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OSHA Hazard Information Bulletins
Potential Carcinogenicity of Diesel Exhaust

November 30, 1988




  • Director
  • Office of Field Programs


  • Director
  • Directorate of Technical Support


  • Hazard Information Bulletin on Potential Carcinogenicity of Diesel Exhaust

The purpose of this bulletin is to alert field personnel to the potential carcinogenicity of whole diesel exhaust and to enumerate the specific gaseous and particulate components that comprise the emission from diesel engines.

Recent animal studies in rats and mice confirm an association between the induction of cancer and exposure to whole diesel exhaust. The lung is the primary site identified with carcinogenic or tumorigenic responses following inhalation exposure. Limited epidemiologic evidence suggests an association between occupational exposure to diesel engine emissions and lung cancer. The consistency of these toxicologic and epidemiologic findings suggest that a potential occupational carcinogenic hazard exists in human exposure to diesel exhaust.

NIOSH estimates that approximately 1.35 million workers are occupationally exposed to the combustion products of diesel fuel in approximately 80,000 workplaces in the United States (NIOSH 1983). Workers who are likely to be exposed to diesel emissions include mine workers, bridge and tunnel workers, railroad workers, loading dock workers, truck drivers, fork-lift drivers, farm workers, and auto, truck, and bus maintenance garage workers.

The emissions from diesel engines consist of both gaseous and particulate fractions. The gaseous constituents include carbon dioxide, carbon monoxide, nitric oxide, nitrogen dioxide, oxides of sulfur, and hydrocarbons (e.g., ethylene, formaldehyde, methane, benzene, phenol, 1,3-butadiene, acrolein, and polynuclear aromatic hydrocarbons).

Particulates (soot) in diesel exhaust are composed of solid carbon cores that are produced during the combustion process and that tend to form chain or cluster aggregates. As much of 15% to 65% of the mass of particulate emissions (soot) of diesel engines is made up of organic compounds absorbed onto the surface of the particulates. Among these compounds is a group of compounds known as polynuclear aromatic hydrocarbons( PAHs), several of which are carcinogens (IARC 1983).

Permissible exposure limits (PELs) established by OSHA and the Mine Safety and Health Administration (MSHA) for some gases typically found in diesel exhaust are listed in Table 1 along with the recommended exposure limits (RELs) established by NIOSH.

OSHA, MSHA, and NIOSH exposure limits relevant to the particulate fraction of diesel engine emissions are listed in Table 2. Because diesel emission particulates are of respirable size, the presence of diesel equipment contributes to the total burden of respirable dust present in an occupational environment. Existing limits for occupational exposures to other respirable dust also limit exposure to the particulate fraction of diesel emissions.

Although no specific recommendations are being made from a compliance standpoint, compliance officers should be aware of the various components of diesel exhaust as this knowledge may aid in evaluating a worker's exposures or the environment in which he or she works.

Please disseminate this bulletin to all Area Offices, State Plan States and Consultation Project Officers.


NIOSH Current Intelligence Bulletin 50, Carcinogenic Effects of Exposure to Diesel Exhaust.

  • DATE:
  • FROM:
Table 1. - Limits for occupational exposure to selected
components of the gaseous fraction of diesel
exhaust; OSHA, MSHA, NIOSH compared
Component OSHA PEL Underground mines
Carbon dioxide (C02) 5,000 ppm (9,000 mg/m3)
8-hr TWA^
5,000ppm (9,000 mg/m3)
8-hr TWA;
30,000 ppm
(54,000 mg/m3).
Carbon dioxide (C02) 50 ppm (55 mg/m3)
8-hr TWA
50 ppm (55 mg/m3)
8-hr TWA;
400 ppm (440 mg/m3
Formaldehyde 1 ppm,
8-hr TWA
2 ppm,
15-minute STEL
1 ppm (1.5 mg/m3).
8-hr TWA;
2 ppm (3 mg/m3).
Nitrogen dioxide (NO2) 5 ppm (9 mg/m3).
3 ppm (6 mg/m3).
8-hr TWA:
5 ppm (10 mg/m3)
Nitric oxide (NO) 25 ppm (30 mg/m3).
8-hr TWA
25 ppm (30 mg/m3).
8-hr TWA
Sulfer dioxide (SO2) 5 ppm (13 mg/m3).
8-hr TWA
2 ppm (5 mg/m3).
8-hr TWA;
5 ppm (10 mg/m3),
  Metal and Nonmetal mines NIOSH REL
Carbon dioxide (C02) 5,000 ppm (9,000 mg/m3)
8-hr TWA;
15,000 ppm (27,000 mg/m3)
10,000 ppm (18,000 mg/m3).
8-hr TWA;
30,000 ppm (54,000 mg/m3)
10-min ceiling
Carbon Monoxide 50 ppm (55 mg/m3)
8-hr TWA
400 ppm (440 mg/m3)
35 ppm (40 mg/m3)
8-hr TWA
200 ppm (230 mg/m3)
(no minimum time)
Formaldehyde 2 ppm (3 mg/m3)
0.016 ppm (0.020 mg/m3)
8-hr TWA;
0.1 ppm (0.12 mg/m3)
15-min ceiling
Nitrogen dioxide (NO2) 5 ppm (9 mg/m3)
1 ppm (1.8 mg/m3)
15-min ceiling
Nitric oxide (NO) 25 ppm (30 mg/m3)
8-hr TWA;
37.5 ppm (46 mg/m3).
25 ppm (30 mg/m3)
10-hr TWA
Sulfur dioxide 5 ppm (13 mg/m3)
8-hr TWA;
20 ppm (52 mg/m3),
0.5 ppm (1.3 mg/m3),
10-hr TWA
* MSHA limits are based on threshold limit values (TLVs) of the American Conference of Governmental Industrial Hygienists (ACGIH). 1973 TLVs are used for metal and nonmetal mines. Current TLVs are used for underground coal mines
^ Time-Weighted average
@ Short-term exposure limit.
Table 2. - OSHA, MSHA, and NIOSH limits relevant to occupational exposure
to the particulate fraction of diesel exhaust
Component OSHA PEL Underground coal mines Metal & Nonmetal mines NIOSH REL
Respirable dust* 5 mg/m3 2 mg/m3 No Limit No REL
Respirable when content is more than 5% of total* 10 mg/m3 10 mg/m3^ no mg/m3@ specific to quartz REL is dust
Coal tar pitch volatiles (CTPV) Not applicable to diesel emissions. Not considered relevant Not considered relevant 0.1 mg/m3, 10-hr TWA (cyclo-hexane-extactables).
Polynuclear aromatic hydrocarbons No PEL No PEL No PEL No PEL
* These limits are not intended for diesel exhaust particulates, but they would inadvertently limit airborne concentrations because diesel particulates would be included in respirable dust samples taken where diesel engines are operating.
^ HRE equivalent concentration.
@ MSHA limits are based on threshold limit values (TLVs) of the American Conference of Governmental Industrial Hygienists (ACGIH). 1973 TLVs are used for metal and nonmetal mines.
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