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    Updating Permissible Exposure Limits (PELS) for Air Contaminants; Meeting


Occupational Safety and Health Administration

Updating Permissible Exposure Limits (PELS) for Air Contaminants; Meeting

AGENCY: The Occupational Safety and Health Administration, Labor.

ACTION: Notice of Public Meeting on Updating Permissible Exposure Limits (PELs) for Air Contaminants.

DATE AND TIME: Thursday, February 22, 1996; 9 a.m. to 5 p.m.

PLACE: Frances Perkins Building, Auditorium, 200 Constitution Ave., NW, Washington, DC 20210. Metro, Judiciary Square Station on the Red Line.

PUBLIC PARTICIPATION: The meeting is open to the public. The room accommodates approximately 240 persons. Pre-registration requested for all participants and required for those planning on making a brief presentation. To register, please send the following information by mail or fax to Julia Pesak at: US Department of Labor/OSHA, Rm. N 3718, 200 Constitution Ave., NW., Washington, DC 20210 Fax: (202) 219-7125 Or, to register by e-mail, send the same information to Lyn Penniman at:


Information required to register: Name of participant, Organization represented by participant, Topic(s) participant desires to address, Approximate time requested for each topic, maximum of 15 minutes total for each participant.

Registration deadline: Received by Monday, February 12, 1996. Registration confirmation: OSHA will confirm all registrations received by the deadline. OSHA will chair the meeting and allot time to cover the agenda and permit differing viewpoints to be aired.

AGENDA FOR PUBLIC MEETING: The first portion of the public meeting will include background information on OSHAs past effort and current strategy for updating Permissible Exposure Limits (PELs), followed by a general discussion of OSHAs method for identifying substances for inclusion in the current phase of rulemaking. The second portion will cover significance of risk, risk assessment methodology as applied to both carcinogenic and noncarcinogenic end points, and feasibility analysis methodology.

FOR FURTHER INFORMATION: Call Phyllis Yates or Julia Pesak at (202) 219-7111. Please note that registrations will not be accepted by telephone.



When the Occupational Safety and Health Administration was established in 1971, the Agency was given two years to adopt existing federal and national consensus standards. Among other standards, OSHA adopted Threshold Limit Values (TLVs) from the American Conference of Governmental Industrial Hygienists (ACGIH), which in turn had become federal standards under the Walsh-Healy Act. These limits, in addition to exposure limits from the American National Standards Institute (ANSI), were codified in the Code of Federal Regulations (CFR) as Permissible Exposure Limits (PELs) in Sec. 1910.1000, Subpart Z. Subpart Z became known as OSHAs Z-Tables, and were enforced by OSHA to protect the health of workers from adverse health effects associated with overexposure to air contaminants in general industry. Minor differences in regulatory history resulted in slightly different limits for the construction and maritime industries.

In the 1980s, it became widely recognized that many of the limits in OSHAs Z-Tables were outdated, and in 1988 OSHA proposed to update approximately 420 of its PELs in its air contaminants rulemaking. The newer PELs were based on more recent scientific information, and that information indicated that all but one of the new PELs needed to be more protective of worker health than were the old limits. OSHA utilized in part the recommendations made by the ACGIH and the National Institute of Occupational Safety and Health (NIOSH) in an effort to streamline the process. Following hearings and written comments OSHA published its final rule on January 19, 1989 (54 FR 2332), reducing 212 PELs, setting 164 PELs for previously unregulated substances, and raising one PEL. OSHA proposed to expand coverage of that rule to the construction and maritime industries on June 12, 1992 (57 FR 26002).

Legal challenges to the standard by industry and labor groups were consolidated and heard in the Eleventh Circuit Court of Appeals. In July of 1992 the Court issued its decision (American Federation of Labor and Congress of Industrial Organizations v. Occupational Safety and Health Administration, 965 F. 2d 962). It stated, in essence, that OSHA should perform quantitative analysis of risk for noncancer endpoints where possible, that more extensive discussions of the health evidence for each substance was needed, and that feasibility analysis should be more detailed. Though only some of the substances were individually challenged, the entire revised air contaminants standard was vacated and remanded back to the Agency. Consequently, the Agency was obligated to revert back to enforcing the limits set in the early 1970s.


Establishing an ongoing mechanism for updating its PELs continues to be a high priority for the Agency. OSHA seeks comment on the current phase of its plan to establish an ongoing, iterative process for updating outmoded Permissible Exposure Limits (PELs). Future phases will differ from the current phase and include a mechanism for establishing PELs for appropriate new substances (not currently regulated) under Sec. 1910.1000, subpart Z. This meeting will be the second on the topic of PELs with interested stakeholders since the standard was remanded in 1992.

The Agency intends to publish a proposal to update PELs for a group of approximately 20 substances in the late spring of 1996. Subsequent to the previous public meeting in July 1995, OSHA has further narrowed its likely priority candidates for proposed PEL rulemaking. The substances included below represent OSHA's current intentions regarding the substances to be included in the air contaminants proposal. The actual proposal, when published, may add or drop a small number of substances.

The list of substances currently slated for rulemaking, along with the agenda of the meeting (including a brief discussion of risk assessment and significance of risk issues of interest to OSHA), are provided here for the purpose of focusing and facilitating substantive discussion during the public meeting for stakeholders. The purpose of this meeting is to discuss those general issues which are germane to the current air contaminants rulemaking. It is not OSHA's intent to discuss health effects information and other issues relevant only to specific substances at this particular meeting. The regulatory process will provide ample opportunity for interested parties to submit oral and written comments on specific substances.

Current Candidates for Proposed Air Contaminants Rulemaking:

Carbon disulfide Carbon monoxide Chloroform Dimethyl sulfate Epichlorohydrin Ethylene dichloride Glutaraldehyde n-Hexane 2-Hexanone Hydrazine Hydrogen sulfide Manganese & compounds Mercury & compounds Nitrogen dioxide Perchloroethylene Sulfur dioxide Toluene Toluene diisocyanate Trimellitic anhydride Vinyl bromide

Issue I: Priority-Setting for PEL Chemicals

OSHA requests comment on its selection of priority substances for this first phase of updating PELs. In identifying the priority substances, OSHA (with assistance from NIOSH) evaluated the following criteria: The inherent toxicity of the substance; the number of workers exposed to the substance (and in some cases, the amount of the substance produced); uses of the substance and prevailing exposure levels; the severity of the resulting adverse health effect(s); the availability of information useful in quantitative risk assessment, and the quality of those data; and the potential for risk reduction. Administrative considerations and professional judgement were also factored in to the decision-making process. OSHA feels that this approach, a hybrid of quantitative and qualitative elements rather than a strictly quantitative formula, was appropriate and rational. The criteria used to identify these substances are similar to those used by OSHA's Priority Planning Process Committee to identify the Agency's priorities for regulatory and other actions.

Although these priority substances were identified on the basis of objective criteria, it should not be concluded that these are the only substances in OSHA's Z-Tables that require new PELs, nor that these are necessarily the highest-risk substances. It is important for worker protection that the Agency propose PELs for noncarcinogens as well as carcinogens, and for substances which have health effects that adversely impact workers' quality of life without necessarily affecting mortality. And, while it is important to establish PELs for these particular substances, it is of equal importance to the Agency to begin to lay the groundwork for a regular and iterative process for updating PELs for air contaminants.

Issue II: Risk Assessment Methodology for Carcinogens

OSHA has gained much experience in conducting quantitative risk assessments for carcinogens from past rulemaking efforts. The approaches most often employed by the Agency, which rely on use of the multistage model with animal data and relative risk models with human data to derive dose-response relationships, are well known in the scientific community and have been routinely upheld by reviewing courts. The Agency does not expect to depart significantly from its use of these approaches to derive revised exposure limits for potential carcinogens included in the present rulemaking effort. However, OSHA is interested in hearing discussion on certain issues regarding the details of dose-response modeling for carcinogens, in particular: (1) The appropriateness of relying on maximum likelihood estimates, upper confidence limits, or other summary statistics for carcinogenic potency such as expected values (for example, see Hattis and Goble 1991) to derive exposure limits; (2) approaches that can be taken to address the issue of interindividual variation in response among humans; (3) the use of various interspecies scaling factors when assessing risks from bioassay data; and (4) criteria for evaluating the adequacy of data to determine when it is appropriate to use pharmacokinetic analysis as part of the risk assessment.

Issue III: Risk Assessment Methodology for Noncarcinogens

OSHA is currently exploring the use of techniques to quantify risks of non-neoplastic health effects associated with occupational exposure to hazardous materials. This effort is designed to address the Eleventh Circuit Court decision. OSHA believes that, wherever data permit, conducting quantitative risk assessments for noncancer health endpoints provides the most direct route for establishing new or revised exposure limits in a manner consistent with the Court decision.

A variety of methods for establishing exposure limits based on noncancer health endpoints have been used by regulatory agencies and scientific bodies. One of the most frequently employed methods involves setting exposure limits by applying uncertainty factors to no-observed-adverse-effect (NOAEL) or lowest-observed-adverse-effect (LOAEL) levels reported in human and animal studies. OSHA relied on this approach to a large extent in the 1989 Air Contaminants rulemaking. Although this approach has been widely used in the past, its chief disadvantage is that it provides little or no information on potential risk levels that may be associated with varying magnitudes of exposure, a limitation that was recognized by the Court.

One of the newer approaches being evaluated by OSHA to conduct noncancer risk assessments is known as the "benchmark dose" method, originally described by Crump (1984). This method is currently being used by the Environmental Protection Agency (EPA) to establish Reference Doses (RfDs) based on noncancer health effects, and its application has been recently studied and described in detail by EPA's Risk Assessment Forum (EPA, 1995). This approach uses formal modeling techniques similar to those used in cancer risk assessment to develop quantitative dose-response relationships based on either human or animal studies. The models are subsequently used to estimate a benchmark dose associated with a specified excess risk level that lies on or just below the observed range of risks (usually 5 or 10 percent). The EPA document discusses two approaches for deriving references doses from benchmark doses: one employs a system of uncertainty factors to account for individual variation in response, extrapolation from animal to humans, and severity of the effect, while the other approach reduces the benchmark dose by some adjustment factor representing the desired reduction in the magnitude of the risk. Thus, the benchmark dose approach differs from those used in cancer risk assessments in that the models developed are not used to extrapolate risks at very low dose levels. Use of the benchmark dose approach has at least two advantages over the traditional NOAEL/LOAEL method: (1) Quantitative dose-response information can be obtained, which should facilitate regulatory decision making; and (2) the approach provides for greater regulatory consistency between substances since decisions can be based on comparable starting points, i.e., risk levels of 5 or 10 percent.

Thus, OSHA believes that the benchmark dose approach shows promise as a consistent and defensible method by which the Agency can establish reasonable exposure limits based on nonneoplastic health effects. As such, OSHA wishes to hear considerable discussion on the experience of those who are familiar with or who have used this method to evaluate public health risks, and what alternative approaches can be utilized that address issues raised by the Court ruling on the Air Contaminants standard. In particular, OSHA is interested in hearing discussion on how to best implement approaches to derive exposure limits from benchmark dose values, and how these methods can be interpreted in terms of the significance of the risk and the magnitude of risk reduction achieved.

Issue IV: Determination of Significant Risk

For significant risk determinations for carcinogens, OSHA has followed the Supreme Court guidance in the Benzene decision. The Court stated: "It is the Agencys responsibility to determine in the first instance what it considers to be a "significant" risk. Some risks are plainly acceptable and others are plainly unacceptable. If, for example, the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. On the other hand, if the odds are one in a thousand that regular inhalation of gasoline vapors that are 2% benzene will be fatal a reasonable person might well consider the risk significant and take the appropriate steps to decrease or eliminate it." (Industrial Union Department, AFL-CIO v. American Petroleum Institute, 448 U.S. 601, 655. (1980)). OSHA would welcome comments that would enable it to shed light on the acceptability of risk levels within this million-fold range.

OSHA has had less experience in evaluating significant risk for the broad range of other adverse health effects experienced by workers who are exposed to hazardous levels of chemical substances. OSHA invites discussion on appropriate risk levels for effects such as neurotoxicity, reproductive effects, and organ toxicity that may represent significant risks, and on appropriate criteria (such as severity and reversibility of the effect) that should be considered to determine when risks of a given magnitude represent a significant risk.


Crump, K.S. 1984. A new method for determining allowable daily intakes. Fund. Appl. Toxicol. 4:854-871 Environmental Protection Agency. February 1995. The Use of the Benchmark Dose Approach in Health Risk Assessment. Publication No. EPA/630/R-94/007, Washington, DC.

Hattis, D. And Goble, R.L. 1991. Expected values for projected cancer risks from putative genetically acting agents. Risk Analysis 11:359-363

Authority: This document was prepared under the direction of Joseph A. Dear, Assistant Secretary of Labor for the Occupational Safety and Health, 200 Constitution Ave. NW., Washington, DC 20210.

Signed at Washington, DC, this 19th day of January, 1996.

Joseph A. Dear,
Assistant Secretary of Labor.

[FR Doc. 96-952 Filed 1-23-96; 8:45 am]