g., fanning, iced garments/towels,
cold fluid intake, cooling vests, water immersion). Additional
recommendations for event organizers included planning for shaded
areas,
cooling and rehydration facilities, and longer recovery periods (i.e.,
break periods) for hydration and cooling.
B. Summary for Systematic Reviews and Consensus Statements
In conclusion, OSHA reviewed three sets of recommendations on
effective controls to prevent HRI developed by scientific experts
following extensive literature reviews. A number of the recommendations
were consistent with requirements or options in OSHA's proposed
standard. For example, all three groups of experts recommended
hydration, rest breaks, shade, cooling measures such as fans, and
acclimatization (Morris et al., 2020; Morrissey et al., 2021b; Racinais
et al., 2015). Two of the expert groups also recommended cooling
methods such as air conditioning (Morris et al., 2020; Morrissey et
al., 2021b). One of the groups recommended environmental monitoring,
development of emergency procedures and plans, training, a buddy system
to monitor for health effects, and communication of heat mitigation
strategies (Morrissey et al., 2021b).
III. Experimental and Observational Evidence
A. Rest Breaks
Administrative controls, such as varying employees' work schedules,
are a well-accepted and long-standing approach to protect workers from
occupational hazards. Administrative controls are regularly used to
address limitations in human capacity for physical work and commonly
include work-rest cycles. Rest breaks provide an opportunity for
workers to reduce their metabolic rate and body temperature
periodically throughout the day. Length and frequency of breaks can be
adjusted based on heat exposure, workload, acclimatization, and
clothing/PPE factors. Such an approach of work-rest cycles that
consider these factors has been recommended by NIOSH and ACGIH (NIOSH,
2016; ACGIH 2023). Observational and experimental studies show the
effectiveness of rest breaks in reducing heat strain that could lead to
HRIs, and those studies are described below. In addition to reducing
heat strain, rest breaks allow workers to take advantage of other
cooling strategies, such as hydrating, removing PPE, and sitting in
areas that are shaded, cooled, or fanned. The literature on the
efficacy of rest breaks described below includes observational studies
of workers, laboratory-based exercise trials, and predictive modeling.
I. Observational Studies
Several observational studies examined participants in work
settings or training exercises while at work and at rest and evaluated
the associations between rest breaks or time at rest and markers of
heat strain.
Horn et al. (2013) evaluated core body temperature and heart rate
(HR) among nine firefighters (six male and three females, ages 20-45
years) over a 3-hour period in which four repeat bouts of firefighting
drills were conducted (approximately 15-30 minutes each) while wearing
full PPE and a self-contained breathing apparatus. The drills were
separated by three rest periods (approximately 20-40 minutes each) in
which the firefighters were encouraged to hydrate and cool down by
removing their gear, while being evaluated/critiqued by instructors and
refilling air cylinders. The study authors estimated the duration of
work and rest cycle lengths based on sustained rates of heart rate
increases and decreases. Ambient temperatures ranged from 15 [deg]C to
25 [deg]C (59-77 [deg]F) during the summer and fall months when this
study was conducted. During work cycles, mean maximum core temperatures
ranged from 38.4-38.7 [deg]C, mean peak heart rate ranged from 181.2-
188.4 beats per minute (bpm), and the mean average heart rate (averaged
over 60 second intervals per work cycle) ranged from 139.6-160.0 bpm.
Mean maximum core temperature and mean average heart rate decreased
during rest periods, and the study authors concluded that physiological
recovery in this study appeared to be closely linked to the duration of
rest periods. Rest break duration was significantly and negatively
correlated with the following measurements taken during rest breaks:
minimum heart rate (r: -0.687, p<0.001), average heart rate (r: -0.482,
p=0.011), and minimum core temperature (r: -0.584, p=0.001), indicating
that longer breaks result in reduced heat strain. The authors concluded
that the association was independent of obesity, fitness, and intensity
of firefighting activities. Limitations noted by study authors included
enrollment of young firefighters who were screened for cardiovascular
disease, and thus might not represent the whole firefighting
population. In addition, ``significant breaks'' were provided and the
duration of exposure to fires was shortened later in the day, both
factors that might underestimate increases in core temperatures with
longer firefighting activities and shorter breaks.
Petropoulos et al. (2023) characterized heat stress and heat strain
in a cohort of 569 male outdoor workers in Nicaragua (sugarcane,
plantain, and brickmaking industries) and El Salvador (sugarcane, corn,
and construction industries) across three workdays in 2018. Median wet
bulb globe temperatures (WBGT) ranged from 26.0-29.2 [deg]C (78.8-84.6
[deg]F) and median heat index ranged from 28.5-36.1 [deg]C (83.3-97.0
[deg]F) at the work sites. Time spent on rest breaks-estimated based on
physical activity data collected with an accelerometer (i.e., a device
that can be used to measure physical activity and sedentary time)--was
estimated at 4.1-21% of the shift. A 10% increase in the time spent on
break was associated with a 1.5% absolute decrease in median percent
maximum heart rate (95% CI: -2.1%, -0.85%; p<0.0001), when adjusting
for industry/company, job task, shift duration, liquid consumption,
median WBGT, and mean metabolic rate. Petropoulos et al. (2023) found
no significant associations between rest breaks and maximum core body
temperature, and concluded that the lack of findings could have been
due to incomplete control of confounding factors.
Lucas et al. (2023) examined the effects of recommended rest breaks
for sugarcane workers in Nicaragua, specifically in male burned cane
cutters, by comparing the period from 2019-2020, identified as Harvest
3 (H3; n=40 burned cane cutters) with the period from 2018-2019,
identified as Harvest 2 (H2; n=12 burned cane cutters). OSHA notes that
a major limitation of the study identified by authors was a shorter
shift duration by 1 to 2 hours for seed cutters (SC) during H2, and
that ``the shorter shifts in H2 likely affected SC workload comparisons
between H2 and H3 and could explain why increasing the rest component
in H3 did not reduce the physiological workload in this group.''
Because of this limitation in seed cutters, this summary focuses on
effects on burned cane cutters. In H3, an extra 10-minute rest break
was recommended (increasing recommended rest breaks to a total of 80
min over a six-hour shift), and interventions from H2 were continued
(e.g., improvements to hydration and movable tents, in addition to
delaying cutting after burning to reduce radiant heat exposure). Daily
average WBGT was higher in H2: 29.5 [deg]C (85.1 [deg]F) than in H3:
26.7 [deg]C (80.6 [deg]F). Rest periods were defined by a greater than
10 bpm drop in heart rate lasting 4 or more minutes, as determined by
continuous measurements by heart rate sensors
worn on the chest; based on those measurements, the rest/work ratio for
burned cane cutters increased slightly from 21% rest in H2 to 26% rest
in H3. Average percent maximum heart rate (adjusted for age) decreased
slightly in H3 compared to H2 (mean [95% CI] 63% [60-65%] to 58% [56-
60%]) across the work shift). No significant differences were noted for
estimated core temperatures (based on modeling) from H2 to H3. The
study authors acknowledged that observational study design, small
number of workers in H2, and the lower temperatures in H3 may make
conclusions uncertain; therefore experimental laboratory studies may
better test the impact of the intervention. OSHA also observes that the
increased number of burned cane cutters observed from H2 to H3 means
that the population of workers observed was different in the two
periods and results may have been affected by different characteristics
of the workers.
Ioannou et al. (2021a) examined the effectiveness of rest breaks of
different durations in agricultural, construction, and tourism
employees. Findings in the intervention group were compared to a
``business as usual'' (BAU) group, where workers followed their normal
routine. Of note, shaded areas, water stations, and air-conditioned
areas to be used for rest breaks were part of BAU for construction
workers in Spain; those same interventions were part of BAU for
construction workers in Qatar, in addition to requiring workers to
carry a water bottle, and education. BAU practices were not specified
for the agriculture and tourism industries, but according to
communications with study authors, the BAU agricultural employees in
Qatar were not offered scheduled work/rest cycles, and agricultural
employees who were monitored in Qatar performed low intensity work
(Communication with Leonidas Ioannou, April 2024). Endpoints observed
included core temperature, skin temperature, heart rate, and metabolic
rate. No significant effects compared to the BAU group were observed
for any of these endpoints for agricultural workers in Cyprus provided
with a 90-second break every 30 minutes, tourism workers in Greece
provided with a 90-second break every 30 minutes or a 2-minute break
every 60 minutes combined with ice slurry ingestion, or construction
workers in Spain provided with two 7-minute breaks over the workday.
For employees in Qatar who were provided with 10-minute breaks every 50
minutes, significant differences in the intervention group compared to
the BAU group included lower mean skin temperature, heart rate, and
metabolic rate for construction employees, but increased heart rate for
agricultural employees. The study authors postulated that the increased
heart rate in agricultural workers resulted from inherent changes in
body posture (i.e., moving from a crouching position while crop picking
to standing and walking during breaks). A limitation in this study is
that some BAU groups, which were used as comparison groups, appeared to
have access to breaks in air-conditioned areas and it was not described
how the frequency or duration of rest breaks varied between the
intervention and BAU groups.
Two additional studies were conducted in utility workers. In a case
study by Meade et al. (2017), conducted in an unspecified location,
four highly experienced electrical utilities workers were observed via
video analysis over two consecutive hot days. The study authors noted
that employees often spent 80% or more of the monitoring period working
in direct sunlight. Meade et al. (2017) reported similar average core
body temperatures and average %HRmax on both days, despite an increase
in the percentage of time spent at rest on Day 2 versus Day 1 (time at
rest: 66 5%, range: 60-71%, on Day 2 versus 51 15%, range: 30-63% on Day 1). Three of the four workers had a
higher peak core temperature on Day 2 than Day 1. The study authors
attributed these core temperature and heart rate trends in part to
residual heat storage or fatigue-related changes in work efficiency
that possibly occurred over two consecutive work shifts. Meade et al.
(2016a) observed work and rest periods in 32 electrical utilities
workers (mean age of 36 years; 11 ground workers, 9 bucket workers, 12
manual pole workers; 17 in West Virginia, 15 in Texas) via video
analysis and accelerometry over 1 day (Heat Index: West Virginia 48
3 [deg]C (118.4 [deg]F), Texas 42 3 [deg]C
(107.6 [deg]F)). On average, the work-to-rest ratio was (3.1 3.9):1 and workers rested for a total of 35.9 15.9%
of the work shift. Heat index, work-to-rest ratios, work shift
duration, and time at rest were not significantly correlated with mean
core temperature or %HRmax. However, time spent or percentage of time
in heavy work was moderately, positively correlated with mean core
temperature (r=0.51) and %HRreserve (r=0.40) (i.e., increased time
spent in heavy work was associated with increased mean core temperature
and %HRmax). OSHA notes limitation in these studies, including, for
example, the very small sample size in Meade et al. (2017) and lack of
adjustment for possible confounding factors in Meade et al. (2016a).
A limited number of cross-sectional studies surveyed or interviewed
employees for self-reported symptoms of HRI to determine possible risks
associated with inadequate breaks. These types of studies are the most
limited because of uncertainties such as recall bias (i.e., inaccurate
recollection of previous events or experiences) and the potential for
dependent misclassification as a result of using self-reporting for
characterizing both the exposure and outcome. Therefore, only brief
summaries of these studies are provided. Two of these studies were
conducted in agricultural workers in the U.S. (Spector et al., 2015;
Fleischer et al., 2013), and one was conducted in pesticide applicators
in Italy (Ricc[ograve] et al., 2020). Spector et al. (2015) found a
significantly increased odds of HRI in workers paid by piece as
compared to workers paid hourly (OR: 6.20, 95% CI: 1.11, 34.54).
Spector et al. (2015) noted that piece rate workers might work harder
and faster because of economic incentives, thus leading to increased
metabolic heat generation; however, adjustment for task and exertion in
the small sample size of employees did not completely attenuate the
observed association, thus suggesting other factors contributed to
development of symptoms. Through population intervention modeling,
Fleischer et al. (2013) estimated that the prevalence of three or more
HRI symptoms could be reduced by 6.0% if workers had access to regular
breaks, and by 9.2% if breaks were taken in shaded areas. Of note,
participants in the study were asked about ``regular breaks,'' but the
term was not specified regarding frequency and duration. Lastly,
Ricc[ograve] et al. (2020) found taking rest breaks in shaded, non-air-
conditioned areas was associated with experiencing HRI (adjusted OR:
5.5, 95% CI: 1.4, 22), while taking rest breaks in cooler, air-
conditioned areas was not. Ricc[ograve] et al. (2020) discussed
possible reasons for the observed association between shaded rest
breaks and incidences of HRI, including that (1) taking breaks in shade
may be insufficient to prevent HRIs among pesticide applicators who
undertake more strenuous tasks or have longer exposures to unsafe
limits, and (2) rest breaks in shade may be taken to alleviate, rather
than prevent, HRI symptoms (i.e. possible reverse causation).
II. Experimental Studies
OSHA examined a number of laboratory studies that provide
information on the efficacy of rest breaks for preventing heat strain
or HRI in subjects exercising under conditions that include high heat
and at least moderate activity. The studies typically measured rectal
temperature, which allowed for an assessment of the efficacy of breaks
in maintaining lower rectal temperatures and slowing the increase in
rectal temperatures. ACGIH (2023) indicates that an increase in rectal
temperature exceeding 1 [deg]C from a ``pre-job'' temperature of less
than 37.5 [deg]C might indicate excessive heat strain. One study
summarized below also examines the effect of rest breaks on the
autonomic nervous system and cardiovascular function.
Smallcombe et al. (2022) conducted a study over a seven-hour period
that was designed to mimic a typical workday in the U.S. In that study,
9 males (average age 23.7 years) of varying fitness levels walked on a
treadmill at speeds to maintain a constant heart rate of 130 bpm, which
the authors indicated to be the demarcation between moderate and heavy
strain. The subjects completed six cycles of exercise for 50 minutes in
the heat chamber separated by 10 minutes of rest at an ambient
temperature of 21 [deg]C (69.8 [deg]F), 50% relative humidity (RH)
while drinking water as desired. A one-hour lunch period was also
provided at 21 [deg]C (69.8 F), 50% RH after the third exercise period,
with all subjects given the same lunch and allowed to drink water as
desired. Each subject was tested under 4 temperature conditions: (1)
referent (cool condition) at 15 [deg]C (59 [deg]F) (WBGT = 12.6
[deg]C); (2) moderate condition at 35 [deg]C (95 [deg]F) (WBGT = 29.4
[deg]C); (3); hot condition at 40 [deg]C (104 [deg]F) (WBGT = 33.4
[deg]C); and (4) very hot condition at 40 [deg]C (104 [deg]F) (WBGT =
36.1 [deg]C). The RH for each temperature condition was approximately
50%, except for the very hot condition, which was 70% RH. In the very
hot condition group, data were limited for the sixth exercise cycle
because an unspecified number of participants reached the cut-off point
for terminating the study (i.e., a heart rate exceeding 130 bpm while
at rest).
Significant increases in mean rectal temperature were observed in
the moderate, hot, and very hot condition groups in work period 1
versus work period 6, but the average rectal temperature remained at or
below 38 [deg]C (100.4 [deg]F) in all groups during each exercise
period (figure S1 and table S2) (Smallcombe et al., 2022). No
individual subject had a rectal temperature that exceeded 38 [deg]C in
the referent and moderate condition groups, however, three subjects
exceeded 38 [deg]C in the hot exposure group, and four subjects
exceeded 38 [deg]C in the very hot exposure group. With the exception
of two subjects whose rectal temperatures were measured at
approximately 38.6 [deg]C (101.5 [deg]F) and 38.7 [deg]C (101.7 [deg]F)
in the very hot exposure group, all rectal temperatures were below 38.5
[deg]C (as estimated from Figure S1). In addition, mean rectal
temperatures dropped during each rest period, with all rectal
temperatures measured near or below 38 [deg]C by the end of the rest
period (as estimated from Figure 4). Skin temperatures did not increase
during work periods. The authors concluded that under the conditions of
this study, which limited metabolic heat production based on the fixed
heart rate protocol, participants rarely reached levels of core
temperature that would be concerning. Study limitations noted by study
authors included possible limited relevance of breaks provided in
cooler areas, and the possibility that thermo-physiological impacts may
have been higher had breaks not been provided in cooler areas or
metabolic heat production not been limited.
In Uchiyama et al. (2022) thirteen males (average age 39 years)
each underwent two 225-minute trials that included 180 minutes of
treadmill walking in a chamber at 37 [deg]C (98.6 [deg]F) and 40% RH
interspersed with 45 minutes of rest breaks in an air-conditioned room
at 22 [deg]C (71.6 [deg]F) and 35% RH, designed to mimic summer working
and rest conditions at mines in Northwest Australia. Participants were
allowed to drink room temperature water during exercise and
refrigerated water while on rest breaks. Two different rest/work cycles
were tested, including (1) current practice: 1 hour of work and 30
minutes of rest, followed by 1 hour of work and 15 minutes rest, and a
final 1 hour work period; and (2) experimental: 1 hour of work and 15
minutes rest, followed by three half hour work periods separated by 10-
minute rest periods and, and a final half hour work period. OSHA
observes that in the current practice group, average core temperature
only increased by more than 1 [deg]C (1.8 [deg]F) of baseline level at
the final measurement reported at 180 minutes into the study (increased
from 37.2 [deg]C at baseline to 38.29 [deg]C at 180 minutes). Average
core temperatures remained within 1 [deg]C of baseline levels in the
experimental group at all time points.
Three studies (Meade et al., 2016b; Lamarche et al., 2017; and
Kaltsatou et al., 2020) conducted 2-hour studies in which small groups
of 9-12 males cycled in a heat chamber at 360 watts (W) of metabolic
heat production (considered moderate-to-heavy intensity and equivalent
to conditions experienced by some workers in the mining and utility
industries). Over the 2-hour period, the effects of various
temperatures (approximate values provided) and work/rest protocols
recommended by ACGIH were examined including: (1) continuous work at
WBGT 28 [deg]C (82.4 [deg]F) (41 [deg]C (105.8 [deg]F) dry-bulb, 19.5%
RH or 36 [deg]C (96.8 [deg]F) dry-bulb, 38% RH); (2) a 3:1 work/rest
ratio (15 min work, 5 min rest) at WBGT 29 [deg]C (84.2 [deg]F) (43
[deg]C (109.4 [deg]F) dry-bulb, 17.5% RH or 38 [deg]C (100.4 [deg]F)
dry-bulb, 34% RH); and (3) a 1:1 work/rest ratio (15 min work, 15 min
rest) at WBGT 30 [deg]C (86 [deg]F) (46 [deg]C (114.8 [deg]F) dry-bulb,
13.5% RH or 40 [deg]C (104 [deg]F) dry-bulb, 30% RH). Meade et al.
(2016b) examined a fourth condition: 4) a 1:3 work/rest ratio (15 min
work, 45 min rest) at WBGT 31.5 [deg]C (88.7 [deg]F) (46.5 [deg]C
(115.7 [deg]F) dry-bulb, 17.5% RH). The mean age of participants in the
Meade et al. (2016b) study was 21 years while the mean age in both the
Lamarche et al. (2017) and Kaltsatou et al. (2020) studies was 58
years.
Meade et al. (2016b) found that among younger males, the
percentages of participants with rectal temperatures exceeding 38
[deg]C over the 2-hour protocol was lower in the groups who took longer
rest breaks, despite those groups also being subjected to a higher
WBGT. Meade et al. (2016b) reported core temperatures exceeding 38
[deg]C in 12% of participants in the 1:3 work/rest at 31.5 [deg]C WBGT
group, 0% in the 1:1 work/rest at 30 [deg]C WBGT group, 33% in the 3:1
work/rest at 29 [deg]C WBGT group, and 33% in the continuous work at 28
[deg]C WBGT group.
Lamarche et al. (2017) found that among older males, the percentage
of participants with rectal temperatures exceeding 38 [deg]C over the
2-hour protocol was lowest in the group with the longest breaks (i.e.,
67% in the 1:1 work/rest at 30 [deg]C WBGT group, 100% in the 3:1 work/
rest at 29 [deg]C WBGT group, and 100% in the continuous work at 28
[deg]C WBGT group) although the findings did not achieve statistical
significance. Lamarche et al. (2017) also reported that time to exceed
a rectal temperature of 38 [deg]C was higher in both groups who
received rest breaks as compared with the continuous work group and
this did reach statistical significance. Specifically, the time to
exceed a rectal temperature of 38 [deg]C was 100 minutes in the 1:1
work/rest at 30 [deg]C WBGT group, 79 minutes in the 3:1 work/rest at
29 [deg]C WBGT group, and 53 minutes in the
continuous work at 28 [deg]C WBGT group. Further, because of heat
exhaustion, five participants in the Lamarche et al. (2017) study did
not complete the continuous work at 28 [deg]C WBGT protocol, one did
not complete the 3:1 work/rest at 29 [deg]C WBGT protocol, but all
completed the 1:1 work/rest 30 [deg]C WBGT protocol. No significant
differences in heart rate were observed.
Kaltsatou et al. (2020) examined autonomic stress and
cardiovascular function in the same subjects examined by Larmarche et
al. (2017). The authors measured 12 markers of heart rate variability
(HRV), a predictor of adverse heart events, most of which are
associated with the autonomic nervous system (i.e., a part of the
nervous system that controls involuntary responses including heart rate
and blood pressure). After one hour of accumulated work and when rectal
temperatures exceeded 38 [deg]C, three markers of HRV were
significantly lower in the continuous work group than in the 3:1 work/
rest at 29 [deg]C WBGT group. One marker of HRV was significantly lower
in the continuous group, compared to the 1:1 work/rest at 30 [deg]C
WBGT group at 1 hour of accumulated work. After 2 hours of accumulated
work, 4 markers of HRV were significantly lower in the continuous work
group compared to the 1:1 work/rest at 30 [deg]C WBGT group. Study
authors interpreted these results to indicate that continuous work was
the least safe for workers, while a 1:1 work/rest ratio offered the
best protection. Kaltsatou al. (2020) concluded that breaks during
moderate-to-heavy work in heat can reduce autonomic stress and increase
the time to exceed a rectal temperature of 38 [deg]C.
In the studies by Meade et al. (2016b), Lamarche et al. (2017), and
Kaltsatou et al. (2020), participants were well-hydrated before the
study period but not provided drinking water during the study.
Kaltsatou et al. (2020) acknowledged that not providing water during
the study could have affected sweat secretion and, as a result heat
balance, hydration status, baroreceptor function (involved in blood
pressure regulation), and the autonomic control of heart rate. OSHA
agrees and also notes that rest breaks were provided in the same
ambient conditions as work periods, and studies were conducted at a
fixed work rate that would have not considered possible effects of
self-pacing. Because hydration and shade or cooling measures during
rest breaks would be provided as part of an effectively implemented
multi-pronged approach to preventing HRI, OSHA preliminarily concludes
that some of the effects observed in these studies might have been less
severe if interventions other than rest were provided.
In a study by Chan et al. (2012), recovery time, as measured by
physiological strain index (based on heart rate and core temperatures),
was determined in 19 healthy construction rebar employees (mean age 45
years) who had worked until exhaustion at building construction sites
in Hong Kong in July and August of 2011. Average recovery during rest
was reported at 94% in 40 minutes, 93% in 35 minutes, 92% in 30
minutes, 88% in 25 minutes, 84% in 20 minutes, 78% in 15 minutes, 68%
in 10 minutes, and 58% in 5 minutes. Yi and Chan (2013) used the field-
based meteorological and physiological data reported by Chan et al.
(2012) to model ideal rest breaks to minimize HRI. Based on a Monte
Carlo simulation, the authors determined that a 15-minute break after
120 minutes of continuous work in the morning at 28.9 [deg]C (84.0
[deg]F) WBGT and a 20-minute break after 115 minutes of continuous work
in the afternoon at 32.1 [deg]C WBGT (90.0 [deg]F) maximized
productivity time while protecting the health and safety of employees.
III. Conclusions for Rest Breaks
OSHA reviewed several studies examining the effectiveness of rest
breaks in preventing heat strain that could lead to HRI and were of
sufficient quality for drawing conclusions (Horn et al., 2013;
Smallcombe et al., 2022; Meade et al., 2016b; Lamarche et al., 2017;
Kaltsatou et al., 2020; Petropoulos et al., 2023). The studies,
involving individuals exposed to conditions of high heat stress,
demonstrated the effectiveness of rest breaks in preventing measures of
heat strain that can lead to HRI. Observational studies with detailed
measurements of temperatures in firefighters doing training exercises
and experimental studies in laboratory settings reported that rest
breaks result in lower core or rectal temperatures during rest periods
following work periods (Horn et al., 2013; Smallcombe et al., 2022),
and lower rectal temperatures over the study period (Meade et al.,
2016b; Lamarche et al., 2017), with all of the studies showing greater
effectiveness of longer compared to shorter duration work breaks.
Similarly, Chan et al. (2012) reported increased physiological recovery
with longer rest periods. Uchiyama et al. (2022) reported little
evidence of heat strain in participants exercising in hot conditions
and provided rest breaks. The study by Lamarche et al. (2017) also
found that rest breaks were effective in preventing heat exhaustion in
a laboratory setting. OSHA also found evidence showing that rest breaks
can reduce cardiovascular strain. For example, Horn et al. (2013) found
that heart rates were lower in rest than in work cycles. One study done
in participants in a laboratory setting showed that rest breaks can
reduce autonomic stress that affects cardiovascular function (Kaltsatou
et al., 2020). Those findings are consistent with an observational
study of employees in occupational settings that found an association
between time spent on rest breaks and decreases in heart rate when
adjusted for industry/company, job task, shift duration, liquid
consumption, WBGT, and metabolic rate (Petropoulos et al., 2023).
In conclusion, OSHA preliminarily finds rest breaks to be effective
in reducing the risk of HRI by modulating increases in heat and
cardiovascular strain.
B. Shade
Working or resting in shade reduces the risk of HRI by decreasing
exposure to solar radiation and in turn reducing overall heat load.
Studies evaluating the impact of shade on heat strain metrics have
predominantly been conducted in controlled settings where participants
exercise in conditions approximating shade and sun exposure. Studies
evaluating the physiological benefits of exercising in shade versus sun
are likely to underestimate the benefits of rest breaks taken in shade
because metabolic heat generation would be slowed while resting.
A number of studies examining the effects of exercising under
natural or simulated conditions of sun or shade have demonstrated
benefits of shade. One group of investigators conducted studies where
participants cycled under simulated laboratory conditions of sun or
shade (Otani et al., 2016; Otani et al., 2021); both studies were
conducted under conditions of 30 [deg]C (86 [deg]F) and 50% RH, and
participants cycled at a rate of 70% maximum oxygen uptake until
reaching full exhaustion. The Otani et al. (2021) study also involved
exposures to low and high wind speeds. The same investigators conducted
45-minute, self-pacing cycling trials outdoors under various natural
sunlight conditions, including clear skies or thick and thin cloud
covers (Otani et al., 2019). These studies reported that higher
exposure to solar radiation resulted in higher skin temperatures (Otani
et al., 2016, 2019, 2021) and reduced work output (measured as
endurance capacity/time-to-exhaustion (Otani et al., 2016; 2021) or
power output (Otani et al., 2019)). In increased
sun conditions, Otani et al. (2021) reported higher rectal
temperatures, heart rates, and thermal sensation. Otani et al. (2019)
reported greater thermal sensations, and body heat gain from the sun,
but no significant effects on rectal temperature or heart rate in
increased sun conditions. Otani et al. (2016) reported no differences
in rectal temperatures or heart rates in increased sun conditions. The
authors speculated in their 2019 paper that the lack of rectal
temperature increase in that study likely resulted from a reduction in
self-regulated exercise under sunny conditions (Otani et al., 2019).
They did not however speculate reasons for the lack of rectal
temperature increases in their 2016 paper. OSHA notes that under
equivalent (full sun) solar radiation levels the time it took
participants to reach exhaustion in the Otani et al. (2021) study under
low wind speeds (35.4 minutes) was longer than the time it took
participants in the Otani et al. (2016) study to reach exhaustion (22.5
minutes), and OSHA expects that the disparate findings on rectal
temperatures may have resulted from differences in total cycling time.
In a study by Nielsen et al. (1988) participants cycled at a fixed
rate outdoors in the sun for 60 minutes, were shaded for 30 minutes
while continuing to cycle, and then cycled again in the sun for another
30 minutes, for a total of 120 minutes. Study authors noted that cloud
formation interrupted 3 of the 20 cycling trials. Average rectal
temperatures rose sharply during the first period of cycling in sun,
dropped slightly (non-significantly) during the period of cycling in
shade, and then gradually increased again during the final cycling
period in full sun. Skin temperatures remained fairly constant during
the initial period of cycling in sun, dropped significantly by 1.5
[deg]C (2.7 [deg]F) while cycling in shade, and rose again sharply
during the final cycling period in the sun. Heart rate, oxygen
consumption, and sweat rate were significantly higher in the final
cycling period in full sun, compared to the cycling period in shade.
Study authors concluded that heat received from direct solar radiation
``imposed a measurable physiological stress.''
In a study examining work capacity in adults walking for one hour
under various conditions of solar radiation (full sun or full shade),
temperature (25 [deg]C through 45 [deg]C; 77 [deg]F through 113
[deg]F), humidity (20% or 80%), and clothing coverage, Foster et al.
(2022b) reported that work capacity (calculated using treadmill speed
and grade) was generally lower under full sun conditions than shaded
conditions. Under humid conditions, work capacity was reduced by solar
radiation for all scenarios. Under dry conditions, work capacity
reduction varied by clothing coverage with those wearing full-body work
coveralls showing reduced work capacity at temperatures >=35 [deg]C
(>=95 [deg]F) and those wearing minimal clothing showing reduced work
capacity at temperatures >=40 [deg]C (>=104 [deg]F). Skin temperature
was generally higher under full sun conditions, and the authors
speculated that a lack of effect on core body temperatures likely
resulted from self-regulation during exercise.
Ioannou et al. (2021b) conducted a laboratory based randomized
control trial in which seven participants completed cycling trials
under full sun (800 W/m\2\) and full shade (0 W/m\2\) in hot (WBGT 30
[deg]C) and temperate (WBGT 20 [deg]C) conditions. The full sun
condition was associated with increased skin temperature at both
temperatures. Average core body temperature was similar between sunny
and shaded conditions (37.7 and 37.6 [deg]C for sun versus shade in hot
conditions and 37.2 [deg]C for both sun and shade in temperate
conditions). Solar radiation had a small, positive relationship with
heart rate (average heart rate of 114.0 and 109.1 bpm in sun versus
shade in hot conditions and 102.6 and 95.4 bpm in sun versus shade in
temperate conditions) (Ioannou et al., 2021b).
Although these experimental studies largely assessed the effects of
shade during exercise and not rest periods, they do support the idea
that shade reduces heat strain generally; therefore, OSHA preliminary
concludes that it is reasonable to assume access to shade would also
reduce heat strain during rest periods. This conclusion is also
supported by evidence that shade reduces heat exposure (see discussion
below) and that heat exposure is positively associated with heat strain
(see discussion in Section IV., Health Effects). OSHA identified no
major limitations in these studies that would preclude their use in
drawing conclusions about effectiveness. One aspect of all these
studies that limit applicability to the larger workforce is that
participants were all young and healthy and all or mostly male (age was
not specified in Ioannou et al. (2021b)), and the studies were done for
relatively short durations of time (2 hours or less). The authors of
the Otani et al. (2021) and Foster et al. (2022b) studies that used
artificial solar radiation noted that their studies would not reflect
changes in the sun's position during the day or changes in radiation
intensity levels, and that limitation would be relevant to the other
studies using artificial sources of solar radiation at one intensity
level.
There are also two observational studies in the peer-reviewed
literature that have evaluated the association between shade and risk
of HRI. In a case-control study of 109 acclimatized construction and
agriculture workers, Ioannou et al. (2021b) monitored workers for four
or more consecutive 11-hour shifts, in which environmental factors were
continuously measured and work hours characterized by the same thermal
stress but different solar radiation levels were isolated. Solar
exposure was categorized as either indoors, mixed indoors and outdoors,
or outdoors, and analyses were done for data collected during
conditions of 30 [deg]C WBGT. Results included a positive association
between sun exposure and skin temperature and a significantly higher
risk for heat strain symptoms (relative risk (RR) = 2.40, 95% CI: 1.78,
3.24) and reported weakness (RR = 3.17, 95% CI: 1.76, 5.71) among
workers exposed to solar exposure characterized as outdoors as compared
to workers exposed to solar exposure characterized as indoors. Core
body temperature, heart rate, and metabolic rate were not found to be
associated with sun exposure. The authors attributed the lack of change
in core temperature and heart rate to the effect of self-pacing. OSHA
notes that the study did not control for confounding variables.
Fleischer et al. (2013) used population intervention modeling of
self-reported HRI symptoms in farmworkers in Georgia to estimate that
the prevalence of three or more HRI symptoms could have been reduced by
9.2% (95% CI: -15.2%, -3.1%) if workers could always or usually take
breaks in the shade. There were limitations to this analysis, including
the cross-sectional study design, the self-reported exposure and
outcome data, and low participation rate.
Additional studies have evaluated differences in microclimatic
conditions between shady and sunny environments, independent of heat
strain metrics measured in human subjects. These studies provide clear
evidence that shade reduces radiant heat (Cheela et al., 2021; do
Nascimento M[oacute]s et al., 2022; Fournel et al., 2017; Karvatte et
al., 2016, 2021; Klok et al., 2019; Lee et al., 2020; Middel and
Krayenhoff, 2019; Sanusi et al., 2016; Zhang et al., 2022). As
discussed above, indicators of heat strain (e.g., rectal temperature)
often increase with exposure to solar radiation. These authors examined
the impact of shade through direct measures that assess radiant heat
(e.g., globe temperature,
mean radiant temperature) or through thermal stress metrics (e.g.,
Universal Thermal Climate Index) that incorporate radiant heat in their
calculation.
The magnitude of the reduction in radiant heat from shade, however,
varies by local conditions, with notable factors including the type of
shade (e.g., trees, buildings, canopies, and other urban structures
such as solar arrays), percent shade cover, time of day, season, and
ground cover (due to its role in radiant heat emission). Fournel et al.
(2017) estimated an average 4.4 [deg]C decrease in black globe
temperature using data from five studies that assessed different shade
interventions, while study-specific reductions ranged from 2 [deg]C to
9 [deg]C. These included a study by Roman-Ponce et al. (1977), who
observed a 9 [deg]C difference in Florida under an insulated metal
roof, and a study by Fisher et al. (2008), who observed a 2 [deg]C
difference in New Zealand under a shade cloth structure. Examples of
other studies that have evaluated the impact of shade on radiant heat
include:
Middel and Krayenhoff (2019) evaluated environmental
conditions across 22 sites in Tempe, Arizona on the hottest day of the
summer. They included diverse types of shade, including trees and urban
structures. The authors concluded that trees decreased afternoon mean
radiant temperature by up to 33.4 [deg]C and estimated that each 0.1
decrease in the sky view factor from trees (where a sky view factor of
1 is a completely open sky and 0 is fully blocked) resulted in an
approximate decrease of 4 [deg]C in mean radiant temperature (Middel
and Krayenhoff, 2019).
Zhang et al. (2022) compared meteorological parameters
among 12 locations in a coastal city in China. Mean globe temperature
over the beach in full sun (40.9 [deg]C) was higher than mean globe
temperatures in areas shaded by dense trees (28.9 [deg]C) or shaded by
a pavilion canopy (30.8 [deg]C) (Zhang et al., 2022).
Karvatte et al. (2016) evaluated the impacts of different
types of natural shade (two densities of eucalyptus trees and isolated
native trees) on environmental conditions in Brazil. Average black
globe temperatures from 12 p.m. to 1 p.m. in the shade ranged from 33.2
[deg]C to 34.3 [deg]C, which were 2.4 [deg]C to 8.2 [deg]C lower than
that measured in nearby sunny areas (Karvatte et al., 2016).
do Nascimento M[oacute]s et al. (2022) evaluated the
effectiveness of four different shade structures (native trees, black
polypropylene netting, heat-reflective netting, and a combination of
both types of netting) in the Brazilian savanna. Mean radiant
temperature was consistently lower under shaded conditions. For
example, at 11 a.m. and 12 p.m., the peak hours, the mean radiant
temperatures were 16[deg]C to 20 [deg]C lower in shady conditions than
sunny conditions (do Nascimento M[oacute]s et al., 2022).
I. Conclusions for Shade
In conclusion, measurements of environmental conditions indicate
that exposure to radiant heat is greater in full sun than in shaded
conditions (e.g., Middel and Krayenhoff, 2019; do Nascimento M[oacute]s
et al., 2022). It is well known that radiant heat contributes to heat
stress (NIOSH, 2016). Studies confirm that indicators of heat strain
(e.g., increased heart rate, increased rectal temperature) are often
higher in participants exercising in conditions with actual or
simulated solar radiation versus shade (e.g., Otani et al., 2021). One
study showed that a 30-minute period of exercising in shade,
interspersed between two periods of exercising in full sun, resulted in
improved physiological responses (e.g., lower heat rate, oxygen
consumption, and sweat loss) compared to the two periods of exercising
in full sun (Nielsen et al., 1988). OSHA expects that improvements in
physiological function might have been even greater if the participants
had rested in shade because resting slows the metabolic generation of
heat.
OSHA preliminarily finds that resting in shade will reduce the risk
of HRI by decreasing exposure to radiant heat that contributes to heat
stress and can lead to heat strain and then HRI.
C. Fans
Fans are engineering controls that increase air movement across the
skin and under the right environmental conditions can increase the
evaporation of sweat, resulting in greater heat loss from the body.
However, they may not be appropriate for all environments, such as at
higher temperatures. Research on the role of fans in HRI prevention
largely focuses on non-occupational and athletic populations, however
some chamber trials have been designed to mimic working conditions. A
summary of the experimental literature is provided here, beginning with
studies that evaluate the use of fans during physical activity, before
or after activity, and while people are at rest, and then concluding
with studies that model efficacy thresholds for fan use.
Studies by Saunders et al. (2005) and Otani et al. (2018, 2021)
examined the effects of different air speeds on individuals cycling in
heated chambers with no rest period included in the study design
(Saunders et al., 2005: 33.0 [deg]C 0.4 [deg]C and 59%
3% RH; air speeds ranging from 0.2 km/hr to 50.1 km/hr;
Otani et al., 2018: 30 [deg]C and 50% RH; air speeds ranging from 0 km/
hr to 30 km/hr; Otani et al., 2021: 30 [deg]C and 50% RH; air speeds of
10 and 25 km/hr). In measures of work output, at higher air velocities
Saunders et al. (2005) reported increased cycling time before
participants' core temperature reached 40 [deg]C (criteria for
terminating the trial) and Otani et al. (2018, 2021) reported increased
time to exhaustion. In lower/no compared to higher air velocities, (1)
Saunders et al. (2005) reported higher mean body temperature (weighted
mean of skin and rectal temperature), higher rectal and skin
temperature, increased heat storage (a measure that considers changes
in body temperature, in addition to body weight and surface area), and
lower evaporative capacity; (2) Otani et al. (2018) reported higher
rectal, skin, and mean body temperature, and lower evaporative heat
loss; while (3) Otani et al. (2021) reported no significant effect on
skin temperature but higher rectal temperatures. Higher heart rates
were also observed at lower/no versus higher air velocities (Saunders
et al., 2005; Otani et al., 2018, 2021).
Other studies have examined the effectiveness of fans during both
exercise and rest periods. In Jay et al. (2019), participants conducted
arm exercises designed to mimic textile work at 30 [deg]C (86 [deg]F)
and 70% RH, with and without fanning. In a study by Wright Beatty et
al. (2015), participants cycled in a chamber at 35 [deg]C (95 [deg]F)
and 60% RH, with air velocities of 0.5 m/s and 3.0 m/s. Wright Beatty
et al. designed the study to mimic occupational conditions, like those
for miners (both workload and clothing). Under the fan/high air
velocity conditions: (1) Jay et al. (2019) observed a smaller increase
in rectal temperature, and lower skin temperature, but there was no
change in heart rate because the study was designed to maintain a
constant heart rate; and (2) Wright Beatty et al. (2015) observed lower
rectal temperatures and heart rates. Jay et al. also compared
effectiveness of fanning to the presence of air-conditioning (7 [deg]C
lower temperature) and found higher work output and lower rectal
temperature in both the fanning and air-conditioning groups (relative
to the hot condition without fanning), while sweat loss was higher with
fanning compared to air-conditioning (Jay et al., 2019). Wright Beatty
et al. tested their conditions among both older (~59 years
old) and younger (~24 years old) participants and observed similar
benefits of higher air velocity among both age groups (Wright Beatty et
al., 2015).
In a handful of other studies, researchers tested the efficacy of
fan use during rest breaks, after subjects exercised under hot
conditions (Sefton et al., 2016; Selkirk et al., 2004; Barwood et al.,
2009; Carter, 1999). Conditions for these studies were (1) Sefton et
al.: 32 [deg]C 0.5 [deg]C and 75% 3% RH, with
shirt and under shirt removed during cooling, with and without misting
fan; (2) Selkirk et al.: 35[deg]C and 50% RH wearing firefighting
protective clothing and breathing apparatuses during exercise and
removal of protective gear during cooling periods with and without a
misting fan; (3) Barwood et al.: 31 [deg]C 0.2 [deg]C and
70% 2% RH, with and without whole body fanning; and (4)
Carter: 40 [deg]C and 70% RH wearing firefighting protective clothing
and breathing apparatuses during exercise and removal or unbuckling of
protective gear during cooling periods with and without a fan. In the
study by Sefton et al. (2016), rectal temperatures rose during the
cooling period, regardless of misting fan use, but heart rate was lower
with misting fan use; the study authors noted that under the high
humidity conditions of their study, misting fans could have increased
the moisture in air, thereby reducing cooling through sweat
evaporation. Other studies found fans or misting fans to be effective
in improving body temperature or cardiac effects. In comparisons of
normal recovery conditions (unbuckling of fire-fighting coat and no fan
use during rest) to enhanced recovery conditions (fire-fighting coat
was removed and fan used during rest), Carter (1999) reported lower
rectal and skin temperatures, heart rate, and oxygen consumption during
enhanced recovery compared to normal recovery conditions. Selkirk et
al. (2004) reported that the use of a misting fan during rest breaks
compared to no fan use resulted in lower rates of rectal temperature
increase, and lower skin temperatures and heart rates. Barwood et al.
(2009) reported that reductions in rectal and skin temperatures during
rest periods were greater with fan use than without, but there was no
significant effect on heart rate. Selkirk et al. (2004) also found that
participants were able to exercise longer when taking rest breaks with
misting fans than they were when taking rest breaks without misting
fans, and Barwood et al. (2009) found that participants were able to
run farther distances following whole-body fanning.
Other studies examined the use of fans during breaks in areas
cooler than where exercise took place. Hostler et al. (2010) conducted
a study similar to that by Selkirk et al., described above, where
subjects exercised on a treadmill while wearing firefighting protective
gear under hot conditions (35.1 2.7 [deg]C, RH not
specified), but in contrast to Selkirk et al. (2004), rest periods took
place at room temperature (24.0 1.4 [deg]C) instead of in
the heat chamber and a non-misting fan was used. In contrast to
findings from Selkirk et al. (2004), Hostler et al. (2010) reported
that fanning during breaks had no significant effects on core
temperature, heart rate, or exercise duration, and they speculated that
this was because rest breaks took place in a cooler area. The authors
conclude that active cooling devices may not be needed if the
temperature of the rest area is below 24 [deg]C (75.2[deg] F). Tokizawa
et al. (2014) reported that after pre-cooling in an area that was 28
[deg]C and had 40% RH, participants walking in a heat chamber (37
[deg]C and 40% RH) wearing protective clothing had lower rectal
temperatures, heart rate, and weight loss when exposed to fans and
water spray in the precooling period than the control condition without
fans and water spray (Tokizawa et al., 2014).
Additional studies provide information on conditions and
populations for which fans may or may not be effective. Ravanelli et
al. (2015; 2017) found that participants (mean age 24 3
years) were able to be exposed to higher levels of humidity at
temperatures of 36 [deg]C or 42 [deg]C when using fans before increases
in esophageal temperatures and heart rate were observed (i.e.,
inflection points) (Ravanelli et al., 2015; Ravanelli et al., 2017). At
42 [deg]C, the inflection points (when core temperature increases were
observed) occurred at a relative humidity level of 55% with fans
compared to 48% without fans. The relative humidity levels where heart
rate increases were observed with and without fans, respectively, were
83% and 62% at 36 [deg]C and 47% and 38% at 42 [deg]C. The researchers
found that heart rate was significantly lower at the end of the trials
with fans compared to without fans (under 36 [deg]C conditions: 74
9 bpm vs. 84 9 bpm; under 42 [deg]C
conditions: 87 9 vs. 94 9). This was also
true for esophageal temperatures at the end of the trials (under 36
[deg]C conditions: 36.7 0.2 [deg]C vs. 36.8
0.2 [deg]C; under 42 [deg]C conditions: 37.2 0.3 [deg]C
vs. 37.4 0.2 [deg]C). Rectal temperatures were higher with
no fans at the end of the trials in both conditions (36 [deg]C and 42
[deg]C), but these differences were not statistically significant
(Ravanelli et al., 2017). In contrast, Gagnon et al. (2016) found that
use of fans did not improve heart rate or core temperature inflection
points in response to increasing humidity levels, and heart rates and
core temperatures were higher with use of fans during exposure of older
adults (mean age 68 4 years) at 42 [deg]C. Gagnon et al.
speculated that lack of benefits may have resulted from age-related
impairments to sweat capacity. Morris NB et al. (2019) found that,
under hot and humid conditions (40 [deg]C, 50% RH; heat index of 56
[deg]C) fans reduced core temperatures and cardiovascular strain, but
were detrimental to all outcome measures under very hot but dry
conditions (47 [deg]C, 10% RH; heat index of 46 [deg]C). The authors
use these findings to caution against using heat index alone for
recommendations on beneficial versus harmful fan use.
While the fan efficacy studies discussed in this section so far
have been interventional in design, modeling studies have estimated the
temperature and RH thresholds at which fans are no longer effective at
reducing heat strain. Jay et al. (2015) argue that public health
guidelines for when fan use is harmful are too ambiguous and/or too low
(e.g., ``high 90s'' from the CDC (CDC, 2022). Morris et al. (2021)
modeled humidity-dependent temperature thresholds at which fans (3.5
meters/second wind velocity) become detrimental using validated
calorimetry equations, which calculate net heat transfer between a
person and their environment. Based on these equations and assumptions
on reduction in sweat rates among older individuals and individuals
taking anticholinergic medications, Morris et al. recommend that fans
should not be used at a humidity-dependent temperature above 39.0
[deg]C (102.2 [deg]F) for healthy young adults, 38.0 [deg]C (100.4
[deg]F) for healthy older adults above the age of 65, and 37.0 [deg]C
(98.6 [deg]F) for older adults taking anticholinergic medication
(Morris et al., 2021). While the authors provide more exact numbers
that account for humidity, they provide these thresholds as simple and
easy guidelines that only require knowing the temperature. Some
limitations of these studies include the use of assumptions in their
models that may not be realistic (e.g., fan producing an air velocity
of 3.5-4.5 meters/second sitting 1 meter away) and the use of
simplified heat-balance models, which predict the potential for heat
exchange rather than outcomes such as heat and
cardiovascular strain metrics (e.g., core temperature, heart rate).
There are many factors that influence an individual's heat exchange
potential, such as sex, hydration status, acclimatization status, and
clothing, and these simplified models often do not account for these
factors.
A recent article by Meade and colleagues criticized the simplified
thresholds published in Morris et al. (2021) as being too high for
general public health guidance (e.g., recommendations for the general
public during heat waves) (Meade et al., 2024). The authors modeled
core temperature changes rather than modeling potential for heat
exchange, arguing that Morris and colleagues did not consider in their
conclusions that the potential for greater heat exchange does not
always translate into increased sweat rates, particularly if core
temperatures are not high enough to elicit that sweat response. Meade
and colleagues modeled fan effectiveness under various hypothetical
environmental conditions and reported the expected impacts on core
temperatures for a young adult (18-40 years old) at rest wearing light
clothing. They estimated that fans (versus no fan) would lead to an
approximately 0.1 [deg]C increase in core temperature at ambient
temperatures of 37 [deg]C/98.6 [deg]F (when RH is 60-90%), 38 [deg]C/
100.4 [deg]F (when RH is 50-80%), and 39 [deg]C/102.2 [deg]F (when RH
is 50-80%) (Meade et al., 2024; Figure 1). Fans were estimated to be of
minimal impact (core temperature change of approximately 0.0 [deg]C) or
beneficial (reduction in core temperature) compared to no fans in drier
conditions at these ambient temperatures (37-39 [deg]C). In their
model, fans were always minimally impactful or beneficial at
temperatures below 37 [deg]C. Above 39 [deg]C, fans were more often
harmful (increase in core temperature greater than 0.2 [deg]C). These
model results were for strong fans (3.5-4.5 m/s air velocity), but in a
sensitivity analysis, Meade and colleagues present predicted core
temperature changes for slower fans (1 m/s air velocity) among young
adults. While these fans are less beneficial than strong fans at low
temperatures (e.g., below 34 [deg]C/93.2 [deg]F), they were predicted
to lead to smaller core temperature increases at higher temperatures
(e.g., 38 [deg]C) and humidities than the stronger fans (Meade et al.,
2024; Figure 4). In another model, the researchers predicted the
effects of fans combined with skin wetting (relative to no fan or skin
wetting) among young adults and found this combination was much more
beneficial than fans alone--they were beneficial or neutral in all
combinations of humidity and ambient temperature when ambient
temperature was 40 [deg]C/104 [deg]F or below (Meade et al., 2024;
Figure 6). One major limitation of these model results is the
assumption that the individual is at rest, rather than working. Fans
may be used in work areas, and it would be expected that they would be
associated with greater heat exchange potential in these scenarios, as
core temperature would be more likely to remain above levels that
prompt a sweat response. In a sensitivity analysis, the authors assumed
a range of metabolic rates, the highest being 90 W/m\2\, which they
describe as the equivalent to a seated person ``performing moderate
arts and crafts.'' In this scenario, fans were predicted to be more
beneficial around 30-34 [deg]C and in drier conditions (RH less than
30%) up to 39 [deg]C. These numbers may not apply to workers, as
evidenced in part by findings from a study described above (Carter,
1999), which found benefits to fans outside the range suggested by
Meade et al.
Another study did evaluate fan efficacy among participants
performing physical work (moderate to heavy workloads), collecting
empirical evidence from fixed heart rate trials and modeling the
effects of fans on heat storage at various temperatures and humidities
(Foster et al., 2022a). Foster et al. conducted 300 trials among 23
participants (24 cool, 15 [deg]C reference trials, 138 hot trials with
still air, and 138 hot trials with fans). The hot trials involved a
range of temperatures and humidities (35-50 [deg]C in 5 [deg]C
increments and 20-80% RH) and two clothing ensembles--low clothing
coverage (shorts and shoes) and higher clothing coverage (full-body
coverall, t-shirt, shorts, and shoes). For the fan trials, they used a
fan with a speed of 3.5 meters/second. The work output from the cool
reference trials was used as a baseline to calculate the change in work
capacity in the hot trials, which was used to validate their
biophysical model predicting change in heat storage (R-squared = 0.66).
The authors created categories for the percent change in work capacity
resulting from fan use relative to no fans--an increase of greater than
5% was termed ``beneficial'', a decrease of greater than 5% was termed
``detrimental'', and if the change was an increase or decrease of 5% or
less, it was called ``ineffective''. In the hot trials, the researchers
found fans to be beneficial or ineffective at both 35 [deg]C and 40
[deg]C (depending on the humidity) and ineffective at 45 [deg]C for the
higher clothing coverage (Figure 1 of Foster et al., 2022a). For the
low clothing coverage, the researchers found that fans had the
potential to be beneficial up to 45 [deg]C (at certain humidities), but
also had the potential to be detrimental at temperatures as low as 35
[deg]C (specifically when RH was 20%).
The biophysical model predicting change in heat storage was only
able to model the effects of fans for the low clothing coverage,
however, the authors note that the effects of fans were similar across
clothing groups except that fans weren't beneficial in the high
clothing coverage at temperatures equal to or above 45 [deg]C. Foster
et al. used a sweat rate in the model of approximately 1 liter per
hour, which was the group average from the trials. In Figure 4, the
authors present the output of their model, which suggests that fans
become detrimental beginning at a temperature of 39 [deg]C (102.2
[deg]F) (at certain humidities). At increasing temperatures, fan use is
detrimental at a wider range of humidity levels (both high and low
humidity), but beneficial or ineffective at other humidity levels.
Foster et al. also present model results with varying assumptions for
sweat rate and fan speed (Figure 6).
As discussed above, in their consensus statement, Morrissey et al.
(2021b) recommend the use of electric fans in an occupational setting
when ambient temperatures are below 40 [deg]C/104 [deg]F.
I. Conclusions for Fans
In conclusion, OSHA preliminarily finds that these studies show
that use of fans during work and/or rest breaks will be effective in
reducing heat strain in the majority of working age adults. Studies
also show that there are certain conditions (e.g., at a temperature of
102.2 [deg]F and above, depending on the humidity) under which fans may
not be beneficial and can be harmful to workers.
D. Water
Working and sweating in the heat put workers at risk for
dehydration and HRIs. Replacing fluids lost as sweat is necessary to
maintain blood volume for cardiovascular function and thermoregulation.
Multiple studies have examined the efficacy of hydration interventions,
while also considering various factors that may affect hydration such
as the quantity of liquid consumed, timing of ingestion, and beverage
temperature.
Studies in the peer-reviewed literature provide evidence that
hydration interventions are effective at combating dehydration and HRI.
For example, McLellan and Selkirk
performed a series of heat stress trials with 15 firefighters in Canada
wearing protective equipment at 35 [deg]C (95 [deg]F) and 50% relative
humidity (McLellan and Selkirk, 2006). During the trials, participants
conducted light exercise in a heat chamber and were provided one of
four fluid replacement quantities: no fluid, one-third fluid
replacement, two-thirds fluid replacement, or complete fluid
replacement (based on previously determined sweat rates). Each
participant completed two 20-minute exercise periods, separated by a
10-minute break for a simulated self-contained breathing apparatus
(SCBA) change, and then followed by a 20-minute rest break. Cool water
was provided during each break. Exercise continued until participants
reached an endpoint, defined as a rectal temperature over 39.5 [deg]C
(103.1 [deg]F), heart rate at 95% of maximum, experiencing dizziness or
nausea, or other safety concerns. Participants who received either two-
thirds or full fluid replacement tolerated approximately 20% more
exposure time (including rest periods spent in the heat chamber) and
approximately 25% more work time (calculated by excluding rest periods)
than those without the fluid replacement. Most participants who were
not provided fluids ended the trial upon experiencing lightheadedness
when attempting to re-initiate exercise after a break, possibly related
to low blood pressure. Those with two-thirds and full fluid replacement
took significantly longer to reach an end point during work time and
those with one-third, two-thirds, or full fluid replacement had
significantly longer exposure time than those without fluid
replacement. The full fluid replacement group also had higher rectal
temperatures at their trial endpoint compared to those without fluid
replacement, possibly indicating that hydration allowed them to
tolerate higher rectal temperatures. The authors state that these
findings are consistent with previous literature that reports
cardiovascular function to be compromised without fluid replacement,
leading to exhaustion at lower core temperatures.
Ioannou et al. (2021a) advised intervention groups made up of
agricultural workers in Qatar and construction workers in Qatar and
Spain to consume 750 milliliters (mL) of water supplemented by one
tablespoon of salt per hour over their work shift. Findings in the
intervention group were compared to a ``business as usual'' (BAU)
group, where workers followed their normal routine, that were
unspecified for the agricultural industry and included shaded areas,
water stations, and air-conditioned rest break areas for construction
workers in Spain; those same BAU conditions were implemented for
construction workers in Qatar, in addition to requiring workers to
carry a water bottle, and education. Results included: (1) 13% to 97%
reductions in prevalence of dehydration in each intervention group; (2)
no significant differences in core temperatures for agricultural
workers in Qatar; (3) significant reductions in core temperature in the
construction intervention groups in Qatar and Spain, and (4) mixed
findings on heart rate and skin temperature across the sites. One
limitation with this paper is the use of BAU as a control group, as it
is not always clear how these scenarios differed from the intervention.
In addition, the quantity of fluid consumed was not measured.
Drinking adequate amounts of water may also reduce the risk of
syncope. Schroeder et al. assessed the effects of water quantity on
orthostatic tolerance (as time to presyncope, the symptomatic period
right before fainting) in healthy individuals (n=13) (Schroeder et al.,
2002). The authors used a controlled, crossover design to test the
effects of consuming 500 versus 50 milliliters of water prior to
attempting to induce presyncope by tilting the head-up and applying
negative pressure to the lower body. They found that drinking the
larger amount of water improved orthostatic tolerance by 5 minutes (+/-
1 minute), increased supine (lying down face up) mean blood pressure
and peripheral resistance, and was associated with smaller increases in
heart rate. A recent study using a similar design found that the
temperature of the water may also have an influence--cold water
consumption was associated with increased systolic blood pressure,
stroke volume (i.e., increased volume of blood pumped out of heart per
beat), cerebral blood flow velocity, and total peripheral resistance,
as well as reduced heart rate relative to consuming room temperature
water (Parsons et al., 2023). They did not find differences in
orthostatic tolerance between the groups. It should be noted that
neither of these papers tested the participants under conditions of
high heat, but as is discussed in Section IV., Health Effects, research
has shown that exposure to heat independently increases the risk of
syncope. In addition, both syncope from exposure to heat and the method
used to induce presyncope in these studies can involve a mechanism in
which blood pools in the lower body.
Public health guidance for workers (e.g., from NIOSH) often
involves recommendations that workers consume 1 cup (237 mL) of water
every 15-20 minutes or approximately 1 liter (711-948 mL) per hour. The
goal is to replenish fluids lost through sweat and avoid a substantial
loss in total body water content. Sweat rates vary between individuals
and conditions. Research conducted among workers performing ``moderate
manual labor e.g., mining or construction work'' in a controlled
laboratory setting (35 [deg]C and 50% RH) demonstrated an average sweat
rate of 410-470 mL per hour (depending on whether the trial was
conducted in winter or summer), but a range of 100 mL to 1 liter per
hour during the presumed unacclimatized trials (conducted in winter)
(Bates and Miller, 2008). These recommendations are also in line with
the Army's fluid replacement guidelines, which recommend 0.75-1 quart
(1 quart is approximately 0.95 liters) per hour for ``moderate work''
(425 W) to ``heavy work'' (600 W) depending on the wet bulb globe
temperature (Department of the Army, April 12, 2022; Table 3-2).
In a randomized crossover study, Pryor et al. (2023) had
participants continuously walk for two hours at 6.4 km/hr in a heat
chamber (34 [deg]C/93.2 [deg]F, 30% relative humidity) while either
drinking 500 mL of water every 40 minutes or 237 mL of water every 20
minutes, followed by two hours of rest. Study authors found both
hydration strategies to be similarly effective based on (1) no
significant differences in body mass, percent change in plasma volume,
plasma osmolality (i.e., volume of particles dissolved in plasma), body
temperature, or heart rate and (2) no difference in thirst or total
gastrointestinal symptom scores. The authors did note, however, that
urine volume was significantly lower after the rest period in the group
receiving 237 mL of water every 20 minutes compared to the group
receiving 500 mL of water every 40 minutes.
Several studies have evaluated the impact of the temperature of
drinking water on dehydration and other measures in occupational
settings. Cold water may serve as a heat sink to cool off the body in
addition to combatting dehydration. In their meta-analysis, Morris et
al. (2020) (described above) considered the effect of cold fluid
ingestion as a personal cooling method, distinct from maintaining
hydration status. Morris and co-authors concluded that cold fluid
ingestion was effective as a heat strain mitigation control.
A systematic review by Burdon et al. reported that palatability was
higher for
cold (32.0-50.0 [deg]F) or cool (50.0-71.6 [deg]F) beverages, as
compared to warmer (greater than 71.6 [deg]F) beverages, during
exercise (Burdon et al., 2012). The authors conducted a meta-analysis
using data from five studies and found that participants drank roughly
50% more cold/cool beverages than warmer beverages. Another analysis of
multiple studies found that when participants were provided cold/cool
beverages rather than warmer ones, there was less of a mismatch between
fluid intake and fluid lost through sweat (measured as percentage of
body mass lost). Participants provided warmer beverages lost, on
average, 1.3% more of their body mass (95% CI: 0.9%, 1.6%) (Burdon et
al., 2012).
I. Conclusions for Water
In conclusion, one experimental study reported that drinking
adequate amounts of water while exercising in high heat prolonged the
time of exposure before experiencing signs of heat strain or HRI
(McLellan and Selkirk, 2006). In addition, studies in which
participants were not exposed to high temperatures found that drinking
adequate amounts of water reduced the risk of laboratory-induced
presyncope (Schroeder et al., 2002), and drinking cool water improved
cardiovascular function (Parsons et al., 2023). Studies have also
reported increased palatability for cool or cold beverages (<=71.6
[deg]F) that is likely to increase consumption and prevent dehydration
compared to warmer beverages (Burdon et al., 2012).
Based on these studies, OSHA preliminarily finds that drinking
adequate amounts of water is an effective intervention for preventing
heat strain that could lead to HRI, and that providing cool drinking
water is especially beneficial. In addition, because cool or cold water
was found to be more palatable than warm water, OSHA preliminarily
finds that providing cool or cold water can lead to higher consumption
of water and thereby reduce the risk of dehydration.
E. Acclimatization
Heat acclimatization refers to the improvement in heat tolerance
that occurs from gradually increasing the intensity and/or duration of
work done in a hot setting. There are several studies examining the
extent and effectiveness of acclimatization achieved on the job. The
effects of acclimatization in allowing individuals to work safely in
higher temperatures than unacclimatized individuals has been
established for decades and is reflected by both the NIOSH REL and the
ACGIH TLV (NIOSH, 2016; ACGIH, 2023).
Early research on the effectiveness of acclimatization was
conducted in the 1950s and 1960s among gold mine workers in South
Africa (Weiner, 1950; Wyndham et al., 1954, 1966). Weiner (1950)
conducted three days of heat stress tests on eight acclimatized mine
workers, with three to six months experience working underground, and
eight new, unacclimatized workers. Workers completed a four-hour
protocol of step climbing sessions (30 mins) with sitting breaks (30
mins) in a mine shaft (dry bulb temperatures: 89.8 [deg]F-90.2 [deg]F,
wet bulb temperatures: 88.8 [deg]F-89.1 [deg]F, air movement: 165-280
ft/min). Multiple unacclimatized workers were not able to complete the
full protocol on the first day (based on symptomology, heart rate and
rectal temperature), while all acclimatized workers were able to do so.
Rectal temperatures and heart rates were higher among the
unacclimatized workers than the acclimatized workers and sweat rate was
lower (Weiner 1950).
Wyndham et al. (1954) describe a two-stage acclimatization protocol
in which workers (n=110) shoveled rock for six days in a cooler section
of the mine (saturated air temperature approximately 86.5 [deg]F, wind
velocity approximately 100 feet/minute), before moving to a hot section
of the mine (saturated air temperature between 91.5 [deg]F and 92.0
[deg]F, wind velocity 100 to 350 feet/minute) to complete the same task
for six more days (Wyndham et al., 1954). Researchers measured rectal
temperatures before the shift, at 9 a.m., at 11 a.m., and at 1 p.m. on
each of the twelve days. Average rectal temperature was 101.0 [deg]F on
the first day in the cooler conditions, which fell to 100.2 [deg]F on
day six. When workers transitioned to the hot conditions, the average
rectal temperature was 100.8 [deg]F on the first day and 100.0 [deg]F
on the sixth day. The authors concluded that the acclimatization method
was a success, as rectal temperatures were on average lower on the
first day in full heat conditions (100.8 [deg]F) than on the first day
of work in cooler conditions (101.0 [deg]F), and mean work output was
also higher on the first day in the full heat (Wyndham et al., 1954).
The researchers also compared the acclimatized workers to a prior
cohort of eight new workers who worked immediately in hot conditions
without any acclimatization--they had an average rectal temperature of
101.8 [deg]F on their first day. The authors noted that the two-stage
acclimatization protocol likely resulted in complete acclimatization,
as earlier monitoring of the eight new workers over 23 workdays showed
that rectal temperatures did not fall much lower than 100 [deg]F, the
average temperature seen after the new two-phase acclimatization
protocol (Wyndham et al., 1954).
In a later study, Wyndham et al. (1966) analyzed the rectal
temperatures of 18 acclimatized men and groups of 20 unacclimatized men
working at a moderate rate for four hours in varying environmental
conditions (Wyndham et al., 1966). The authors found that the
acclimatized men, on average, could work at higher effective
temperatures (a heat metric that accounts for ambient temperature,
humidity, and air movement) than the unacclimatized men while still
maintaining a steady rectal temperature (Wyndham et al., 1966).
Van der Walt and Strydom analyzed fatal heat stroke cases among
miners in South Africa from 1930-1974 (Van der Walt and Strydom, 1975).
Changes in cooling, mechanization, and acclimatization practices
occurred at different points in time. Van der Walt and Strydom divided
1930-1974 into four periods based on interventions implemented during
each period. They discussed changes in heat stroke fatality in relation
to the interventions that were implemented. During the earliest period
(1930-1939), acclimatization practices were introduced and ventilation
improved, and the annual heat stroke mortality rate decreased from 93
to 44 deaths/100,000 workers. During the following period, which
coincided with the war and post-war time (1940-1949), mines continued
and improved the practices introduced in the first period. There was a
drop in mortality rate from approximately 26 to 16 deaths/100,000
workers. During the third period (1950-1965), mines began using two-
stage acclimatization, and the annual heat stroke mortality rate
decreased from 15 to 5.6 deaths/100,000 workers. During the fourth
period (1966-1974), mines began using climatic room acclimatization,
and the annual heat stroke mortality rate decreased even further to 2.3
deaths/100,000 workers (Van der Walt and Strydom, 1975). The authors
concluded that the controls they implemented over this period--namely
introducing and improving their acclimatization procedures--were
important in reducing the heat stroke fatality rates over time.
However, they also introduced other controls during this time
(ventilation and mechanization) so it is difficult to determine the
efficacy of acclimatization independent of those controls (and other
potential confounding factors).
Recent research on acclimatization has also included studies that
assess acclimatization achieved while on the job. Lui et al. (2014)
conducted a study to evaluate acclimatization among firefighters before
and after a four-month wildland fire season, in May and September,
respectively. The researchers assessed various physiological markers of
heat acclimatization among a cohort of 12 U.S. male wildland
firefighters and a group of 14 adults who were not firefighters,
matched on age and fitness level. Participants completed a 60-minute
walk at 50% of peak oxygen consumption (VO2) in a chamber at 43.3
[deg]C and 33% relative humidity. At 60 minutes, firefighters were
found to have lower average core body temperatures after the wildfire
season than before the season (after: 38.2 [deg]C 0.4;
before: 38.5 [deg]C 0.3), while the comparison group
showed no difference from the pre-season to post-season trials.
Similarly, firefighters had significantly lower physiological strain
index scores (a variable derived from core temperature and heart rate)
after the wildfire season (p<0.05), while scores did not change for the
comparison group. No pre- to post-season changes were observed for
heart rate. The authors found no evidence of acclimatization in the
comparison group over the study period. Study results suggest that the
firefighters were acclimatized due to occupational exposures during the
wildfire season rather than exposure to higher seasonal heat (Lui et
al., 2014).
Dang and Dowell (2014) compared heat strain markers among
acclimatized and unacclimatized potroom workers at an aluminum smelter
in Texas in July as they conducted various smelting activities in high
heat. Workers were defined as unacclimatized if they had not been
working or had been working solely outside of the potrooms for four or
more consecutive days in the prior two weeks. WBGT values in work areas
ranged from 83 [deg]F to 120 [deg]F. Among the eight unacclimatized
workers and 48-50 acclimatized workers with heat strain measurements,
unacclimatized workers had significantly higher average heart rates
than acclimatized workers (118 bpm vs. 107 bpm, p<0.01). Unacclimatized
workers also had higher average and average maximum core temperatures,
but these differences were not significantly different (average maximum
core temperature: 101.0 [deg]F vs. 100.7 [deg]F; average core
temperature: 99.7 [deg]F vs. 99.6 [deg]F) (Dang and Dowell, 2014).
Watkins et al. (2019) evaluated the heat tolerance of fire service
instructors (FSIs), which researchers describe as fire personnel who
provide firefighting training courses and have more frequent fire
exposure than firefighters. The researchers conducted two heat
tolerance tests, separated by two months on a cohort of 11 FSIs and 11
unexposed controls (university lecturers), matched on age, sex, and
body composition. Controls had not had more than three consecutive days
of heat exposure (<25 [deg]C) or taken part in heat acclimatization
training in the month prior to the study. On average, FSIs experienced
five fire exposures in the two weeks prior to each heat tolerance test.
Each test was composed of a 10-minute rest period (22.9
1.2 [deg]C, 31.2 6.8% RH) followed by a 40-minute walk in
a heat chamber (50 1.0 [deg]C, 12.3 3.3% RH)
wearing fire protective equipment. At the end of the first heat
tolerance test, FSIs on average had significantly lower maximum rectal
temperature (-0.42 [deg]C, p<0.05), less change in rectal temperature
(-0.33 [deg]C, p<0.05), and reported less thermal sensation and, among
males only, a higher sweat rate (+0.25 Liters/hour, p<0.05) than the
controls. Heart rate, skin temperature, and physiological strain index
did not differ between groups. Rectal temperature at the end of the
heat test was negatively correlated with the number of fire exposures
experienced in the prior two weeks (r= -0.589, p=0.004) (Watkins et
al., 2019).
The effectiveness of acclimatization in high heat conditions has
also been an important topic for militaries. Charlot et al. (2017)
studied the effects of training on acclimatization in 60 French
soldiers who arrived in United Arab Emirates (UAE) in May of 2016, and
were not stationed in a hot climate over the previous year. On day 1,
all soldiers completed a heat stress test while running. On days 2-6,
the 30 soldiers in the training group trained outdoors by running at
50% VO2 max, with durations of training sessions ranging from 32-56
minutes. Both the soldiers in the training group and 30 soldiers in a
control group (no training; performed usual activities) spent
approximately six hours outdoors per day conducting standard military
tasks. The heat stress test was repeated on day 7, with WBGTs ranging
from 1.1 [deg]C warmer to 0.9 [deg]C cooler compared to day 1. In both
groups, rectal temperature, heart rate, sweat loss, sweat osmolality,
perceived exertion, and thermal discomfort were lower after the stress
test on day 7 compared to day 1. Compared to the control group, the
training group had significantly greater decreases in heart rate (20
13 bpm lower versus 13 6 bpm lower), rate of
perceived exertion, and thermal discomfort after the stress test on day
7 compared to day 1. Charlot et al. (2017) concluded that addition of
short, moderate-intensity training sessions resulted in further heat
acclimatization, beyond the acclimatization observed across all
participants.
In another study of military trainees, Lim et al. (1997) assessed
the degree to which passive heat exposure and military training
resulted in the acclimatization of army recruits in Singapore across a
16-week military training program. Participants completed a heat stress
test, while marching, at four time points: (1) before starting the
program, (2) on the second week, (3) on the sixth week and (4) on the
sixteenth/final week of the program. For the nine individuals who
attended all tests, heart rate significantly decreased across the study
period, while results for skin temperature, tympanic temperature (i.e.,
within ear canal), and average body temperature were mixed, and there
were no significant differences in sweat loss or sweat rate.
Researchers interpreted these findings to mean that passive heat
acclimatization from living in a hot climate had resulted in partial
acclimatization, but that physical conditioning was necessary for
triggering beneficial cardiovascular adaptations (Lim et al., 1997).
Sports teams have also evaluated the effectiveness of heat
acclimatization among their athletes. Three studies conducted among
professional soccer players found that athletes training in hot outdoor
conditions experienced improvements in plasma volume, heart rate,
rectal and skin temperature, and/or sweat sodium concentration over the
course of their training (Buchheit et al., 2011; Racinais et al., 2012,
2014).
Acclimation (i.e., improvement in heat tolerance under laboratory
conditions) was also studied in heat chamber studies. In a study using
90-minute treadmill sessions designed to mimic the metabolic rate of
manual laborers, Chong et al. (2020) found that over the course of a12-
day acclimatization period at 28 [deg]C WBGT or 30 [deg]C WBGT, peak
core temperature, heart rate, and skin temperature decreased and sweat
rate increased even before the end of the 12-day period (Chong et al.,
2020). Zhang and Zhu (2021) acclimated participants using 10 daily 90-
minute treadmill sessions (at a speed of 5 kilometers/hour) in 38
[deg]C and 40% RH and found that after acclimation, rectal temperature
and heart rate during exercise increased at a slower rate, but there
was no effect on
skin temperature. OSHA notes that Zhang and Zhu (2021) did not
gradually increase daily heat exposure, as is typically recommended.
Shvartz et al. (1977) studied the effects of work and heat on
orthostatic tolerance among 12 trained men (i.e., trained three time a
week in endurance sports) and 16 untrained men, none of whom were
exposed to exercising in the heat in the two months before testing
(Shvartz et al., 1977). The trained participants had better orthostatic
tolerance to laboratory-induced syncope compared to the untrained
participants (2 vs. 8 fainting episodes after exercise in ambient
conditions; 4 versus 9 fainting episodes after exercise in heat). Heat
acclimation improved orthostatic response, as fainting episodes after
exercise decreased in the 8 untrained participants who were later
acclimated to heat for 7 additional days (4 versus 0 fainting episodes
after exercising in temperate conditions and 4 versus 2 after
exercising in hot conditions, before and after acclimation,
respectively). At the end of the acclimation period for those 8
untrained participants, significant reductions were observed for heart
rate and rectal temperature, while significant increases in sweat rate
and maximum VO2 occurred. Shvartz et al. (1977) concluded that both
general physical fitness and heat acclimation contributed to better
orthostatic responses and fewer fainting episodes.
Parsons et al. (2023) evaluated the effects of heat acclimation in
20 endurance-trained athletes (15 males, 5 females) randomly assigned
to a heat group that was acclimated for 8 days or control group that
was not acclimated to heat. Heat stress testing (at approximately 32
[deg]C and 71% or 72% RH) revealed that in the post-intervention
period, the heat group compared to the control group, had significantly
decreased peak heart rate; resting, mean, and peak rectal temperature;
and peak and mean skin temperature. No significant differences were
observed in measures of sweat and hydration. Plasma volume was
significantly increased in the heat compared to control group post
intervention. Orthostatic tolerance (at approximately 32.0 [deg]C, 20%
RH) determined by the time to laboratory-induced presyncope, was
significantly increased in the heat group (pre: 28 9 min.
vs. post: 40 7 min.) compared to control group (pre: 30
8 min. vs. post: 33 5 min.) post-
intervention. The authors concluded that plasma volume expansion was
the likely mechanism behind improved orthostatic tolerance; they
further noted that participants were physically fit at baseline and
that they would expect a less robust acclimation regimen would likely
yield beneficial results for populations with lower physical fitness
(Parsons et al., 2023).
I. Evidence of Tenure as a Risk Factor
Multiple investigations of occupational HRIs have identified tenure
in the job as a risk factor. Workers who are new on the job are often
overrepresented in HRI and heat-related fatality reports. In many of
these cases, this apparent increased risk presumably results from not
being acclimatized to hot working conditions. Studies documenting
tenure as a risk factor include case series from OSHA reports, analyses
of State workers' compensation databases, and research on military
populations. For reference, the most recent (2023) monthly estimates of
new hires in the U.S. suggest that over the summer months (June to
September), the percent of workers who have been in their job for a
month or less ranges from 3.7%-4.1% (BLS JOLTS 2023). Therefore, the
percent of workers who are in their first day, first week, or first two
weeks on the job would be expected to be lower than 3.7%-4.1%.
Several reports have evaluated OSHA enforcement cases of HRI and
heat-related fatalities. Arbury et al. identified 20 citations
involving indoor or outdoor HRIs and fatalities cited under the general
duty clause in 2012 and 2013 (Arbury et al., 2014). Of the 13
fatalities, 4 (31%) occurred on the worker's first day on the job or
after returning from time away, while 9 (69%) occurred in the first
three days of the worker's tenure on the job. Arbury et al. expanded
this work in a follow-on report that included all of OSHA's heat
enforcement cases in both indoor and outdoor workplaces between 2012
and 2013 (n=84). Of the 23 cases involving a heat-related fatality, 17
(74%) occurred in the worker's first three days on the job and 8 (35%)
on the worker's first day (Arbury et al., 2016). Tustin et al. (2018a)
identified 66 HRI cases among OSHA enforcement investigations conducted
between 2011 and 2016 for which OSHA's Office of Occupational Medicine
and Nursing (OOMN) was consulted. Among the fatality cases with job
tenure information (n=22), 45.5% occurred on the first day of or
returning to the job and 72.8% occurred during the first week. Among
the non-fatal HRI cases with job tenure information (n=32), 3.1%
occurred on the first day and 18.7% occurred during the first week. In
a related analysis focusing on outdoor workers, Tustin et al. (2018b)
evaluated 25 outdoor occupational HRI and fatalities investigated by
OSHA between 2011 and 2016. Eleven (78.6%) of the 14 fatalities and one
of the 11 non-fatal illnesses (9.1%) occurred in workers who had
started the job within the preceding two weeks or returned from an
absence of greater than one week (Tustin et al., 2018b).
Arbury et al. 2014, Arbury et al. 2016, Tustin et al. 2018a, and
Tustin et al. 2018b are all retrospective case series that used OSHA
databases to identify cases of HRI and heat-related fatalities. As
such, they rely on previously collected information about working
conditions and worker characteristics, which may not be complete or
reflect all factors. In addition, there may be selection bias
introduced by the type of cases referred to OSHA's OOMN for review
(i.e., they may represent more severe cases).
Several studies and reports have used data from California to
describe characteristics of occupational HRI and heat-related
fatalities in the State. From May through November of 2005, there were
25 heat-related Cal/OSHA enforcement investigations (Prudhomme and
Neidhardt, 2006). When combining fatal and non-fatal outcomes, most
workers (80%) had been on the job for four or fewer days before their
HRI event, and almost half (46%) occurred on the workers' first day on
the job (Prudhomme and Neidhardt, 2006). In 2006, Cal/OSHA confirmed 46
cases of HRI in their 38 investigations of heat-related allegations (4
investigations involved more than 1 case) (Prudhomme and Neidhardt,
2007). 15% of the HRI events and fatalities occurred on the first day
of work or the first day of a heat wave, while 30% occurred after
working one to four days on the job or into a heat wave (Prudhomme and
Neidhardt, 2007). It should be noted that both Cal/OSHA reports only
capture cases investigated by Cal/OSHA, and as such, may reflect more
severe cases of HRI. They are also not expected to be exhaustive of all
occupational HRIs occurring in the State during these time periods.
Heinzerling et al. (2020) investigated occupational HRIs across
industry sectors in California from 2000 to 2017 using the California
Workers' Compensation Information System (Heinzerling et al., 2020) and
identified 15,996 cases of occupational HRI. The authors reported that
1,427 cases (8.9%) occurred within two weeks of hire and 410 (2.6%)
occurred on the first day on the job.
Several analyses of Washington State Department of Labor and
Industries (WA L&I) data have also investigated job tenure in relation
to heat-related workers' compensation claims. Bonauto
et al. identified 308 claims between 1995 and 2005 with information on
employment duration, 43 (14%) of which reported job tenure of one week
or less (Bonauto et al., 2007). In comparison, across all claims (i.e.,
not just heat-related) with employment duration information during the
same period, 3.3% of claims reported a job tenure of one week or less,
suggesting that this pattern is more common among heat-related claims.
A more recent analysis by WA L&I reports the percent of accepted HRI
claims occurring during the first one and two weeks of work in
Washington between 2006 and 2021 (SHARP 2022). Across all industries,
12.5% of accepted HRI claims were filed in the first week at a job and
16.1% of accepted HRI claims occurred during the first two weeks of
work. The percentage of HRI claims filed in the first week and first
two weeks of working at a job was higher than the percentage among all
workers' compensation claims filed in the first week (2.2%) or two
weeks (3.7%) on a job. Spector et al. conducted an analysis similar to
Bonauto et al. 2007, but restricted to the agriculture and forestry
sectors and included claims through 2009 (Spector et al., 2014). The
researchers identified 84 HRI claims in the agriculture and forestry
sectors, approximately 15% of which reported that claimants had been
working at their job for less than two weeks at the time of the injury.
As discussed in Section V.A., Risk Assessment, occupational HRIs,
particularly those not requiring medical treatment, are subject to
underreporting in workers' compensation systems. Therefore, injuries
and illnesses that are captured are likely to be more severe cases.
The U.S. military has also studied HRIs among its recruits
extensively. Among all U.S. Marine recruits entering basic training at
the Marine Corps Recruit Depot, Parris Island in South Carolina between
1988 and 1996, the number of HRI cases were higher in early training
periods (processing week and weeks 1-4) compared to late training
period (training weeks 5-12) for females but were similar for males
(Wallace 2003). Among males, weeks 1, 8, and 9 of training had the
highest numbers of HRI cases. Physical intensity of training varied
each week during the 12 weeks of training, which likely had an impact
on rates of HRI. Dellinger et al. reported on HRIs among more than
7,000 Army National Guard soldiers deployed to Illinois from July 5th
to August 18th, 1993, in response to severe flooding (Dellinger et al.,
1996). Researchers identified 23 heat-related medical claims, which
excluded those treated by on-site first aid. 65% of the 23 HRI claims
occurred during the first two weeks of the deployment; researchers note
that this was also the period of greatest work intensity.
II. Conclusions for Acclimatization
In conclusion, numerous studies have reported the benefits of heat
acclimatization for employees in workplace settings. For example,
adoption of workplace acclimatization protocols was followed by reduced
rates of heat stroke-related fatalities in South African miners (Van
der Walt and Strydom, 1975). Acclimatization was also reported to
result in reduced signs of heat strain or improved physiological
responses to heat for miners (Weiner, 1950; Wyndham et al., 1966), fire
fighters (Lui et al., 2014; Watkins et al., 2019) and aluminum smelter
potroom workers (Dang and Dowell, 2014). Similarly, studies in military
personnel have reported responses to heat following physical training
in hot climates (Charlot et al., 2017; Lim et al., 1997). Improvements
in physiological responses to heat were also observed in athletes after
training in hot climates (Buchheit et al., 2011; Racinais et al., 2012,
2014) and participants exercising in heat chambers (Chong et al., 2020;
Zhang and Zhu, 2021). Studies have also shown that heat acclimation
while exercising reduces the risk of laboratory-induced syncope
(Shvartz et al., 1977) or presyncope (Parsons et al., 2023).
Additionally, retrospective examination of limited data from State
and Federal enforcement and surveillance cases demonstrates over-
representation of workers during the first days or weeks of employment
or return to work among HRI cases and fatalities (Arbury et al., 2014,
2016; Tustin et al., 2018a, b; Prudhomme and Neidhardt, 2006, 2007;
Heinzerling et al., 2020; Bonauto et al., 2007; SHARP, 2022). This
suggests that these workers are at increased risk of HRI and fatality,
which may be (or at least in part) the result of lack of
acclimatization.
Based on the evidence presented in this section, OSHA preliminarily
finds acclimatization to be an effective intervention in reducing the
risk of HRI and heat-related fatality by improving physiological
responses to heat.
IV. Evidence on the Effectiveness of Multicomponent Interventions
A. Civilian Workers
OSHA identified a small number of studies that examined the
effectiveness of multi-pronged interventions implemented at workplaces.
Three evaluated the effectiveness of a multi-pronged intervention at
reducing the risk of heat-related illness (McCarthy et al., 2019;
Perkison et al., 2024) or self-reported symptoms of heat-related
illness (Bodin et al., 2016) by comparing the same study population
before and after an intervention was implemented. OSHA does note that
the studies lacked a control group which received no intervention and
would have allowed for the authors to examine the effect of potential
temporal confounders that changed across the study period. In addition,
there was no data to indicate how thoroughly the interventions were
implemented or how much employees adhered to them. However, the studies
provide strong and consistent evidence of the effectiveness of multi-
intervention programs in preventing heat-related illnesses and are
supported on a mechanistic basis by the laboratory and other
experimental evidence presented above.
McCarthy et al. (2019) compared HRI events and costs from workers'
compensation data before and after a Heat Stress Awareness Program
(HSAP) intervention among workers in a mid-sized city in Central Texas
that was implemented in March 2011. The study population consisted of
municipal workers whose jobs involved work in hot, humid conditions
with moderate to heavy physical demands, excluding firefighters. The
HSAP was based on NIOSH's Criteria for a Recommended Standard:
Occupational Exposure to Heat and Hot Environments (2016) and included
in-person training of supervisors and workers, a medical monitoring
program, and specific recommendations to supervisors such as providing
unlimited access to water, sports drinks, and shade, as well as
establishing acclimatization schedules, work-rest procedures, and first
aid protocols. Before the intervention, workers completed a self-
administered questionnaire to determine their level of HRI risk, which
the researchers then used to categorize them into four risk levels
(McCarthy et al., 2019). Those who reported two or more HRI risk
factors (i.e., high body mass index, medication use, chronic illnesses,
alcohol and energy drink use, history of prior HRI, work in a second
hot job, and extensive skin pathology) but not an ``unstable health
condition'' received individualized HRI prevention counseling or
education.
McCarthy et al. (2019) compared the rates of heat-related illness
across the study period of 2009-2017, before and after the HSAP
intervention was implemented in 2011. In the pre-intervention period
(2009-2010), the
annual average claim rate for heat-related illnesses was 25.5 claims/
1,000 workers. The average annual rate of HRI claims in fell by 37% in
2012-2014 (16 claims/1,000 workers) and by 96% in 2015-2017 (1 claim/
1,000 workers) compared to the pre-intervention period. No workers'
compensation claims for HRI were submitted in the final 2 years of the
study period.
OSHA observes the potential for healthy worker selection bias in
this study that might have occurred if employees with medical
conditions were more likely to leave their job and therefore the cohort
during the study period.
Perkison et al. (2024) reported that the program in the central
Texas Municipality employees (referred to in this study as the heat
illness prevention program (HIPP)) and described by McCarthy et al.
2019) ended in 2017 and was replaced by a modified HIPP (mHIPP) that
included only employee and supervisor training and employee
acclimatization. In an analysis to determine the impact of dropping
medical surveillance from the HIPP, the study authors reported that the
rate of heat illness and injury, which averaged 19.5/1,000 employees
during the first four years of the HIPP (2011-2014), fell to 1.0/1,000
employees over the next three years (2015-2017), but increased to 7.6
per 1,000 workers during the mHIPP (2018-2019). Although heat-related
illness claim rates increased during implementation of the mHIPP, the
rate of heat-related illness during implementation of the mHIPP (7.6/
1,000) was still 70% lower than the period with no intervention (25.5/
1,000).
Bodin et al. (2016) reported on productivity, HRI symptoms, and
hydration practices before and after a water-rest-shade (WRS) and
efficiency intervention among sugarcane cutters in El Salvador. The
intervention began two months into the 5-month harvest season of 2014-
2015. The WRS intervention included: 3-liter water bladders carried in
backpacks and refilled during breaks; an initial 1.5 to 2-hour work
interval followed by a 10 to 15-minute break, then hour-long work
periods with 10 to 15-minute rest breaks and a 45-minute lunch break;
and a portable shade canopy for breaks. The efficiency intervention
consisted of a machete with an improved blade and handle, fewer rows
cut, and a stacking method to reduce workload. Due to challenges during
data collection, a relatively small sample size of 41 workers completed
follow-up. Bodin et al. (2016) reported that, among those 41 sugarcane
cutters, average daily water intake (5.1 liters pre-intervention, 6.3
liters post-intervention) and average daily production (5.1 tons pre,
7.3 tons post) increased after the intervention. An analysis of self-
reported heat stress and dehydration-associated symptoms showed that
reporting of most symptoms decreased after the intervention, such as
feeling feverish (40% to 10%), exhaustion (37% to 14%), nausea (35% to
12%), very dry mouth (49% to 26%), very little urine (37% to 19%),
cramps (30% to 17%), diarrhea (14% to 0%), disorientation (12% to 0%),
and fainting (5% to 2%). However, self-reported rates of vomiting (9%
to 10%) and dysuria (i.e., pain during urination) (42% to 45%) remained
similar in pre- and post-intervention periods (Bodin et al., 2016)
(Communication with David Wegman, November 2023).
B. Military Personnel
OSHA also identified studies which examined the effectiveness of
interventions in reducing risk of heat-related illness among military
personnel. OSHA acknowledges differences between military personnel and
typical civilian worker populations, such as health status, fitness
levels, and the types of physical activities performed by military
personnel (e.g., long-distance running). The military also employs
certain controls that aren't typically used in workplaces, such as work
stoppage criteria. However, OSHA finds the studies in military
personnel useful for showing that multi-component interventions can
reduce the risk of heat-related illness.
Kerstein et al. (1986) conducted a randomized control trial in
military reservists exposed to hot and humid conditions and found that
the incidence of heat illness was 54% lower in a group exposed to
intervention measures. Those measures included a lecture on water as
prevention, training on and use of portable WBGT monitors, and a
special briefing for Commanding Officers. Incidence rates of HRI
(defined as ``any person with heat symptoms, including exhaustion,
cramps, and headaches that the corpsman could clearly relate to the
environment and cause the individual to be non-functional for at least
one hour or more'') were 13 out of 306 participants in the intervention
group (4.2%) and 20 out of 220 in the control group (9.1%).
Stonehill and Keil examined the number of heat stroke cases at
Lackland Air Force Base in San Antonio, Texas after they implemented a
series of interventions over a period from 1956 through 1959 (Stonehill
and Keil, 1961). Interventions that were implemented before 1958
included education on heat illness and prevention, pausing training
based on dry bulb temperatures, shifting harder exercises to cooler
hours, treating heat rash, providing clothing with better ventilation,
improving personal hygiene, providing special advice for overweight
individuals, and implementing immediate medical treatment for heat
stroke. Despite these measures, they still observed 39 cases of heat
stroke in 1957 (a rate of 0.87/1,000). After making improvements to
their prevention measures in the summer of 1958 (increased water and
salt tablet availability, removing fatigue shirts inside classrooms,
using WBGT to determine when to pause training, and avoiding intense
outdoor training in the first week of training), they observed only 2
heat stroke cases that summer (a rate of 0.05/1,000), a reduction of
95% from 1957.
Minard (1961) evaluated the effectiveness of interventions in
reducing HRIs in a study of the Marine Corps Recruit Depot in Parris
Island, South Carolina. During the summer of 1952, the mean weakly HRI
incidence rate was 53 per 10,000 recruits. A program to address HRI was
adopted in 1954 and later modified in 1956. Minard reported a lower
mean weekly HRI rate with the enhanced interventions in 1956 (4.7 per
10,000 recruits) compared to the initial intervention in 1955 (12.4 per
10,000 recruits), despite higher temperatures in 1956. Initial
interventions included curtailing physical activity during high heat
and numerous behavioral changes, such as modifications to uniforms and
leadership training; while the most substantial changes to enhance the
interventions included curtailing physical activity based on WBGT and
differentiating physical activity guidance for acclimatized versus
unacclimatized recruits. Later enhancements to the intervention
included conditioning recruits with substandard fitness, shade for
outdoor classrooms, cooling for indoor classrooms, modification of the
clothing policy to allow for only t-shirts, light duty status for
recently vaccinated recruits, one hour rest or classroom instruction
after meals, better ventilation in barracks to improve sleep, and
strategies to increase water and salt intake. The mean weekly HRI rate
for all summers with the enhanced intervention (1956-1960) was 4.3 per
10,000 recruits. Four fatalities from heat stroke occurred from 1951 to
1953, but no fatalities occurred since 1953.
C. Conclusions for Multicomponent Interventions in Civilian and
Military Employees
In conclusion, three studies in civilian worker populations found
that multicomponent heat stress interventions reduced the incidence of
HRI claims and self-reported heat strain and dehydration symptoms and
increased work output. The findings of these studies are supported by
studies among military personnel, which also found multicomponent
interventions to be effective in reducing incidence of HRI, as well as
data on the effectiveness of individual control measures reported in
laboratory and experimental studies, which are summarized above. The
findings of these multicomponent intervention studies are summarized in
table V-3.
Table V-3--Summary of Evidence of the Effectiveness of Multicomponent
Interventions in Reducing HRIs and Heat-Related Symptoms
------------------------------------------------------------------------
Evidence Notes
------------------------------------------------------------------------
Multi-component Interventions
------------------------------------------------------------------------
McCarthy et al. (2019): In a comparison The program involved
of heat-related illness claims before medical monitoring and
and after the implementation of a heat training.
stress awareness program that began in Recommendations made
2011 in a Texas municipality, the to supervisors included
average annual rate of HRI claims fell unlimited access to water,
[by 37%] in 2012-2014 (16 claims/1,000 sports drinks, and shade, as
workers) and [by 96%] in 2015-2017 (1 well as establishing
claim/1,000 workers) compared to the acclimatization schedules,
pre-intervention period (25.5 claims/ work/rest procedures, and
1,000 workers). first aid protocols.
It is not known if and
to what extent recommendations
were implemented.
Perkison et al. (2024). The program in The study authors
Texas municipality workers reported by concluded ``medical
McCarthy et al. (2019) was modified in surveillance may be an
2017 to include only training and important component in
acclimatization, and no longer include lowering workforce heat-
medical surveillance. Rate of heat- related illness,'' but noted
related illness did increase after the small sample size and
these changes (to 7.6 claims/1,000 short evaluation period.
workers) but remained [70%] lower than
when no program was implemented.
Bodin et al. (2016) reported that three Most of the
months after implementation of interventions were consistent
interventions, self-reported heat with the main interventions of
stress and dehydration-associated the proposed standard (i.e.,
symptoms decreased as follows: feeling providing drinking water, and
feverish (40% to 10% [[darr]76%]), shaded rest breaks and a lunch
exhaustion (37% to 14% [[darr]62%]), break).
nausea (35% to 12% [[darr]66%]), very Ergonomic improvements
dry mouth (49% to 26% [[darr]46%]), were also implemented.
very little urine (37% to 19% [[darr] Non-U.S. workers (El
49%]), cramps (30% to 17% Salvador) in sugar cane
[[darr]45%]), diarrhea (14% to 0% industry.
[[darr]100%]), disorientation (12% to
0% [[darr]100%]), and fainting (4.7%
to 2.4% [49%]) Rates of vomiting and
dysuria were similar.
Kerstein et al. (1986) reported a [54%] Military study.
decrease in heat illnesses in military Intervention: A
reservists after an intervention. lecture on water as
prevention, training on and
use of portable WBGT monitors,
and a special briefing for
Commanding Officers.
Stonehill and Keil (1961) reported the Military study.
number of heat stroke cases and the Intervention being
number of troops in the summers of tested: In addition to
1957 and 1958, before and after existing prevention measures,
additional protective measures were they added increased water and
implemented. salt tablet availability,
The heat stroke rate in summer removing fatigue shirts inside
1958 after implementing additional classrooms, using WBGT to
protective measures was [95%] lower determine when to pause
[0.05/1,000 troops] than the summer training, and avoiding intense
before [0.87/1,000 troops]. outdoor training in the first
week of training.
Minard (1961) study of military Military study.
recruits: Examples of
The rate of HRI after intervention measures:
implementation of the program (12.4/ curtailing physical activity
10,000 recruits) was [77%] lower than during high heat,
before the program was implemented (53/ modifications to uniforms,
10,000) recruits. leadership training,
The rate of HRI after enhanced curtailing physical activity
interventions (4.7 per 10,000 based on WBGT, differentiating
recruits) was [62%] lower than the physical activity guidance for
rate after initial interventions (12.4 acclimatized versus
per 10,000 recruits) and [91%] lower unacclimatized recruits,
than the period before the program (53/ conditioning recruits with
10,000). substandard fitness, shade for
outdoor classrooms, cooling
for indoor classrooms,
modification of the clothing
policy to allow for only t-
shirts, light duty status for
recently vaccinated recruits,
one hour rest or classroom
instruction after meals,
better ventilation in barracks
to improve sleep, and
strategies to increase water
and salt intake.
------------------------------------------------------------------------
Numbers in brackets calculated and rounded by OSHA.
V. Governmental and Non-Governmental Organizations' Requirements and
Recommendations
A number of governmental and non-governmental organizations
recommend or require heat injury and illness prevention programs or
multiple controls to address risks related to occupational heat
exposure. This shows that OSHA's proposal continues to reflect the
growing consensus that HRIs can be avoided or minimized when employers
address conditions that have been shown to increase the risk of HRI.
OSHA's proposal also continues to reflect a consensus that, to be most
effective, an HRI prevention program should incorporate multiple
interventions.
A. Governmental Requirements and Recommendations
As of April 2024, five States had heat injury and illness
prevention standards, reflecting a recognition by these States that
certain measures can reduce heat-related risks posed to workers. These
standards have many of the same types of controls OSHA is proposing
(e.g., a written heat safety plan, emergency response protocols, rest
breaks, training on HRI recognition and prevention). For a more
detailed discussion of existing State standards see Section III.,
Background. In addition, numerous States have published heat illness
and injury prevention guidance for workers.
NIOSH has issued a number of guidance products and provided expert
advice on heat injury and illness prevention and developed a
programmatic approach to reduce the risks associated with heat for
workers. For example, in 2016, NIOSH updated its Criteria for a
Recommended Standard: Occupational Exposure to Heat and Hot
Environments, first published in 1972 and updated in 1986, stating,
``compliance with this recommended standard should prevent or greatly
reduce the risk of adverse health effects to exposed workers.'' NIOSH
recommends that employers ``establish and implement a written program
to reduce exposures to or below the applicable RAL or REL'' (which
considers exposure to environmental heat and metabolic heat (i.e., work
intensity) for unacclimatized and acclimatized employees, respectively)
with engineering and work practice controls. Examples of engineering
controls include ventilation to increase air movement, air-
conditioning, screening, and insulation. Examples of administrative
controls include rest breaks to decrease exposure time and metabolic
heat loads, increasing distance from radiant sources, and implementing
acclimatization protocols, health and safety training, medical
screening for heat intolerance, and a heat alert program. If
engineering and administrative controls do not reduce exposure below
the applicable RAL or REL, NIOSH also recommends cooling clothing/PPE.
NIOSH states, ``the reduction of adverse health effects can be
accomplished by the proper application of engineering and work practice
controls, worker training and acclimatization, measurements and
assessment of heat stress, medical monitoring, and proper use of heat-
protective clothing and personal protective equipment (PPE)'' (NIOSH,
2016).
In another example of NIOSH guidance, NIOSH investigated a number
of heat-related workplace fatalities to assess the hazards and propose
recommendations for preventing similar fatalities, as part of the
Fatality Assessment and Control Evaluation (FACE) Program. In four heat
fatality investigations that affected landscapers (NIOSH, 2015), farm
workers (NIOSH, 2007), firefighters (NIOSH, 1997), and construction
laborers (NIOSH, 2004), collective recommendations related to heat
included: development, implementation and training on a safety and
health program that is made available to all workers; providing rest
breaks and accessible hydration; training workers and supervisors on
recognizing HRI; providing prompt medical assistance for HRI;
monitoring of worker symptoms by supervisors; implementing
acclimatization programs; informing workers of drinks (e.g., alcoholic)
that can increase risk; having medical providers inform workers taking
certain drugs or with certain medical conditions of their increased
risk; and factoring in clothing and weather to determine firefighter
workloads.
Additionally, there is a recognition amongst other Federal
regulatory agencies that employers can implement control measures to
reduce heat-related risks and harms. The Mine Safety and Health
Administration (MSHA) first published heat guidance for mines in 1976,
and most recently published ``Heat Stress in Mining'' which provides
guidance on reducing heat stress (MSHA, 2012). The report states that a
combination of engineering controls, administrative controls and work
practices, and PPE can reduce heat and prevent employee's core
temperatures from rising. MSHA recommendations include mine planning to
provide cool rest areas, implementing exhaust ventilation and air-
conditioning in mines, using canopies in the sun, using skillful
blasting procedures to reduce excessive heat, using automation/remote
controls to reduce metabolic heat, implementing work-rest regimens with
frequent breaks, pacing work tasks, performing heavy tasks in cooler
areas or at cooler times, rotating personnel through hot work tasks,
providing readily accessible, cooler rest areas and drinking water,
acclimatizing new and returning employees, and ensuring employees and
supervisors are knowledgeable about heat related topics such as risk,
prevention, and symptoms.
In 1993, the EPA published ``A Guide to Heat Stress Management in
Agriculture'' to ``help private and commercial applicators and
agricultural employers protect their workers from heat illness'' (EPA,
1993). The guide outlines the development of a basic program to control
heat stress which includes: designating one person to manage the heat
stress program; training workers and supervisors on heat illness
prevention; acclimatizing workers when they begin to work under hot
conditions; evaluating weather conditions, workload, necessary
protective equipment or garments, and the physical condition of the
employee; managing work activities by setting up rest breaks, rotating
tasks among workers, and scheduling heavy work for cooler hours;
establishing a drinking water program; taking additional measures such
as providing special cooling garments, shade or air-conditioned mobile
equipment; and giving first aid when workers become ill (EPA, 1993).
In 2023, the U.S. Army updated its Training and Doctrine Command
(TRADOC) Army Regulation 350-29 which ``prescribes policy and provides
guidance to commanders in preventing environmental (heat or cold)
casualties.'' It includes requirements for rest in shade and water
consumption according to specific WBGT levels and work intensity, and
consideration of heat stress when planning training events (Department
of the Army, June 15, 2023). In 2022, the U.S. Department of the Army
issued the technical heat stress bulletin ``TB MED 507: Heat Stress
Control and Casualty Management'' that contains measures to prevent
indoor and outdoor HRIs in soldiers, with recommendations for
acclimatization planning, work-rest cycles, fluid and electrolyte
replacement, and cooling methods (e.g., shade, fans for prevention, and
iced sheets and ice water immersion for treatment) (Department of the
Army, April 12, 2022).
The U.S. Department of the Navy has published additional guidance
on heat injury and illness prevention particular to naval conditions
(Department of the Navy, 2023). When Navy personnel are ``afloat'',
they use Physiological Heat Exposure Limits (PHEL) curves to manage
heat stress based on exposure limits/stay times for acclimatized
personnel under various conditions of environmental heat and work
intensity. The PHEL curves were designed to allow core body temperature
to rise to 102.2 [deg]F (39 [deg]C) among healthy and acclimatized
individuals who have rested and recovered from prior heat exposures.
In 2023, the Heat Injury and Illness Prevention Work Group of the
National Advisory Committee on Occupational Safety and Health (NACOSH)
presented to OSHA recommendations on potential elements of a proposed
heat injury and illness prevention standard. The Work Group recommended
that OSHA include the following measures in a potential standard: a
written exposure control plan (heat illness prevention plan); training
on heat illness prevention; environmental monitoring; provision of
water, breaks, and shade or cool-down areas; other administrative
controls (e.g., rotating workers through work tasks and implementing a
communication system for regular check-ins); other engineering control
measures (e.g., ventilation, exhaust fans, and portable cool-down
mechanisms including fans, tents, shielding/
insulation, proactive misting); workplace practice controls (e.g.,
providing coolers with ice and scheduling work during the coolest part
of day); personal protective equipment; acclimatization procedures;
worker participation in planning activities; and emergency response
procedures (NACOSH, May 31, 2023).
B. National Non-Governmental Organizations
ACGIH first recommended a standard for heat stress in 1971 (ACGIH,
2021), and most recently updated it in 2023 (ACGIH, 2023). The TLV is a
value that is determined with the goal of maintaining thermal
equilibrium for healthy acclimatized employees and is based on WBGT
adjusted for work intensity and clothing/PPE. An action limit (AL)
considers those same factors for unacclimatized employees. ACGIH
recommends that whenever heat stress among workers is suspected (based
on factors such as environmental conditions, work demands, work-rest
patterns, and acclimatization states), employers have a Heat Stress
Management Program (HSMP) that includes written plans for ``General
Controls'' and as appropriate, ``Job Specific Controls'' (Table 5 of
the Heat Stress and Strain section of the TLV Booklet). ACGIH states
``The principal objective of a HSMP is the prevention of excessive heat
strain among workers that may result in heat-related disorders.''
General controls include environmental surveillance, medical clearance
and counseling by a healthcare provider, training, acclimatization
planning, fluid replacement, symptom monitoring, breaks in the shade,
and an emergency response plan. Job specific controls include
engineering controls (e.g., air movement, shade, radiant heat shields),
administrative controls (e.g., limiting exposure time and allowing for
enough recovery time), personal cooling, and physiological monitoring.
In 2024, the American National Standards Institute/American Society
of Safety Professionals A10 Committee (ANSI/ASSP) released the American
National Standard A10.50 Standard for Heat Stress Management in
Construction and Demolition Operations. The voluntary consensus
standard ``establishes procedures for the management of heat stress
hazards and the selection and use of appropriate controls and practices
to reduce risks presented by heat stress and prevention of heat
illnesses for all work environments.'' The standard recommends that
employers develop and implement the following: heat stress management
program; acclimatization plan; workplace surveillance/risk assessment;
provision of water and sodium electrolyte supplements; provision of
rest breaks and shaded break locations; buddy system; first aid and
emergency action plan; medical surveillance; employee participation;
implementation of heat stress controls including engineering controls
such as air-conditioning, radiant heat control (barrier), convection
controls (cooling), evaporative controls such as misting fans, and
metabolic controls (e.g., mechanical equipment or tools to reduce
metabolic demands of work tasks); administrative controls such as
scheduling for cooler times and allowing self-paced work; personal
protective equipment; and training on heat illness prevention (ANSI/
ASSP, 2024). More specific recommendations (e.g., frequency of rest
breaks; monitoring employees) are provided when certain triggers are
exceeded.
In 2021, the American Society for Testing and Materials (ASTM)
finalized its Standard Guide for Managing Heat Stress and Heat Strain
in Foundries (E3279-21) which establishes ``best practices for
recognizing and managing occupational heat stress and heat strain in
foundry environments.'' The standard outlines employer responsibilities
and recommends elements for a `Heat Stress and Heat Strain Management
Program.' Employer responsibilities include evaluating temperature and
issuing heat alerts; ensuring control measures are in place; and
reviewing heat exposure incidents to implement corrective actions.
Program elements include worker preparation (i.e., only assigning
workers to tasks involving heat exposure ``who are prepared for work in
those environments and can tolerate the heat exposure associated with
the assignments'') and workplace and work preparation (i.e.,
implementing controls that reduce heat stress through process heat
emission control and ventilation of work areas, adjusting work
schedules, providing heat relief crews (e.g., crew rotation), providing
personal protective equipment, employing personal and portable cooling
devices, providing readily available water, and providing cooled
location for work break) (ASTM, 2021). The standard also recommends
employers and workers monitor heat strain and establish emergency
response protocols.
C. Conclusion on Governmental and Non-Governmental Recommendations
In closing, a number of governmental and non-governmental groups
have either promulgated regulations or published recommendations for
protecting workers from HRI. Many of those regulations or
recommendations contain components that are consistent with protections
in the proposed rule, including plans to prevent heat stress, rest
breaks in shaded or cooled areas, cool drinking water, ventilation or
cooling methods (e.g., fans exhaust), acclimatization, observation of
symptoms in workers, environmental monitoring, and emergency response
procedures. Many of these protections have been recognized for decades
as being effective in reducing the risk of HRI in workers. This shows
that OSHA's proposal continues to reflect the growing consensus that
HRIs can be avoided or minimized when employers address conditions that
have been shown to increase the risk of HRI and incorporate these
protections as part of a program that is tailored to each workplace.
VI. Conclusion
OSHA reviewed a number of studies that provided quantitative
evidence of the effectiveness of multi-component interventions in
reducing heat-related illness or HRI; the results of those studies are
summarized in table V-3 above. Studies among Texas municipality
employees show that a multi-component intervention approach reduced HRI
claims by 37 to 96 percent compared to pre-intervention levels,
depending on the period of intervention and the types of interventions
applied (McCarthy et al., 2019; Perkison et al., 2024). Implementation
of multi-component interventions in military studies resulted in
slightly lower reductions in HRI from pre- to post-intervention (54-95
percent), again depending on the types of interventions applied in
different implementation periods (Kerstein et al., 1986; Minard, 1961;
Stonehill and Keil, 1961).
OSHA acknowledges that several of the interventions implemented
among the Texas municipality employees and military personnel differ
from the interventions in the proposed standard. However, interventions
focusing on water, rest, and shade among sugar cane employees in El
Salvador resulted in similar reductions for several common (i.e.,
occurring in 30% or more of employees pre-intervention) symptoms of
heat-related illness (e.g., 45% reduction in cramps, 46% reduction in
very dry mouth, 49% reduction in very little urine, 62% reduction for
exhaustion, 66% reduction for nausea, 76% reduction for feeling
feverish) (Bodin et al., 2016; communication with David Wegman,
November 2023). Because of the small number of workers completing the
study (n=41), results
regarding less common symptoms (reported in less than 15% of workers
pre-intervention) are more uncertain, but Bodin et al. reported a
decrease in fainting and no incidents of diarrhea or disorientation
after the interventions were implemented. Therefore, the study by Bodin
et al. (2016) supports the finding that a multi-intervention approach
that includes several interventions in common with the proposed
standard is likely to result in substantial reductions in HRI symptoms.
Despite several limitations that were acknowledged for these multi-
intervention studies, the results for all are of a large magnitude and
consistently show effectiveness for multi-component interventions in
preventing HRIs. In addition, the results are mechanistically supported
by experimental studies showing the effectiveness of individual
interventions in preventing signs and symptoms related to heat strain.
OSHA finds the studies looking at multi-component approaches to be more
relevant for looking at quantitative reductions in HRI because each
individual component would contribute to the overall effect.
In addition to studies showing effectiveness of multi-component
interventions in preventing HRIs, two studies also show that effective
treatments are available to prevent death if heat stroke does occur. As
reported in more detail under the Explanation of Proposed Requirements
for paragraph (g)(3), Heat illness and emergency response and planning,
studies examining the effectiveness of treating individuals suffering
from exertional heat stroke reported 99.8% survival in military
personnel treated with ice sheets (bed sheets soaked in water) (DeGroot
et al., 2023) and 100% survival in marathon runners doused with cold
water and massaged with ice bags (McDermott et al., 2009a).
OSHA preliminarily finds that the totality of the evidence reviewed
supports that the approach outlined in the proposed standard, which
consists of a heat injury and illness prevention plan and the
application of multiple control measures, will result in a substantial
reduction in HRIs (range: 37-96%) and heat-related fatalities (range:
99.8-100%) in employees who would be covered under the proposed
standard.
VII. Requests for Comments
For the controls proposed, OSHA requests information and comment on
the following questions and requests that stakeholders provide any
relevant data, information, or additional studies (or citations)
supporting their view, and explain the reasoning or recommendations for
including such studies:
OSHA recognizes that a number of States (e.g., California,
Oregon, Washington) have implemented standards to prevent HRIs and
heat-related fatalities among workers. OSHA is aware that there are
existing and emerging data on the efficacy of the State standards in
preventing and reducing HRIs and heat-related fatalities. OSHA welcomes
proposed analytical methods or analyses of existing data (see e.g.,
discussion in V.A., Risk Assessment of existing data sources,
www.dir.ca.gov/dosh/reports/State-OSHA-Annual-Report-(SOAR)-FY-
2022.pdf) or unpublished data that may be used to estimate the effects
of these State standards on heat-related injury, illness, and fatality
rates among workers. OSHA is also interested in comments on how to
account for the differences (some of which are significant) between the
State standards and OSHA's proposed standard in estimating efficacy of
OSHA's proposed standard. Are there studies, data, or other evidence
that demonstrate the efficacy of and/or describe employers' or workers'
experiences with these heat-specific State standards?
Has OSHA adequately identified and documented the studies
and other information relevant to its conclusion regarding the
effectiveness of these controls in reducing heat strain and the risk of
HRIs, and are there additional studies OSHA should consider?
Are there additional studies or evidence available that
identify appropriate frequencies and durations of rest breaks for
reducing heat strain and risk of HRIs?
Are OSHA's conclusions about the effectiveness of controls
in preventing HRI reasonable?
VI. Significance of Risk
As explained in Section II., Pertinent Legal Authority, prior to
the issuance of a new standard, OSHA must make a threshold finding that
a significant risk of material harm exists, and that issuance of the
new standard will substantially reduce that risk.
In Section IV., Health Effects, OSHA presents data and information
demonstrating the range of heat-related injuries and illnesses (HRIs)
that can be caused by occupational exposure to heat. This discussion
demonstrates that HRIs often result in material harm, as they are
potentially disabling, can result in lost work time, require medical
treatment or restricted work, and in certain cases, can lead to death.
In Section V., Risk Assessment, OSHA presents the best available
evidence on the risk of incurring these heat-related material health
impairments among workers in the U.S., which clearly demonstrates that
there exists a significant risk of material harm to workers from
occupational exposure to heat. As OSHA's analysis of BLS data shows,
there was an average of 40 heat-related deaths (2011-2022) and 3,389
HRIs involving days away from work (2011-2020) among U.S. workers per
year. Additionally, based on OSHA's review of workers' compensation
claim data, OSHA found that workers in sectors and industries where
they are likely exposed to heat in their job (and therefore are more
likely to be covered by this standard) have far higher estimated
incidence of HRI than the national average, indicating that the risk to
heat-exposed workers is much higher than nationwide data suggests.
Furthermore, both the annual and working lifetime incidence rates
underestimate the true risk for heat-exposed workers given
underreporting of workplace injuries and illnesses. Thus, as explained
in sections A and B below, OSHA preliminarily determines that a
significant risk of material harm from occupational exposure to
hazardous heat exists, and issuance of this standard would
substantially reduce that risk.
A. Material Harm
As discussed in Section IV., Health Effects, the risks posed by
exposure to workplace heat hazards are significant and can result in
serious HRIs or even death. As discussed in Section IV.B., General
Mechanisms of Heat-Related Health Effects, heat stress can result in
increased core body temperature and blood flow being shunted towards
the skin and away from major organs (e.g., brain, liver, kidneys) and
muscles. Sweating, which is a healthy and normal response to heat
stress, can also contribute to a reduction in circulating blood volume
if fluids are not adequately replaced. This increase in core body
temperature and reduced blood flow can lead to health effects like heat
stroke, heat exhaustion, heat syncope, and rhabdomyolysis. If not
treated promptly, heat stroke can cause permanent organ damage and lead
to death. Treatment often requires hospitalization and time away from
work (see discussion in Section IV.E., Heat Stroke). Other health
effects, such as heat exhaustion, may also require time away from work
if recommended by a medical professional. Many heat-related health
effects, such as heat cramps and heat exhaustion, can impair
a worker's functional capacity while on the job. Heat syncope can pose
additional dangers to workers if they are in precarious work
environments, such as on rooftops or while operating machinery. Heat
exhaustion can also rapidly progress to heat stroke if not recognized
and treated early. As discussed in Section IV.P., Heat-Related
Injuries, heat-induced impairments in functional capacity on the job
can lead to traumatic injuries, which are more likely to occur on hot
days.
The studies that OSHA relied on in Section V.A., Risk Assessment
leverage data from multiple surveillance databases (e.g., BLS SOII,
workers' compensation claims databases, and hospital discharge data)
that have inclusion criteria that OSHA preliminarily concludes would
clearly indicate that captured cases of HRIs represent material
impairment of health. For example, the estimated number of work-related
HRIs reported in the BLS SOII capture only those that involved days
away from work (Note: For 2021-2022 biennial data, SOII additionally
reports cases involving job restriction or transfer). Similarly,
hospital discharge datasets would represent only cases that involved an
emergency department visit and/or inpatient hospitalization. While
workers' compensation eligibility varies, all of the claims would
involve either a visit with a medical professional and/or lost
worktime. HRIs resulting in lost work time and/or the need for medical
care beyond first aid clearly constitute material harm.
However, HRIs constituting material harm are not limited to those
rising to the level of lost work time and/or the need to seek care from
a medical professional. Based on the evidence discussed in this and
other sections of this preamble, OSHA has preliminarily concluded that
many of the HRIs associated with workplace exposure to heat hazards
constitute material harm, even if they are not captured in the
databases OSHA relied on in its risk assessment. OSHA recognizes that
many of these HRIs may be reversible, particularly if early
intervention is provided. Nonetheless, OSHA presents evidence in
Section IV., Health Effects that these HRIs can be debilitating. In
addition to lost work time and the need for treatment by a medical
professional, HRIs can cause reduction or loss of the worker's normal
functional capacity in work tasks and loss of productivity.
Additionally, where preventive action or early treatment is not
provided, these disorders can rapidly progress to more serious
conditions, and have the potential to result in permanent damage to
organs, causing short-, medium-, and long-term health effects, or
death. Thus, while some of the health effects OSHA has identified may
not rise to the level of material harm in all cases, the agency
believes that each can be material in severe cases.
B. Significant Risk
Peer-reviewed studies and State or national statistics are
available to demonstrate the high incidence of work-related HRIs
occurring among workers exposed to heat hazards at work. Estimates of
the risk of harm confronting exposed workers can be based directly on
the rates of work-related HRIs currently being reported.
In Section V.A., Risk Assessment, of this preamble, OSHA evaluated
the risk to workers of a heat-related injury, illness, or fatality.
OSHA's analysis of BLS data indicated an annual average of 40 heat-
related deaths (2011-2022) and 3,389 HRIs involving days away from work
(2011-2020) among U.S. workers. These annual heat-related death and HRI
numbers alone clearly constitute a significant risk and are in line
with OSHA's significant risk findings in previous safety standards
(see, e.g., Confined Spaces in Construction, 80 FR 25366, 25371 (May 4,
2014); Electric Power Generation, Transmission, and Distribution;
Electrical Protective Equipment, 79 FR 20316, 20321-20322 (April 11,
2014); Cranes and Derricks in Construction, 75 FR 47906, 47913 (Aug. 9,
2010)). However, as discussed in Section V.A., Risk Assessment, many of
the sources that OSHA reviewed reported HRI data in terms of incidence
rates, and OSHA has considered these rates in assessing significant
risk, to the extent they capture populations that are actually exposed
to hazardous occupational heat.
Unfortunately, the available data is insufficient to precisely
estimate the risk to only workers who are exposed to hazardous
occupational heat. But by examining incidence estimates derived from
various datasets, including State workers' compensation systems, OSHA
was able to determine a range of HRI incidence rates among workplaces
where employees are likely to be exposed to heat in their job. In
Section V.A., Risk Assessment, OSHA identified various sector incidence
estimates of HRI over a working lifetime (i.e., 45 years), including:
234 to 1,737 cases per 100,000 workers in agriculture, forestry,
fishing, and hunting; 63 to 545 cases per 100,000 workers in
construction; 131 to 396 cases per 100,000 workers in administrative
and support and waste management and remediation services; 49.5 to 171
cases per 100,000 workers in transportation and warehousing; and 513
cases per 100,000 workers in utilities, among others. The working
lifetime incident rates were even higher in specific industries, such
as an estimated 3,479 cases of HRI per 100,000 workers for farm labor
contractors and crew leaders and 2,439 cases per 100,000 structural
steel and precast concrete workers over a working lifetime of 45 years
(see Section V. A., Risk Assessment, table V-1). OSHA preliminarily
concludes that these incidence rates, though as explained below
substantially underestimate actual risk, are the best available
evidence and sufficient to make a finding of significant risk of HRIs
among workers who are exposed to occupational heat.
While the data are not sufficient to develop a single point
estimate of the risk posed to heat-exposed workers, OSHA has
preliminarily determined that the available data from BLS and workers'
compensation claims support an estimate of working lifetime risk of HRI
ranging from 135 cases per 100,000 workers (calculated based on the BLS
average estimated annual incidence of HRIs for all workers for 2011-
2020) to 3,479 cases per 100,000 workers (based on workers'
compensation claims). Even the lowest estimate within this range
exceeds the 1/1000 threshold that OSHA has historically found to
clearly constitute a significant risk.
As noted above, OSHA believes that these data from BLS and workers'
compensation claims substantially understate the true risk to workers.
For one, the inclusion criteria for the surveillance systems used to
estimate incidence would exclude a large proportion of HRI cases. For
instance, prior to this year, the BLS SOII only reported the estimated
number of HRIs that involved days away from work, which may be less
than 50% of all OSHA-recordable work-related HRIs (see, e.g., BLS, IIF
Latest Numbers for 2022, https://www.bls.gov/iif/latest-numbers.htm).
Additionally, the majority of incidence estimates identified by OSHA
are based on the risk of HRIs confronting an entire working population
(e.g., all workers in a particular industry or sector), both exposed
and non-exposed. Clearly, the risk of experiencing a work-related HRI
is considerably higher among the subset of workers exposed to heat
hazards in their jobs than it is for the rest of the working
population. For example, the annual BLS incidence estimates are
susceptible to understating risk in this way because when BLS
calculates annual incidence estimates, it captures the entire U.S.
workforce in the denominator, which includes a large
number of unexposed workers (e.g., office workers in climate-controlled
buildings). Consequently, the working lifetime risk of HRI estimate
based on BLS's annual incidence estimates (i.e., 135 cases per 100,000
workers), also substantially underestimates the true risk for heat-
exposed workers. There is also a large body of literature demonstrating
the general underreporting of work-related injuries and illnesses, the
findings of which OSHA believes would also apply to HRIs. See Section
V.A., Risk Assessment, for additional discussion of underreporting of
heat-related fatalities and HRIs.
As discussed in Section V.C., Risk Reduction, dozens of peer-
reviewed studies and multiple authoritative bodies (e.g., NIOSH, ACGIH,
ANSI/ASSP) indicate that the provisions outlined in this proposed rule
would, if promulgated, substantially reduce risk to workers. A large
body of data demonstrates that workplace interventions--such as rest
breaks, cool drinking water, acclimatization, shade, and fans--can be
very effective in reducing heat strain, which is responsible for
causing HRIs. This reduction in heat strain and/or reduction in HRI
risk has been shown in studies that have examined the impact of
interventions in an experimental setting, as well as studies that have
documented reductions in HRI prevalence following the implementation of
heat injury and illness prevention measures. OSHA preliminarily
concludes that implementation of the proposed standard will result in a
substantial reduction in HRIs (range of estimates: 37-96%) and heat-
related fatalities (range of estimates: 99.8-100%) in employees who
would be covered under the proposed standard.
C. Preliminary Conclusions
OSHA preliminarily concludes that HRIs associated with workplace
exposure to heat hazards constitute material harm. Further, based on
the evidence discussed in this section, the agency preliminarily
concludes that heat-exposed workers are at significant risk of
experiencing a work-related HRI or heat-related death, and compliance
with the proposed standard would substantially reduce that risk.
VII. Explanation of Proposed Requirements
A. Paragraph (a) Scope and Application
Paragraph (a) establishes the scope of the proposed standard.
Paragraph (a)(1) would require all employers subject to OSHA's
jurisdiction--including general industry, construction, maritime, and
agriculture--to comply with the proposed requirements, subject to the
exemptions in proposed paragraphs (a)(2) and (3). The scope of the
proposed standard applies to a wide range of sectors that include both
indoor and outdoor work areas. The proposed standard aims to provide
protections while accounting for the different work areas, anticipated
exposures, and other conditions in these sectors.
Paragraph (a)(2) describes the exemptions for the proposed standard
based on work activities. Employers would be responsible for
determining which work activities are covered by the standard. Although
an employer may have some work activities exempt from the proposed
standard, other activities may be covered (except for organizations
whose primary function is the performance of firefighting. See the
discussion of paragraph (a)(2)(iii) below). Under paragraph (a)(3), if
an employer's employees exclusively perform the work activities in
paragraphs (a)(2)(i) through (vi), then that employer would be exempt
from this proposed standard.
Paragraph (a)(2)(i) would exclude work activities for which there
is no reasonable expectation of exposure at or above the initial heat
trigger. This exception recognizes that some workplaces would not
reasonably be expected to reach or exceed the initial heat trigger
(e.g., because of their location and/or seasonal variations in
temperature). This exclusion may apply to work activities such as
operating seasonal businesses outdoors (e.g., during winter months),
when temperatures are lower than the initial heat trigger. For
instance, if a business that exclusively operates an outdoor holiday
market during the winter season in a location where daily high
temperatures are always below the initial heat trigger, this standard
would not apply to work activities performed at that market.
Paragraph (a)(2)(ii) would exclude short duration employee
exposures at or above the initial heat trigger of 15 minutes or less in
any 60-minute period. OSHA has preliminarily concluded that
intermittent exposures within this duration are not likely to
significantly raise core body temperature and result in heat-related
injuries and illnesses (HRIs). Numerous studies (many described in
Section V.C., Risk Reduction) evaluated the effect of hotter
temperatures on participants' core body temperatures under various
scenarios (e.g., clothing type, level of activity, work/rest periods,
acclimatization status) of different durations. Overall, evidence
suggests that heat exposure of 15 minutes or less does not tend to
cause an elevation of at least 1 [deg]C (1.8 [deg]F) in participants'
core body temperatures, which would be indicative of potential heat
stress (McLellan & Selkirk, 2006; Meade et al., 2016b; Lamarche et al.,
2017; Seo et al., 2019; Kaltsatou et al., 2020; Notley et al., 2022a;
Notley et al., 2022b).
This exemption recognizes that while typical work activities may
take place below the initial heat trigger, employees may experience
short exposures to heat at various times during their shift. For
example, an employer who is otherwise exempt from the standard but has
employees who occasionally walk to collect mail outside in temperatures
at or above the initial heat trigger for 15 minutes or less in any 60-
minute period, would still be exempt. This exemption is consistent with
the scope exemptions of Colorado, Washington, and Oregon's State
standards (7 Colo. Code Regs. section 1103-15:3 (2023); Wash. Admin.
Code 296-307-09710 (2023); Or. Admin. R. 437-002-0156 (2024)).
In addition, in order for this exemption to apply for employees
whose work activities are primarily performed in air-conditioned
vehicles, employers must ensure employees are not exposed to
temperatures at or above the initial heat trigger for more than 15
minutes in any 60-minute period. For instance, where an employee who
drives an air-conditioned vehicle repeatedly exits the vehicle to
deliver product in temperatures at or above the initial heat trigger,
this activity would only be exempt from the standard if cumulative
exposure in any 60-minute period at or above the initial heat trigger
is for 15 minutes or less. If delivery tasks, such as unloading product
from the vehicle and moving product to its destination, occur at or
above the initial heat trigger for more than 15 minutes in any 60-
minute period, these work activities would be covered by the standard.
Paragraph (a)(2)(iii) would exclude organizations whose primary
function is the performance of firefighting. It would also exclude
emergency response activities of workplace emergency response teams,
emergency medical services (EMS), or technical search and rescue; \4\
and any emergency response
activities already covered under 29 CFR 1910.120, 1910.146, 1910.156,
part 1915, subpart P, 1926.65, and 1926.1211. Fire departments,
workplace emergency response teams, EMS, and technical search and
rescue are covered by OSHA's proposed Emergency Response standard (89
FR 7774, Feb. 5, 2024), which would replace the existing Fire Brigades
standard, 29 CFR 1910.156. The update to 29 CFR 1910.156 would expand
coverage from only fire brigades, industrial fire departments, and
private or contractual type fire departments, to include protections
for all employees who perform firefighting, EMS, or technical search
and rescue, as part of their regularly assigned duties as well as
employees who are members of a workplace emergency response team. If
the Emergency Response standard is finalized before this proposed
standard, OSHA intends to revise this exemption to reflect the updated
29 CFR 1910.156.
---------------------------------------------------------------------------
\4\ ``Technical search and rescue'' refers to a type of
emergency service that utilizes special knowledge and skills and
specialized equipment to resolve unique or complex search and rescue
situations, such as rope rescue, vehicle/machinery rescue,
structural collapse, trenches, and technical water rescue. OSHA
intends the phrase to have the same meaning as used in the proposed
Emergency Response standard (see 89 FR 7804).
---------------------------------------------------------------------------
The exemption would apply to all activities (including, e.g.,
training activities) at organizations whose primary function is the
performance of firefighting. In order to comply with the proposed
updates to 29 CFR 1910.156, firefighting organizations would have
programs in place that address heat-related hazards for their
employees.
For employers with employees who perform emergency response
activities as members of workplace emergency response teams (i.e.,
groups of employees who prepare for and respond to emergency incidents
at their workplace as a collateral duty to their regular daily work
assignments; see 89 FR at 7803), or who perform emergency medical
services or technical search and rescue, this exemption would only
apply when employees are performing emergency response activities. This
means during periods while these employees are performing other duties
unrelated to emergency response, employers would be required to comply
with the provisions of the standard, unless subject to another
exemption. For example, employees who are part of a manufacturing
plant's emergency response team would be exempt from the standard while
responding to an incident, such as a medical emergency, but would be
covered by the standard when performing their regular daily work
assignments. All other employees not engaged in emergency response
would also be covered by this proposed standard. Although OSHA is
proposing to exempt fire departments entirely, the agency is not
proposing to entirely exempt organizations that have employees who
perform EMS or technical search and rescue. This is because many
organizations who perform EMS (e.g., hospitals) or technical search and
rescue also conduct many other activities unrelated to emergency
response and OSHA intends these other activities to be covered by this
proposed standard unless another exemption applies.
The Emergency Response proposal includes several hazard assessment
and risk management requirements that would encompass heat hazards
faced by emergency responders (see 89 FR at 7813-7814). Further, in the
NPRM for Emergency Response, OSHA noted this rulemaking on heat illness
prevention and invited comment on whether the agency should include
specific requirements related to heat for some non-emergency activities
of emergency responders. At the same time, the agency recognized that
at times emergency responders must perform their duties regardless of
environmental conditions (89 FR at 7801). OSHA has preliminarily
concluded that it is appropriate to address any heat-related hazards
posed by emergency response activities in this separate rulemaking.
This proposed standard would also not apply to employees when they
are undertaking emergency response activities under 29 CFR 1910.120,
1910.146, 1910.156, subpart P, 1926.65, and 1926.1211. Many of these
standards provide employees protection from heat exposure during
emergency activities. In addition, OSHA believes that the emergency
nature of these activities warrant special consideration and the agency
is therefore exempting them from this proposed standard. However, this
proposed standard would otherwise apply to these employees during non-
emergency regular operations unless another exemption applies. For
example, with regard to the Hazardous Waste Operations and Emergency
Response Standard (HAZWOPER) (29 CFR 1910.120 and 1926.65), which
covers employees who are exposed or potentially exposed to hazardous
substances and engaged in one of the operations as specified by 29 CFR
1910.120(a)(1)(i) through (v) and 1926.65(a)(1)(i) through (v), such as
clean-up operations, employees would only be exempt when responding to
emergency situations and would be covered by the standard when
participating in general hazardous waste operations.
Paragraph (a)(2)(iv) would exclude work activities performed in
indoor work areas or vehicles where air-conditioning consistently keeps
the ambient temperature below 80 [deg]F. OSHA specifies using ambient
temperature, as most heating, ventilation, and air-conditioning (HVAC)
systems automatically report ambient temperature. Properly functioning
HVAC units also regulate indoor humidity levels, which would result in
similar measures of ambient temperature and heat index.
This exemption would only apply to indoor work areas and vehicles
that are consistently below an ambient temperature of 80 [deg]F. The
employer must ensure that the air-conditioning system consistently
maintains an ambient temperature below 80 [deg]F during work activities
for the exemption to apply. OSHA recognizes that there may be
unexpected malfunctions of air-conditioning systems that result in
periods of time without air-conditioning before a system is repaired.
In these situations, OSHA would expect that the employer takes steps to
expeditiously repair the air-conditioning system and return the
workplace to an ambient temperature below 80 [deg]F.
Paragraph (a)(2)(v) would exclude telework (i.e., work done from
home or another remote location of the employee's choosing). OSHA
generally does not hold employers liable for employees' home offices
and conditions of the telework environment (see CPL 02-00-125,
available at https://www.osha.gov/enforcement/directives/cpl-02-00-125). However, only the work activities employees perform while
teleworking would be exempt and employers would be required to comply
with the standard when employees are on site if other exemptions do not
apply. For example, the standard would not cover work activities
conducted at an employee's home on Tuesdays and Thursdays in a given
week but would cover the employee's work activities at their employer's
office on Mondays, Wednesdays, and Fridays (unless another exemption
applies).
Paragraph (a)(2)(vi) would exclude sedentary work activities at
indoor work areas that only involve some combination of the following:
sitting, occasional standing and walking for brief periods of time, and
occasional lifting of objects weighing less than 10 pounds. The
exemption is intended to apply to work sites such as offices where
employees perform sedentary work activities for extended periods of
time (e.g., all or most of the workday). This exemption only applies to
indoor work activities, which are not generally subject to factors such
as solar radiation, which are common in outdoor exposures. OSHA
preliminarily concludes that employees engaged in
indoor sedentary work activities are at lower risk of heat-related
injury and illness, as production of metabolic heat is not
substantially elevated. Experimental studies of groups exposed to heat
(111.4 [deg]F (44 [deg]C), 30% relative humidity) while resting in a
seated position indicate core body temperature does not rise more than
1 [deg]C (1.8 [deg]F) over multiple hours (Kenny et al., 2017; Notley
et al., 2020). In addition to sitting, the exemption allows for indoor
work activities to include occasional standing and walking for brief
periods of time, and occasional lifting of objects weighing less than
10 pounds. When using the term ``occasional'' OSHA means up to one-
third of the workday (BLS, 2021), however these activities could only
be performed for brief periods of time over the course of the day for
the exemption to apply. For example, work activities performed at a
desk indoors, where the employee is seated and performing computer work
for the majority of their shift, but with occasional standing, as well
as walking short distances (e.g., to use the photocopier, to collect
office mail), would be exempt from the standard.
In addition, this exemption would apply to indoor operation of
vehicles while seated. For example, operation of a forklift inside of a
warehouse while seated would be considered an indoor sedentary work
activity and would be exempt. However, if a forklift operator's duties
involved loading and unloading heavy objects (greater than 10 pounds),
they would not be exempt from the standard. Other examples of
activities that would be exempt include indoor operation of reach
trucks, tow trucks, pallet trucks, golf carts, and other vehicles where
employees are seated.
This exemption would apply where employees are engaged in sedentary
work activities regardless of indoor temperature. While employees
performing these activities are likely at lower risk of experiencing
heat-related injury and illness, OSHA seeks comment as to whether the
sedentary work activities exemption should be limited to work
activities performed in indoor environments below a specified threshold
temperature (e.g., the high heat trigger) or whether this exemption
should account for certain workplace conditions. For example, should
this exemption cover an employer with employees who meet the criteria
in this proposed exemption, but whose work area is near a heat
generating process and impacted by radiant heat?
Paragraph (a)(3) specifies that employers whose employees all
exclusively perform activities described in paragraphs (a)(2)(i)
through (vi) are exempt from this standard. Employers may have
employees who would be exempt from the standard (e.g., employees
working indoors where air-conditioning consistently keeps the ambient
temperature below 80 [deg]F), as well as employees who would be covered
by the standard (e.g., employees harvesting produce outdoors). These
employers would be required to comply with the provisions of the
standard for the employees who perform work activities that are covered
by the standard. However, some employers may only have employees that
exclusively perform work activities that are exempt from the proposed
standard. For example, an employer with employees who all either
telework from home or other locations of their choosing or work inside
a building with air-conditioning that consistently keeps the ambient
temperature below 80 [deg]F would be exempt from the standard.
I. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether any of the proposed exclusions of emergency
response activities already covered under the standards listed in
proposed paragraph (a)(2)(iii) should be covered by this proposed
standard. If so, provide evidence and describe reason for why these
activities should not be excluded;
Where an employer relies on the exemption in proposed
paragraph (a)(2)(iv) to exclude work activities performed in indoor
work areas or vehicles where air-conditioning consistently keeps the
ambient temperature below 80 [deg]F, whether the standard should
address situations where the air-conditioning system does not function
properly and the ambient temperature reaches or exceeds 80 [deg]F; for
example, should certain requirements of the standard apply in this
scenario? Additionally, whether the standard should specify how long
the air-conditioning system can be out of order before the exemption no
longer applies;
Whether the description of sedentary work in the proposed
standard is appropriate, and if not, what revisions would be
appropriate;
Whether the standard should exempt all sedentary work
activities indoors or limit the exemption to only activities performed
below an upper limit (e.g., below the high heat trigger) at or above
which the exemption would no longer apply, and if so, what the upper
limit should be and what evidence exists demonstrating that even
sedentary work performed indoors can be a hazard to workers at or above
that limit; and
Whether the exemption for sedentary work activities should
be expanded to include work performed outdoors.
B. Paragraph (b) Definitions
Paragraph (b) defines several terms used in the proposed standard.
First, it defines Acclimatization to mean the body's adaptation to work
in the heat as a person is exposed to heat gradually over time, which
reduces the strain caused by heat stress and enables a person to work
with less chance of heat illness or injury.
Section V.C., Risk Reduction contains more information on
effectiveness of acclimatization. This definition is included because
paragraph (e)(7) of the proposed standard establishes requirements to
protect new and returning employees who are not acclimatized. Proposed
paragraph (e)(7) requires that employers implement one of two
acclimatization protocols for new and returning employees when the
initial heat trigger is met or exceeded. Under paragraph (j), employers
must implement acclimatization protocols at no cost to the employee. In
addition, proposed paragraph (h)(1)(iii) requires that employees be
trained that lack of acclimatization is a risk factor for HRI.
Ambient temperature means the temperature of the air surrounding a
body. Other terms for ambient temperature include ``air temperature''
or ``dry bulb temperature.'' Ambient temperature is measured by a
standard thermometer and often what people refer to when using the term
``temperature.'' Ambient temperature is defined because it is used in
the definitions for heat index and wet bulb globe temperature, in
addition to proposed paragraphs (a) Scope and application, (d)
Identifying heat hazards, (e) Requirements at or above the initial heat
trigger, and (f) Requirements at or above the high heat trigger.
Cooling personal protective equipment (PPE) means equipment that is
worn to protect the user against heat-related injury or illness. This
definition is included to clarify the requirement under proposed
paragraph (e)(1) that if the employer provides employees with cooling
PPE, the cooling properties must be maintained during use.
Cooling PPE is gear designed to help maintain a safe body
temperature for individuals working in hot environments or engaged in
physically demanding activities. Cooling PPE typically employs various
technologies to facilitate heat dissipation and
enhance comfort, such as water absorption crystals or phase change
materials (PCM) which draw heat away from the wearer. Cooling bandanas
and neck wraps are worn around the neck and can be soaked in cold
water. Additionally, other types of clothing may incorporate materials
that have cooling properties.
Heat index means the National Weather Service heat index, which
combines ambient temperature and humidity. It provides a number that
can be used to indicate how hot it feels. There are several tools for
measuring heat index in both indoor and outdoor work areas. For outdoor
work areas, the OSHA-NIOSH Heat Safety Tool app and other phone-based
weather apps can be used to show the heat index by location as well as
hourly forecasts. For indoor work areas, employers can enter
measurements of humidity and ambient temperature into the NOAA Heat
Index Calculator. There are also monitoring devices that report heat
index. Heat index is defined because the term is used in definitions of
high heat trigger and initial heat trigger. The term is also used in
proposed paragraphs (c) Heat injury and illness prevention plan, (d)
Identifying heat hazards, and (e) Requirements at or above the initial
heat trigger.
High heat trigger means a heat index of 90 [deg]F or a wet bulb
globe temperature (WBGT) equal to the NIOSH Recommended Exposure Limit.
See explanations for the definitions of wet bulb globe temperature
(WBGT) and Recommended Exposure Limit (REL) for more information about
those terms. OSHA is including a definition for high heat trigger
because exposures at or above the high heat trigger would require the
implementation of a number of controls, in addition to the controls
that would be implemented under the initial heat trigger in proposed
paragraph (e). The controls implemented under the initial heat trigger
are described below under the definition for Initial Heat Trigger. The
additional controls that would be implemented under the high heat
trigger under proposed paragraph (f) include required rest breaks,
observation for signs and symptoms, hazard alerts, and warning signs
for excessively high heat areas. See Section VII.F., Explanation of
Proposed Requirements for more information on these controls. The
scientific basis supporting the establishment of the high heat trigger
at a heat index of 90 [deg]F or a WBGT equal to the NIOSH REL is
explained in in Section V.B., Basis for Initial and High Heat Triggers.
Indoor/indoors means an area under a ceiling or overhead covering
that restricts airflow and has along its entire perimeter walls, doors,
windows, dividers, or other physical barriers that restrict airflow,
whether open or closed. Possible examples for indoors include work in a
garage, even if the garage door is open; the interior of a warehouse,
even if multiple doors are open on loading docks; and a shed with four
walls and a ceiling, even if the windows are open. Construction
activity is considered to be work in an indoor environment when
performed inside a structure after the outside walls and roof are
erected. This definition is included because the term is used in
definitions for outdoor/outdoors, and proposed paragraphs (a) Scope and
application, (d) Identifying heat hazards, (e) Requirements at or above
the initial heat trigger, (f) Requirements at or above the high heat
trigger, and (i) Recordkeeping.
Initial heat trigger means a heat index of 80 [deg]F or a WBGT
equal to the NIOSH Recommended Alert Limit (RAL). See explanations for
the definitions of wet bulb globe temperature (WBGT) and Recommended
Alert Limit (RAL) for more information about those terms. OSHA is
including a definition for initial heat trigger because exposures at or
above the initial heat trigger would require the implementation of a
number of controls under proposed paragraph (e), including requirements
for drinking water, break area(s) for indoor and outdoor work sites,
indoor work area controls, acclimatization of new and returning
employees, rest breaks if needed to prevent overheating, effective
communication, and maintenance of PPE cooling properties if PPE is
provided. See Section VII.E., Explanation of Proposed Requirements for
more information on these controls. The scientific basis supporting the
establishment of the initial heat trigger at a heat index of 80 [deg]F
or a wet bulb globe temperature (WBGT) equal to the NIOSH RAL is
explained in detail in Section V.B., Basis for Initial and High Heat
Triggers.
Outdoor/outdoors means an area that is not indoors, as defined
above. The definition also specifies that vehicles operated outdoors
are considered outdoor work areas for purposes of this standard unless
exempted by paragraph (a)(2). Examples of outdoor work include tasks
performed in agricultural fields and under canopies and pavilions. This
term is defined because it is used in proposed paragraphs (d)
Identifying heat hazards, (e) Requirements at or above the initial heat
trigger, and (h) Training.
Radiant heat means heat transferred by electromagnetic waves
between surfaces. This definition further notes that sources of radiant
heat include the sun, hot objects, hot liquids, hot surfaces, and fire.
Radiant heat is transferred from a hotter object to a cooler
object. The transfer of radiant heat can occur across distances and
does not require objects to touch each other. Infrared radiation is a
common source of radiant heat that is encountered in foundries, and in
iron, steel, and glass industries (NIOSH, 2016). Sources of exposure to
radiant heat in the workplace can include furnaces, ovens, and
combustion. Radiant heat is defined because it is included in the
definition for wet bulb globe temperature (WBGT) and is used in
paragraph (e) Requirements at or above the initial heat trigger.
Recommended Alert Limit (RAL) means the NIOSH-recommended heat
stress alert limits for unacclimatized workers. OSHA is proposing to
incorporate by reference NIOSH Publication No. 2016-106 Criteria for a
Recommended Standard: Occupational Exposure to Heat and Hot
Environments (NIOSH, 2016). OSHA is including a definition for RAL
because the initial heat trigger incorporates the NIOSH RAL. Thus,
several provisions of the standard are triggered by either a heat index
of 80 [deg]F or a wet bulb globe temperature (WBGT) equal to the NIOSH
RAL. See Explanation of Proposed Requirements for Definitions (initial
heat trigger, wet bulb globe temperature) and proposed paragraph (e),
Requirements at or above the Initial heat trigger for more details.
NIOSH (2016) developed the RAL to protect most healthy non-
acclimatized employees from adverse effects of heat stress and
recommends that total heat exposure for non-acclimatized employees be
controlled to maintain combinations of environmental and metabolic heat
below the applicable RAL in order to maintain thermal equilibrium.
Environmental exposures are based on WBGT, which accounts for the
contributions of ambient temperature, radiant heat, humidity, and wind
speed. Metabolic heat production is estimated by workload. The RAL
assumes employees are wearing ``the conventional one-layer work
clothing ensemble,'' but NIOSH provides guidance for adjusting the WBGT
based on the types of clothing or PPE worn. The formula for calculating
the RAL is: RAL [ [deg]C-WBGT] = 59.9-14.1 log10M[W], where
M is metabolic rate in watts (W).
Recommended Exposure Limit (REL) means the NIOSH-recommended heat
stress exposure limits for acclimatized workers. OSHA is proposing to
incorporate by reference NIOSH Publication No. 2016-106 Criteria for a
Recommended Standard: Occupational Exposure to Heat and Hot
Environments (NIOSH, 2016). OSHA is including a definition for REL
because the high heat trigger incorporates the NIOSH REL. Thus, several
provisions of the standard are triggered by either a heat index of 90
[deg]F or a wet bulb globe temperature (WBGT) equal to the NIOSH REL.
See Explanation of Proposed Requirements for Definitions (high heat
trigger, wet bulb globe temperature) and proposed paragraph (f),
Requirements at or above the high heat trigger for more details.
NIOSH (2016) developed the REL to protect most healthy acclimatized
employees from adverse effects of heat stress and recommends that total
heat exposure for acclimatized employees be controlled to maintain
combinations of environmental and metabolic heat below the applicable
REL in order to maintain thermal equilibrium. Environmental exposures
are based on WBGT, which accounts for the contributions of ambient
temperature, radiant heat, humidity, and wind speed. Metabolic heat
production is estimated by workload. The REL assume employees are
wearing ``the conventional one-layer work clothing ensemble,'' but
NIOSH provides guidance for adjusting WBGT based on the types of
clothing or PPE worn. The formula for calculating the REL is: REL [
[deg]C-WBGT]= 56.7-11.5 log10M[W], where M is metabolic rate
in watts (W).
Shade is defined as the blockage of direct sunlight, such that
objects do not cast a shadow in the area of blocked sunlight. This
definition is included to clarify the requirements for use of shade as
a control in outdoor break areas under proposed paragraph (e)(3)(i).
Shade can be artificial or naturally occurring. See Explanation of
Proposed Requirements for paragraph (e)(3).
Signs and symptoms of heat-related illness means the physiological
manifestations of a heat-related illness and includes headache, nausea,
weakness, dizziness, elevated body temperature, muscle cramps, and
muscle pain or spasms. This term is used throughout the proposal to
refer to a range of signs and symptoms that may result from a variety
of heat-related illnesses (see Section IV., Health Effects for a
detailed discussion of heat-related illnesses and the accompanying
symptoms). This term is defined to provide clarity about scenarios for
which an employer must develop procedures for responding to employees
experiencing signs and symptoms of heat-related illness in their heat
emergency response plan, as well as the scenarios that an employer
would be required to take specific actions to aid affected employees
under proposed paragraph (g). This definition also provides clarity on
the requirements to train employees on signs and symptoms of heat-
related illness (see proposed paragraph (h)(iv)) and monitor employees
for signs and symptoms of heat-related illness (see proposed paragraph
(f)(3).
Signs and symptoms of a heat emergency means the physiological
manifestations of a heat-related illness that require emergency
response and include loss of consciousness (i.e., fainting, collapse)
with excessive body temperature, which may or may not be accompanied by
vertigo, nausea, headache, cerebral dysfunction, or bizarre behavior.
This could also include staggering, vomiting, acting irrationally or
disoriented, having convulsions, and (even after resting) having an
elevated heart rate. This term is defined to provide clarity about
scenarios for which an employer must develop procedures to respond to
employees experiencing signs and symptoms of a heat emergency in their
heat emergency response plan, as well as the scenarios in which an
employer would be required to take specific actions to aid affected
employees under proposed paragraph (g). This definition also provides
clarity on the requirements to train employees on signs and symptoms of
heat-related illness and which ones require immediate emergency action
(see proposed paragraph (h)(iv)).
Vapor-impermeable clothing means full-body clothing that
significantly inhibits or completely prevents sweat produced by the
body from evaporating into the outside air. The definition further
indicates that examples include encapsulating suits, various forms of
chemical resistant suits, and other forms of non-breathable PPE. This
definition is included because under proposed paragraph (c)(3)
employers that have employees who wear vapor-impermeable clothing would
be required to evaluate heat stress hazards resulting from these
clothing and implement policies and procedures based on reputable
sources to protect employees while wearing this clothing. Vapor-
impermeable clothing is also referred to as ``vapor barrier'' clothing.
It is a type of protective clothing that employers may provide to
employees to protect them from chemical, physical, or biological
hazards for work tasks such as hazardous waste clean-up. Examples
include metallic reflective clothing or chemical resistant clothing
made from plastics such as vinyl or nylon-reinforced polyethylene
(Mihal, 1981). Materials made from 100% high density polyethylene
(e.g., Tyvek[supreg]) that allow water vapor and gases to pass through
are not vapor-impermeable, but lamination of the materials with some
substances such as polyvinyl chloride (PVC) can change the
breathability of the materials and render them vapor-impermeable
(DuPont, 2024; Paull and Rosenthal, 1987). Because the proposed
definition indicates ``full-body clothing'', it would not include
vapor-impermeable PPE that covers small areas of the body (e.g.,
gloves, boots, aprons, leggings, gauntlets). However, clothing such as
boots and gloves made from vapor-impermeable materials such as rubber
may be part of whole-body, vapor-impermeable clothing ensembles (Mihal,
1981; Paull and Rosenthal, 1987). Employers could check product
information provided by manufacturers to determine if clothing worn by
their employees qualifies as vapor-impermeable clothing.
Vehicle means a car, truck, van, or other motorized means of
transporting people or goods. Other examples may include a forklift,
reach truck, tow truck, pallet truck, or bus, among others. In
addition, vehicles may also include equipment such as a bulldozer, road
grader, farm tractor, or crane. Under the proposed definitions, a
vehicle would be a work area when a worker's work activities occur in
the vehicle.
Wet Bulb Globe Temperature (WBGT) is a heat metric that takes into
account ambient temperature, humidity, radiant heat from sunlight or
artificial heat sources, and air movement. It can be measured in both
indoor and outdoor work areas, however there are separate formulas
depending on whether the device is being used indoors or outdoors. WBGT
is used by NIOSH and ACGIH in their guidance for evaluating
occupational heat stress. The term is defined because it is used in the
definitions for the high and initial heat triggers and in proposed
paragraphs (c) Heat injury and illness prevention plan and (d)
Identifying heat hazards.
Work area means an area where one or more employees are working
within a work site. This includes any area where an employee performs
any work-related activity. A work area may be located at the employer's
premises or other locations where an employee may be engaged in work-
related activities or is present as a condition of their employment.
Work area is defined because it is referenced in several provisions of
the proposed standard, including (a) Scope and application, (c)
Heat injury and illness prevention plan (HIIPP), (d) Identifying heat
hazards, (e) Requirements at or above the initial heat trigger, (f)
Requirements at or above the high heat trigger, and (i) Recordkeeping.
Work site means a physical location (e.g., fixed, mobile) where the
employer's work or operations are performed. It includes outdoor and
indoor areas, individual structures or groups of structures, and all
areas where work or any work-related activity occurs (e.g., taking
breaks, going to the restroom, eating, entering or exiting work). The
work site includes the entirety of any space associated with the
employer's operations (e.g., workstations, hallways, stairwells,
breakrooms, bathrooms, elevators) and any other space that an employee
might occupy in arriving, working, or leaving. A work site may or may
not be under the employer's control. Work site is defined because it is
referenced in several provisions of the proposed standard including
Heat Injury and Prevention Plan (HIIPP) (proposed paragraph (c)),
Identifying heat hazards (proposed paragraph (d)), Requirements at or
above the initial heat trigger (proposed paragraph (e)), Requirements
at or above the high heat trigger (proposed paragraph (f)), Heat
illness and emergency response and planning (proposed paragraph (g)),
and Training (proposed paragraph (h)).
I. Requests for Comments
OSHA requests comments as to whether the proposed definitions are
appropriate, and whether any additional terms should be defined in the
standard.
C. Paragraph (c) Heat Injury and Illness Prevention Plan
Proposed paragraph (c) includes provisions for the development and
implementation of a work site heat injury and illness prevention plan,
referred to as a ``HIIPP'' or ``plan'' for the remainder of this
section, as well as requirements regarding what would need to be in the
plan. The development of a HIIPP, including comprehensive policies and
procedures, is necessary to ensure that all affected employees,
including exposed workers, supervisors, and heat safety coordinators,
understand where heat hazards exist at the workplace and the workplace-
specific measures that must be utilized to address those hazards. The
NIOSH Criteria Document provides information on the importance of a
HIIPP to reduce the risk of heat-related injuries and illness (NIOSH,
2016). Requiring a HIIPP is also consistent with regulations from
several of the States that have enacted or proposed heat-specific
standards. There is a plan requirement in existing heat standards from
California (Cal. Code of Regs. tit. 8, section 3395 (2005)), Washington
(Wash. Admin. Code sections 296-62-095 through 296-62-09560; 296-307-
097 through 296-307-09760 (2023)); and Oregon (Or. Admin. R. 437-002-
0156 (2022); Or. Admin. R. 437-004-1131 (2022)). Maryland and Nevada
proposed heat standards that would also require a HIIPP (MD, 2024; NV,
2022). Additionally, this requirement aligns with the recommendations
from the NACOSH Heat Injury and Illness Prevention Work Group, where
the group provided a list of potential elements to include in a HIIPP.
All the requirements in paragraph (c) would have to be included in the
employer's HIIPP.
Paragraph (c)(1) would require employers to develop and implement a
comprehensive HIIPP for each work site. Under proposed paragraph (b), a
work site is defined as a physical location (e.g., fixed, mobile) where
the employer's work or operations are performed. If an employer has
multiple work sites that are substantially similar, the HIIPP may be
developed by work site type rather than by individual work sites so
long as any site-specific information is included in the plan (e.g.,
phone numbers and addresses or site-specific heat sources). For
example, if an employer has developed a corporate HIIPP that includes
information about job tasks or exposure scenarios that apply at
multiple work sites, this information can be used in the development of
HIIPPs for individual work sites. When employees are in work areas not
controlled by the employer (like private residences), employers would
need procedures for how they will ensure compliance with the standard
(e.g., ensure that effective communication is being maintained
(proposed paragraph (f)(3)(iii)) and employees are receiving hazard
alerts to remind them of protections such as the importance of drinking
plenty of water, their right to take breaks, and locations of break
sites and drinking water (proposed paragraph (f)(4)). These employers
must include such policies and procedures in their HIIPP to protect
their employees entering those locations not controlled by the
employer.
Proposed paragraph (c)(2) specifies the contents of the HIIPP.
Proposed paragraph (c)(2)(i) would require the HIIPP to include a
comprehensive list of the types of work activities covered by the plan.
For example, a landscaping company could indicate that all employees
conducting outdoor work at or above the initial heat trigger for at
least 15 minutes in any 60-minute period (e.g., lawn care workers,
gardeners, stonemasons, and general laborers) would be covered by the
HIIPP. (See proposed paragraphs (a)(2)(i), (ii), and (iv) and
Explanation for Proposed Requirements for Paragraph (a) Scope and
Application for more detail about coverage under the standard.)
Paragraph (c)(2)(ii) would require the inclusion of the policies and
procedures that are necessary to comply with the requirements of this
proposed standard. See Explanation of Proposed Requirements for
paragraphs (d) through (j) for examples of how employers could comply
with the proposed provisions. OSHA understands that a HIIPP must be
adaptable to the physical characteristics of the work site and the job
tasks performed by employees, as well as the hazards identified by the
employer when designing their HIIPP. Employers could also include other
policies, procedures, or information necessary to comply with any
applicable Federal, State, or local laws, standards, and guidelines in
their HIIPPs. Paragraph (c)(2)(iii) would require that employers
identify the heat metric (i.e., heat index or wet bulb globe
temperature) that the employer will monitor to comply with paragraph
(d). For more information on heat metrics, see Explanation for Proposed
Requirements for Paragraph (b) Definitions for heat index and WBGT.
Paragraph (c)(3) would require that, in cases where employees wear
vapor-impermeable clothing (also called vapor barrier clothing),
employers must evaluate heat stress hazards resulting from this
clothing and implement policies and procedures based on reputable
sources to protect employees while wearing these clothing. The employer
must include these policies and procedures and document the evaluation
in the HIIPP. Under proposed paragraph (b), vapor-impermeable clothing
is defined as full-body clothing that significantly inhibits or
completely prevents sweat produced by the body from evaporating into
the outside air. The definition further indicates that examples include
encapsulating suits, various forms of chemical resistant suits, and
other forms of non-breathable PPE. For more information on vapor-
impermeable clothing, see the Explanation for Proposed Requirements for
paragraph (b) Definitions. This attention to vapor-impermeable clothing
is essential given that significant or complete inhibition of sweat
evaporation can greatly increase the potential for heat stress and
resulting heat strain and HRI (Mihal, 1981).
The requirement that employers evaluate heat stress and develop
policies and procedures to protect employees based on reputable sources
allows for flexibility, given that there is variability in duration of
use of the vapor-impermeable clothing and that workload also varies
across job tasks and occupations. Examples of reputable sources
employers can consult to assess heat stress and develop policies and
procedures to protect employees wearing vapor-impermeable clothing
include recommendations by NIOSH (2016) and ACGIH (2023). An example of
a policy employers might adopt to protect employees wearing vapor-
impermeable clothing is implementing the protections in the standard at
a lower temperature threshold. Such an approach has been used in State
standards such as the Washington heat standard for outdoor workplaces
(Wash. Admin. Code 296-307-09747 (2023)). In Washington State's heat
standard, employers must implement certain controls when employees are
wearing vapor barrier clothing, and the temperature is above 52 [deg]F.
Paragraph (c)(3) does not apply to vapor-permeable clothing or PPE such
as cotton coveralls, SMS polypropylene or polyolefin coveralls, double
layer woven clothing, or wool shirts (ACGIH, 2023; ACGIH, 2017; NIOSH,
2016).
Paragraph (c)(3) would require the employer to document in the
HIIPP the hazard evaluation performed to comply with this provision and
to include in the HIIPP the policies and procedures developed to
protect employee's wearing vapor-impermeable clothing. Although OSHA is
not specifying a particular form for the required hazard evaluation, an
effective hazard evaluation would include a review of environmental
heat exposures, a review of the high-risk area(s), tasks, and
occupations, and an evaluation of the length of time and intensity of
task when wearing vapor-impermeable clothing. Policies and procedures
should include communication of the status of planned or completed
actions to employees who may have to wear vapor-impermeable clothing to
complete work tasks. For more information on identifying heat hazards,
see Explanation of Proposed Requirements for paragraph (d) below.
Under proposed paragraph (c)(4), an employer with more than 10
employees would be required to develop and implement a written HIIPP.
While OSHA has concluded that a HIIPP is necessary for all employers
covered by the standard, OSHA has determined that only employers with
more than 10 employees need to have a written plan. This cutoff of 10
employees is consistent with OSHA's practice of allowing employers with
10 or fewer employees to communicate their emergency action plans (29
CFR 1910.38) and fire prevention plans (29 CFR 1910.39) orally to
employees. OSHA expects that small employers with 10 or fewer employees
are likely to have less complicated HIIPPs and will communicate with
employees verbally. The agency does not believe that there is a high
likelihood of misunderstanding when employers communicate their HIIPPs
to employees verbally. As a result, OSHA does not believe the added
burden on small employers of establishing a written plan is necessary.
However, small employers may opt to create a written HIIPP if they find
doing so is helpful in developing and implementing their plans.
In contrast, the agency is concerned that when employers have more
than 10 employees, there is likely sufficient complexity in the
employer's operation that putting the HIIPP in writing is necessary to
establish clear expectations and prevent miscommunication. For example,
employers with more than 10 employees may have employees working in
multiple locations or on multiple shifts, increasing the likelihood
that verbally communicating the employer's HIIPP will be ineffective.
Therefore, OSHA preliminarily finds that having a written HIIPP that
employees of larger employers can easily access is essential to ensure
those employees are informed about policies, programs, and protections
implemented by their employers to protect them from hazardous heat
exposure.
An employer may have already developed and implemented a HIIPP.
Existing plans may fulfill some of the requirements in this section. It
is not OSHA's intent for employers to duplicate current effective
HIIPPs, but each employer with a current HIIPP would have to evaluate
that plan for completeness to ensure it satisfies all the requirements
of this section. Employers with existing plans would be required to
modify and/or update their current HIIPP plans to incorporate any
missing required elements and provide training on these new updates or
modifications to all employees (see the Explanation of Proposed
Requirements for Paragraph (h) Training). Employers with more than 10
employees would have to ensure their existing HIIPP is in writing.
Paragraph (c)(5) would require the employer to designate one or
more workplace heat safety coordinators to implement and monitor the
HIIPP. Any employee(s) capable of performing the role who receives the
training required by proposed paragraphs (h)(1) and (2) can be
designated heat safety coordinator(s). This employee(s) does not need
to be someone with specialized training. The heat safety coordinator(s)
could be a supervisor or an employee that the employer designates. The
heat safety coordinator(s) must have the authority to ensure compliance
with all aspects of the HIIPP. This requirement would ensure heat
safety coordinators can take prompt corrective measures when hazards
are identified. Proposed paragraph (c)(5) would also require that for
employers with more than 10 employees, the identity of the heat safety
coordinator(s) must be documented in the written HIIPP. Employers must
designate a heat safety coordinator(s) to implement and monitor the
HIIPP plan, but the exact responsibilities of a heat safety
coordinator(s) may vary based on the employer and work site. Some
possible duties of the heat safety coordinator(s) could include
conducting regular inspections of the work site to ensure the HIIPP is
being implemented appropriately and to monitor the ongoing
effectiveness of the plan. During such inspections, the heat safety
coordinator(s) could observe employees to ensure they are protecting
themselves by frequently drinking water or taking rest breaks that
employers would be required to provide.
Under proposed paragraph (c)(6), the employer would be required to
seek the input and involvement of non-managerial employees and their
representatives, if any, in the development and implementation of the
HIIPP. An employer could seek feedback from employees through a variety
of means, including safety meetings, a safety committee, conversations
between a supervisor and non-managerial employees, a process negotiated
with the exclusive bargaining agent (if any), or any other similarly
interactive process. The method of soliciting employee input is
flexible and may vary based on the employer and the work site. For
example, a large employer with many employees may find a safety
committee with representatives from various job categories combined
with anonymous suggestion boxes to be more effective than individual
conversations between supervisors and non-managerial employees. In the
case of a unionized workplace, a safety committee established through a
collective bargaining agreement may be the appropriate source for this
input,
based on the definition and scope of the committee's work. In contrast,
a small employer might determine that an ongoing interactive process
between the employer and employees (e.g., regular safety meetings) is a
more effective means of soliciting employee feedback. OSHA understands
employees often know the most about potential hazards associated with
their jobs. As such, employee participation is a key component of
effective safety and health programs.
Paragraph (c)(7) would require the employer to review and evaluate
the effectiveness of the HIIPP whenever a heat-related injury or
illness occurs that results in death, days away from work, medical
treatment beyond first aid, or loss of consciousness, but at least
annually. Following each review, the employer would be required to
update the HIIPP as necessary. The employer would have to seek input
and involvement of non-managerial employees and their representatives,
if any, during any reviews and updates. OSHA preliminarily finds that a
heat-related illness or injury that results in death, days away from
work, medical treatment beyond first aid, or loss of consciousness
warrants an evaluation of the HIIPP because it could potentially
indicate a deficiency of the HIIPP. Additionally, the heat safety
coordinator might learn of a deficiency during an inspection or from
another employee. OSHA expects that employers would immediately address
any identified deficiencies and update the HIIPP accordingly. Under
proposed paragraph (h)(4)(iv), all employees would have to be retrained
following a heat-related injury or illness that results in death, days
away from work, medical treatment beyond first aid, or loss of
consciousness, and under proposed paragraph (h)(4)(ii) employees would
have to be retrained if identification of a deficiency results in an
update to the HIIPP. OSHA preliminarily finds that effective heat
injury and illness prevention plans would require periodic evaluation
to ensure they are implemented as intended and continue to achieve the
goal of preventing heat injury and illness and promoting workplace
safety and health. This re-evaluation can result in improvements in
controls to help reduce hazards.
Paragraph (c)(8) would require the employer to make the HIIPP
readily available at the work site to all employees performing work at
the work site. The HIIPP would have to be readily accessible during
each work shift to employees when they are in their work area(s). Paper
copies, electronic access (i.e., accessible via smart phone) and other
alternatives to maintaining paper copies of the HIIPP are permitted as
long as no barriers to immediate employee access in each work site are
created by such options.
Paragraph (c)(9) would require the employer to ensure the HIIPP is
available in a language each employee, supervisor, and heat safety
coordinator understands. Under proposed paragraph (c)(4), this would
require written translations of the plan in all languages that
employees, supervisors, and heat safety coordinators understand.
Employers could comply with this requirement by utilizing one of the
numerous translator programs available online if the employer has a way
to ensure accuracy of the translated materials. In cases where an
employee, supervisor, or heat safety coordinator can read and
comprehend English, but prefers to read in another language, the
employer would have no obligation to provide a written translation of
the plan in that individual's preferred language. If one or more
employees are not literate, the employer would have to ensure that
someone is available to read the written plan in a language that each
employee understands. Likewise, for employers who have less than 10
employees, the employer would have to ensure that someone is available
to explain the plan in a language that each employee, supervisor, and
heat safety coordinator understands. OSHA expects that an individual
who speaks employees' languages will be available in all workplaces
since effective communication between individuals such as employers,
supervisors, and employees would need to occur in order for employees
to understand the details about the work tasks they need to complete.
I. Requests for Comments
OSHA requests comments and evidence regarding the following:
The approaches that stakeholders are taking to assess heat
stress and prevent HRI in employees wearing vapor-impermeable clothing;
Whether OSHA should specify a temperature that would
trigger all or certain requirements of the standard for employees
wearing vapor-impermeable clothing;
Additional approaches that OSHA should consider to protect
employees wearing vapor-impermeable clothing;
Whether the proposed requirement to seek input and
involvement from non-managerial employees and their representatives
under paragraph (c)(6) is adequate, or whether the explanation should
be expanded or otherwise amended (and if so, how and why);
Whether OSHA should define ``employee representative''
and, if so, whether the agency should specify that non-union employees
can designate a non-employee third-party (e.g., a safety and health
specialist, a worker advocacy group, or a community organization) to
provide expertise and input on their behalf;
Whether it is reasonable to require the HIIPP be made
available in a language that each employee, supervisor, and heat and
safety coordinator understands;
What methods and programs are available to provide
employees documents and information in multiple languages, whether
there are languages for which these resources are not available, and
how employers can provide adequate quality control to ensure that the
translations are done properly; and
Whether individuals are available at workplaces to provide
verbal translations of the plan for employees who are not literate or
do not speak English.
D. Paragraph (d) Identifying Heat Hazards
Proposed paragraph (d) sets forth requirements for assessing where
and when employees are exposed to heat at or above the initial and high
heat triggers. It would require employers with outdoor work sites to
monitor heat conditions at outdoor work areas by tracking local heat
index forecasts or measuring the heat metric of their choosing (heat
index or wet bulb globe temperature (WBGT)). It would require employers
with indoor work sites to identify work areas where there is a
reasonable expectation that employees are or may be exposed to heat at
or above the initial heat trigger and implement a plan for monitoring
these areas to determine when exposures above the initial and high heat
triggers occur, using the heat metric of their choosing (heat index or
WBGT). Determining when employees are exposed to heat at or above the
initial and high heat triggers is critical for ensuring that employees
are provided with appropriate protections (outlined in paragraphs (e)
and (f)).
Proposed paragraph (d)(1) would require employers whose employees
perform work outdoors to monitor the heat conditions at the work areas
where employees are working. Employers would have two options for
complying with this requirement--tracking local heat index forecasts
provided by National Weather Service (NWS) or other reputable sources
or making on-
site measurements using monitoring device(s).
Employers who choose to track local forecasts would need to consult
a reputable source for local heat index forecasts such as their local
NWS Weather Forecast Office, the OSHA-NIOSH Heat Safety Tool cell phone
application, or another weather forecast website or cell phone
application. When using these sources, employers would need to
accurately enter the location of the work area. The OSHA-NIOSH Heat
Safety Tool (and other cell phone applications) will automatically use
GPS to determine the user's location, so the forecast may be inaccurate
if using the tool at home and employers will need to manually enter the
work area location in these situations.
Employers who choose to conduct on-site monitoring would need to
set up monitoring devices at or as close as possible to the work area.
This could mean setting up the device(s) on a tripod a few yards away
from an employee. When there are multiple work areas at the same work
site, the employer could use a single monitoring device to measure heat
exposure for multiple work areas if there is no reasonable anticipation
that the heat exposure will differ between work areas. For example, if
employees are harvesting crops on different fields but are within a
mile of one another under similar work conditions, the employer could
use a single monitoring device. If there is reasonable anticipation
that employees at a work site have different levels of exposure,
employers could measure the exposure at the work area of the
employee(s) reasonably expected to have the highest exposure and apply
that value to all employees at the work site instead of measuring the
exposure for each work area.
Employers using heat index as their heat metric could either use
heat index monitors or measure temperature and humidity with separate
devices. In the latter situation, these employers would need to use a
heat index calculator, such as the one provided on the NWS website
(NWS, 2023), to calculate heat index from the separate temperature and
humidity readings. Employers using WBGT as their heat metric would need
to take into account differences in solar radiation and wind between
work areas when deciding whether a single measurement could be used for
multiple work areas. For example, measurements of WBGT in a work area
in the shade should not be applied to another work area that is not in
the shade. Regardless of which metric they choose to use, employers
conducting on-site monitoring should consult user manuals and ensure
devices are calibrated and in working order. Employers should follow
the device manufacturer's manual when conducting monitoring.
Proposed paragraph (d)(2) would require employers whose employees
perform work outdoors to consult the weather forecast or their
monitoring device(s)--whichever they are using to comply with paragraph
(d)(1)--frequently enough to determine with reasonable accuracy when
conditions at the work area reach the initial and high heat triggers.
Employers consulting forecasts would need to check the forecast as
close to the start of the work shift as possible to determine whether
and when the heat index at the work area may be at or above the initial
or high heat triggers. Depending on the forecast or conditions at the
work site, the employer then may or may not need to conduct further
monitoring during the day. If, for example, the employer consulted the
OSHA-NIOSH Heat Safety Tool before the work shift and it indicated that
the heat index would exceed the initial heat trigger but not the high
heat trigger during the last four hours of the work shift, the employer
would need to either: (1) implement control measures in accordance with
paragraph (e) for those four hours, or (2) consult the Heat Safety Tool
again later in the day and implement control measures in accordance
with paragraph (e) only for the hours during which real-time conditions
reported by the application exceed the initial heat trigger (which may
be more or less than four hours if the forecast earlier in the day
underestimated or overestimated the heat index). However, if the
employer consulted the OSHA-NIOSH Heat Safety Tool before the work
shift and it indicated that the heat index would be close to the
initial heat trigger but not exceed it, employers would need to check
the forecast again later in the day to determine whether the trigger
was exceeded. Employers would need to use short-term forecasts (i.e.,
hourly) rather than long-term forecasts (e.g., weekly, monthly) to
comply with proposed paragraphs (d)(1) and (2). Ultimately, the
employer is responsible for ensuring that the controls required at the
initial and high heat trigger are in place when those triggers are met,
and they should make decisions regarding the frequency of monitoring
with this in mind.
Likewise, employers who conduct on-site monitoring in order to
comply with paragraph (d)(1) will need to develop a reasonable
measurement strategy that is adapted to the expected conditions. If
forecasts provide no suggestion that the initial heat trigger could be
reached during the work shift, an employer may not need to take any
measurements. Where temperatures are expected to approach the initial
or high heat triggers, several measurements may be necessary,
particularly as the hottest part of the day approaches. For example, if
the employer measures at 10 a.m. and the heat index is very close but
below the initial heat trigger, the employer would likely need to
either check again sometime shortly thereafter or assume that the
trigger is exceeded. WBGT accounts for additional parameters--air speed
and radiant heat--so employers using WBGT may need to make additional
measurements when these conditions change at the work site.
Proposed paragraphs (d)(3)(i) and (ii) outline the requirements for
assessing heat hazards in indoor work sites, which differ slightly from
the requirements for outdoor work sites, in that employers would need
to identify the work areas where they reasonably expect employees to be
exposed to heat at or above the initial heat trigger and then create a
monitoring plan to determine when employees in those work areas are
exposed to heat at or above the initial and high heat triggers.
Employers could determine which work areas are expected to have
employee exposure at or above the initial heat trigger by consulting
various data sources, such as previously collected monitoring data,
site or process surveys, employee interviews and input, and heat injury
and illness surveillance data. Work areas near heat-generating
machinery are one example of where there may be a reasonable
expectation of employee exposure at or above the initial heat trigger.
In addition to heat-generating equipment, employers must determine
whether there is a reasonable expectation that an increase in the
outdoor temperature would increase temperatures in their indoor work
site, thereby exposing employees to heat at or above the initial heat
trigger.
Employers would be required to develop a monitoring plan that
covers each work area they identified in the prior step. The monitoring
plan is intended to determine when employees are exposed (e.g.,
specific times of day, during certain processes, certain months of the
year) to heat at or above the initial and high heat triggers for each
work area. When developing a monitoring plan(s), employers would need
to take into account the circumstances that could impact heat
conditions specific to each work area and work site. The monitoring
plan(s) would need to be included in the employer's HIIPP.
In complying with proposed paragraph (d)(3)(ii), employers would
need to outline in their monitoring plan how they will monitor either
heat index or WBGT using on-site monitors that are set up at or as
close as possible to the work area(s) identified under paragraph
(d)(3)(i). OSHA intends the phrase ``as close as possible'' to mean the
closest possible location that won't otherwise create inaccurate
measurements. The employer should ensure that their monitoring plan
outlines the appropriate frequency of measurements, which should be of
sufficient frequency to determine with reasonable accuracy employees'
exposure to heat. For example, if the employer determines there is only
a reasonable expectation that employees are or may be exposed to heat
at or above the initial heat trigger when a certain process is
happening or during certain times of the year, then they would only
need to monitor when that process is happening or during that time of
the year.
Employers using heat index as their heat metric could either use
heat index monitors or measure temperature and humidity with separate
devices. In the latter situation, these employers would need to use a
heat index calculator, such as the one provided on the NWS website
(NWS, 2023), to calculate heat index from the separate temperature and
humidity readings. Employers using WBGT as their heat metric would need
to take into account differences in radiant heat and air movement
between work areas when deciding whether a single measurement can be
used for multiple work areas. For example, measurements of WBGT in a
work area without a radiant heat source should not be applied to
another work area that is near a radiant heat source. Regardless of
which metric they choose to use, employers should consult user manuals
and ensure devices are calibrated and in working order. Employers
should follow the device manufacturer's manual when conducting
monitoring.
If there are multiple work areas where there is a reasonable
expectation that employees are or may be exposed to heat at or above
the initial heat trigger at a work site, the employer could conduct
representative sampling instead of taking measurements at each
individual work area. If using this approach, the employer would be
required to sample the work area(s) expected to be the hottest. For
example, this may involve monitoring the work area closest to a heat-
generating process. The employer cannot put a monitoring device in a
work area known or expected to be cooler and consider that
representative of other work areas.
If any changes occur that could increase employee exposure to heat
(i.e., a change in production, processes, equipment, controls, or a
substantial increase in outdoor temperature which has the potential to
increase heat exposure indoors), proposed paragraph (d)(3)(iii) would
require that the employer must evaluate any affected work area(s) to
identify where there is reasonable expectation that employees are or
may be exposed to heat at or above the initial heat trigger. Examples
of changes that could increase employee exposure to heat include the
installation of new equipment that generates heat in a work area that
didn't previously have heat-generating equipment or a local heat wave
that increases the heat index in a warehouse without air-conditioning.
The employer would be required to update their monitoring plan or
develop and implement a monitoring plan, in accordance with paragraph
(d)(3)(ii), to account for any increases in heat exposure.
Proposed paragraph (d)(3)(iv) would require employers to involve
non-managerial employees (and their representatives, if applicable) in
the determination of which work areas have a reasonable expectation of
exposing employees to heat at or above the initial heat trigger (which
is described in paragraph (d)(3)(i)). Employers would also be required
to involve non-managerial employees (and their representatives, if
applicable) in developing and updating the monitoring plan(s) outlined
in paragraph (d)(3)(ii) through (iii). One example of this involvement
would be employees providing input in identifying processes or
equipment that give off heat and times of the day or year when certain
areas of the building feel uncomfortably hot and warrant monitoring.
Employees are often the most knowledgeable about the conditions in
which they work and their involvement will help ensure the accuracy and
sufficiency of the employer's monitoring plan(s).
Proposed paragraph (d)(4) specifies that the heat metric (i.e.,
heat index or WBGT) that the employer chooses to monitor determines the
applicable initial and high heat triggers under the standard.
Specifically, as defined in paragraph (b), if the employer chooses to
monitor heat index, they would be required to use the initial heat
trigger of 80 [deg]F (heat index) and the high heat trigger of 90
[deg]F (heat index). If the employer chooses to use WBGT, they would be
required to use the NIOSH Recommended Alert Limit (RAL) as the initial
heat trigger and the NIOSH Recommended Exposure Limit (REL) as the high
heat trigger. As outlined in paragraph (c), the employer would be
required to identify which heat metric they are monitoring in their
HIIPP. If they do not do this, proposed paragraph (d)(4) specifies that
the initial and high heat trigger will be based on the heat index.
Proposed paragraph (d)(5) would provide an exemption from
monitoring requirements for employers who choose to assume that their
employees are exposed to heat at or above both the initial and high
heat triggers. In these cases, employers would not need to conduct
monitoring, but they would be required to provide all controls outlined
in paragraphs (e) and (f) while making this assumption. For the period
of time that employers choose to make this assumption and are therefore
exempt from monitoring requirements, they would not be required to keep
records of monitoring data (see paragraph (i), Recordkeeping).
I. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether the proposed requirement to monitor outdoor work
areas with ``sufficient frequency to determine with reasonable accuracy
employees' exposure to heat'' is adequate or whether the standard
should specify an interval of monitoring (and if so, what frequency and
why);
Whether OSHA should specify an interval of monitoring for
indoor work areas (and if so, what frequency and why);
Whether the standard should include a specific increase in
outdoor temperature that would trigger the requirements in paragraph
(d)(3)(iii) for indoor work areas, rather than the trigger being a
``substantial increase'', and if so, what magnitude of increase;
Whether there could be situations in which a lack of
cellular service prevents an employer from using weather forecasts or
real-time predictions, and if so, what alternatives would be
appropriate;
Whether the standard should require specifications related
to monitoring devices (e.g., in accordance with user manuals, properly
calibrated) and whether the standard should specify a permissible
accuracy level for monitoring devices; and
Whether the standard should further specify which sources
of forecast data employers can use to comply with paragraph (d)(1)(i)
and if so, what criteria should be used.
E. Paragraph (e) Requirements at or Above the Initial Heat Trigger
I. Timing
Paragraph (e) of the proposed standard would establish requirements
when employees are exposed to heat at or above the initial heat
trigger. As discussed in Section V.B., Basis for Initial and High Heat
Triggers, OSHA has preliminarily determined that the experimental and
observational evidence support that heat index triggers of 80 [deg]F
and 90 [deg]F are highly sensitive and therefore highly protective of
employees. Exposures at or above the initial heat trigger, a heat index
of 80 [deg]F or a corresponding wet bulb globe temperature equal to the
NIOSH Recommended Alert Limit, would require the employer to provide
the protections outlined in paragraphs (e)(2) through (10).
The employer would only be required to provide the specified
protections during the time period when employees are exposed to heat
at or above the initial heat trigger. In many cases, employees may only
be exposed at or above the initial heat trigger for part of their work
shift. For example, employees who work outdoors may begin work at 9
a.m. and finish work at 5 p.m. If their exposure is below the initial
heat trigger from 9 a.m. until 12 p.m., and at or above the initial
heat trigger from 12 p.m. to 5 p.m., the employer would only be
required to provide the protections specified in this paragraph from 12
p.m. to 5 p.m. Additional protective measures, outlined in paragraph
(f) Requirements at or above the high heat trigger, would be required
when employees are exposed to heat at or above the high heat trigger.
II. Drinking Water
Paragraph (e)(2) of the proposed standard would establish
requirements for drinking water when employees are exposed to heat at
or above the initial trigger. The proposed requirements of paragraph
(e)(2) are in addition to the requirements in existing OSHA sanitation
standards applicable to the employer, including the general industry
sanitation standard (29 CFR 1910.141); construction industry sanitation
standard (29 CFR 1926.51); field sanitation standard (29 CFR 1928.110);
shipyard employment sanitation standard (29 CFR 1915.88); marine
terminals sanitation standard (29 CFR 1917.127); and temporary labor
camp standard (29 CFR 1910.142). In addition to requirements for
drinking water, these standards require access to toilet facilities,
which is important to ensure that employees are not discouraged from
drinking adequate amounts of drinking water. As discussed in Risk
Reduction, Section V.C., drinking water has been shown to be an
effective intervention for preventing dehydration, heat strain, and
HRI. It allows employees to replace fluids lost by sweat and is
necessary to maintain blood volume for cardiovascular function and
thermoregulation.
Proposed paragraph (e)(2)(i) would require that employers provide
access to potable water that is placed in locations readily accessible
to employees. To ensure employees have sufficient drinking water
whenever needed, the drinking water should be located as close as
possible to employees, to facilitate rapid access. Employers could
comply with this provision by providing water coolers or food grade
jugs on vehicles if drinking water fountains or taps are not nearby, or
by providing bottled water or refillable water bottles so that
employees always have access to water. Employers supplying water
through a common source such as a tap or jug would have to provide a
means for employees to drink the water. This could include providing
disposable cups or single-user refillable water bottles. Under OSHA's
sanitation standards, common drinking cups or other shared utensils are
prohibited. Open containers such as barrels, pails, or tanks for
drinking water from which water must be dipped or poured, whether or
not they are fitted with a cover, are also prohibited under these
standards. In cases where employers provide single-user, refillable
water bottles, they should keep extra bottles or disposable cups on
hand in case employees misplace or forget to bring the bottle the
employer provided them.
OSHA notes that water would not be readily accessible if it is in a
location inaccessible to employees (e.g., the drinking water fountain
is inside a locked building or trailer). Water would also not be
readily accessible if it is placed at a distant or inconvenient
location in relation to where employees work. OSHA expects that
employers will have incentive to place the drinking water as close to
employees as feasible to minimize the amount of time needed to access
water, which must be paid. Explanation of Proposed Requirements for
paragraph (j) Requirements implemented at no cost to employees).
Proposed paragraph (e)(2)(ii) would require that employers provide
access to potable water that is suitably cool. As discussed in Risk
Reduction, Section V.C., the temperature of drinking water impacts
hydration levels, as cool or cold water has been found to be more
palatable than warm water, thus leading to higher consumption of cool
water and decreased risk of dehydration. Additional evidence
highlighted in Risk Reduction, Section V.C., shows that cool fluid
ingestion has beneficial effects for reducing heat strain. The
requirement that drinking water be ``suitably cool'' is consistent with
OSHA's existing field sanitation standard (29 CFR 1928.110(c)(1)(ii))
and with California's heat standard for outdoor workplaces (Cal. Code
Regs. tit. 8, section 3395). OSHA has previously stated that to be
suitably cool, the temperature of the water ``must be low enough to
encourage employees to drink it and to cool the core body temperature''
(Field Sanitation, 52 FR 16050, 16087 (May 1, 1987)). Employers could
comply with this provision by providing drinking water from a tap or
fountain that maintains a cooler temperature, providing water in
coolers or by providing ice or ice packs to keep drinks cool.
In addition to providing palatable and potable water, the NACOSH
Heat Injury and Illness Prevention Work Group recommended that
employers consider providing electrolyte supplemental packets that can
be added to water or electrolyte-containing sports drinks (NACOSH
Working Group on Heat, 2023). While employers could choose to offer
electrolyte supplements or electrolyte-containing sports drinks, they
would not be required under the standard. Providing electrolyte
supplements or sports drinks alone would not meet the proposed
requirement. OSHA has preliminarily determined that electrolyte
supplementation may not be necessary in a majority of situations if
workers are consuming adequate and regular meals (NIOSH, 2017a). OSHA
has also received feedback from stakeholders that some workers may be
unable to consume certain electrolyte supplements or solutions due to
their sugar content.
Proposed paragraph (e)(2)(iii) would require that employers provide
access to one quart of drinking water per employee per hour. Employers
could comply with this provision by providing access to a drinking
water tap or fountain that has a continuous supply of drinking water,
or providing coolers or jugs that are replenished with water as the
quantity diminishes. As discussed in more detail in Section V.C., Risk
Reduction, that volume of water intake ensures adequate replenishment
of fluids lost through sweat to avoid a substantial loss in total body
water content for employees working in the
heat. OSHA is specifying the amount of water that employers need to
provide to employees, not an amount that employees need to drink.
However, as discussed in the Explanation of Proposed Requirements for
paragraphs (f)(3) and (h), the employer must inform employees of the
importance of drinking water to prevent HRIs during initial training,
annual refresher training, and whenever the high heat trigger is met.
Finally, in accordance with paragraph (j) of the proposed standard,
all drinking water requirements must be implemented at no cost to
employees. Accordingly, employers may not charge employees for the
drinking water required by paragraph (e)(2) nor for the equipment or
supplies needed to access it.
A. Requests for Comments
OSHA requests comments and information on the following:
Whether OSHA should require a specific temperature or
ranges of temperature for drinking water as some State regulations do
(e.g., Colorado requires that drinking water is kept 60 [deg]F or
cooler);
Whether the agency should require the provision of
electrolyte supplements/solutions in addition to water;
Whether the requirement to provide a minimum of 1 quart
per hour per employee is appropriate; and
Whether there are any challenges to providing the required
amount of drinking water (e.g., for employees who work on foot in
remote areas) and, if so, alternatives that OSHA should consider.
III. Break Area(s) at Outdoor Work Sites
Paragraph (e)(3) contains the proposed requirements for outdoor
break areas when temperatures meet or exceed the initial heat trigger.
Adequate break areas where employees can hydrate, remove PPE, and cool
down is considered a vital component in preventing HRIs and necessary
part of a multilayered strategy to control exposure to high heat. The
requirements for both outdoor and indoor break areas in this proposed
standard are in addition to employers' obligations under OSHA's
sanitation standards (29 CFR 1910.141, 1915.88, 1917.127, 1918.95,
1926.51, 1928.110). Because the sanitation standards address workplace
hazards other than heat exposure, employers must continue to comply
with their obligations under those standards. OSHA highlights these
sanitations standards because employees are likely to eat and drink
water in the indoor break areas, which may implicate certain provisions
of these standards.
Specifically, proposed paragraph (e)(3) requires employers to
provide one or more employee break areas at outdoor work sites that can
accommodate the number of employees on break, is readily accessible to
the work area(s) and has either shade (paragraph (e)(3)(i)), or air-
conditioning if in an enclosed space (paragraph (e)(3)(ii))). As
explained more in detail in Section V.C., Risk Reduction, shade reduces
exposure to radiant heat which can contribute to heat stress and lead
to heat strain and HRI. Further, air-conditioning is effective in
reducing heat stress and resulting heat strain because it reduces
exposure to heat. Accordingly, OSHA has preliminarily determined that
requirements for break areas, including the use of controls to
facilitate cooling while employees are on break, are effective at
preventing HRIs among workers and should be included in the proposed
standard. This determination is supported by NIOSH's criteria for a
recommended standard, several State standards, and existing guidance
(Cal. Code Regs. tit. 8, section 3395 (2024); 7 Colo. Code Regs.
section 1103-15:3 (2023); Or. Admin. R. 437-002-0156 (2024); Or. Admin.
R. 437-004-1131 (2024); Wash. Admin. Code 296-307-09747 (2023); NIOSH,
2016).
Proposed paragraph (e)(3) would require the employer to ensure the
break area(s) can accommodate all employees on break. This provision is
intended to ensure that all employees taking rest breaks that employers
would need to provide under proposed paragraphs (e)(8) and (f)(2) are
able to do so in an appropriate break area(s). If the break area cannot
accommodate the number of employees on break, some employees may not
have access to adequate cooling controls while on break, increasing
their risk of HRIs. In addition, adequate space allows for ventilation
and airflow, contributing to a more effective cooling.
While OSHA is not proposing a minimum square footage requirement
per employee, break areas that can only fit the anticipated number of
employees on break if employees stand shoulder to shoulder, or in such
close proximity that heat cannot dissipate, would not be large enough
to accommodate the number of employees on break. Break areas that are
not large enough to allow employees to move in and out freely or access
necessary amenities, such as water and air-conditioning or shade, would
also not be considered large enough to accommodate the number of
employees on break.
Proposed paragraph (e)(3) does not require that the break area(s)
be able to accommodate an employer's entire workforce at the same time.
However, the employer must evaluate the needs of the work site and
ensure the break area(s) is large enough to accommodate all employees
reasonably expected to be on break at the same time. When making this
determination, employers would need to consider factors such as how
many employees are reasonably expected to be taking breaks to prevent
overheating under proposed paragraph (e)(8) at any given time, as well
as the breaks required under proposed paragraph (f)(2) (e.g., are
paragraph (f)(2) breaks staggered or will large groups of employees be
taking them at the same time?). However, the minimum frequency and
duration of breaks under paragraph (f)(2) must be met.
Similarly, where an employer has multiple break areas on-site, OSHA
does not expect each of these multiple break areas to be able to
accommodate an employer's entire workforce. Instead, OSHA expects that
employers who utilize multiple break areas will determine the number of
employees anticipated to access each break area and ensure the break
areas are sufficient in size to accommodate the need for break space in
each location. When making this determination, employers would need to
consider factors such as the distribution of employees across different
areas and any employee movement throughout the areas during a work
shift.
OSHA also acknowledges that some employers may have facilities
where both outdoor and indoor work occurs. OSHA requests comments on
whether the agency should permit all employees in these facilities to
utilize indoor break areas.
Proposed paragraph (e)(3) would require that break areas be readily
accessible to the work area(s). It is important that break areas be
readily accessible to ensure that employees can take breaks promptly,
particularly in situations where employees are experiencing early
symptoms of HRIs, as quick access to a break area can help limit the
further progression of illness. In addition, break areas within close
proximity to employees encourages use. OSHA does not expect the
employer to have break areas located immediately adjacent to every
employee and understands that exact distance may vary depending on
factors such as the size and layout of the workplace, the number of
employees, and the nature of the work being performed.
Locations that are so far from work area(s) that they deter
employees from taking breaks would not be considered readily
accessible. When determining
the location of the break area(s), the employer would be expected to
evaluate the duration of travel to the area. Break areas requiring more
than a few minutes to reach would increase the heat stress on employees
as they walk to the area and thus not be considered reasonably
accessible. The break area must be situated close enough to work areas
to minimize the time and effort required for employees to access it.
Break areas should be as close as possible to employees so that an
employee in distress could easily access the area to promptly cool
down. OSHA expects that employers will have incentive to place the
break areas as close as practical to the work areas to minimize travel
time, which must be paid (see Explanation of Proposed Requirement for
paragraph (j) Requirements implemented at no cost to employees).
For mobile work sites, such as in road construction or utility
work, the employer would be expected to relocate the break area as
needed to ensure it is readily accessible to employees or ensure each
work site has its own break area for use. This requirement would also
apply to large work sites where employees are continually changing
their work area, such as in agricultural work. The employer would be
required to pay employees their normal rate of pay for time to get to
the break area, as well as the time on break (see the Explanation of
the Proposed Requirements for paragraph (j)).
In addition to ensuring the break area(s) is large enough to
accommodate all employees on break and readily accessible to the work
area(s), employers would have to provide at least one of the following:
shade (paragraph (e)(3)(i)); or air-conditioning, if in an enclosed
space (paragraph (e)(3)(ii)). As discussed above, break areas are
intended to provide employees a spot to cool down and reduce body
temperature. Also, controls such as shade and air-conditioning are
proven methods to prevent HRIs. Without controls such as these in
place, break areas could become uncomfortable and even continue to
expose individuals to the risk of HRI. OSHA understands that the scope
of the standard includes a broad variety of outdoor industries, and
that even within one industry, workplaces can be vastly different. The
proposed requirements for outdoor break areas give employers
flexibility in their compliance.
Paragraph (e)(3)(i) of the proposal outlines the requirements for
employers who use shade. The provision would require that the break
area have artificial shade (e.g., tent, pavilion) or natural shade
(e.g., trees), but not shade from equipment, that provides blockage of
direct sunlight and is open to the outside air. By incorporating shade
into break areas, whether through natural foliage, awnings, or
umbrellas, employees are able to reduce exposure to radiant heat and
benefit from conditions that are more conducive to increasing
evaporative cooling as air moves across the skin. The benefits of
shaded break areas have also been recognized by several States and
incorporated into State standards, including California, Colorado,
Oregon, and Washington (Cal. Code Regs. tit. 8, section 3395 (2024); 7
Colo. Code Regs. section 1103-15:3 (2023); Or. Admin. R. 437-002-0156
(2024); Or. Admin. R. 437-004-1131 (2024); Wash. Admin. Code 296-307-
09747 (2023)).
To ensure shade is effective, OSHA would require the shade to block
direct sunlight for the break area. OSHA does not expect employers to
measure shade density using shade meters or solarimeters. As defined
under proposed paragraph (b) Shade means the blockage of direct
sunlight, such that objects do not cast a shadow in the area of blocked
sunlight. Therefore, verifying that employees' shadows are obstructed
from being visible due to the presence of shade would be sufficient. In
addition, shaded break area(s) must be open to the outside air. To
satisfy this requirement, the shaded break area must be sufficiently
open to the outside air to ensure that air movement across the skin
(promoting the evaporation of sweat) can occur and to prevent the
buildup of humidity and heat that can become trapped due to limited
airflow and stagnant air. For example, a pop-up canopy with one
enclosed side would comply with the provisions for a shade structure;
however, a closed trailer having four sides and a roof would not.
Employers could also incorporate other cooling measures, such as fans
or misting devices, in their shaded break area, although the proposed
standard does not require them to do so.
Both portable and fixed shade would be permitted to comply with the
proposed requirements under (e)(3)(i). However, as stated above,
employers must ensure shaded break areas remain readily accessible to
employees. At mobile work sites or work sites where employee move to
various locations throughout the day, such as, but not limited to those
commonly found in agriculture, landscaping, forestry, and utility work,
employers would need to ensure that shade structures are relocated near
the work area as needed or that natural sources of shade (e.g., from
trees) are readily available at each work location. OSHA understands
that in some mobile outdoor work environments shade structures may not
be practical and employers may wish to utilize the flexibility of shade
provided by large vehicles that are already on-site. Large vehicles
such as trucks and vans which are used to transport employees or goods
to the work site, but not as part of the work itself could be used as
shade as long as the vehicle is not running. OSHA is not allowing the
use of equipment used in work process, such as tractors, for shade due
to the risk of accidental run-overs caused by the start-up and movement
from operators who are not aware of the presence of workers nearby.
Additionally, equipment used in work processes is likely to emit
radiant heat after use, which may impede employee cooling. However,
shade provided by buildings could be used, provided it is reasonably
accessible to employee work areas. Additionally, as previously
explained, the break area(s) must be large enough to accommodate all
employees on break. Therefore, employers utilizing shade cast by
buildings or trees would need to consider the path of shade movement
throughout the day to ensure adequate areas of shade coverage are
maintained and the shade is able to accommodate all employees on break.
Paragraph (e)(3)(ii) of the proposal describes the requirements for
the use of air-conditioned break areas. Specifically, the proposed
provision indicates that a break area could be an area that has air-
conditioning if that area is in an enclosed space like a trailer,
vehicle, or structure. As with the shaded areas, the air-conditioned
break area would need to be large enough to accommodate the number of
employees on rest breaks and be readily available. The use of air-
conditioned spaces is consistent with State requirements and existing
guidance. In their State regulations, both Colorado and Washington
include the use of an air-conditioned site, such as a vehicle or
structure, as an alternative to providing shade for employee rest
breaks (7 Colo. Code Regs. section 1103-15:3 (2023); WA, 2008b; Wash.
Admin. Code 296-307-09747 (2023). It is well established that the use
of air-conditioned spaces reduces the air temperature employees are
exposed to (NIOSH, 2016).
Employers using air-conditioned vehicles as a break area would need
to ensure that the vehicle remains readily available during work
periods when the initial heat trigger is met or exceeded. For mobile
employees, such as delivery drivers, employers could have employees
take breaks in an air-conditioned convenience store,
restaurant, or similar establishment as long as all other requirements
for break areas are met.
A. Requests for Comments
OSHA seeks comments and additional information whether it should
further specify break area requirements (e.g., square footage per
employee), and what those requirements should be. Also, OSHA seeks
additional comments on break areas where employers have both indoor and
outdoor work areas including:
Whether OSHA should maintain separate break area
requirements for these employees;
Whether OSHA should allow outdoor employees in these
facilities to utilize indoor break areas under paragraph (e)(4); and
Whether OSHA should limit the use of indoor break areas to
those that are equipped with air-conditioning.
OSHA seeks comments and additional information regarding the use of
shade, including:
Whether OSHA appropriately defined shade; if not, how
should OSHA define shade for outdoor break areas;
Whether there are situations where shade is not protective
and should not be permitted; and in these cases, what should be
required for break areas;
Whether there are additional options for shade that are
protective, but which OSHA has not included;
Whether there are situations when trees are not
appropriate for use as shade and other measures should be required;
Whether there are situations when employers should be
permitted to use equipment as shade; in those situations, how would
employers mitigate other safety concerns such as run-over incidents;
Whether there are situations when employers should not be
able to use large vehicles as shade or concerns, including those
related to safety, with generally allowing the use of large vehicles
for shade; and
Whether there are situations when artificial shade should
not be permitted, such as during high winds.
OSHA seeks comments and additional information regarding the use of
air-conditioned spaces, including:
Whether OSHA should define or specify the levels at which
air-conditioning must operate; and
Whether OSHA should require that break rooms and vehicles
used for breaks be pre-cooled prior to the start of the employee's
break.
OSHA seeks comments and additional information regarding the use of
other cooling strategies (beside shade and air-conditioning) that could
be used in break areas, including:
Whether there are other control options that would be both
as effective as shade at reducing heat strain and feasible to
implement;
OSHA seeks comments and additional information regarding break area
requirements for mobile workers:
OSHA did not include separate requirements and seeks
additional information on the feasibility and effectiveness of the
proposed controls listed under paragraph (e)(3) including the use of
vehicles as a break area; and
Whether there are control options OSHA should require for
vehicles, either when used for work activities or when used as a break
area.
IV. Break Area(s) at Indoor Work Sites
Paragraph (e)(4) of the proposed standard outlines the requirements
for break areas at indoor work sites. Specifically, it would require
that the employer provide one or more area(s) for employees to take
breaks (e.g., break room) that is air-conditioned or has increased air
movement and, if appropriate, de-humidification; can accommodate the
number of employees on break; and is readily accessible to the work
area(s). As explained above in the Explanation of Proposed Requirements
for paragraph (e)(3), the requirements for both outdoor and indoor
break areas in this proposed standard are in addition to employers'
obligations under OSHA's sanitation standards (29 CFR 1910.141,
1915.88, 1917.127, 1918.95, 1926.51, 1928.110).
Information regarding compliance with the requirements that break
area(s) be large enough to accommodate all employees on break and
readily accessible can be found in the Explanation of Proposed
Requirements for paragraph (e)(3). Break area(s) at indoor work sites
will often likely be specific rooms in a facility (e.g., a break room).
To ensure that the break areas are readily accessible, employers would
need to make sure that employees can enter the break areas for heat-
related breaks (e.g., keep the break room unlocked).
At indoor work sites, the break area(s) must be air-conditioned or
have a combination of increased air movement and, if appropriate, de-
humidification. The importance and effectiveness of air-conditioning
and air movement in preventing HRIs were explained above in the
Explanation of Proposed Requirements for paragraph (e)(3). OSHA is
requiring de-humidification, if appropriate, in addition to increased
air movement because humidity levels directly impact the body's ability
to cool itself through evaporation. Humidity control is integrated into
modern air-conditioning units and therefore OSHA is only requiring de-
humidification to be implemented in high temperature and high humidity
environments when employers are relying on increased air movement to
comply with this requirement. To determine when de-humidification may
be appropriate in the context of fan use, employers should consult the
Explanation of Proposed Requirements for paragraph (e)(6).
To comply with the requirements under proposed paragraph (e)(4),
employers who operate in arid environments could use evaporative or
``swamp'' coolers as a form of air-conditioning. Note, however, that
such coolers are not effective in humid environments. It is also
important to note that OSHA is not requiring employers install a
permanent cooling system. The use of portable air-conditioning units or
high-powered fans and portable dehumidifiers in designated break areas
could also be used to comply with requirements for break areas under
the proposed standard. As discussed in the Explanation of Proposed
Requirements for paragraph (e)(6), fan use when ambient temperatures
exceed 102 [deg]F has been demonstrated to be harmful under some
conditions and employers must evaluate humidity levels to determine if
fan use should be avoided.
Under the proposal, indoor break area(s) do not necessarily need to
be located in a separate room but can be integrated within the main
workspace. For example, in a manufacturing facility, there could be a
designated corner or section within the main production area where
employees could take their breaks. This break area could be demarcated
by partitions, screens, or signage to distinguish it from the active
work zones and be equipped with fans. Alternatively, an employer, who
is unable to establish a break area in their main workroom because of
sensitive or hazardous work equipment or processes, can establish a
break area in a separate area away from the work zone, provided that
area is readily accessible to employees. Regardless of where a break
area is located, the break area must allow employees to cool down
effectively and drink water to hydrate.
For indoor workplaces that experience temperatures above the heat
triggers but have employees who spend part of their time in air-
conditioned control booths or control rooms and part of their time in
other, hotter areas of the facility, the employer could utilize the
control booth/room as a break area and
would not need to provide a separate break area for those employees.
Control booths/rooms are commonly found in industries such as
manufacturing, food processing, electronics assembly, processing
facilities, power plants, water treatment plants, and more.
Furthermore, these spaces would qualify as break areas for other
employees provided that the requirements for size and location are met.
Control booths/rooms that are locked or have restricted accessibility
would not be acceptable under the proposal.
A. Requests for Comments
OSHA seeks comments and additional information regarding the use of
engineering controls for indoor break areas, including:
Whether OSHA should specify how effective engineering
controls need to be in cooling the break area(s), including other
measures determining effectiveness beyond temperature and humidity;
Whether OSHA should define a temperature differential
between work areas and break areas; and
Whether OSHA should specify a temperature that break areas
must be kept below.
OSHA seeks comments and additional information regarding the use of
other cooling strategies (besides fans and air-conditioning) that could
be used in break areas, including:
Whether there are other control options that would be both
effective at reducing heat strain and feasible to implement.
OSHA did not include an option for the use of outdoor break areas
for indoor work sites and seeks comment and information on the use of
outdoor break areas for employees in indoor work sites, including:
Whether there are situations where an outdoor break area
could be more effective at cooling and should be permitted; and
Whether certain conditions must be provided for these
outdoor break areas.
OSHA seeks additional comments on break areas where employers have
both indoor and outdoor work areas. See Explanation of Proposed
Requirements paragraph (e)(3), Requests for Comments.
V. Indoor Work Area Controls
Paragraph (e)(5) contains the proposed requirements for indoor work
area controls when temperatures meet or exceed the initial heat
trigger. Indoor work areas would be required to be equipped with a
combination of increased air movement and, if appropriate, de-
humidification (paragraph (e)(5)(i)); air-conditioning (paragraph
(e)(5)(ii)); or, in the case of radiant heat sources, other cooling
measures that effectively reduce employee exposure to radiant heat in
the work area (paragraph (e)(5)(iii)). The importance and effectiveness
of air-conditioning and air movement (including dehumidification) in
preventing HRIs were explained above in the Explanation of Proposed
Requirements for paragraphs (e)(3). In addition to these, OSHA is
permitting the use of other control measures for radiant heat sources
because these controls result in less heat being radiated to employees.
As discussed above in the Explanation of Proposed Requirements for
paragraph (d)(3)(i), employers would be expected to determine which
work areas of indoor work sites, if any, are reasonably expected to
meet or exceed the initial heat trigger. For work areas at or above the
trigger, such as those near heat-generating machinery, paragraph (e)(5)
would require employers to implement work area controls. OSHA
understands that effective control methods can vary based on workspace
circumstances and the nature of the heat source and is therefore giving
employers options regarding indoor work area controls. However, each
work area with exposures at or above the initial heat trigger would
need be to be equipped with at least one control option. Additionally,
employers could choose to use a combination of control measures.
Employers could use increased air movement (e.g., fans) and, if
appropriate, de-humidification, or air-conditioning to cool the work
area under paragraphs (e)(5)(i) and (ii). Under paragraph (e)(5)(i),
fans could be used to increase the air movement in the work area.
Employers could use overhead ceiling fans, portable floor fans, or
other industrial fans to comply. Employers could also increase the air
flow using natural ventilation by opening doors and windows, or vents,
to allow fresh air to flow into the space, but only when doing so would
be comparable to the use of fans. Natural ventilation would not be
acceptable if it does not produce air movement equivalent to a fan, or
if the outdoor temperature is such that natural ventilation increases
the work area temperature.
Depending on the type of work being done and the location of
employees in a facility, employers could choose to use ventilation to
cool the entire space or just those areas where employees are present.
Although paragraph (e)(5) only applies to work areas, it may be more
efficient for the employer to implement the control for an entire
space. With either strategy, the employer should consider the facility
layout, equipment placement, and potential obstructions to ensure
optimal airflow when determining where to place fans. For example, an
employer could use fans to cool a warehouse by strategically
positioning them near entrances and exits to create airflow and
facilitate the circulation of fresh air into the warehouse.
Additionally, utilizing high-velocity fans along aisles or in areas
where employees are concentrated can help dissipate heat and provide a
cooling effect. Conversely, if employees only work in a discrete
area(s) of a facility, an employer may choose to only provide fans in
those work areas. For example, the employer could place fans in the
area where employees are stationed. Adjustable fans or fans with
oscillating features could be used in those areas to allow employers to
direct airflow where it is most needed. Additionally, employers could
consider installing overhead fans or mounting fans on adjustable stands
to ensure optimal coverage and airflow distribution.
As discussed in the Explanation of Proposed Requirements for
paragraph (e)(4), employers using fans or relying on natural
ventilation in humid environments would still be expected to decrease
humidity levels where appropriate. OSHA is not proposing a specific
temperature or humidity level be maintained in the work areas; however,
employers should ensure that the combination of air movement and
humidity level effectively reduces employees' heat strain. As discussed
in the Explanation of Proposed Requirements for paragraph (e)(6), OSHA
has preliminarily determined that under some conditions, fan use may be
harmful when ambient temperatures exceed 102 [deg]F and employers must
evaluate humidity levels to determine if fan use is harmful when
temperatures reach this threshold. Employers should consult the
Explanation of Proposed Requirements for paragraph (e)(6) to determine
when de-humidification may be appropriate in the context of fan use.
Under paragraph (e)(5)(ii) employers could use air-conditioning to
meet the requirement for controlling heat exposures in indoor work
areas. In arid environments, evaporative coolers, also known as ``swamp
coolers,'' could be used and would be considered air-conditioners, even
if portable. It is important to note that while an employer may choose
to provide air-conditioning to the entire facility, they
would not be required to do so under the proposed standard. Employers
who choose to provide air-conditioning under paragraph (e)(5)(ii) would
only need to implement it in areas where employees work and are exposed
to temperatures above the initial heat trigger. Similar to fan use, if
employees only work from fixed or designated locations in the
workplace, the employer would only need to provide air-conditioning to
those spaces under paragraph (e)(5)(ii). For example, if employees work
only from a control booth or control room, employers could choose to
install air-conditioning in the control booth or control room to comply
with paragraph (e)(5)(ii). Similarly, portable air-conditioning units
could be used throughout the facility to cool smaller areas where
employees work. For example, an employer could position portable
evaporative coolers near the entrance of a loading dock to provide
immediate relief from the heat when an employee is loading or unloading
goods inside the building, or a machine shop may choose to use portable
air-conditioners around the workstation to cool the employee.
Alternatively, a manufacturing facility may choose to install a small,
air-conditioned control booth for operators to work from. All of these
options would be acceptable under the proposal.
Under paragraph (e)(5)(iii), in indoor work areas with radiant heat
sources, employers could choose to implement other measures that
effectively reduce employee exposure to radiant heat in the workplace.
Paragraph (e)(5)(iii) would allow the use of controls such as shielding
or barriers, isolation, or other measures that effectively reduce
employee exposure to radiant heat, in areas where employees are exposed
to radiant heat created by heat-generating processes. The use of
control methods for radiant heat is consistent with guidance issued by
Minnesota regarding the implementation of their heat standard (MNOSHA,
2009). Options for complying with this proposed provision could include
installing shielding or barriers that are radiant-reflecting to reduce
the amount of radiant heat to which employees would otherwise be
exposed; isolating the source of radiant heat, such as using thermal
insulation on hot pipes and surfaces; increasing the distance between
employees and the heat source; and modifying the hot process or
operation.
If the employer chooses to utilize radiant heat controls under
paragraph (e)(5)(iii) in lieu of air-conditioning or fan use, the
controls would need to effectively reduce employee exposure to radiant
heat. For example, in facilities with industrial ovens, kilns, or
process heat, employees may be exposed to radiant heat during loading,
unloading, or maintenance tasks. Installing shielding around these heat
sources can help protect employees from radiant heat during these
tasks. In another example, an employer may choose to install heat-
resistant barriers or insulating materials around welding stations to
contain heat and prevent its transmission to adjacent work areas.
A. Requests for Comments
OSHA seeks comments and additional information regarding the use of
engineering controls for indoor work areas, including:
Whether the standard should specify how effective
engineering controls need to be in cooling the work area(s);
Whether there are other control options (besides fan use
or air-conditioning) that would be both effective at reducing heat
strain and feasible to implement in cases where indoor employees are
exposed to ambient heat; and
Whether there are work areas where maintaining a high
ambient temperature is necessary for the work process and, if so, how
OSHA should address these work areas in the standard.
VI. Evaluation of Fan Use
Paragraph (e)(6) of the proposed standard would require employers
using fans under certain conditions to determine if fan use is harmful.
Specifically, when ambient temperatures exceed 102 [deg]F (39.0
[deg]C), employers using fans to comply with paragraphs (e)(4) or (5)
would be required to evaluate the humidity levels at the work site and
discontinue the use of fans if the employer determines that fan use is
harmful.
As discussed in Section V.C., Risk Reduction, researchers in the
past 10 years have increasingly evaluated the conditions under which
fan use becomes harmful, using both experimental and modeling
approaches. Most of this work has assumed individuals are seated and at
rest; to OSHA's knowledge, only one paper has evaluated the threshold
at which fans become harmful for individuals performing physical work
(Foster et al., 2022a). The impact of fans is determined by both air
temperature and humidity, as well as factors influencing sweat rates.
Researchers have demonstrated that neither heat index nor ambient
temperature alone can be used to determine beneficial versus harmful
fan use; instead, ambient temperature and relative humidity must both
be known (Morris NB et al., 2019; Foster et al., 2022a).
The 102 [deg]F threshold in proposed paragraph (e)(6) is derived
from Figure 4 of Foster et al. 2022a and represents the lowest ambient
temperature at which fan use has been demonstrated to be harmful in the
researchers' model. As proposed, paragraph (e)(6) does not specify how
employers must make the determination whether fan use is harmful above
this threshold. However, using the other results from Figure 4 of
Foster et al. 2022a, OSHA has developed the following table which
identifies scenarios where the agency believes fan use would or would
not be harmful:
------------------------------------------------------------------------
Fan speed: 3.5 m/s
------------------------------------------------------------------------
Humidity range: Humidity range:
Ambient temperature fan use allowed turn off fans
------------------------------------------------------------------------
102.2 [deg]F (39 [deg]C)........ 15-85%............ <15% or >85%.
104.0 [deg]F (40 [deg]C)........ 20-80%............ <20% or >80%.
105.8 [deg]F (41 [deg]C)........ 30-65%............ <30% or >65%.
107.6 [deg]F (42 [deg]C)........ 30-65%............ <30% or >65%.
109.4 [deg]F (43 [deg]C)........ 35-60%............ <35% or >60%.
111.2 [deg]F (44 [deg]C)........ 35-55%............ <35% or >55%.
113.0 [deg]F (45 [deg]C)........ 40-55%............ <40% or >55%.
>113.0 [deg]F (>45 [deg]C)...... Discontinue all Discontinue all
fan use. fan use.
------------------------------------------------------------------------
Using the information from this table, an employer could identify
the row most closely matching the ambient temperature of the work or
break area and then find the corresponding humidity range for when fans
are acceptable to use. For example, if the ambient temperature of the
work or break area is 104 [deg]F and the relative humidity is 50%, fans
could be used. However, if the ambient temperature of the work or break
area is 108 [deg]F and the relative humidity is 70%, fans should not be
used.
A. Requests for Comments
OSHA recognizes that there are several limitations with the
analyses by Foster et al. 2022a, and the application of those results
for this purpose. For one, the model results reported by Foster et al.
assume ``light clothing'' only and not ``work clothing,'' which would
be more similar to a typical work uniform than the ``light clothing.''
While the empirical evidence that the researchers collected on
individuals wearing ``work clothing'' is largely consistent with the
modeled results presented for ``light clothing,'' there are some
differences, such as the finding that fans are never beneficial at or
above an ambient temperature of 45 [deg]C (113.0 [deg]F) when wearing
``work clothing'' (which OSHA has reflected in the table). The authors'
recommendations for fan use also included a category that represented
scenarios in which fans have a ``minimal impact'' (i.e., the effect of
fans on body heat storage is close to zero). OSHA has combined this
category with the category for scenarios in which fans are beneficial
to produce the table above. Another limitation is the assumption of a
sweat rate of approximately 1 liter per hour (the group average from
empirical trials in the same study). However, factors such as
acclimatization status, age, and medical history can influence sweat
rates, which would influence when fan use is beneficial (see Figure 6
[panels a and b] from Foster et al., 2022a). Finally, Foster et al.
tested a fan with a velocity of 3.5 meters per second. OSHA has
preliminarily determined that this is a reasonable assumption but
acknowledges that varying wind velocity would also influence when fan
use is beneficial (see Figure 6 [panel c] from Foster et al., 2022a).
OSHA understands the complexity and uncertainty around an
evaluation of fan use and is therefore considering a simplified
approach for employers to use. OSHA is requesting comments on this
simplified approach and the assumptions underlying it.
More specifically, OSHA requests comments regarding its preliminary
determinations on fan use and seeks the following information:
Whether OSHA has appropriately derived recommendations for
fan use from Foster et al., 2022a, and whether additional data or
research should be used to supplement or revise the recommendations;
Whether OSHA should include the above table derived from
Foster et al., 2022a, or a similar table, in paragraph (e)(6), either
as a mandatory requirement or as a compliance option; and,
Whether the standard should require alternative methods
for cooling employees when fans are harmful, and if so, what
alternative control measures should be used.
VII. Acclimatization
Paragraph (e)(7) of the proposed standard would establish
requirements to protect new and returning employees who are not
acclimatized. Evidence indicates that new and returning employees are
at increased risk for HRIs. As explained in Section V.C., Risk
Reduction, employees who are new on the job are often overrepresented
in HRI and heat-related fatality reports. Additionally, the NACOSH Heat
Injury and Illness Prevention Work Group recommended acclimatization
protections for new and returning employees, such as heightened
monitoring (NACOSH Working Group on Heat, 2023), and NIOSH recommends
an acclimatization plan that gradually increases new employees' work in
the heat starting with 20% of the usual work duration and increasing by
no more than 20% on each subsequent day (NIOSH, 2016). For returning
employees, NIOSH recommends an acclimatization plan that starts with no
more than 50% of the usual work duration of heat exposure that then
gradually increases on each subsequent day (NIOSH, 2016). Therefore,
OSHA has preliminarily determined that the requirements in paragraph
(e)(7) are important for preventing HRIs and fatalities from
occupational heat exposures among these employees.
Proposed paragraph (e)(7)(i) would require that employers implement
one of two options for an acclimatization protocol for new employees
during their first week on the job. The first option that an employer
may choose, under proposed paragraph (e)(7)(i)(A) (Option A), is a plan
that, at a minimum, includes the measures required at the high heat
trigger set forth in paragraph (f), when the heat index is at or above
the initial heat trigger during the employee's first week of work.
Proposed paragraph (f)(2) requires a minimum 15-minute paid rest break
at least every two hours in the break area that meets the requirements
of the proposed standard, proposed paragraph (f)(3) requires
observation for signs and symptoms of heat-related illness, and
proposed paragraph (f)(4) requires providing hazard alerts with
specified information about heat illness prevention and how to seek
help if needed. See the Explanation of Proposed Requirements for
paragraph (f), Requirements at the high heat trigger, for a detailed
explanation of the requirements of that section. Option A gives
employers flexibility to choose an option that works best for their
work site while still making sure that employees are informed, are
under observation, and receive breaks, all of which will help better
equip employers and employees to monitor and mitigate the effects of
heat exposure in situations where the gradual acclimatization option
may not be practical. While this option does not require gradual
exposure, OSHA believes that, in situations where gradual exposure may
not be practical, rest breaks, observation, and hazard alerts will help
protect new workers as they adjust to heat during their first week of
work.
The second option that an employer may choose, under proposed
paragraph (e)(7)(i)(B) (Option B), would require a gradual exposure to
the heat at or above the initial heat trigger to allow for
acclimatization to the heat conditions of the workplace. The gradual
exposure protocol would involve restricting employee exposure to heat
to no more than 20% of a normal work shift exposure duration on the
first day of work and increasing exposure by 20% of the work shift
exposure duration on each subsequent day from day 2 through 4. This is
consistent with NIOSH's recommended acclimatization plan for new
employees (NIOSH, 2016).
Employers may satisfy Option B requirements by utilizing some of
the employees' work time in ways that do not require exposure to heat
at or above the initial heat trigger. Examples include completing
training activities or filling out work-related paperwork in an air-
conditioned building. Employers may also fulfill this requirement
through task replacement, whereby an employee completes another
necessary task in an area that does not require exposure at or above
the initial heat trigger (e.g., office work).
Additionally, if the temperature of the work site fluctuates such
that the initial heat trigger is only exceeded for a portion (e.g., 2
hours) of the work shift
on some or all of the days during the initial week of work, employers
choosing Option A would only be required to implement the requirements
of paragraph (f) during those time periods. If they choose the gradual
heat exposure option for acclimatization, employers would need to
coordinate the employees' heat exposure for those days with the parts
of the day that are expected to meet or exceed the initial heat
trigger.
Under proposed paragraph (j), employers would be required to
implement the acclimatization protocols at no cost to employees. This
means that employers could not relieve employees from duty after the
allotted time of heat exposure under the acclimatization protocol and
not pay them for the remainder of the work shift. Because benefits
would also be considered compensation, this would mean that an employer
could not use an employee's paid leave to cover the hours not worked
during the acclimatization period.
Proposed paragraph (e)(7)(ii) would require that employers
implement one of two options for an acclimatization protocol for
returning employees who have been away from the job for more than 14
days, during their first week back on the job.
The first option that an employer may choose, under proposed
paragraph (e)(7)(ii)(A) (Option A), is an employer-developed plan, that
at a minimum, includes the measures that would be required under
proposed paragraph (f) whenever the initial heat trigger is met or
exceeded, during the employee's first week of returning to work. See
explanation above for new employees and the Explanation of Proposed
Requirements for paragraph (f), Requirements at the High Heat Trigger,
of the proposed standard for a detailed explanation of the requirements
of that section.
The second option that an employer may choose under proposed
paragraph (e)(7)(ii)(B) (Option B), is a protocol that requires a
gradual exposure to heat at or above the initial heat trigger to allow
for acclimatization to the heat conditions of the workplace. The
gradual exposure protocol would restrict employee exposure to heat to
no more than 50% of a normal work shift exposure duration on the first
day of work, 60% on the second day of work, and 80% of the third day of
work. This is consistent with NIOSH's recommended acclimatization plan
for returning employees (NIOSH, 2016). Employers may satisfy these
requirements by utilizing employees' work time in ways that do not
require heat exposure at or above the initial heat trigger, as
described above for new employees.
For occupations where returning employees may have shift schedules
such as two weeks on and then two weeks off, the acclimatization
protocol requirement would not go into effect because the two weeks off
would not exceed 14 days. However, in situations where time off exceeds
14 days, the requirement would apply.
Proposed paragraph (e)(7)(iii) would set forth an exception to
acclimatization requirements of paragraphs (e)(7)(i) and (ii) if the
employer can demonstrate that the employee consistently worked under
the same or similar conditions as the employer's working conditions
within the previous 14 days. Same or similar conditions means that new
employees must have been doing work tasks that are similar or higher in
level of exertion to the tasks that are required in the new job and
that they conducted these tasks in similar or hotter heat conditions
than the new job (e.g., at or above the heat index for current
conditions in the new job). Employers should not assume that employees
who recently came from climates that are perceived to be similar or
hotter (e.g., Mexico) were actually exposed to similar or hotter
conditions because climate can vary dramatically based on factors such
as elevation levels and humidity. Therefore, employers could check
weather records to determine heat indices for the location that the
employee worked at during the previous two weeks to determine if the
employee was actually exposed to conditions at least as hot as in the
new position.
In determining if tasks the employee conducted in the past two
weeks were similar or higher in level of exertion to the tasks that are
required in the new job, employers could generally consider factors
such as weight carried and intensity of activity (e.g., walking versus
climbing). For example, picking tomatoes and picking watermelons would
generally not be considered similar tasks because of the heavier weight
of the watermelons. However, picking tomatoes and picking cucumbers
could generally be considered similar tasks if other job conditions are
similar. Installing telephone wires on poles and laying out
communication wires in a trench dug using machinery would generally not
be considered similar to laying out communication wires in a trench dug
manually because of the greater work intensity involved with digging a
trench manually. Laying communication wire in a pre-dug trench and
conducting inspections on the ground might be considered similar tasks
if both tasks primarily involve walking. Landscaping work involving
weeding and laying out mulch versus hand digging trenches for drainage
systems would generally not be considered similar tasks because of the
greater work involved in digging trenches. However, hand digging
trenches for drainage and hand digging holes to install trees and
shrubs could generally be considered similar tasks if those are the
primary tasked performed throughout the workday.
The employee must have engaged in similar work activities in the
similar heat conditions consistently over the preceding 14 days. OSHA
intends ``consistently'' to mean the employee engaged in the task for
at least two hours per day on a majority of the preceding 14 days. This
aligns with recommendations from NIOSH (NIOSH, 2016).
Examples of when this exception would not apply include when new
employees' previous positions, which included similar heat conditions
and exertion levels, ended longer than 14 days ago, when new employees'
previous positions ended within the last 14 days and involved similar
work tasks but in cooler conditions, or when new employees' previous
positions ended within the last 14 days and involved hotter conditions
but less exertion. The exemption would also not apply if new employees'
previous positions ended less than 14 days ago but they were not
performing similar work tasks in similar heat conditions for at least
two hours per day on a majority of the preceding 14 days.
To demonstrate that a new employee consistently worked under the
same or similar conditions as the employer's working conditions within
the prior 14 days, the employer could obtain information directly from
the new employee to confirm the requirements of proposed paragraph
(e)(7) are met considering the explanation of same or similar working
conditions provided above. The employer could ask questions verbally or
in writing about the prior work (i.e., timing, location, duration, type
of work). If an employer asked new employees ``in the past 14 days, did
you consistently work under the same or similar conditions as the
employer'' but did not ask for any supporting details, the requirement
would not be satisfied.
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Data or examples of successful implementation of an
acclimatization program;
Whether the term ``same or similar conditions'' is
sufficiently clear so that employers know when the exception to the
acclimatization requirement would apply for new employees, and if not,
how should OSHA clarify the requirement;
Whether a minimum amount of heat exposure to achieve
acclimatization should be specified under Option B, the gradual
acclimatization option;
Whether the requirement to demonstrate that an employee
consistently worked under the same or similar conditions as the
employer's working conditions within the prior 14 days is sufficiently
clear, and if not, how should OSHA clarify the requirement;
Whether the standard should require acclimatization
protocols during local heat waves, and if so, how OSHA should define
heat waves;
Whether the standard should require annual acclimatization
of all employees at the beginning of each heat season (e.g., the first
hot week of the year) and approaches for doing so;
Examples that OSHA should consider of acclimatization
protocols for industries or occupations where it may not be appropriate
for an employee to conduct heat-exposed work tasks during the first
week on the job (e.g., what activities would be appropriate for these
workers to achieve acclimatization);
Data or examples that OSHA should consider in determining
if acclimatization should be required in certain situations for
existing employees and examples of successful acclimatization programs
for such employees;
Which option (i.e., following requirements of the high
heat trigger or gradual increase in exposure to work in heat) presented
in the proposal would employers implement and whether the standard
should include other options;
Whether the standard should include any additional
acclimatization requirements for employees returning after less than 14
days away from work after acute illnesses that may put them at
increased risk of heat-related illness (i.e., illnesses involving fever
or gastrointestinal infections), and if so, suggestions and evidence
for the additional requirements; and
Considering that employees starting or returning when the
heat index is above 90 [deg]F would not receive unique acclimatization
benefits if the employer chose Option A, whether the standard should
specify additional requirements for these scenarios, such as breaks
that are more frequent or of longer duration.
OSHA has concerns that the proposed exception in paragraph
(e)(7)(iii) could create incentives for employees to lie and/or
employers to pressure employees to lie about their acclimatization
status. For example, an employer could pressure an employee to report
that they consistently worked under the same or similar conditions
within the prior 14 days, so that the employer does not need to comply
with paragraph (e)(7) during the employee's first week on the job.
These incentives could put new and returning employees at increased
risk because they are not receiving appropriate protection based on
their acclimatization status. OSHA seeks comments and evidence on the
likelihood of this happening and what OSHA could do to address these
potential troubling incentives.
VIII. Rest Breaks if Needed
Proposed paragraph (e)(8) would require employers to allow and
encourage employees to take paid rest breaks in break areas that would
be required under paragraphs (e)(3) or (4) if needed to prevent
overheating. As discussed in Section V.C., Risk Reduction, rest breaks
have been shown to be an effective intervention for preventing HRI by
allowing employees to reduce their work rate and body temperature. Rest
breaks allow employees time to hydrate and cool down in areas that are
shaded, air-conditioned, or cooled with other measures. Therefore, OSHA
preliminary finds that allowing employees to take rest breaks when they
are needed to prevent overheating is an important control for
preventing or reducing HRIs in the workplace.
Providing employees the opportunity to take unscheduled rest breaks
to prevent overheating helps to account for protecting employees who
vary in susceptibility to HRI and address scenarios where employees
might experience increased heat strain. For example, unscheduled rest
breaks may help to protect employees who are more susceptible to HRI
for reasons such as chronic health conditions, recent recovery from
illness, pregnancy, prior heat-related illness, or use of certain
medications (see Section IV.O., Factors that Affect Risk for Heat-
Related Health Effects). Unscheduled rest breaks may also help reduce
heat strain in employees who are assigned new job tasks that are more
strenuous than the tasks they were performing. Additionally, rest
breaks would allow employees an opportunity to remove any PPE that may
be contributing to heat strain.
Under proposed paragraph (e)(8), employees would be allowed to
decide on the timing and frequency of unscheduled rest breaks to
prevent overheating. However, unscheduled rest breaks must be heat-
related (i.e., only if needed to prevent overheating). In addition, if
the work process is such that allowing employees to leave their work
station at their election would present a hazard to the employee or
others, or if it would result in harm to the employer's equipment or
product, the employer could require the employee to notify a supervisor
and wait to be relieved, provided a supervisor is immediately available
and relieves the employee as quickly as possible.
An example of a scenario where an employee may decide they need a
rest break is if the employee experiences certain symptoms that
suggests the employee is suffering from excessive heat strain but does
not have an HRI that would need to be addressed under proposed
paragraph (g)(2) (e.g., excessive thirst, excessive sweating, or a
general feeling of unwellness that the employee attributes to heat
exposure). However, rest breaks to prevent overheating do not need to
be tied to onset of symptoms. For example, if an employee starts to
have trouble performing a task on a hot day that they do not normally
have trouble performing, that may be a sign they need a break. OSHA
expects that most unscheduled rest breaks to prevent overheating would
typically last less than 15 minutes. In some cases, a rest break that
extends beyond 15 minutes or frequent unscheduled rest breaks may be a
sign that the employee may be experiencing an HRI.
As noted, proposed paragraph (e)(8) requires employers to both
encourage and allow employees to take a paid rest break if needed.
Employers can encourage employees to take rest breaks by periodically
reminding them of that option. Although employers must allow employees
to take breaks if the employee determines one is needed, nothing
precludes an employer from asking or directing an employee to take an
unscheduled paid rest break if the employer notices signs of excessive
heat strain in an employee.
Slowing the pace of work would not be considered a rest break, and
as specified in proposed paragraph (e)(8), rest breaks if needed must
be provided in break areas required under paragraph (e)(3) or (4) (see
Explanation of Proposed Requirements for paragraphs (e)(3), Break
area(s) at outdoor work sites and (e)(4), Break area(s) at indoor work
sites for additional discussion of break areas and Explanation of
Proposed Requirements for paragraph
(f)(2), Rest breaks, for additional discussion related to rest breaks.)
Proposed paragraph (e)(8) would require that employees be paid
during the time they take rest breaks needed to prevent overheating.
OSHA preliminary finds it is important that these breaks be paid so
that employees are not discouraged from taking them. The reason for
requiring these breaks be paid is further explained in the Explanation
of Proposed Requirements for paragraph (j), Requirements implemented at
no cost to employees, including the importance of the requirement and
how employers can ensure that employees are compensated to ensure they
are not financially penalized for taking breaks that would be allowed
or required under the proposed standard.
Evidence indicates that employees are often reluctant to take
breaks and thus, are not likely to abuse the right to take rest breaks
if needed to prevent overheating; to the contrary, the evidence shows
that employees are more likely to continue working when they should
take a rest break to prevent overheating. A review of the evidence
showing that many employees are reluctant to take rest breaks is
included in the Explanation of Proposed Requirements for paragraph
(f)(2) Rest breaks.
A. Requests for Comments
OSHA seeks comments and information on the proposed requirement to
provide employees with rest breaks if needed to prevent overheating,
including:
If there are specific signs or symptoms that indicate
employees need a rest break to prevent overheating;
If employers currently offer rest breaks if needed to
prevent overheating, and if so, whether employees take rest breaks when
needed to prevent overheating;
The typical duration of needed rest breaks taken to
prevent overheating; and
Any challenges to providing rest breaks if needed to
prevent overheating.
In addition, OSHA encourages stakeholders to provide information
and comments on the questions regarding compensation of employees
during rest breaks in the Explanation of Proposed Requirements for
paragraph (j), Requirements implemented at no cost to employees.
IX. Effective Communication
Paragraph (e)(9) of the proposed standard establishes requirements
for effective communication at the initial heat trigger. Early
detection and treatment of heat-related illness is critical to
preventing the development of potentially fatal heat-related
conditions, such as heat stroke (see Section V., Health Effects).
Effective two-way communication provides a mechanism for education and
notification of heat-related hazards so that appropriate precautions
can be taken. It also provides a way for employees to communicate with
the employer about signs and symptoms of heat-related illness, as well
as appropriate response measures (e.g., first aid, emergency response).
The NACOSH Heat Injury and Illness Prevention Work Group
recommended that elements of a proposed standard for prevention of HRIs
address communication needs to meet the objective of monitoring the
work site to accurately assess conditions and apply controls based on
those conditions. The Work Group recommended addressing communications
needs for tracking to facilitate monitoring and check-ins so that
employees can report back to employers (NACOSH Working Group on Heat,
2023).
OSHA preliminarily finds that two-way, regular communication is a
critical element of HRI prevention. Paragraph (e)(9) requires the
employer maintain effective, two-way communication with employees and
regularly communicate with employees. The means of communication must
be effective. In some cases, voice (or hand signals) may be effective,
but if that is not effective at a particular workplace (e.g., if
employees are not close together and/or not near a supervisor), then
electronic means may be needed to maintain effective communication
(e.g., handheld transceiver, phone, or radio). If the employer is
communicating with employees by electronic means, the employer must
respond in a timely manner for communication to be effective (e.g.,
providing a phone number for employees to call would not be effective
if no one answers or responds in a timely manner).
The means of communication must also be ``two-way'' (i.e., a way
for the employer to communicate with employees, and for employees to
communicate with the employer). This is important because this provides
a means for employees to reach the employer when someone is exhibiting
the signs and symptoms of heat-related illness.
Paragraph (e)(9) also requires that employers regularly communicate
with employees. The employer could comply with this requirement by
regularly reaching out to employees, or setting up a system by which
employees are required to make contact, or check in, with the employer.
However, it is the employer's responsibility to ensure that regular
communication is maintained with employees (e.g., every few hours). If
a system is chosen whereby the employer requires employees to initiate
communication with the employer, and if the employer does not hear from
the employee in a reasonable amount of time, the employer must reach
out to the employee to ensure that they are not experiencing heat-
related illness symptoms. Employers must ensure that when it is
necessary for an employee to leave a message (e.g., text) with the
employer, the employer will respond, if necessary, in a reasonable
amount of time.
This proposed requirement also applies for employees who work alone
on the work site. This means that the communication system chosen by
the employer must allow for communication between these employees and
the employer, although the means may be different than for employees
who work on a work site with multiple employees (e.g., by electronic
means).
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
How employers currently communicate with employees working
alone, including any challenges for effectively communicating with
employees working alone and any situations where communication with
employees working alone may not be feasible; and
Whether OSHA should specify a specific time interval at
which employers must communicate with employees and, if so, what the
interval should be, and the basis for such a requirement.
X. Personal Protective Equipment (PPE)
Paragraph (e)(10) of the proposed standard would require employers
to maintain the cooling properties of cooling PPE if provided to
employees. The proposed standard does not require employers to provide
employees with cooling PPE. However, if employers do provide cooling
PPE, they must ensure the PPE's cooling properties are maintained at
all times during use. It is critical that employers who provide cooling
PPE maintain the equipment's cooling properties; when these properties
are not maintained, the defective equipment can heighten the risk of
heat injury or illness with continued use. Reports from employees
indicate that the use of cooling PPE, such as cooling vests, is
burdensome and increases heat retention once the
cooling properties are lost or ice packs have melted (Chicas et al.,
2021).
A. Requests for Comments
OSHA requests comments and evidence as to whether there are any
scenarios in which wearing cooling PPE is warranted and feasible and
OSHA should require its use.
F. Paragraph (f) Requirements at or Above the High Heat Trigger
I. Timing
Paragraph (f) of the proposed standard would establish requirements
when employees are exposed to heat at or above the high heat trigger.
As discussed in Section V.B., Basis for Initial and High Heat Triggers,
OSHA has preliminarily determined that the experimental and
observational evidence support that heat index triggers of 80 [deg]F
and 90 [deg]F are highly sensitive and therefore highly protective of
employees. Exposures at or above the high heat trigger, a heat index of
90 [deg]F, or a corresponding wet bulb globe temperature equal to the
NIOSH Recommended Exposure Limit, would require the employer to provide
the protections outlined in paragraphs (f)(2) through (5). These
protections would be in addition to the measures required by paragraph
(e) Requirements at or above the initial heat trigger, which remain in
effect after the high heat trigger is met.
The employer would only be required to provide the protections
specified in paragraph (f) during the time period when employees are
exposed to heat at or above the high heat trigger. In many cases,
employees may only be exposed at or above the high heat trigger for
part of their work shift. For example, employees may begin work at 9
a.m. and finish work at 5 p.m. If their exposure is below the high heat
trigger from 9 a.m. until 2 p.m., and at or above the high heat trigger
from 2 p.m. to 5 p.m., the employer would only be required to provide
the protections specified in this paragraph from 2 p.m. to 5 p.m.
Protective measures outlined in paragraph (e) Requirements at or above
the initial heat trigger, would be required at any time when employees
are exposed to heat at or above the initial heat trigger.
II. Rest Breaks
Proposed paragraph (f)(2) specifies the minimum frequency and
duration for rest breaks that would be required (i.e., 15 minutes every
two hours) when the high heat trigger is met or exceeded and provides
clarification on requirements for those rest breaks.
A. Background on the Provision
As discussed in Section V.C., Risk Reduction, rest breaks have been
shown to be an effective intervention for preventing HRI by allowing
employees to reduce their work rate and body temperature. Rest breaks
also allow employees time to hydrate and cool down in areas that are
shaded, air-conditioned, or cooled with other measures. OSHA
preliminarily finds there are at least two reasons that warrant the
inclusion of rest breaks at a minimum frequency and duration when the
high heat trigger is met or exceeded. The first is that heat strain is
greater in employees exposed to higher levels of heat. (See Section
IV., Health Effects).
The second is that the available evidence shows many employees are
not taking adequate or enough rest breaks. This evidence shows that
while workers paid on a piece-rate basis (e.g., compensated based on
factors such as quantity of produce picked, jobs completed, or products
produced) may be especially reluctant to take breaks because of
financial concerns (Lam et al., 2013; Mizelle et al., 2022; Iglesias-
Rios et al., 2023; Spector et al., 2015; Wadsworth et al., 2019), a
significant portion of employees paid on an hourly basis are also not
taking adequate breaks for other reasons such as pressure from co-
workers or supervisors, high work demands, or attitudes related to work
ethics (Arnold et al., 2020; Wadsworth et al., 2019). For example,
Langer et al. (2021) surveyed 507 Latinx California farmworkers (77%
paid hourly) during the summers of 2014 and 2015, when California
regulations to protect employees from heat required employers to
provide rest breaks if needed but did not require rest breaks at a
minimum frequency and duration; 39% of surveyed employees reported
taking fewer than 2 rest breaks (not including lunch) per day.
Additionally, in a study of 165 legally employed child Latinx farm
employees (64% hourly workers) ranging in age from 10-17 years in North
Carolina, 88% reported taking breaks in shade, but based on some
interviews, the breaks appeared to be of short duration (e.g., ``for
some five minutes;'' ``you can take a break whenever you want . . . not
for a long time . . . if you wanna get a drink of water only for a
couple of minutes, three or five'') (Arnold et al., 2020). The children
who were interviewed by Arnold et al. (2020) reported pressure to keep
up with the pace of work and being discouraged to take breaks by co-
workers or supervisors. In interviews of 405 migrant farmworkers in
Georgia, 20% reported taking breaks in the shade (Fleischer et al.,
2013).
In a study of 101 farmworkers (61% paid hourly) in the Florida/
Georgia region, Luque et al. (2020) reported that only 23% took breaks
in the shade. The need for breaks was supported by observations that
while some employees carried water bottles, most were only seen
drinking during rest breaks. In another study, focus group discussions
with piece-rate farm employees revealed that many expressed concerns
about possible losses in earnings and that they might be replaced by
another employee if they took breaks. Many such employees brought their
own water to work to reduce the time they are not picking produce
(Wadsworth et al., 2019). In that same study by Wadsworth et al.
(2019), piece rate farmworkers also described ``their desire to be seen
as a good worker, with great fortitude.'' Good workers were described
by the farmworkers as those who ``work fast and do not slow things down
and jeopardize success for the group. They continue working in spite of
the conditions or how they feel.'' (Wadsworth et al., 2019, p. 224). A
case study highlighted in the NIOSH criteria document discusses a
migrant farmworker who died from HRI after he continued to work despite
a supervisor instructing him to take a break because he was working
slowly (NIOSH 2016, pp. 46-47). On the day of his death, the heat index
ranged from 86 to 112 [deg]F.
Evidence supporting the need for required rest breaks is not
limited to farmworkers. For example, a NIOSH health hazard evaluation
(HHE) indicated that truck drivers for an airline catering facility
often skipped breaks they were allowed to take between deliveries in an
air-conditioned room at the catering facility to keep up with job
demands (NIOSH, 2016, p. 44). Such attitudes appear common in employees
of all sectors. Phan and Beck (2023) surveyed 107 office workers, and
25-33% of those employees reported they skipped breaks because of a
high workload, not wanting to lose momentum, or to reduce the amount of
work to be completed in the future. A number of informal surveys
reported similar findings for office and remote workers. In those
surveys, many employees (approximately 40%) skip some breaks,
particularly lunch breaks (Tork, June 14, 2021; Joblist, July 5, 2022).
Common reasons for skipping lunch breaks included work demands and
feelings of guilt or being judged for taking a break (Tork, June 14,
2021; Joblist, July 5, 2022). One survey also reported that a major
reason why many employees do not take paid time off is
because of concerns for coworkers (Joblist, July 5, 2022). Although
these informal surveys cover employees who would likely not be covered
by the scope of this proposed standard, these informal surveys echo the
findings of the studies in the preceding paragraphs and show that
employees generally do not take rest breaks or other paid time off.
Studies of presenteeism (i.e., working while ill or injured)
suggest that employees may be more likely to ignore signs of excessive
heat strain than they are to take breaks needed to prevent overheating.
Hemp (October 2004, pp. 3-4) stated ``[u]nderlying the research of
presenteeism is the assumption that employees do not take their jobs
lightly, that most of them need and want to continue working if they
can.'' Although financial reasons such as lack of paid leave are often
drivers of presenteeism, non-financial considerations also play a major
role. One study analyzed presenteeism in many of the industries covered
by the proposed standard including in the categories of agriculture,
utilities, manufacturing, transportation and storage, and construction
(Marklund et al., 2021). Non-financially related reasons for
presenteeism reported by Marklund et al. (2021) were not wanting to
burden coworkers, perception that no one else can do the work,
enjoyment of work, not wanting to be perceived as lazy or unproductive,
and pride. Similar reasons were reported in other studies including
wanting to spare co-workers from additional work, pressure from
coworkers, strong teamwork and good relationships with coworkers,
examples set by management, institutional loyalty, or a perception that
taking time off is underperformance (Garrow, February 2016; Lohaus et
al., 2022).
The proposed requirement to include mandatory rest breaks is
consistent with recommendations by authoritative sources. For example,
NIOSH recommends mandatory rest breaks (NIOSH, 2016, p. 45; NIOSH,
2017b, p.1). Additionally, ACGIH (2023) lists ``appropriate breaks with
shade'' as an essential element of a heat stress management program.
The NACOSH Working Group on Heat also recommended that scheduled,
mandatory rest breaks be provided without retaliation (NACOSH Working
Group on Heat, 2023, pp. 6-7).
OSHA examined a number of studies to determine an appropriate
frequency and duration of rest breaks. First, a series of laboratory
studies by Notley et al. (2021; 2022a, b) provide insight on the
appropriate frequency of rest breaks. In those studies, unacclimatized
participants wearing a single clothing layer exercised at a moderate
intensity level until stay time was reached (i.e., core temperatures
reached 38 [deg]C (100.4 [deg]F) or increased by at least 1 [deg]C) at
various ambient temperatures and at a relative humidity of 35% (Notley
et al., 2021; 2022a, b).\1\ In a study of younger (18-30 years old) and
older men (50-70 years old), data from all participants were pooled to
calculate initial stay times of 111 minutes at ambient conditions of
34.1 [deg]C (93.4 [deg]F) (heat index = 93.9 [deg]F) and 44 minutes at
ambient conditions of 41.4 [deg]C (106.5 [deg]F) (heat index = 119.8
[deg]F) (Notley et al., 2022b). In a study of unacclimatized younger
men (mean age 22 years), older men (mean age 58 years), and older men
with diabetes (mean age 60 years) or hypertension (mean age 61 years),
median stay times were 128 minutes at 36.6 [deg]C (97.9 [deg]F) (heat
index = 101.5 [deg]F) and 68 minutes at 41.1 [deg]C (106.5 [deg]F)
(heat index = 118.5 [deg]F) (Notley et al., 2021). In a third study,
unacclimatized men and women were able to work for a median time of 117
minutes at 36.6 [deg]C (97.9 [deg]F) (heat index = 101.5 [deg]F) and 63
minutes at 41.4 [deg]C (106.5 [deg]F) (heat index = 119.8 [deg]F)
(Notley et al., 2022a). Overall, the results of these studies support
work times ranging from 111 minutes to 128 minutes at heat indices of
93.9 [deg]F to 101.5 [deg]F and 44 to 68 minutes at heat indices of
118.5 [deg]F to 119.8 [deg]F.
Two laboratory studies support a preliminary conclusion that rest
breaks contribute to the protection of workers from the effects of heat
(Uchiyama et al., 2022; Smallcombe et al., 2022). These studies were
conducted over periods that could represent all or part of a workday,
with light exertion exercise conducted under hot conditions (e.g., 37
;C (98.6 [deg]F) and 40% relative humidity (heat index = 106 [deg]F))
in Uchiyama et al. (2022), and moderate to heavy exertion exercise
conducted under four conditions: 15 [deg]C (59 [deg]F) and 50% relative
humidity (referent group, heat index not relevant), 35 [deg]C (95
[deg]F) 50% relative humidity (heat index = 105 [deg]F); 40[deg]C (104
[deg]F) and 50% relative humidity (heat index = 131 [deg]F); and 40
[deg]C (104 [deg]F), and 70% relative humidity (heat index=161 [deg]F)
in Smallcombe et al. (2022). In both studies, breaks were provided in
air-conditioned or cooler areas. The studies show little evidence of
excessive heat strain in participants as mean core temperatures
remained within 1 [deg]C of 37.5 [deg]C (99.5 [deg]C) (ACGIH, 2023, p.
244). Uchiyama et al. (2022) evaluated two work/rest protocols,
including one in which participants exercised for 1 hour, rested for 30
minutes, exercised for 1 hour, rested for 15 minutes, and then
exercised for another hour; increases in mean core temperatures were
less than 1 [deg]C above mean baseline temperature (37.2 [deg]C) in
five of the six time points reported and slightly exceeded a 1 [deg]C
increase at 180 minutes, the final time point of measurement (38.29
[deg]C). OSHA finds these work/rest cycles to be similar to a late
morning period of work, followed by a 30-minute lunch and then an early
afternoon work/rest period, although acknowledges that the duration
between rest periods is longer in the proposed rule than in this study.
Also, in the Uchiyama et al. (2022) study, a lack of heat strain was
also observed in a protocol consisting of 1 hour of work and 15 minutes
rest, followed by three half hour work periods separated by 10-minute
rest periods and, and a final half hour work period.
The Smallcombe et al. (2022) study most closely reflected a typical
workday because it was conducted over a 7-hour period with cycles of
50-minute work/10-minute rest and a 1-hour lunch. Participants were
tested under one referent conditions and three hot temperature
conditions and average rectal temperature remained at or below 38
[deg]C (100.4 [deg]F) in all groups during each exercise period at heat
indices ranging from 105 [deg]F to 161 [deg]F (table S2).
Overall, OSHA preliminarily finds that these studies show that 15-
minute rest breaks would offer more protection for employees than
shorter duration rest breaks, because the frequency of rest breaks in
these studies by Uchiyama et al. (2022) and Smallcombe et al. (2022)
was greater than what OSHA is proposing and rest breaks were provided
in air-conditioned or cooler areas. OSHA expects some employees will
not have access to air-conditioned areas during break periods. OSHA
acknowledges uncertainties in determining a precise rest break
frequency and duration, but preliminarily concludes that a minimum of a
15-minute rest break every two hours would be highly protective in many
circumstances at or above the high heat trigger, while offering
employers administrative convenience. For example, other approaches
such as adjusting rest break frequency and duration based on weather
conditions, work intensity, or protective clothing are likely to be
difficult for many employers to implement. A 15-minute break every two
hours is administratively convenient to implement because, as explained
below, a standard meal break could qualify as a rest break, and
therefore, assuming an 8-hour workday with a meal break in the middle
of the day, paragraph (f)(2) would only require two other breaks, one
break in the morning and a second break in the afternoon, assuming the
high heat trigger is met or exceeded the entire day.
The frequency and duration of these proposed rest breaks are within
the ranges of frequencies and durations required by four U.S. States
that have finalized regulations protecting against HRI by requiring
rest breaks under high heat conditions. First, the California
regulation for outdoor employees requires a minimum ten-minute rest
period every two hours for agricultural employees, when temperatures
reach or exceed 95 [deg]F (Cal. Code Regs. tit. 8, section 3395
(2024)). Second and similarly, the Colorado regulation for agricultural
employees requires a minimum 10-minute rest period every two hours
under increased risk conditions that include a temperature at or above
95 [deg]F (7 Colo. Code Regs. section 1103-15:3 (2023)). Third, in
Oregon rules applying to agriculture as well as indoor and outdoor
workplaces, employers can select from three different options for work-
rest periods at high heat, including: (1) an employer-designed program
with a minimum of a 10-minute break every two hours at a heat index of
90 [deg]F or greater and a 15-minute break every hour at a heat index
of 100 [deg]F or greater, with possible increased frequency and
duration of breaks based on PPE use, clothing, relative humidity, and
work intensity; (2) development of work/rest schedules based on the
approach recommended by NIOSH (see NIOSH, 2016), or (3) a simplified
rest break schedule that calls for a 10-minute break every two hours,
with durations and frequencies of rest breaks increasing with increases
in heat index (Or. Admin. R. 437-002-0156 (2024); Or. Admin. R. 437-
004-1131 (2024)). Fourth and finally, for outdoor workplaces,
Washington requires a minimum 10-minute rest period every two hours at
an air temperature at or above 90 [deg]F and a minimum 15-minute rest
period every hour at an air temperature at or above 100 [deg]F (Wash.
Admin. Code 296-307-09747 (2023)).
A NIOSH guidance document recommends work/rest cycles for employees
wearing ``normal clothing'' that considers temperature adjusted for
humidity levels and cloud cover and work intensity; in that guidance,
when the need for rest cycles is triggered, work/rest cycles range from
45 minutes work/15 minutes rest to 15 minutes work/45 minutes rest,
with extreme cautioned urged under some conditions (NIOSH, 2017b).
OSHA acknowledges the requirements of some States and
recommendations by NIOSH to increase frequency and duration of rest
breaks as heat conditions increase, but OSHA has preliminarily decided
on a more simplified approach, in part because of implementation
concerns raised by stakeholders, such as difficulty in implementing a
more complex approach (e.g., longer and more frequent rest breaks with
increasing temperature), and interference with certain types of work
tasks (e.g., continuous production work and tasks such as pouring
concrete that could be disrupted by more frequent breaks). In addition,
the requirement to continue providing paid breaks if needed above the
high heat trigger, coupled with the requirement to encourage employees
to take these breaks, will help ensure that any employee that needs an
additional break can take one. However, OSHA acknowledges that, for the
reasons discussed above, this encouragement may become more vital as
the temperature increases to ensure that employees don't forego the
breaks they are entitled to. OSHA welcomes comment and data on the
appropriateness of this approach.
B. Complying With Rest Break Provisions
The required break periods under paragraph (f)(2) are a minimum.
Nothing in the proposed standard would preclude employers from
providing longer or more frequent breaks. Additionally, employers would
need to comply with paragraph (e)(8) (i.e., providing rest breaks if
needed to prevent overheating), which may include situations where
employees need more frequent or longer break periods. Paragraph (f)(2)
requires employers to ensure that employees have at least one break
that lasts a minimum of 15 minutes every two hours when the high heat
trigger is met or exceeded. The requirement is in addition to
employers' obligation under paragraph (e)(8) to allow and encourage
rest breaks if needed to prevent overheating, which continues after the
high heat trigger is met. However, if an employee takes a rest break
under paragraph (e)(8) that lasts at least 15 consecutive minutes, that
would impact when the employer would next need to provide a break under
paragraph (f)(2). For example, if the high heat trigger is exceeded for
an entire 8-hour work day, and the employee takes a 15-minute break
after their first hour of work because they need one to prevent
overheating, the employer would not be required to provide another 15-
minute break under paragraph (f)(2) for the next two hours. However,
the employer's on-going obligation under paragraph (e)(8) would remain.
Employers would also need to comply with paragraph (g)(2) (i.e.,
relieving an employee from duty when they are experiencing signs and
symptoms of heat-related illness).
Under proposed paragraph (f)(2), when the high heat trigger is met
or exceeded, employers would be required to provide a minimum 15-minute
paid rest break at least every two hours in the break area that would
be required under paragraph (e)(3) or (4). These rest breaks would be
mandatory, and the employer would need to ensure that rest breaks are
taken as required.
Proposed paragraphs (f)(2) and (e)(8) would require that employees
be paid during rest breaks. As discussed further in the Explanation of
Proposed Requirements for paragraph (j), Requirements implemented at no
cost to employees, OSHA finds it important that employees be paid
during the time they are taking breaks that are mandatory or needed to
prevent overheating so that employees are not financially penalized and
thus discouraged from taking advantage of those protections. See
Explanation of Proposed Requirements for paragraph (j) for Requirements
implemented at no cost to employees for a discussion of approaches
employers can take to ensure that both hourly employees and piece rate
employees are compensated for time on rest breaks.
Rest breaks are not the same as slowing down or pacing. In
addition, performing a sedentary work activity, even if done in an area
that meets the requirements of a break area under proposed paragraphs
(e)(3) or (4), would not be considered a rest break under the proposed
standard. This ensures that employees can rest (thus modulating
increases in heat strain) and hydrate during that rest break.
OSHA recognizes that providing a rest break every two hours might
be challenging for some employers. However, employers could consider
approaches such as staggering employee break times, within the required
two-hour period, to ensure that some employees are always available to
continue working. In other cases, employers who have concerns about
employee safety, such as having to climb up and down from high
locations to take a break, might be able to provide portable shade
structures, if safe to use under the conditions (e.g., elevation, wind
conditions). In addition, employers could consider scheduling work
tasks during cooler parts of the day to avoid required rest breaks.
Proposed paragraphs (f)(2)(i) indicates that a meal break that is
not required to be paid under law may count as a rest break. Whether a
meal break must be paid is governed by other laws, including State
laws. Under the Federal Fair Labor Standards Act, bona fide meal
periods (typically 30 minutes or more) generally do not need to be
compensated as work time (see 29 CFR 785.19). The employee must be
completely relieved from duties for the purpose of eating regular
meals. Furthermore, an employee is not relieved if they are required to
perform any duties, whether active or inactive, while eating.
Proposed paragraphs (f)(2)(ii) and (iii) further clarify that total
time of the rest break would not include the time that employees take
to put on and remove PPE or the time to walk to and from the break
area. OSHA preliminarily finds it important to exclude this time from
the 15-minute rest period so employees have the full 15 minutes to cool
down.
C. Requests for Comments
OSHA requests comments and evidence regarding the following:
Stakeholders' experiences with rest breaks required under
law or by the employer, including successes and challenges with such
approaches;
Whether there is additional evidence to support a 15-
minute rest break every 2 hours as effective in reducing heat strain
and preventing HRIs;
Whether OSHA should consider an alternative scheme for the
frequency and/or duration of rest breaks under paragraph (f)(2). If so,
what factors (such as weather conditions, intensity of work tasks, or
types of clothing/PPE) should it be based on and why;
Whether varying frequency and duration of rest breaks
based on factors such as the heat index would be administratively
difficult for employers to implement and how any potential
administrative concerns could be addressed;
Whether employees could perform certain sedentary work
activities in areas that meet the proposed requirements for break areas
without hindering the effectiveness of rest breaks for preventing HRI,
including examples of activities that would or would not be acceptable;
and
Whether OSHA should require removal of PPE that may impair
cooling during rest breaks.
III. Observation for Signs and Symptoms
Paragraph (f)(3) of the proposed standard would establish
requirements for observing employees for signs and symptoms of heat-
related illness when the high heat trigger is met or exceeded. As
explained in Section IV., Health Effects, heat-related illnesses can
progress to life-threatening conditions if not treated properly and
promptly. Therefore, it is important to identify the signs and symptoms
of heat-related illness early so appropriate action can be taken to
prevent the condition from worsening. OSHA preliminarily finds that
observation for signs and symptoms of heat-related illness in employees
is a critical component of heat injury and illness prevention.
NIOSH recommends observation for signs and symptoms of heat-related
illness by a fellow worker or supervisor (NIOSH, 2016). The NACOSH Heat
Injury and Illness Prevention Work Group also provided recommendations
related to observation for signs and symptoms of heat-related illness
in its recommendations to OSHA on potential elements of heat injury and
illness prevention standard. The NACOSH Work Group recommended that
there be additional requirements for workers who work alone since a
buddy system is not possible in those cases, including a communication
system with regular check-ins (NACOSH Working Group on Heat, 2023).
Paragraph (f)(3) would require that the employer implement at least
one of two methods of observing employees for signs and symptoms of
heat-related illness, with a third option for employees who work alone
at a work site. As defined under proposed paragraph (b), Signs and
symptoms of heat related illness means the physiological manifestations
of a heat-related illness and includes headache, nausea, weakness,
dizziness, elevated body temperature, muscle cramps, and muscle pain or
spasms.
The first option, under proposed paragraph (f)(3)(i), that an
employer may choose is to implement a mandatory buddy system in which
co-workers observe each other. Employers could satisfy this requirement
by pairing employees as ``buddies'' to observe each other for signs and
symptoms of heat-related illness. Co-workers assigned as buddies would
need to be in the same work area so that it is possible for them to
observe each other. Co-workers could also use visual cues or signs and/
or verbal communication to communicate signs and symptoms of heat-
related illness to each other.
The second option, under proposed paragraph (f)(3)(ii), that the
employer may choose is for observation to be carried out by a
supervisor or heat safety coordinator. If the employer chooses this
option, proposed paragraph (f)(3)(ii) specifies that no more than 20
employees can be observed per supervisor or heat safety coordinator.
OSHA preliminarily finds that it is important to limit the number of
employees being observed to ensure that each employee is receiving the
amount of observation needed to determine if they are experiencing any
signs and symptoms of heat-related illness. Supervisors or heat safety
coordinators would need to be in a position to observe the employees
they are responsible for observing for signs and symptoms (e.g., in
close enough proximity to communicate with and see) when observing for
signs/symptoms. The supervisor or heat safety coordinator could have
other tasks or work responsibilities while implementing the observation
role, but they must be able to be within close enough proximity to
communicate with and see those they are observing and be able to check
in with the employee regularly (e.g., every two hours). When the high
heat trigger is met, employers would still be responsible for meeting
the proposed requirements of paragraph (e)(9), Effective Communication.
Employees need to have a means of effective communication with a
supervisor (e.g., phone, radio) and employers must regularly
communicate with employees at or above both the initial and high heat
triggers.
Because symptoms of heat-related illness may not be outwardly
visible (e.g., nausea, headache), employers should ensure employees are
asked if they are experiencing any signs and symptoms. This is
especially true if the employee shows changes in behavior such as
working more slowly or dropping things because this could indicate that
the employee is experiencing heat-related illness but not recognizing
it. It is also important that employees report any signs and symptoms
they are experiencing or that they observe in others in order to
prevent development of potentially life-threatening forms of heat-
related illness (see proposed paragraph (h)(1)(x), Training).
Additionally, as discussed below, certain signs and symptoms indicate a
heat-related emergency.
Employees who work alone at a work site do not have a co-worker,
supervisor, or heat safety coordinator present who can observe them to
determine if they are experiencing signs and symptoms of heat-related
illness. For employees working alone at a work site, the employer would
instead need to comply with proposed paragraph (f)(3)(iii) and maintain
a means of effective, two-way communication with those employees and
make contact with them at least
every two hours. This means that employers must not only reach out to
lone employees, but also receive a communication back from the
employees. Receiving communication back from the employee allows the
employee to report any symptoms. If no communication is received, this
may be a sign that the employee is having a problem.
Under proposed paragraph (h)(1)(iv), employers would be required to
train employees on signs and symptoms of heat-related illness and which
ones require immediate emergency action. Proposed paragraph (b) defines
signs and symptoms of a heat emergency as physiological manifestations
of a heat-related illness that requires emergency response and includes
loss of consciousness (i.e., fainting, collapse) with excessive body
temperature, which may or may not be accompanied by vertigo, nausea,
headache, cerebral dysfunction, or bizarre behavior. This could also
include staggering, vomiting, acting irrationally or disoriented,
having convulsions, and (even after resting) having an elevated heart
rate. Employer obligations when an employee is experiencing signs and
symptoms of a heat-related illness or heat emergency are addressed
under proposed paragraph (g).
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Stakeholders' experiences with implementing observational
systems such as those that OSHA is proposing and examples of the
implementation of other observational systems for signs and symptoms of
heat-related illness that OSHA should consider;
Data of the effectiveness of such observation systems;
The frequency at which observation as described in this
section should occur;
Whether there are alternative definitions of signs and
symptoms of heat-related illness that OSHA should consider;
Whether employers should be able to select a designee to
implement observation in situations where it may not be possible to
have a supervisor or heat safety coordinator present;
Possible logistical concerns regarding proposed
requirements for communication at least every two hours for employees
who work alone at the work site; whether there are examples of
successful implementation of these types of communication systems;
examples of the types of technologies or modes of communication that
most effectively support this type communication; and whether there are
innovative approaches for keeping employees working alone safe from HRI
and allowing for prompt response in an emergency; and
For employees who work alone at the work site, whether the
employer should know the location of the employee at all times.
IV. Hazard Alert
Paragraph (f)(4) of the proposed standard would require employers
to issue a hazard alert to employees prior to a work shift or when
employees are exposed to heat at or above the high heat trigger.
As explained in Section IV., Health Effects, hazardous heat can
lead to sudden and traumatic injuries and heat-related illnesses can
quickly progress to life threatening forms if not treated properly and
promptly. To protect employees, it is not sufficient to respond to HRIs
after they occur. Prevention of HRIs is critical. A hazard alert will
help prevent HRIs by notifying employees of heat hazards, providing
information on HRI prevention, empowering employees to utilize
preventative measures, and providing practical information about how to
access prevention resources (e.g., drinking water, break areas to cool
down) and seek help in case of emergency.
Heat alert programs have been identified as important prevention
strategies (NIOSH, 2016; Khogali, 1997). NIOSH identified heat alert
programs as a strategy to prevent excessive heat stress and recommended
that heat alert programs be implemented under certain high heat
conditions (NIOSH, 2016, p. 10). NIOSH further describes an example of
an effective heat alert program, drawing in part on recommendations
described by Dukes-Dobos (1981). Effective elements of a hazard alert
program include similar elements to the proposed provision (f)(4), such
as ``Establish[ing] criteria for the declaration of a heat alert'' and
``Procedures to be followed during the state of [the] [h]eat [a]lert''
(e.g., reminding employees to drink water) (NIOSH, 2016, pp. 80-81).
Employees may face pressure or incentives to work through hazardous
heat which can increase their risk of heat-related illness; some
employees also may not recognize that they are developing signs and
symptoms of a heat-related illness (see Section IV., Health Effects).
The hazard alert provision would require that employers provide
information about prevention measures, including employees' right to
take rest breaks if needed, at the employees' election, and the rest
breaks required by paragraph (f)(2), which will empower employees to
utilize the preventative measures available. This requirement would
also enable effective response in the event of a heat emergency by
requiring employers to remind employees in advance of its heat
emergency procedures.
OSHA preliminarily finds that the hazard alert requirement in
proposed paragraph (f)(4) is an important strategy for the prevention
of HRIs. The provision includes minimum requirements for the hazard
alert and provides flexibility for employers in how they implement the
provision. Additionally, employers may choose to include additional
information in the alert that is appropriate for their work sites.
Paragraph (f)(4) would require that prior to the work shift or upon
determining the high heat trigger is met or exceeded, the employer must
notify employees of specific information relevant to the prevention of
heat hazards. Specifically, the employer would be required to notify
employees of the following: the importance of drinking plenty of water;
employees' right to, at employees' election, take rest breaks if needed
and the rest breaks required by paragraph (f)(2); how to seek help and
the procedures to take in a heat emergency; and for mobile work sites,
information on the location of break area(s) required by paragraph
(e)(3) or (4) and drinking water required by paragraph (e)(2). Because
the location of break area(s) and drinking water may change frequently
for mobile work sites, it is important to make sure employees at those
work sites are reminded of their location on high heat days. Mobile
work sites include work sites that change as projects progress or when
employees relocate to a new project (e.g., landscaping, construction).
Paragraph (f)(4) would require the employer to issue the hazard
alert prior to the work shift or upon determining the high heat trigger
is met or exceeded. However, issuing the alert prior to the start of
the work shift would not be required unless exposures will be at or
above the high heat trigger at the start of the work shift. If the
start of the work shift is below the high heat trigger and the hazard
alert is not issued at the start of the work shift, then the hazard
alert must be issued when the high heat trigger is met and ideally
before exposure occurs. For example, if a work shift runs from 8 a.m.
to 5 p.m. and the high heat trigger is not met until 10 a.m., the
employer must either issue the alert at the beginning of the work
shift, or issue the alert when the high heat
trigger is met at 10 a.m. If an employer regularly communicates with an
employee via a particular means of communication and uses that form of
communication to issue the alert, then the employer can presume the
notification was received. If, however, the employer has reason to
believe the hazard alert was not received, they would need to take
additional steps to confirm.
Employers could satisfy the requirements of this provision by
posting signs with the required information at locations readily
accessible and visible to employees. For example, some employers may
choose to post signs at the entrance to the work site. Signs are not an
option for all employers as they may not be sufficient to ensure
employees receive the hazard alert (e.g., employers with mobile
employees or employees who work alone on a work site). Additionally,
signs may not be an option for employers who choose not to provide the
hazard alert at the start of the work shift. For example, posting a
sign at the entrance to the work site would not be sufficient to ensure
employees are notified after all employees have already entered the
work site. Employers may also satisfy the hazard alert notification
requirement by issuing the alert electronically (e.g., via email, text
message) or through verbal means (e.g., an in-person meeting, radio or
voicemail). Employers may be able to use the system they have in place
to meet the requirements of paragraph (e)(9) for effective, two-way
communication with employees to issue the hazard alert.
For any method the employer chooses to issue the hazard alert
notification, the hazard alert must be sufficient to ensure all
employees are notified of the information in paragraphs (f)(2)(i)
through (iv). To ensure this, the hazard alert must be issued in
languages and at a literacy level understood by employees.
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether any additional information should be required in
the hazard alert;
The frequency of the hazard alert, particularly in
locations that frequently exceed the high heat trigger; and
Any alternatives to a hazard alert requirement that OSHA
should consider.
V. Excessively High Heat Areas
Paragraph (f)(5) of the proposed standard would require that
employers place warning signs at indoor work areas with ambient
temperatures that regularly exceed 120 [deg]F. The warning signs must
be legible, visible, and understandable to employees entering the work
area. Specifying the requirement for warning signs ensures that all
employees and contractors at the work site are aware of areas with
excessively high heat. Warning signs signal a hazardous situation that,
if not avoided, could result in death or serious injury and, if
employees need to enter the areas, serve as a reminder to take
appropriate precautions.
The warning signs must be legible, visible, and understandable to
employees entering the work areas. The sign must be in a location that
employees can clearly see before they enter the excessively high heat
area. To maintain visibility of the warning signs, employers must
ensure that there is adequate lighting in the area to read the signs
and that the signs are not blocked by items that would prevent
employees from seeing them. The signs would have to be legible (e.g.,
writing or print that can be read easily). The proposed standard does
not specify contents of the sign, but signs could include a signal word
such as ``Danger'', the hazard (e.g., ``High Heat Area''), possible
health effects (e.g., May Cause Heat-Related Illness or Death),
information pertaining to who is permitted to access the area (e.g.,
Authorized Personnel Only), and what precautions entrants would have to
take to safely enter the area. Employees must be able to understand the
signs. Therefore, the signs must be printed in a language or languages
that all potentially exposed employees understand. If it is not
practical to provide signs in a language or languages spoken by all
employees, employers still must ensure all employees understand what
the signs mean. Employers could do this by training on what the warning
signs mean and providing those employees with information regarding the
extent of the hazardous area as indicated on the signs.
Employers would have to place warning signs at indoor work areas
with ambient temperatures that regularly exceed 120 [deg]F. The term
``regularly'' means a pattern or frequency of occurrence rather than
isolated incidents. This would mean that the indoor work areas
experience temperatures exceeding 120 [deg]F on a frequent or recurring
basis, such as daily during certain seasons or under specific
operational conditions. The process of identifying heat hazards
pursuant to proposed paragraph (d) may help employers identify
excessively high heat areas. Under proposed paragraph (d)(3), employers
would be required to identify each work area(s) where employees are
reasonably expected to be exposed to heat at or above the initial heat
trigger and develop a monitoring plan. If, while monitoring, an
employer determines temperatures in an indoor work area regularly
exceed the 120 [deg]F threshold, then the employer would need to ensure
that warning signs are placed at that work area to alert employees to
the potential hazards associated with such extreme temperatures.
If an employer's work site contains an excessively high heat
area(s), the employer must train employees in the procedures to follow
when working in these areas (see proposed provision (h)(1)(xvi)).
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether OSHA should further specify the required location
of warning signs;
Whether OSHA should specify the wording/contents of the
warning signs; and
Whether OSHA should consider defining ``excessively high
heat area'' as something other than a work area in which ambient
temperatures regularly exceed 120 [deg]F; and evidence available to
support a different temperature threshold or other defining criteria.
G. Paragraph (g) Heat Illness and Emergency Response and Planning
Paragraph (g) of the proposed standard would establish requirements
for heat illness and emergency response and planning. It would require
that employers develop and implement a heat emergency response plan as
part of their HIIPP, as well as specify what an employer's
responsibilities would be if an employee experiences signs and symptoms
of heat-related illness or a heat emergency. Effective planning and
emergency response measures can minimize the severity of heat-related
illnesses when they occur and allow for more efficient access to
medical care when needed.
Proposed paragraph (g)(1) specifies that the employer would be
required to develop and implement a heat emergency response plan as
part of their HIIPP and specifies the elements that would be required
in an employer's emergency response plan. Because the emergency
response plan is part of the HIIPP, some of the requirements in
paragraph (c) are relevant to the emergency response plan. For example,
the employer would need to seek the input and involvement of non-
managerial employees and their representatives, if any, in the
development and implementation of the emergency response plan (see
proposed paragraph (c)(6)). See Explanation of Proposed Requirements
for paragraph (c), for a detailed explanation of the requirements that
apply to the HIIPP. Only one plan would be required for each employer
(i.e., for the whole company). However, if the employer has multiple
work sites that are distinct from each other, the plan would be
tailored to each work site or type of work site. For instance, if an
employer has employees engaged in work activities outdoors on a farm,
as well as employees loading and unloading product from vehicles at
various locations, the employer could have one emergency response plan
with the specifications for each of these types of work sites
represented. Employers may also choose to include other elements in the
plan to account for any work activities unique to their workplace.
Proposed paragraph (g)(1)(i) would require employers to include a
list of emergency phone numbers (e.g., 911, emergency services) in
their emergency response plan. Indicating the most appropriate phone
number(s) to contact in the case of an emergency helps ensure medical
support and assistance are provided timely and efficiently during a
heat emergency. Examples of other phone numbers for assistance aside
from 911 that employers might include in the plan are those for on-site
clinicians or nurses to be contacted if an employee is experiencing
signs and symptoms of a heat-related illness.
Proposed paragraph (g)(1)(ii) would require employers to include a
description of how employees can contact a supervisor and emergency
medical services in their emergency response plan. Because time is of
the essence in emergency situations, it is important that employees
know beforehand how to contact a supervisor and emergency medical
services in the event of a heat emergency. For example, if employees do
not have phone service or access to a phone to call for medical help,
but they do have access to other means of communication such as radios,
walkie-talkies, personal locator beacons, and audio signals, the
employer's plan would describe how to use these other means of
communication to contact a supervisor and emergency medical services.
Proposed paragraph (g)(1)(iii) would require the emergency response
plan to include the individual(s) designated to ensure that heat
emergency procedures are invoked when appropriate. Clearly assigning
this responsibility to an individual(s) can reduce confusion and allow
for swift action in the event of a heat emergency. Employers with
multiple work sites or dispersed work areas may not be able to ensure
heat emergency procedures are invoked without designating different
individuals for each work site/area. For example, an employer with work
activities inside two factories in different geographic locations would
need to designate an individual(s) to ensure heat emergency procedures
are invoked at each factory location.
Proposed paragraph (g)(1)(iv) would require the emergency response
plan to have a description of how to transport employees to a place
where they can be reached by an emergency medical provider. Planning
for where employees can access emergency medical services can ensure
aid is provided efficiently. This is especially important for employers
with employees engaging in work activities in remote locations, where
medical services cannot reach them. For example, an employee working in
an area of a farm not easily accessible by vehicle or an employee in a
difficult to reach location inside a building being constructed.
Proposed paragraph (g)(1)(v) would require the emergency response
plan to include clear and precise directions to the work site,
including the address of the work site, which can be provided to
emergency dispatchers. For certain work sites that are remote/hard to
reach or do not have an address, GPS coordinates may be necessary to
share with emergency responders, or a description of how to get to
their location from the main road, entrance, building, etc. If an
employee's work site changes frequently, the emergency response plan
would need to include a clear strategy to account for their changing
locations and ensure directions to the work site are readily accessible
when needed to provide to emergency dispatchers.
Proposed paragraph (g)(1)(vi) would require the emergency response
plan to include procedures for responding to an employee experiencing
signs and symptoms of heat-related illness, including heat emergency
procedures for responding to an employee with suspected heat stroke.
Prior development of emergency response procedures can ensure
assistance and medical attention are provided efficiently and quickly.
In developing the procedures, OSHA expects that employers would look to
resources such as OSHA guidance (e.g., www.osha.gov/heat-exposure/illness-first-aid) and NIOSH recommendations (NIOSH, 2016) for more
information.
The proposed standard does not require employers to develop a plan
for each work site. However, the employer's emergency response plan(s)
must contain all the information required by paragraphs (g)(1)(i)
through (vi), some of which will vary based on work site. The employer
may be able to incorporate the information needed for different work
sites into the same emergency response plan. For instance, if an
employer has employees engaged in work activities outdoors on a farm,
as well as employees loading and unloading product from vehicles at
various locations, the employer could have one emergency response plan
with the specifications for each of these types of work sites
represented. Employers may also choose to include elements beyond those
required by paragraphs (g)(1)(i) through (vi) in their plan to account
for any work activities unique to their workplace.
Proposed paragraph (g)(2) specifies the actions employers would be
required to perform if an employee is experiencing signs and symptoms
of heat-related illness. Under proposed paragraph (b) signs and
symptoms of heat-related illness means the physiological manifestations
of a heat-related illness and includes headache, nausea, weakness,
dizziness, elevated body temperature, muscle cramps, and muscle pain or
spasms.
Proposed paragraph (g)(2)(i) would require employers to relieve
from duty employees who are experiencing signs and symptoms of heat-
related illness. Relieving the employee from duty would allow the
employer to address the heat-related illness according to the
procedures outlined in proposed paragraphs (g)(2)(ii) through (v). This
relief from duty, including the time it takes to address the heat-
related illness according to the procedures outlined in proposed
paragraphs (g)(2)(ii) through (v), must be with pay and must continue
at least until symptoms have subsided.
Proposed paragraph (g)(2)(ii) would require that employers monitor
employees who are experiencing signs and symptoms of heat-related
illness, and proposed paragraph (g)(2)(iii) would require employers to
ensure that employees who are experiencing signs and symptoms of heat-
related illness are not left alone. Continuous monitoring of employees
who are experiencing signs and symptoms of a heat-related illness is
important to ensure that if the employee's condition progresses to a
heat emergency, someone is there to observe it and quickly respond.
Proposed paragraph (g)(2)(iv) would require employers to offer
employees who are experiencing signs and
symptoms of heat-related illness on-site first aid or medical services
before ending any monitoring. This requirement is intended to be
consistent with existing first aid standards (e.g. 29 CFR 1910.151,
1915.87, 1926.23 and 1926.50), which require accessibility of medical
services and first aid to varying degrees depending on the industry or
whether the workplace is near an infirmary, clinic or hospital.
Proposed paragraph (g)(2)(iv) would not add new requirements for staff
to be fully trained in first aid. Employers would offer the first aid
or medical resources they have available to employees on site to the
extent already required by first aid standards and follow the
procedures developed in paragraph (g)(1)(vi) as applicable.
Proposed paragraph (g)(2)(v) would require employers to provide
employees who are experiencing signs and symptoms of heat-related
illness with means to reduce their body temperature. Examples of means
to reduce body temperature are instructing those employees to remove
all PPE and heavy outer clothing (e.g., heavy/impermeable protective
clothing) and moving them to a cooled or shaded area (e.g., the break
areas required under paragraphs (e)(3) and (4)) where they can sit and
drink cool water. If the employer has cooling PPE (e.g., cooling
bandanas or neck wraps, and vests and cooling systems such as hybrid
personal cooling systems (HPCS), and fans) available on site, those
could also be used to cool employees as well. (For information related
to the requirement to reduce an employee's body temperature in the case
of a heat emergency, see discussion below.)
Proposed paragraph (g)(3) specifies the actions employers would
have to perform if an employee is experiencing signs and symptoms of a
heat emergency. Proposed paragraph (b) defines signs and symptoms of a
heat emergency as the physiological manifestations of a heat-related
illness that requires emergency response and includes loss of
consciousness (i.e., fainting, collapse) with excessive body
temperature, which may or may not be accompanied by vertigo, nausea,
headache, cerebral dysfunction, or bizarre behavior. This could also
include staggering, vomiting, acting irrationally or disoriented,
having convulsions, and (even after resting) having an elevated heart
rate.
Proposed paragraph (g)(3)(i) would require employers to take
immediate actions to reduce the employee's body temperature before
emergency medical services arrive. Rapid cooling of body temperature
during a heat emergency is essential because the potential for organ
damage and risk of death increase in a short period of time, often
before medical personnel can respond, transport, and treat the affected
individual (Belval et al., 2018). Immersion in ice water or cold water
has been reported to have the fastest cooling rates (McDermott et al.,
2009b; Casa et al., 2007). However, OSHA realizes that immersing an
employee in a tub of ice/cold water is not an option that will be
available at most work sites. Other, more practical methods of reducing
employee body temperature using materials that employers are likely to
have, or are similar to materials that an employer is likely to have,
on site have been reported to be highly effective in preventing death
from exertional heat stroke. DeGroot et al. (2023) reported survival of
362 of 363 military personnel who were suffering from exertional heat
stroke and were treated with strategically placed ``ice sheets'' (i.e.,
bed sheets soaked in ice water). McDermott et al. (2009a) reported 100%
survival in nine marathon runners who were suffering from exertional
heat stroke and treated by dousing with cold water and rubbing of ice
bags over major muscle groups. Another possible approach is the tarp-
assisted cooling oscillation (TACO) method that involves wrapping the
affected individual in a tarp with ice (Luhring et al., 2016).
Proposed paragraph (g)(3)(ii) would require employers to contact
emergency medical services immediately for employees experiencing signs
and symptoms of a heat emergency, and proposed paragraph (g)(3)(iii)
would require employers to also perform the activities described in
paragraphs (g)(2)(i) through (iv) to aid an employee during a heat
emergency until emergency medical services arrives. Some heat-related
illnesses can quickly progress and become fatal (see Section IV.,
Health Effects). The severity and survival of heat stroke is highly
dependent on how quickly effective cooling and emergency medical
services are provided (Vicario et al., 1986; Demartini et al., 2015;
Belval et al., 2018).
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether OSHA should require a minimum duration of time an
employee who has experienced signs and symptoms of heat-related illness
must be relieved from duty, and what an appropriate duration of time
would be before returning employees to work;
Whether OSHA should add or remove any signs or symptoms in
the definitions of signs and symptoms of heat-related illness and signs
and symptoms of a heat emergency in proposed paragraph (b). If so,
provide clear and specific evidence for inclusion or exclusion;
Whether paragraph (g)(3)(i) should require specific
actions that the employer must take to reduce an employee's body
temperature before emergency medical services arrive, rather than
merely requiring unspecified ``immediate actions''. If so, describe
those specific actions; and
Whether paragraph (g)(3)(i) should prohibit certain
actions to reduce an employee's body temperature before emergency
medical services arrive. If so, indicate if there is evidence or
observations that certain actions are not helpful or are
counterproductive.
H. Paragraph (h) Training
Paragraph (h) of the proposed standard establishes requirements for
training on HRI prevention. It addresses the topics to be addressed in
training, the types of employees who are to be trained, the frequency
of training, triggers for supplemental training, and how training is to
be conducted. OSHA regularly includes training requirements in its
standards to ensure employees understand the hazards addressed by the
standard, the protections they are entitled to under the standard, and
the measures to take to protect themselves. Here, OSHA believes that it
is essential that employees are trained on heat-related hazards and how
to identify signs and symptoms of HRIs as well as on the requirements
of the proposed standard and the employer's heat-related policies and
procedures. This training ensures that employees understand heat
hazards and the workplace specific control measures that would be
implemented to address the hazard. The effectiveness of the proposed
standard would be undermined if employees did not have sufficient
knowledge and understanding to identify heat hazards and their health
effects or sufficient knowledge and understanding of their employer's
policies and procedures for addressing those hazards.
Surveys and interviews with diverse working populations highlight
the need for additional education and training on HRIs and prevention
strategies amongst employees (Luque et al., 2020; Smith et al., 2021;
Fleischer at al., 2013; Stoecklin-Marois et al., 2013; Langer et al.,
2021; Jacklitsch et al., 2018). The NACOSH Heat Injury and Illness
Prevention Work Group recommended that both workers and supervisors are
trained in heat illness and injury
prevention strategies. Additionally, the Work Group recommended that
the training program includes the following elements: identification of
hazards; mitigation of hazards through prevention; reporting of signs
and symptoms; and emergency response. OSHA preliminarily finds that
effective training is an essential element of any heat injury and
illness prevention program and that the requirements in proposed
paragraph (h) are necessary and appropriate to ensure the effectiveness
of the standard as a whole.
Proposed paragraph (h)(1) establishes the initial training
requirements for all exposed employees. It would require employers to
ensure that each employee receives, and understands, training on the
topics outlined in proposed paragraphs (h)(1)(i) through (xvi) prior to
the employee performing any work at or above the initial heat trigger.
Requiring that initial training occur before employees perform any work
at or above the initial heat trigger ensures that the employees have
all the knowledge necessary to protect themselves prior to their
exposure to the hazard.
This provision, like paragraphs (h)(2) through (h)(4), would
require employers to ensure that employees, including supervisors and
heat safety coordinators, understand the training topics. While OSHA
does not mandate testing or specific modes of ascertaining employee
understanding of the training materials, OSHA expects that all required
training will include some measure of comprehension. Different ways
that employers could ensure comprehension of the training materials
include a knowledge check (e.g., written or oral assessment) or
discussions after the training. Post training assessments may be
particularly useful for ensuring employee participation and
comprehension when employers offer online training. Proposed paragraph
(h)(5), discussed below, includes additional requirements for
presentation of the training.
Proposed paragraph (h)(1)(i) would require employers to provide
training on heat stress hazards. Heat stress is the total heat load on
the body. There are three major types of hazards which contribute to
heat stress: (1) environmental factors such as high humidity, high
temperature, solar radiation, lack of air movement, and process heat
(i.e., radiant heat produced by machinery or equipment, such as ovens
and furnaces), (2) use of personal protective equipment or clothing
that can inhibit the body's ability to cool itself, and (3) the body's
metabolic heat (i.e., heat produced by the body during work involving
physical activity and exertion). Employers should make employees aware
of all the sources of heat at the workplace that contribute to heat
stress.
Proposed paragraph (h)(1)(ii) would require employers to provide
training on heat-related injuries and illnesses. See Section IV.,
Health Effects, for a discussion of HRIs. Examples of heat-related
illnesses include heat stroke, heat exhaustion, heat cramps, heat
syncope, and rhabdomyolysis. Heat-related injuries that could result
from heat illness include slips, trips, falls, and other injuries that
could result from the mishandling of equipment due to the effects of
heat stress.
Proposed paragraph (h)(1)(iii) would require employers to provide
training on risk factors for heat-related injury or illness, including
the contributions of physical exertion, clothing, personal protective
equipment, a lack of acclimatization, and personal risk factors (e.g.,
age, health, alcohol consumption, and use of certain medications). As
noted above, physical exertion, clothing, and personal protective
equipment all increase an employee's heat load. More information on
acclimatization and how it affects risk is included in Section V.C.,
Risk Reduction, and more information about personal risk factors is
included in Section IV.O., Factors that Affect Risk for Heat-Related
Health Effects.
Proposed paragraph (h)(1)(iv) would require employers to provide
training on signs and symptoms of heat-related illness and which ones
require immediate emergency action. As defined in proposed paragraph
(b), signs and symptoms of heat-related illness means the physiological
manifestations of a heat-related illness and includes headache, nausea,
weakness, dizziness, elevated body temperature, muscle cramps, and
muscle pain or spasms. Also defined in proposed paragraph (b), signs
and symptoms of a heat emergency means the physiological manifestations
of a heat-related illness that requires emergency response and includes
loss of consciousness (i.e., fainting, collapse) with excessive body
temperature, which may or may not be accompanied by vertigo, nausea,
headache, cerebral dysfunction, or bizarre behavior. This could also
include staggering, vomiting, acting irrationally or disoriented,
having convulsions, and (even after resting) having an elevated heart
rate. Employers must train employees on how to identify these signs and
symptoms of heat-related illness in themselves and their coworkers and
when to employ the employer's emergency response procedures, as
required under proposed paragraph (g). That provision specifies the
actions that an employer must take both when an employee experiences
signs and symptoms of a heat-related illness and when an employee
experiences signs and symptoms of a heat emergency. For further
discussion see the Explanation of Proposed Requirements for Paragraph
(g).
Proposed paragraphs (h)(1)(v) through (vii) would require employers
to train employees on the importance of removing PPE that may impair
cooling during rest breaks, taking rest breaks to prevent heat-related
illness or injury, and that rest breaks are paid, and drinking water to
prevent heat-related illness or injury. Removing PPE when possible,
allows employees to cool down faster during rest breaks. As discussed
in Section V.C., Risk Reduction, drinking adequate amounts of water and
taking rest breaks are important for reducing heat strain that could
lead to HRI. Training on these topics could give the employer an
opportunity to address common misperceptions regarding heat, such as
that drinking cold water in the heat is harmful. In addition, proposed
paragraph (h)(1)(viii) and (ix) would require that employers train
employees on where break areas and employer provided water are located.
This would ensure employees are aware of the locations of break areas
and water and encourage their effective utilization.
Proposed paragraph (h)(1)(x) would require employers to train
employees on the importance of reporting signs and symptoms of heat-
related illnesses that they experience personally or those they observe
in co-workers. Training employees to be observant of and to report
early any signs and symptoms of heat-related illnesses they see at the
workplace is a key factor to identifying and addressing potential heat-
related incidents before they result in a serious illness or injury. In
addition, employers should ensure that employees are familiar with the
employer's own procedures for reporting signs and symptoms of a heat
emergency or heat-related illness pursuant to its heat emergency
response plan as required in proposed paragraph (g).
Proposed paragraph (h)(1)(xi) would require employers to train
employees on all the policies and procedures applicable to the
employee's duties, as indicated in the work site's HIIPP. Employees
play an important role in effective implementation of the employer's
work site-specific policies and procedures to prevent heat-related
illnesses and injury, and training on these policies and procedures is
necessary to ensure that they are implemented effectively. OSHA
recognizes that employees perform various duties and therefore likely
need different types of training, and the proposed requirement allows
employers flexibility to account for these differences in their
training programs. Thus, certain components of the training may need to
be tailored to an employee's assigned duties. For example, while all
employees would require training on recognizing signs and symptoms of
heat-related illness, employees observing a co-worker as part of buddy
system under proposed paragraph (f)(3)(i) may require additional
training on how to report signs and symptoms according to the policies
and procedures established and implemented by the employer. In another
example, the individual designated by the employer to ensure that
emergency procedures are invoked when appropriate under proposed
paragraph (g)(1)(iii) might require more detailed training on the
employer's heat emergency response procedures. Another example could be
training employees who wear vapor-impermeable clothing on the policies
and procedures the employer has implemented to protect them under
proposed paragraph (c)(3).
Proposed paragraph (h)(1)(xii) would require employers to train
employees on the identity of the heat safety coordinator. Under
proposed paragraph (c)(5), the heat safety coordinator would be
designated to implement and monitor the HIIPP and would be given
authority to ensure compliance with the HIIPP. Therefore, employees
could contact the heat safety coordinator to ask questions about the
HIIPP, to provide feedback on the policies and procedures, or report
possible deficiencies with implementation of the HIIPP. Employers
should encourage employees to contact the heat safety coordinator for
these reasons. To ensure that employees are able to contact the heat
safety coordinator, employers could provide the name of the individual
and other information needed to contact them as part of the training
required under this paragraph.
Proposed paragraph (h)(1)(xiii) would require employers to train
employees on the requirements of this standard. While proposed
paragraph (h)(1)(xi) would require training on all policies and
procedures applicable to an employee's duties as noted in the
employer's HIIPP, training under (h)(1)(xiii) would ensure that
employees are familiar with all requirements of this proposed standard.
For example, employees would have to be informed of the requirements
related to employee participation, including in the development,
implementation, review and update of the HIIPP under proposed paragraph
(c), and identifying work areas with reasonable expectations of
exposures at or above the initial heat trigger, and in developing and
updating the monitoring plan under proposed paragraph (d). Employees
would also need to be informed that requirements of the proposed
standard would be implemented at no cost to employees under proposed
paragraph (j). The proposed provision would also ensure that employees
are made familiar with the employer's heat-related policies and
procedures.
Proposed paragraph (h)(1)(xiv) would require employers to train
employees on how to access the work site's HIIPP. If relevant this
would include training on how to access both digital or physical
copies.
Proposed paragraph (h)(1)(xv) would require employers to train
employees on their right to protections under this standard (e.g., rest
breaks, water), and that employers are prohibited from discharging or
in any manner discriminating against any employee for exercising those
rights. Employees' right to be free from retaliation for availing
themselves of the protections of the standard or for raising safety
concerns comes from section 11(c) of the OSH Act, 29 U.S.C. 660(c), and
requiring employers to train on these protections is consistent with
the purpose of that provision. Proposed paragraph (h)(1)(xv) is also
consistent with section 8(c)(1) of the Act, 29 U.S.C. 657(c)(1), which
directs the Secretary to issue regulations requiring employers to keep
their employees informed of their protections under the Act and any
applicable standards, through posting of notices or ``other appropriate
means.'' This training ensures that employees know that they have a
right to the protections required by the standard. Having employers
acknowledge and train their employees about their rights under this
standard provides assurance that employees are aware of the protections
afforded them and encourages them to exercise their rights without fear
of reprisal. They may otherwise fear retaliation for utilizing the
protections afforded them under the standard or for speaking up about
workplace heat hazard concerns. This fear would undermine the
effectiveness of the standard because employee participation plays a
central role in effectuating the standard's purpose.
Proposed paragraph (h)(1)(xvi) would require that if the employer
is required under paragraph (f)(5) to place warning signs for
excessively high heat areas, they would be required to train employees
on procedures to follow when working in these areas. These procedures
could include, but are not limited to, any PPE that might be required
when working in those areas, if relevant, and reminders to remove PPE
when taking rest breaks in break areas and should reinforce employees'
access to rest breaks in break areas, required under paragraph (f)(2),
and drinking water, required under paragraph (e)(2), as appropriate.
Proposed paragraph (h)(2) would require the employer to ensure that
each supervisor responsible for supervising employees performing any
work at or above the initial heat trigger and each heat safety
coordinator receives training on, and understands, both the topics
outlined in paragraph (h)(1) and the topics outlined in paragraphs
(h)(2)(i) and (ii). Proposed paragraph (h)(2)(i) would require the
employer to train supervisors and heat safety coordinators on the
policies and procedures developed to comply with the applicable
requirements of this standard, including the policies and procedures
for monitoring heat conditions developed to comply with paragraphs
(d)(1) and (d)(3)(ii). Proposed paragraph (h)(2)(ii) would require the
employer to train supervisors and heat safety coordinators on
procedures they would have to follow if an employee exhibits signs and
symptoms of heat related illness, which an employer is required to
develop for its HIIPP pursuant to proposed paragraph (g)(1)(vi). This
would ensure effective and rapid treatment and care for employees
experiencing signs and symptoms of heat-related illness. OSHA included
these proposed provisions to ensure that supervisors and heat safety
coordinators receive additional training needed to perform their duties
as specified in the proposed standard.
Proposed paragraph (h)(3) would require the employer to ensure that
each employee receives annual refresher training on, and understands,
the subjects addressed in paragraph (h)(1) of the proposed standard.
This paragraph would also require that each supervisor and heat safety
coordinator additionally receive annual refresher training on, and
understands, the topics addressed in paragraph (h)(2). OSHA
preliminarily finds that annual training is needed to refresh and
reinforce an employee's recollection and knowledge about the topics
addressed in this paragraph. This proposed provision also indicates
that for employees who perform work outdoors, the employer must conduct
the annual refresher training before or at the start of the heat
season. This can
vary depending on the weather conditions in the geographic region where
the employer is located. Accordingly, OSHA intends this requirement to
be flexible and to allow employers leeway to determine the start of the
heat season, so long as those determinations are reasonable. For
example, in northern States such as Michigan, employers might find it
best to do annual training before the time when temperatures commonly
reach the initial heat trigger or above. In those cases, temperatures
are likely to be below the initial heat trigger for a substantial
portion of the year and employees are likely to need reminders of all
policies and procedures related to heat, both for the initial and high
heat triggers. Employers can determine when heat season is for them
based on normal weather patterns and would be required to conduct
training prior to or at the start of the heat season. In most
instances, OSHA expects that employers would do this no sooner than 30
days before the start of their heat season, so that employees can
recall training materials easily, rather than for example, 6-months
before the start of heat season. For new employees at outdoor work
sites, this may result in some employees receiving the annual refresher
training less than a year after the initial training.
Proposed paragraph (h)(4) specifies when supplemental training
would be required. Proposed paragraph (h)(4)(i) would require the
employer to ensure that employees promptly receive and understand
additional training whenever changes occur that affect the employee's
exposure to heat at work (e.g., new job tasks, relocation to a
different facility or area of a facility). For example, if an employee
is assigned to a new task or workstation that exposes them to high
process heat or to outdoor work where the employee is exposed to
hazardous heat, and such employee was not previously trained on the
necessary topics required under this paragraph, then the employer would
have to provide that employee with the requisite training. Similarly,
if an employee is assigned to a new work area to which different heat-
related policies and procedures apply, they would need to be trained on
these area-specific policies and procedures. Additional examples could
include when an employer's work site experiences heat waves, when new
heat sources are added to the workplace, or when employees are assigned
to a new task where they need to wear vapor-impermeable PPE (i.e., non-
breathable). In these instances, the training required under this
provision would have to comport with the requirements of the rest of
this paragraph.
Proposed paragraph (h)(4)(ii) would require that each employee
promptly receives, and understands, additional training whenever
changes occur in policies and procedures addressed in paragraph
(h)(1)(xi) of this proposed standard. Proposed paragraph (c) would
require employers to monitor their HIIPP to ensure ongoing
effectiveness. When doing so, the employer may find that the policies
and procedures are inadequate to protect employees from heat hazards.
If so, the employer would have to update those policies and procedures.
When this happens, employers would be required to train all employees
on the new or altered policies and procedures so that the employees are
aware of the new policies and procedures and how to follow them to
reduce their risk of developing heat-related illnesses and injuries.
Proposed paragraph (h)(4)(iii) would require that each employee
promptly receives, and understands, additional training whenever there
is an indication that an employee(s) has not retained the necessary
understanding. Examples of this would include employees who appear to
have forgotten signs and symptoms of heat-related illnesses or how to
respond when an employee is experiencing those signs and symptoms. It
is essential that employees remain familiar with training they have
received so they continue to have the knowledge and skills needed to
protect themselves and possibly co-workers from heat hazards.
Supplemental training under paragraph (h)(4)(iii) must be provided to
those employees who have demonstrated a lack of understanding or
failure to follow the employer's heat policies and procedures or comply
with the requirements of this proposed standard.
Proposed paragraph (h)(4)(iv) would require that each employee
promptly receives, and understands, additional training whenever a
heat-related injury or illness occurs at the work site that results in
death, days away from work, medical treatment beyond first aid, or loss
of consciousness. Occurrences of these types of heat-related injuries
and illnesses could indicate that one or more employees are not
following policies and procedures for preventing or responding to heat-
related illnesses and injuries. After a heat-related illness or injury
in the workplace occurs that meets the requirements of proposed
paragraph (h)(4)(iv), OSHA expects that each employee would receive
supplemental training. This training could be a ``lessons learned'' or
``alert'' type training.
Both initial and supplemental training are important components of
an effective heat injury and illness prevention program. Initial
training provides employees with the knowledge and skills they need to
protect themselves against heat hazards, and also emphasizes the
importance of following workplace policies and procedures in the HIIPP.
Supplemental training ensures employees continue to have the knowledge
and skills they need to protect themselves from heat hazards. It
provides an opportunity to present new information that was not
available during the initial training or that becomes relevant when an
employee's duties change. Additionally, supplemental training is
necessary when an employee demonstrates that they have not retained
information from the initial training (e.g., by failing to follow
appropriate policies and procedures). Supplemental training does not
necessarily need to include all information covered in the initial
training, as only some policies or procedures may need to be reviewed,
and employees will receive a full refresher training annually.
Proposed paragraph (h)(5) would require that all training provided
under paragraphs (h)(1) through (4) is provided in a language and at a
literacy level each employee, supervisor, and heat safety coordinator
understands. In addition, the provision would require that the employer
provide employees with an opportunity for questions and answers about
the training materials. For the training to be effective, the employer
must ensure that it is provided in a manner that the employee is able
to understand. Employees have varying educational levels, literacy, and
language skills, and the training must be presented in a language, or
languages, and at a level of understanding that accounts for these
differences. This may mean, for example, providing materials,
instruction, or assistance in Spanish rather than English if the
employees being trained are Spanish-speaking and do not understand
English. The employer is not required to provide training in the
employee's preferred language if the employee understands both
languages; as long as the employee is able to understand the material
in the language used, the intent of the proposed standard would be met.
As explained above with respect to paragraph (h)(1), OSHA does not
mandate testing or specific modes of ascertaining employee
understanding of the training materials, but expects that
all required training will include some measure of comprehension.
The proposed provision does not specify the manner in which
training would be delivered. Employers may conduct training in various
ways, such as in-person (e.g., classroom instruction or informal
discussions during safety meetings/toolbox talks), virtually (e.g.,
videoconference, recorded video, online training), using written
materials, or any combination of those methods. However, this paragraph
would require the employer to provide an opportunity for employees to
ask questions regardless of the medium of training. It is critical that
trainees have the opportunity to ask questions and receive answers if
they do not fully understand the material that is presented to them. If
it is not possible to have someone present or available during the
training, employers could provide the contact information of the
individual that employees can contact to answer their questions (e.g.,
an email or telephone contact). OSHA expects employers to make an
effort to respond to questions promptly.
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether the agency should require other training topics in
the standard;
Whether the inclusion of separate training requirements
for supervisors and heat safety coordinators is appropriate, or whether
the duty-specific training requirements in proposed paragraph (h)(1)
are sufficient;
Whether the agency has identified appropriate triggers for
supplemental training;
Whether the agency should require annual refresher
training or whether the more performance-based supplemental training
requirements are sufficient; and
Whether the agency should specify certain criteria that
define the start of heat season.
I. Paragraph (i) Recordkeeping
Paragraph (i) of the proposed standard would require certain
employers to create written or electronic records of on-site
temperature measurements and establishes the duration of time that
employers must retain those records. Specifically, it applies to
employers that have indoor work areas where there is a reasonable
expectation that employees are or may be exposed to heat at or above
the initial heat trigger, and that are therefore required to conduct
on-site temperature measurements under paragraph (d)(3)(ii). These
employers must have and maintain written or electronic records of these
measurements. Under paragraph (i), employers must retain these records
for a minimum of six months.
Maintaining these records, whether written or electronic, serves
several purposes. It will assist OSHA in determining conditions at the
work site, which will facilitate OSHA's ability to verify employers'
compliance with the standard's provisions. Additionally, these records
may facilitate employers identifying trends in indoor temperatures and
their effect on employee health and safety. In the event of a heat-
related injury or illness, these records can help employers assess the
conditions at the time of the injury or illness in order to prevent
such an event from recurring.
Paragraph (i) applies to indoor work areas only. This is because
employers cannot accurately rely on weather forecasting to predict and
monitor temperatures in these areas like they can for outdoor work
areas. It is therefore not possible for OSHA or the employer to
recreate historic temperature records for indoor work areas in the
absence of on-site temperature measurement records. OSHA has
preliminarily determined that six months is an appropriate timeframe
for records retention because this is the maximum time permitted for an
OSHA investigation (see 29 U.S.C. 658(c)). There are several
commercially available heat monitoring devices that are capable of
maintaining electronic logs of recorded measurements for six months
(ERG, 2024b). Therefore, employers can comply with the recordkeeping
requirement by using monitoring devices with sufficient storage
capability. Alternatively, employers could comply by creating and
maintaining written records based on monitoring devices that do not
have digital recording capabilities.
A. Requests for Comments
OSHA requests comments and evidence regarding the following:
Whether six months is an appropriate and feasible duration
of time to maintain records of monitoring data;
Whether permitting employers to maintain records on
devices that store data locally is appropriate; and
Whether the standard should require retention of any other
records, and if so, for what duration.
J. Paragraph (j) Requirements Implemented at no Cost to Employees
Proposed paragraph (j) provides that implementation of all
requirements of the standard must be at no cost to employees, including
paying employees their normal rate of pay when compliance requires
employee time. This provision is included to make it clear that the
employer is responsible for all costs associated with implementing the
standard, including not only direct monetary expenses to the employee,
but also reasonable time to perform required tasks and training.
This proposed requirement is consistent with the OSH Act, which
requires employers to ensure a safe and healthful workplace. The OSH
Act reflects Congress's determination that the costs of compliance with
the Act and OSHA standards are part of the cost of doing business and
OSHA may foreclose employers from shifting those costs to employees
(see Am. Textile Mfrs. Inst., Inc. v. Donovan, 452 U.S. 490, 514
(1981); Phelps Dodge Corp. v. OSHRC, 725 F.2d 1237, 1239-40 (9th Cir.
1984); see also Sec'y of Labor v. Beverly Healthcare-Hillview, 541 F.3d
193, 198-201 (3d Cir. 2008)). The proposed requirement is also
consistent with OSHA's longstanding practice in prior rulemakings. See,
e.g., Employer Payment for Personal Protective Equipment; 72 FR 64342,
64344 (Nov. 15, 2007); Occupational Exposure to Bloodborne Pathogens,
56 FR 64004, 64125 (Dec. 1991). The intent of proposed paragraph (j) is
that the standard be implemented at no cost to employees because
employer payment for items, such as access to water and shade, is
necessary to ensure employees are provided safe working conditions and
are protected from the hazard of heat stress. Employees are more likely
to take advantage of various workplace protections if such protections
are provided at no cost to them. Moreover, as explained in Section
VIII., Distributional Analysis, workers from underserved populations
are disproportionately exposed to occupational heat hazards. For all
workers, but particularly more vulnerable workers, protection from
occupational hazards must not depend on workers' ability to pay for
those protections. In indicating that the implementation of all
requirements of this standard must be at no cost to the employee, OSHA
considers costs to include not only direct monetary expenses to the
employee, but also the time and other expenses necessary to perform
required tasks.
The following discussion highlights specific proposed requirements
in paragraphs (c) Heat injury and illness prevention plan, (d)
Identifying heat hazards, (e) Requirements at or above the initial heat
trigger, (f) Requirements at or above the high heat trigger, (g) Heat
illness and emergency response
and planning, and (h) Training. This discussion is illustrative of the
requirement that employees are not to bear the costs of implementing
the standard. However, the requirement in proposed paragraph (j)
applies to all provisions of the proposed standard, including employee
time spent to implement or comply with those provisions.
Proposed paragraphs (c)(6) and (7) would require employers to seek
the input and involvement of non-managerial employees and their
representatives, if any, in the development and implementation of the
heat injury and illness prevention plan (HIIPP) and during any reviews
or updates of the HIIPP. Similarly, proposed paragraph (d)(3)(iv) would
require the employer to seek the input and involvement of non-
managerial employees and their representatives, if any, when evaluating
the work site to identify work areas with a reasonable expectation of
exposures at or above the initial heat trigger and in developing and
updating monitoring plans. Under these paragraphs, the employer would
be required to cover the expenses of non-managerial employees such as
any travel costs that may be necessary, and to pay employees their
normal rate of pay for the time necessary to engage in the development,
implementation, and the required reviews and updates of the employer's
HIIPP and monitoring plan.
Proposed paragraph (e)(2) would require the employer to provide
access to potable water for drinking that is placed in locations
readily accessible to the employee, suitably cool, and of sufficient
quantity to provide access to 1 quart of drinking water per employee
per hour. To ensure this is provided at no cost to employees, the
employer would not only need to pay for the water, its container, and
the means to utilize the water (cups, bottles, etc.) but would be
required to pay employees their normal rate of pay for time necessary
to consume water and any time that may be necessary to travel to and
from the location where water is provided. For example, if an employee
works in an area where water cannot be made available due to safety
considerations (e.g., certain areas in foundries) or because of the
presence of toxic materials, and must walk to a water fountain in a
break room to obtain water, the employer would be required to pay the
employee for the time required to walk to the water fountain, consume
water, and return to the work area.
Proposed paragraph (e)(7) would require employers to implement an
acclimatization protocol for new and returning employees when they
would be exposed to heat at or above the initial heat trigger except
when the employer can demonstrate the employee consistently worked
under the same or similar conditions as the employer's working
conditions within the prior 14 days. An acclimatization protocol sets
forth the process whereby employees gradually adapt to work in the
heat. Proposed paragraph (e)(7)(i) specifies the acclimatization
protocol for new employees exposed to heat at or above the initial heat
trigger during their first week on the job. The employer would have a
choice to either: (A) implement an acclimatization plan that, at
minimum, would include the measures in proposed paragraph (f) (i.e.,
rest breaks, observation for signs and symptoms of heat-related
illness, a hazard alert, and warning signs at excessively high heat
areas); or (B) provide for gradual acclimatization to heat in which
employee exposure to heat is restricted to no more than 20% of a normal
work shift exposure duration on the first day of work, 40% on the
second day of work, 60% of the third day of work, and 80% on the fourth
day of work. Proposed paragraph (e)(7)(ii) specifies the
acclimatization protocol for returning employees (i.e., employees who
have been away (e.g., on vacation or sick leave) for more than 14 days)
exposed to heat at or above the initial heat trigger during their first
week back on the job. The employer would have a choice to either: (A)
implement an acclimatization plan that, at minimum, would incorporate
the measures in proposed paragraph (f) whenever the heat index is at or
above the initial heat trigger during the employee's first week upon
returning to work; or (B) provide for gradual acclimatization to heat
in which employee exposure to heat is restricted to no more than 50% of
a normal work shift exposure during the first day of work, 60% on the
second day of work, and 80% on the third day of work.
An employer who chooses to provide a plan for gradual
acclimatization to heat in which employee exposure to heat is
restricted would be required to compensate the employee for the hours
they would typically be expected to work, i.e., the employee's normal
full shift, after acclimatization. For example, if a new employee would
be expected to work 8 hours on a normal shift after acclimatization and
the new employee would be restricted to 50% exposure during the normal
work shift or 4 hours on the first day, the employer would be required
to compensate the employee at their normal rate of pay for the full 8
hours even if the employee worked for only 4 hours.
OSHA anticipates that many employers would provide employees with
other work (e.g., work activities performed in indoor work areas or
vehicles where air-conditioning consistently keeps the ambient
temperature below 80 [deg]F, sedentary work activities at indoor work
sites) during the acclimatization period when they are restricted from
duties that involve exposure to heat at or above the initial heat
trigger. Employees would still be able to work a full 8-hour shift as
long as their duration of exposure to heat at or above the initial heat
trigger is limited to the specified duration.
Proposed paragraphs (e)(8) and (f)(2) would require that employees
be paid during the rest breaks required by those provisions. OSHA finds
it important that employees be paid during the breaks to which they are
entitled under the standard so that employees are not financially
penalized and thus discouraged from taking advantage of those
protections. For employees compensated on an hourly basis, this means
employees would need to receive the same hourly rate of pay during rest
breaks required by paragraphs (e)(8) and (f)(2) as they would receive
while working.
Some employees are paid on a piece-rate basis, meaning they are
compensated based on factors such as jobs completed, quantity of
produce picked, or products produced. Examples of employees compensated
on a piece-rate basis include agricultural employees paid by the pound
of produce picked, mechanics paid for each type of job completed (e.g.,
oil change or tune-up), warehouse employees paid by the number and size
of orders filled, manufacturing employees paid by the number of
products manufactured, or construction employees paid by the size and
type of job completed. Employees paid on a piece-rate basis may be
especially reluctant to take breaks. In a study by Wadsworth et al.,
2019, focus group discussions with piece-rate farm employees revealed
that many expressed concerns about possible losses in earnings and that
they might be replaced by another employee if they took breaks, and
many such employees brought their own water to work to reduce the time
they are not picking produce.
To ensure piece rate employees are not discouraged from taking rest
breaks, the proposed standard would require employers to compensate
them at their normal rate of pay for time necessary for rest breaks. In
the context of piece rate
employees and for purposes of this proposed standard, OSHA intends the
phrase ``normal rate of pay'' to mean the rate that results from the
following approach, which has also been adopted by the State of
California (Cal. Lab. Code section 226.2 (eff. Jan 1, 2021)): employers
would determine the normal rate of pay for piece-rate employees by
dividing the total weekly pay by the total hours worked during the work
week, not including heat-related rest breaks. That value would be
multiplied by the total time of heat-related rest breaks to determine
how much employees need to be paid for those breaks. For example, if a
piece-rate employee works a 5-day work week, 8 a.m. to 4:30 p.m. with a
30-minute unpaid lunch break from 12-12:30 each day, and earns $600 in
piece rate pay for the week, and under proposed paragraph (f)(2) the
employer would be obligated to provide two 15-minute heat-related rest
breaks per day (i.e., the employee is exposed at or above the high heat
trigger from 8 a.m. to 4:30 p.m. each day), that employee would receive
a normal rate of pay of $16/hour for heat-related rest breaks based on
the following formula:
Formula for Heat-Related Rest Break Compensation of Piece-rate
Employees
Total heat-related rest break time/week = 0.5 hours/day x 5 days/
week = 2.5 hours/week
Hours worked, excluding non-meal heat-related breaks = 40 hours-2.5
hours = 37.5 hours
Heat-related rest break compensation per hour = $600 / 37.5 hours =
$16/hour
For an employee who also took rest breaks needed to prevent
overheating under proposed paragraph (e)(8), the time of those rest
break(s) would be added to the total heat-related rest break time per
week to calculate the employee's normal rate of pay. OSHA has
preliminarily determined that this approach accurately represents the
normal rate of pay for piece-rate workers and thereby ensures that
these workers would not lose pay when taking advantage of the
standard's protection.
Proposed paragraph (g)(2)(i) would require that an employee
experiencing signs and symptoms of heat-related illness must be
relieved from duty. The proposed standard would require the employer to
pay employees their normal pay while they are relieved from duty until
the signs and symptoms subside.
Proposed paragraph (h) would establish requirements for training on
heat hazards and associated protective measures. All training provided
by the employer to meet the requirements of the standard would be
required to be provided at no cost to the employee. The employer would
be required to pay employees for time spent in training, including any
time needed to travel to and from training.
A. Requests for Comments
OSHA requests comments and information on the following:
Whether OSHA should consider an alternative approach to
calculating normal rate of pay for piece-rate employees, and what those
alternative approaches are;
Whether OSHA should make the calculation for piece rate
workers' normal rate of pay explicit in paragraph (j); and
Whether proposed paragraph (j) mandating that requirements
be implemented at no cost to employees is adequate, or whether there
are other potential costs to employees that OSHA should take into
consideration.
K. Paragraph (k) Dates
Paragraph (k) of the proposed standard would establish the
effective date for the final standard and the date for compliance with
the requirements specified in the standard. In paragraph (k)(1), OSHA
proposes an effective date 60 days after the date of publication of the
final standard in the Federal Register. This period is intended to
allow affected employers the opportunity to familiarize themselves with
the standard.
Paragraph (k)(2) of the proposed standard would require employers
to comply with all requirements of the standard 90 days after the
effective date (150 days after the date of publication of the final
standard in the Federal Register). The proposed compliance date is
intended to allow adequate time for employers to undertake the
necessary planning and preparation steps to comply with the standard.
OSHA has preliminarily concluded that 90 days is sufficient time for
employers to develop a heat injury and illness prevention plan (HIIPP),
identify heat hazards in their workplace(s), implement the protective
measures required under the standard, and provide required training to
employees.
A. Requests for Comments
OSHA solicits comment on the adequacy of the proposed effective and
compliance dates. OSHA aims to ensure that protective measures are
implemented as quickly as possible, while also ensuring that employers
have sufficient time to implement these measures. In addition, the
agency is interested in whether there are any circumstances that would
warrant an alternative timeframe for compliance, including a shorter
timeframe, and seeks comment on approaches that would phase in
requirements of the standard.
L. Paragraph (l) Severability
The severability provision, paragraph (l) of the proposed standard,
serves two purposes. First, it expresses OSHA's intent that the general
presumption of severability should be applied to this standard; i.e.,
if any section or provision of the proposed standard is held invalid or
unenforceable or is stayed or enjoined by any court of competent
jurisdiction, the remaining sections or provisions should remain
effective and operative. Second, the severability provision also serves
to express OSHA's judgment, based on its technical expertise, that each
individual section and provision of the proposed standard remains
workable in the event that one or more sections or provisions are
invalidated, stayed, or enjoined; thus, the severance of any
provisions, sections, or applications of the standard will not render
the standard ineffective or unlawful as a whole. Consequently, the
remainder of the standard should be allowed to take effect.
With respect to this rulemaking, it is OSHA's intent that all
provisions and sections be considered severable. In this regard, the
agency intends that: (1) in the event that any provision within a
section of the standard is stayed, enjoined, or invalidated, all
remaining provisions within remain workable and shall remain effective
and operative; (2) in the event that any whole section of the standard
is stayed, enjoined, or invalidated, all remaining sections remain
workable and shall remain effective and operative; and (3) in the event
that any application of a provision is stayed, enjoined, or
invalidated, the provision shall be construed so as to continue to give
the maximum effect to the provision permitted by law.
Although OSHA always intends for a presumption of severability to
be applied to its standards, the agency has opted to include an
explicit severability clause in this standard to remove any potential
for doubt as to its intent. OSHA believes that this clarity is useful
because of the multilayered programmatic approach to risk reduction it
proposes here. The agency has preliminarily determined that the suite
of programmatic requirements described in Section VII., Explanation of
Proposed Requirements, is reasonably necessary and appropriate to
protect employees from the significant risks posed by exposure to heat
in the
workplace. While OSHA preliminarily finds that these requirements
substantially reduce the risk of occupational injury and illness from
exposure to heat when implemented together, the agency also believes
that each individual requirement will independently reduce this risk to
some extent, and that each requirement added to the first will result
in a progressively greater reduction of risk. For example, should a
reviewing court find the requirement of paragraph (f)(2), requiring 15
minute rest breaks every two hours in high heat conditions invalid for
some reason, the remainder of controls required by the standard in
those conditions would still provide necessary protections to
employees, and OSHA would intend that the rest of the standard should
stand. Therefore, OSHA intends to have as many of the protective
measures in this standard implemented as possible to reduce employees'
risk of occupational injury, illness, and death from exposure to heat.
Should a court of competent jurisdiction determine that any provision
or section of this standard is invalid on its face or as applied, the
court should presume that OSHA would have issued the remainder of the
standard without the invalidated provision(s) or application(s).
Similarly, should a court of competent jurisdiction determine that any
provision, section, or application of this standard is required to be
stayed or enjoined, the court should presume that OSHA intends for the
remainder of the standard to take effect. See, e.g., Am. Dental Ass'n
v. Martin, 984 F.2d 823, 830-31 (7th Cir. 1993) (affirming and allowing
most of OSHA's bloodborne pathogens standard to take effect while
vacating application of the standard to certain employers).
VIII. Preliminary Economic Analysis and Initial Regulatory Flexibility
Analysis
OSHA has examined the impacts of this rulemaking as required by
Executive Order 12866 on Regulatory Planning and Review (September
30,1993), Executive Order 13563 on Improving Regulation and Regulatory
Review (January 18, 2011), Executive Order 14094 entitled ``Modernizing
Regulatory Review'' (April 6, 2023), the Regulatory Flexibility Act
(RFA) (September 19, 1980, Pub. L. 96354), section 202 of the Unfunded
Mandates Reform Act of 1995 (March 22, 1995; Pub. L. 104-4), and
Executive Order 13132 on Federalism (August 4, 1999).
Executive Orders 12866 and 13563 direct agencies to assess all
costs and benefits of available regulatory alternatives and, if
regulation is necessary, to select regulatory approaches that maximize
net benefits (including potential economic, environmental, public
health and safety effects, distributive impacts, and equity).\5\ The
Executive Order 14094 entitled ``Modernizing Regulatory Review''
(hereinafter, the Modernizing E.O.) amends section 3(f)(1) of Executive
Order 12866 (Regulatory Planning and Review). The amended section 3(f)
of Executive Order 12866 defines a ``significant regulatory action'' as
an action that is likely to result in a rule: (1) having an annual
effect on the economy of $200 million or more in any 1 year (adjusted
every 3 years by the Administrator of the Office of Information and
Regulatory Affairs (OIRA) for changes in gross domestic product), or
adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local, territorial, or Tribal governments
or communities; (2) creating a serious inconsistency or otherwise
interfering with an action taken or planned by another agency; (3)
materially altering the budgetary impacts of entitlement grants, user
fees, or loan programs or the rights and obligations of recipients
thereof; or (4) raise legal or policy issues for which centralized
review would meaningfully further the President's priorities or the
principles set forth in this Executive Order, as specifically
authorized in a timely manner by the Administrator of OIRA in each
case.
---------------------------------------------------------------------------
\5\ While OSHA presents the following analysis under the
requirements of Executive Orders 12866 and 13563, the agency
ultimately cannot simply maximize net benefits due to the overriding
legal requirements in the OSH Act.
---------------------------------------------------------------------------
A regulatory impact analysis (RIA) must be prepared for regulatory
actions that are significant per section 3(f)(1) ($200 million or more
in any 1 year). OMB's OIRA has determined this rulemaking is
significant per section 3(f)(1) as measured by the $200 million or more
in any 1 year. Accordingly, OSHA has prepared this Preliminary Economic
Analysis (PEA) \6\ that to the best of the agency's ability presents
the costs and benefits of the rulemaking. OIRA has reviewed this
proposed standard, and the agency has provided the following assessment
of its impact.
---------------------------------------------------------------------------
\6\ OSHA historically has referred to their regulatory impact
analyses (RIAs) as Economic Analyses in part because performing an
analysis of economic feasibility is a core legal function of their
purpose. But a PEA (or Final Economic Analysis) should be understood
as including an RIA.
---------------------------------------------------------------------------
A. Market Failure and Need for Regulation
I. Introduction
Executive Order 12866 (58 FR 51735 (September 30, 1993)) and
Executive Order 13563 (76 FR 3821 (January 18, 2011)) direct regulatory
agencies to assess whether, from a legal or an economic view, a Federal
regulation is needed to the extent it is not ``required by law.''
Executive Order 12866 states: ``Federal agencies should promulgate only
such regulations as are required by law, are necessary to interpret the
law, or are made necessary by compelling public need, such as material
failures of private markets to protect or improve the health and safety
of the public, the environment, or the well-being of the American
people.'' This Executive Order further requires that each agency
``identify the problem that it intends to address (including, where
applicable, the failures of private markets or public institutions that
warrant new agency action)'' and instructs agencies to ``identify and
assess available alternatives to direct regulation.'' (58 FR 51735
(September 30, 1993)). This section addresses those issues of market
failure and alternatives to regulation as directed by the Executive
Order.
OSHA is proposing a new standard for Heat Injury and Illness
Prevention in Outdoor and Indoor Work Settings (29 CFR 1910.148)
because the agency has preliminarily determined, based on the evidence
in the record, that there is a compelling public need for a
comprehensive standard addressing employees' occupational exposure to
hazardous heat. OSHA presents the legal requirements governing this
standard and its preliminary findings and conclusions supporting the
proposed standard in Section II., Pertinent Legal Authority, and
throughout other sections of the preamble.
As detailed in Section VIII.B., Profile of Affected Industries,
OSHA has preliminarily determined that millions of employees are
exposed to occupational heat hazards that place them at a significant
risk of serious injury, illness, and death. Employees exposed to heat
suffer higher rates of non-fatal heat-related injuries and illnesses
(HRIs) and heat-related fatalities, including heat stroke, heat
exhaustion, heat syncope, rhabdomyolysis, heat cramps, hyponatremia,
heat edema, and heat rash; and heat-related injuries, including falls,
collisions, and other workplace accidents (see Section IV., Health
Effects for additional information). OSHA estimates that the
proposed standard would prevent 531 heat-related fatalities (of the
estimated 559 annual fatalities) and 16,027 HRIs per year (of the
estimated 24,656 annual HRIs).
These estimates have potential limitations. The parameters used to
estimate the magnitude of underreporting of HRIs and the effectiveness
of the proposed standard have considerable uncertainty. Furthermore,
these estimates do not account for other expected benefits from the
rule (e.g., reduction in indirect traumatic injuries due to heat and
reduction in worker disutility). For additional discussion see Sections
VIII.E.IV., Additional Unquantified Potential Benefits and VIII.E.V.,
Uncertainty in Benefits.
OSHA has also preliminarily determined that the standard is
technologically and economically feasible (see Section IX.,
Technological Feasibility and Section VIII.D., Economic Feasibility).
The agency not only finds that this proposed standard is necessary and
appropriate to ensure the safety and health of employees exposed to
heat, as required by the OSH Act, but also demonstrates, in this
section, that this standard corrects a market failure in which labor
markets fail to adequately protect employee health and safety.
Even a perfectly functioning market maximizes efficient allocation
of goods and services at the expense of other important social values
to which the market (as reflected in the collective actions of its
participants) is indifferent or undervalues. In such cases, government
intervention might be justified to address a compelling public need.
The history and enactment of the OSH Act indicate a Congressional view
that American markets undervalued occupational safety and health when
it set forth the Act's protective purposes and authorized the Secretary
of Labor to promulgate occupational safety and health standards.
As discussed in this section, OSHA concludes there is a
demonstrable failure of labor markets to protect employees from
exposure to significant, unnecessary risks from heat exposure. The
agency recognizes that many firms and governments have responded to the
risks from heat exposure by implementing control programs for their
employees. Information that OSHA has collected suggests that many
employees with occupational exposure to hazardous heat currently
receive some level of protection against heat hazards and some existing
control programs may be as protective as the proposed standard.
Nevertheless, the effectiveness of labor markets in providing the level
of employee health and safety required by the OSH Act is not universal,
as many other employers in the same sectors fail to provide their
employees with adequate protection against heat hazards. This is
evidenced by the documented injuries, illnesses, and deaths discussed
throughout this preamble. Accordingly, the existence of adequate
protections in some workplaces speaks to the feasibility of the
standard, not necessarily to the lack of need.
In this case, OSHA has preliminarily determined that protections
are needed to ensure the safety and health of employees exposed to
heat. This section is devoted to showing that markets fail with respect
to optimal risk for occupational exposure to heat hazards. Other
sections of this preamble address whether, given that markets fail, a
new regulation is needed.
The discussion below considers why labor markets, as well as
information dissemination programs, workers' compensation systems, and
tort liability options, each may fail to protect employees from heat
hazards, resulting in the need for a more protective OSHA standard.
II. Labor Market Imperfections
Under suitable conditions, a market system is economically
efficient in the following sense: resources are allocated where they
are most highly valued; the appropriate mix of goods and services,
embodying the desired bundle of characteristics, is produced; and
further improvements in the welfare of any member of society cannot be
attained without making at least one other member worse off.
Economic theory, supported by empirical data, posits that, in the
labor market, employers and their potential employees bargain over the
conditions of employment, including not only salary and other employee
benefits, but also occupational risks to employee safety and health.
Employers compete among themselves to attract employees. In order to
induce potential employees to accept hazardous jobs, employers must
offer a higher salary--termed a ``wage premium for risk'' or ``risk
premium'' for short--to compensate for the additional job risk.\7\
Because employers must pay higher wages for more hazardous work, they
have an incentive to make the workplace safer by making safety-related
investments in equipment and training or by using more costly but safer
work practices. According to economic theory, the operation of the
labor market will provide the optimal level of occupational risk when
each employer's additional cost for job safety just equals the avoided
payout in risk premiums to employees (Lavetti, 2023). The theory
assumes that each employer is indifferent to whether it pays the higher
wage or pays for a safer or more healthful workplace but will opt for
whichever costs less or improves productivity more.
---------------------------------------------------------------------------
\7\ The concept of compensating wage differentials for
undesirable job characteristics, including occupational hazards,
goes back to Adam Smith's The Wealth of Nations, which was
originally published in 1776. More recent empirical investigation
has tended to validate the core theory, with the acknowledgement of
labor market imperfections, as otherwise noted in this section
(e.g., Lavetti, 2023).
---------------------------------------------------------------------------
For the labor market to function in a way that leads to optimal
levels of occupational risk, three conditions must be satisfied. First,
potential employees and employers must have the same, perfect
information--that is, they must be fully informed about their workplace
options, including job hazards, or be able to acquire such information.
Second, participants in the labor market must directly bear all the
costs and obtain all the benefits of their actions. In other words,
none of the direct impacts of labor market transactions can be
externalized to outside parties. Third, the relevant labor markets must
be perfectly competitive, which requires a large number of employers, a
large number of employees, and other conditions such that no individual
economic agent is able to influence the risk-adjusted wage, and such
that the risk-adjusted wage, net of other amenities, is equal to the
marginal revenue associated with their output (Card, 2022).
The discussion below examines (1) imperfect information, (2)
externalities, and (3) imperfect competition in the labor market in
more detail, with particular emphasis on employee exposure to heat
hazards, as appropriate.\8\
---------------------------------------------------------------------------
\8\ The section on workers' compensation insurance later in this
section identifies and discusses other related market imperfections.
---------------------------------------------------------------------------
A. Imperfect Information
As described below, imperfect information about job hazards is
present at several levels that reinforce each other: employers
frequently lack knowledge about workplace hazards and how to reduce
them; employees are often unaware of the workplace risks to which they
are exposed; and employees typically have difficulty in understanding
the risk information they are able to obtain. Imperfect information at
these various levels has likely
impeded the efficient operation of the labor market regarding workplace
risk because employees--unaware of job hazards--do not seek, or
receive, full compensation for the risks they bear. As a result, even
if employers have full knowledge about the risk, their employees do
not. If employees do not have full knowledge about the risk, employers
have less incentive to invest in safer working conditions than they
would in the presence of full information since wages are suppressed
below what full knowledge by the employees would yield.
I. Lack of Employer Information
In the absence of regulation, employers may lack economic
incentives to optimally identify the safety and health risks that their
employees face.\9\ Furthermore, employers have an economic incentive to
withhold the information they do possess about job hazards from their
employees, whose response would be to demand safe working conditions or
higher wages to compensate for the risk. Relatedly, in the absence of
regulation, employers, as well as third parties, may have fewer
incentives to develop new technological solutions to protect employees
on the job.\10\
---------------------------------------------------------------------------
\9\ Other private parties may lack sufficient incentives to
invest resources to collect and analyze occupational risk data due
to the public-good nature of the information. See Ashford and
Caldart (1996).
\10\ For evidence of regulatory stimuli inducing innovations to
improve employee health and safety, see, for example, Ashford et al.
(1985), as well as more recent evidence from OSHA's regulatory
reviews under section 610 of the RFA (5 U.S.C. 610).
---------------------------------------------------------------------------
This suggests that, without regulation, and the incentives that
come with it, many employers are unlikely to make themselves aware of
the magnitude of heat-related safety and health risks in the workplace
or of the availability of effective ways of ameliorating or eliminating
these risks. OSHA believes that requiring employers to monitor heat
conditions will help to alleviate situations in which employers and/or
employees may not realize situations when heat becomes hazardous.
II. Lack of Employee Information About Health Hazards
Markets cannot adequately address the risks of occupational heat
exposure if employees and employers are unaware of the changes in risk
brought about by an employer's actions or inaction. Even if employees
and employers are aware of a risk, the employer may have limited
economic motivation to install controls unless the employees are able
to accurately assess the effects of those controls on their
occupational risks.
Accordingly, even if employees have a general understanding that
they are at increased risk of injury or illness from occupational
exposure to heat, it is unrealistic to expect, absent mandatory
regulatory requirements, that they know the precise risks associated
with different exposure levels or the exposures they are experiencing,
much less that they can use that knowledge to negotiate a significant
reduction in exposures and other protections or (if more desirable)
trade it for greater hazard pay.
Both experimental studies and observed market behavior suggest that
individuals have considerable difficulty rationally processing
information about low-probability, high-consequence events such as
occupational fatalities and long-term disabilities.\11\ For example,
many individuals may not be able to comprehend or rationally act on
risk information when it is presented, as risk analysis often is, in
mathematical terms--a 1/1,000 versus a 1/10,000 versus a 1/100,000
annual risk of death from occupational causes.
---------------------------------------------------------------------------
\11\ The literature documenting risk perception problems is
extensive. See the classic work of Tversky and Kahneman (1974). For
a recent summary of risk perception problems and their causes
(Thaler and Sunstein, 2009).
---------------------------------------------------------------------------
Of course, in the abstract, many of the problems that employers and
employees face in obtaining and processing occupational risk can lead
employees to overestimate as well as underestimate the risk. However,
some of the impacts of heat exposure may be sufficiently infrequent,
unfamiliar, or unobvious that many employees (and at least some
employers) may be completely unaware of the risk, and therefore will
underestimate it.
In addition, for markets to optimally address this risk, employees
need to be aware of the changes in risk brought about by an employer's
actions. Even if employees are aware of a risk, the employer may have
limited economic motivation to install controls or implement protective
measures unless the employees are able to accurately assess the effects
of those controls or measures on their occupational risks. Furthermore,
there is substantial evidence that most individuals are unrealistically
optimistic, even in high-stakes, high-risk situations and even if they
are aware of the statistical risks (Thaler and Sunstein, 2009).
Although the agency lacks specific evidence on the effect of these
attitudes on assessing occupational safety and health risks, this
suggests that some employees underestimate their own risk of work-
related injury or illness and, therefore, even in situations where they
have the bargaining power to do so, may not bargain for or receive
adequate compensation for bearing those risks. Finally, the difficulty
that employees have in distinguishing marginal differences in risk at
alternative worksites, both within an industry and across industries,
creates a disincentive for employers to incur the costs of reducing
workplace risk.
B. Externalities
Externalities arise when an economic transaction generates direct
positive or negative spillover effects on third parties not involved in
the transaction. The resulting spillover effect, which leads to a
divergence between private and social costs, undermines the efficient
allocation of resources in the market because the market is imparting
inaccurate cost and price signals to the transacting parties. Applied
to the labor market, when costs are externalized, they are not
reflected in the decisions that employers and their potential employees
make--leading to allocative distortions in that market.
Negative externalities exist in the labor market because many of
the costs of occupational injury and illness are borne by parties other
than individual employers or employees. The major source of these
negative externalities is the occupational injury or illness cost that
workers' compensation does not cover.\12\ Employees and their employers
often bear only a portion of these costs. Outside of workers'
compensation, employees incapacitated by an occupational injury or
illness and their families often receive health care, rehabilitation,
retraining, direct income maintenance, or life insurance benefits, much
of which are paid for by society through Social Security and other
social insurance and social welfare programs.\13\
---------------------------------------------------------------------------
\12\ Workers' compensation is discussed separately later in this
section. As described there, in many cases (particularly for smaller
firms), the premiums that an individual employer pays for workers'
compensation are only loosely related, or unrelated, to the
occupational risks that that employer's employees bear. In addition,
workers' compensation does not cover chronic occupational diseases
in most instances. For that reason, negative externalities tend to
be a more significant issue in the case of occupational exposures
that result in diseases.
\13\ In addition, many occupational injuries and most
occupational illnesses are not processed through the workers'
compensation system at all. In these instances, employees receive
care from their own private physician rather than from their
employer's physician.
---------------------------------------------------------------------------
Furthermore, substantial portions of the medical care system in the
United States are heavily subsidized by the
government so that part of the medical cost of treating injured or ill
employees is paid for by the rest of society (Nichols and Zeckhauser,
1977). To the extent that employers and employees do not bear the full
costs of occupational injury and illness, they will ignore these
externalized costs in their labor market negotiations. The result may
be an inefficiently high level of occupational risk.
C. Imperfect Competition
In the idealized labor market, the actions of large numbers of
buyers and sellers of labor services establish the market-clearing,
risk-compensated wage, so that individual employers and employees
effectively take that wage as given. However, the labor market is not
one market, but many markets differentiated by location, occupation,
and other factors; entrants in the labor market face search frictions
because of limited information on employment options; and, furthermore,
in wage negotiations with their own employees, employers are typically
in an advantageous position relative to all other potential employers
(e.g., Card, 2022). In these situations, discussed below, employers may
have sufficient power to influence or to determine the wage their
employees receive. This may undermine the conditions necessary for
perfect competition and can result in inadequate compensation for
employees exposed to workplace hazards. Significant unemployment
levels, local or national, may also undermine the conditions necessary
for adequate compensation for exposure to workplace hazards (Hirsch et
al., 2018).
Beyond the classic--but relatively rare--example of a town
dominated by a single company, there is significant evidence that some
employers throughout the economy are not wage-takers but, rather, face
upward-sloping labor supply curves and enjoy some market power in
setting wages and other conditions of employment.\14\ An important
source of this phenomenon is the cost of a job search and the
employer's relative advantage, from size and economies of scale, in
acquiring labor market information.\15\ Another potentially noteworthy
problem in the labor market is that, contrary to the model of perfect
competition, employees with jobs cannot without cost quit and obtain a
similar job at the same wage with another employer. Employees leaving
their current job may be confronted with the expense and time
requirements of a job search, the expense associated with relocating to
take advantage of better employment opportunities, the loss of firm-
specific human capital (i.e., firm-specific skills and knowledge that
the employee possesses \16\), the cost and difficulty of upgrading job
skills, and the risk of a prolonged period of unemployment. Finally,
employers derive market power from the fact that a portion of the
compensation their employees receive is not transferable to other jobs.
Examples include job-specific training and associated compensation,
seniority rights and associated benefits, and investments in a pension
plan.
---------------------------------------------------------------------------
\14\ See Borjas (2000), Ashenfelter et al. (2010), and Boal and
Ransom (1997). The term ``monopsony'' power or ``oligopsony'' power
are sometimes applied to this situation.
\15\ See Borjas (2000). As supplemental authorities, Weil (2014)
presents theory and evidence both in support of this proposition and
to show that, in many situations, larger firms have more market
power than smaller firms, while Boal and Ransom (1997) note that the
persistent wage dispersion observed in labor markets is a central
feature of equilibrium search models.
\16\ MacLeod and Nakavachara (2007) note the correlation between
firm-specific skills and relatively high income.
---------------------------------------------------------------------------
Under the conditions described above, employers would not have to
take the market-clearing wage as given but could offer a lower wage
than would be observed in a perfectly competitive market,\17\ including
less than full compensation for workplace health and safety risks. As a
result, relative to the idealized competitive labor market, employers
would have less incentive to invest in workplace safety. In any event,
for reasons already discussed, an idealized wage premium is not an
adequate substitute for a workplace that puts a premium on health and
safety.
---------------------------------------------------------------------------
\17\ For a graphical demonstration that an employer with
monopsony power will pay less than the competitive market wage, see
Borjas (2000).
---------------------------------------------------------------------------
III. Non-Market and Quasi-Market Alternatives
The following discussion considers whether non-market and quasi-
market alternatives to the proposed standard would be capable of
protecting employees from heat hazards. The alternatives under
consideration are information dissemination programs, workers'
compensation systems, and tort liability options.
A. Information Dissemination Programs
One alternative to OSHA's proposed standard could be the
dissemination of information, either voluntarily or through compliance
with a targeted mandatory information rule, akin to OSHA's Hazard
Communication standard (29 CFR 1910.1200), which would provide more
information about the safety and health risks associated with exposure
to environmental heat. Better informed potential employees could more
accurately assess the occupational risks associated with different
jobs, thereby facilitating, through labor market transactions, higher
risk premiums for more hazardous work and inducing employers to make
the workplace less hazardous. The proposed standard recognizes the link
between the dissemination of information and workplace risks by
requiring that employees exposed to heat be provided with information
and training about the risks they encounter and ways to mitigate those
risks. There are several reasons, however, why reliance on information
dissemination programs alone would not yield the level of employee
protection achievable through the proposed standard, which incorporates
hazard communication as part of a comprehensive approach designed to
control the hazard in addition to providing for the disclosure of
information about it.
First, in the case of voluntary information dissemination programs,
absent a regulation, there may be significant economic incentives, for
all the reasons discussed in section VIII.A.II. above, for the employer
not to gather relevant exposure data or distribute occupational risk
information so that the employees would not change jobs or demand
higher wages to compensate for their newly identified occupational
risks.
Second, even if employees were better informed about workplace
risks and hazards, all of the defects in the functioning of the private
labor market previously discussed--the limited ability of employees to
evaluate risk information, externalities, and imperfect competition--
would still apply. Because of the existence of these defects, better
information alone would not lead to wage premiums for risk that would
incentivize employers to make workplaces safer, in accordance with
compensating differentials theory (Lavetti, 2023). Regardless, as
mentioned above in section VIII.A.I., even the level of employee safety
and health attained by the wage premium under efficient markets may be
lower than the level justified by other important social values that
efficient markets may undervalue. Finally, as discussed in Section
VIII.E., Benefits, a number of additional safety provisions under the
proposed standard would complement information and training provided by
other regulatory vehicles.
Thus, while improved access to information about heat-related
hazards can provide for more rational decision-making in the private
labor market,
OSHA concludes that information dissemination programs would not, by
themselves, produce an adequate level of employee protection.
B. Workers' Compensation Systems
Another theoretical alternative to OSHA regulation could be to
determine that no standard is needed because State workers'
compensation programs augment the workings of the labor market to limit
occupational risks to employee safety and health. After all, one of the
objectives of the workers' compensation system is to shift the costs of
occupational injury and illness from employees to employers in order to
induce employers to improve working conditions. Two other objectives
relevant to this discussion are to provide fair and prompt compensation
to employees for medical costs and lost wages resulting from workplace
injury and illness and, through the risk-spreading features of the
workers' compensation insurance pool, to prevent individual employers
from suffering a catastrophic financial loss (Ashford, 2007).
OSHA identifies two primary reasons, discussed below, why the
workers' compensation system has fallen short of the goal of shifting
to employers the costs of workplace injury and illness--including, in
particular, the costs of employee exposure to heat-related hazards. As
a result, OSHA concludes that workers' compensation programs alone do
not adequately protect employees.
I. Limitations on Payouts
The first reason that employers do not fully pay the costs of work-
related injuries and illnesses under the workers' compensation system
is that, even for those claims that are accepted into the system,
States have imposed significant limitations on payouts. Depending on
the State, these limitations and restrictions include:
Caps on wage replacement based on the average wage in the
State rather than the injured employee's actual wage;
Restrictions on which medical care services are
compensated and the amount of that compensation;
No compensation for non-pecuniary losses, such as pain and
suffering or impairment not directly related to earning power;
Either no, or limited, cost-of-living increases;
Restrictions on permanent, partial, and total disability
benefits, either by specifying a maximum number of weeks for which
benefits can be paid or by imposing an absolute ceiling on dollar
payouts; and
A low absolute ceiling on death benefits.
II. A Divergence Between Workers' Compensation Premiums and Workplace
Risk
The second reason workers' compensation does not adequately shift
the costs of work-related injuries and illnesses to employers is that
the risk-spreading objective of workers' compensation conflicts with,
and ultimately helps to undermine, the cost-internalization
objective.\18\ For the 99 percent of employers who rely on workers'
compensation insurance,\19\ the payment of premiums represents their
primary cost for occupational injuries and illnesses, such as heat-
related injuries and illnesses. However, the mechanism for determining
an employer's workers' compensation insurance premium typically fails
to reflect the actual occupational risk present in that employer's
workplace.
---------------------------------------------------------------------------
\18\ Recall from the earlier discussion of externalities that
the failure to internalize costs leads to allocative distortions and
inefficiencies in the market.
\19\ Only the largest firms, constituting approximately 1
percent of employers and representing approximately 15 percent of
employees, are self-insured. These individual firms accomplish risk-
spreading as a result of the large number of employees they cover
(Ashford, 2007). From 2000 to 2020, the share of Workers'
Compensation Benefits paid by self-insured employers rose from 22.0
percent to 24.7 percent (Murphy and Wolf, 2022).
---------------------------------------------------------------------------
Approximately 85 percent of employers have their premiums set based
on a ``class rating,'' which is based on industry illness and injury
history. Employers in this class are typically the smallest firms and
represent only about 15 percent of employees (Ashford, 2007). Small
firms are often ineligible for experience rating because of
insufficient claims history or because of a high year-to-year variance
in their claim rates. These firms are granted rate reductions only if
the experience of the entire class improves. The remaining 14 percent
of employers, larger firms representing approximately 70 percent of
employees, have their premiums set based on a combination of ``class
rating'' and ``experience rating,'' which adjusts the class rating to
reflect a firm's individual claims experience. A firm's experience
rating is generally based on the history of workers' compensation
payments to employees injured at that firm's workplace, not on the
quality of the firm's overall employee protection program or safety and
health record. Thus, for example, the existence of circumstances that
may lead to catastrophic future losses are not included in an
experience rating--only actual past losses are included.\20\ Insurance
companies do have the right to refuse to provide workers' compensation
insurance to an employer--and frequently exercise that right based on
their inspections and evaluations of a firm's health and safety
practices. However, almost all States have assigned risk pools that
insist that any firm that cannot obtain workers' compensation policies
from any insurer must be provided workers' compensation insurance at a
State-mandated rate that reflects a combination of class and experience
rating. Workers' compensation insurance does protect individual
employers against a catastrophic financial loss due to work-related
injury or illness claims. As a result of risk spreading, however,
employers' efforts to reduce the incidence of occupational injuries and
illnesses are not fully reflected in reduced workers' compensation
premiums. Conversely, employers who devote fewer resources to promoting
employee safety and health may not incur commensurately higher workers'
compensation costs. This creates a type of moral hazard, in that the
presence of risk spreading in workers' compensation insurance may
induce employers to make fewer investments in equipment and training to
reduce the risk of workplace injuries and illnesses.
---------------------------------------------------------------------------
\20\ In order to spread risks in an efficient manner, it is
critical that insurers have adequate information to set individual
premiums that reflect each individual employer's risks. As the
preceding discussion has made clear, by and large, they do not. In
that sense, insurers can be added to employers and employees as
possessing imperfect information about job hazards.
---------------------------------------------------------------------------
In short, the premiums most individual employers pay for workers'
compensation insurance coverage do not reflect the actual cost burden
those employers impose on the worker's compensation system.
Consequently, employers considering measures to lower the incidence of
workplace injuries and illnesses can expect to receive a less-than-
commensurate reduction in workers' compensation premiums. Thus, for all
the reasons discussed above, the workers' compensation system does not
provide adequate incentives to employers to control occupational risks
to worker safety and health.
C. Tort Liability Options
Another alternative to OSHA regulation could be for employees to
use the tort system to seek redress for work-related injuries and
illnesses, including heat-related ones.\21\ A tort is a civil
wrong (other than breach of contract) for which the courts can provide
a remedy by awarding damages. The application of the tort system to
occupational injury and illness would allow employees to sue their
employer, or other responsible parties where applicable (e.g., ``third
parties'' such as suppliers of hazardous material or equipment used in
the workplace) to recover damages. In theory, the tort system could
shift the liability for the direct costs of occupational injury and
illness from the employee to the employer or to other responsible
parties. In turn, the employer or third parties would be induced to
improve employee safety and health.
---------------------------------------------------------------------------
\21\ The OSH Act does not provide a private right of action that
would allow affected workers to sue their employers for safety
hazards subject to the Act (see Am. Fed. of Gov. Employees, AFL-CIO
v. Rumsfeld, 321 F.3d 139, 143-44 (DC Cir. 2003)).
---------------------------------------------------------------------------
With limited exceptions, the tort system has not been a viable
alternative to occupational safety and health regulation. In addition,
State statutes make workers' compensation the ``exclusive remedy'' for
work-related injuries and illnesses. Workers' compensation is
essentially a type of no-fault insurance. In return for employers'
willingness to provide, through workers' compensation, timely wage-loss
and medical coverage for workers' job-related injuries and illnesses,
regardless of fault, employees are barred from suing their employers
for damages, except in cases of intentional harm or, in some States,
gross negligence (Ashford and Caldart, 1996). Even in cases of gross
negligence where it is possible for employees to sue, establishing
gross negligence in these incidences is complicated by heat conditions
as these conditions may be temporary and localized, and not necessarily
measured at the time of incident. Practically speaking, in most cases,
workers' compensation is the exclusive legal remedy available to
employees for workplace injuries and illnesses.
Employees are thus generally barred from suing their own employers
in tort for occupational injuries or illnesses but may attempt to
recover damages for work-related injuries and illnesses, where
applicable, from third parties through the tort system. However, it is
unlikely that a third party could be successfully sued for workplace
exposure to hazardous heat since there is no third party responsible
for exposing employees to dangerous conditions in these circumstances.
This means that even this inadequate remedy would be unavailable to
employees injured from heat exposure.
In sum, the use of the tort system as an alternative to regulation
is severely limited because of the ``exclusive remedy'' provisions in
workers' compensation statutes; because of the various legal and
practical difficulties in seeking recovery from responsible third
parties or the lack of a responsible third party altogether; and
because of the substantial costs associated with a tort action. The
tort system, therefore, does not adequately protect employees from
exposure to hazards in the workplace.
IV. Summary
OSHA's primary reasons for proposing this standard are based on the
requirements of the OSH Act, which are discussed in Section II.,
Pertinent Legal Authority. As shown in the preamble to the proposed
standard and this PEA, OSHA has determined that employees in many
industries are exposed to safety and health hazards from exposure to
environmental and process heat in the workplace. This section has shown
that labor markets--even when augmented by information dissemination
programs, workers' compensation systems, and tort liability options--
still operate at a level of risk for these employees that is higher
than socially optimal due to a lack of information about safety and
health risks, the presence of externalities or imperfect competition,
and other factors discussed above.
B. Profile of Affected Industries
I. Introduction
This section presents a profile of the entities and employees for
all industries that would be affected by OSHA's proposed standard for
Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings.
OSHA first outlines all industries that would be subject to the
proposed standard. Next, OSHA summarizes the number of entities and
employees that would be exempt from this proposed standard based on
coverage under existing standards, jurisdiction of local or State
government entities, or based on one of the exemptions in paragraph
(a)(2) of this proposed standard. Lastly, OSHA provides summary
statistics for the affected entities,\22\ including the number of
affected entities and the number of affected employees. This
information is provided for each industry (1) in total, (2) for small
entities as defined by the Regulatory Flexibility Act (RFA) and by the
Small Business Administration (SBA), and (3) for very small entities
with fewer than 20 employees.
---------------------------------------------------------------------------
\22\ Spreadsheet detailing all calculations discussed in this
analysis are available in Analytical Support for OSHA's Preliminary
Economic Analysis for the Heat Injury and Illness Prevention (OSHA,
2024c).
---------------------------------------------------------------------------
II. Potentially Affected Industries and Employees
This section characterizes the industries and employees that are
likely to be affected by the proposed standard.
A. Potentially Affected Industries
OSHA broadly characterizes industries that are potentially within
the scope of the regulatory framework as core industries \23\ and all
other covered industries. OSHA considers core industries to be those
industries where employees have the most exposure to heat-related
hazards, such as through exposure to high outdoor temperatures, radiant
heat sources, or insufficient temperature control or ventilation in
indoor work settings. Core industries include:
---------------------------------------------------------------------------
\23\ To identify core industries, OSHA reviewed multiple
sources. The agency reviewed its OSHA Information System (OIS)
database to identify industries with fatal and non-fatal heat-
related injuries and illnesses. In addition, OSHA identified
occupations with the most exposure to heat-related hazards by
analyzing (1) occupational information on outdoor work settings from
the Occupational Information Network (O*NET) and (2) occupation-
level data from the Occupational Requirements Survey (ORS) on
exposure to process heat. Occupations flagged by those two data
sources were then mapped to detailed 2012 North American Industry
Classification System (NAICS) codes using the Occupational
Employment and Wage Statistics (OEWS). Finally, OSHA evaluated
industries that were included in OSHA's National Emphasis Program
for Outdoor and Indoor Heat Related Hazards, ANPRM comments, and
stakeholder comments.
---------------------------------------------------------------------------
Agriculture, Forestry, and Fishing;
Building Materials and Equipment Suppliers;
Commercial Kitchens;
Construction;
Drycleaning and Commercial Laundries;
Landscaping and Facilities Support;
Maintenance and Repair;
Manufacturing;
Oil and Gas;
Postal and Delivery Services;
