Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and no longer represents OSHA Policy. It is presented here as historical content, for research and review purposes only.

Diesel Exhaust

Diesel exhaust is a pervasive airborne contaminant in workplaces where diesel-powered equipment is used. Due to expanding use of diesel equipment, more and more workers are exposed to diesel exhaust. Over one million workers exposed to diesel exhaust face the risk of adverse health effects ranging from headaches to nausea to cancer and respiratory disease. Currently available control technology could significantly limit many diesel exhaust exposures, although additional information and research are needed on the methods to monitor diesel particulates and determine the level of risk such particulates cause. OSHA is developing an action plan to reduce worker exposures to this hazard but is not initiating rulemaking at this time.

Hazard Description

Over one million workers exposed to diesel exhaust face the risk of adverse health effects ranging from headaches to nausea to cancer and respiratory disease, including mine workers, bridge and tunnel workers, railroad workers, loading dock workers, truck drivers, material handling machine operators, farm workers, auto, truck and bus maintenance garage workers, and longshoring employees. (1)

Studies show exposed workers have an elevated risk of lung cancer. There is some evidence of risk of bladder cancer. Workers also may experience dizziness, drowsiness, headaches, nausea, decrement of visual acuity, and decrement in forced expiratory volume. (2-4)

Diesel exhaust has been implicated as a cause of reactive airway disease. (5)

Laboratory tests have shown diesel exhaust to be toxic, mutagenic and carcinogenic. (1-4, 6)

Numerous studies with rats have consistently demonstrated significant increases in pulmonary tumors with at least 24 months of exposure to concentrations greater than 2 mg/m3. While these studies are of good quality, there are uncertainties about the factors for extrapolating animal data to predict human risk. (1-4, 6)

Numerous epidemiological studies showed a positive carcinogenic risk associated with exposure to diesel exhaust. (1-4, 11) although no study has been fully successful in estimating historical exposures and using those estimates to establish a dose-response curve, at least two recent major studies have published quantitative assessments of current exposures in groups of workers studied epidemiologically. (7-10) One study found that current exposures to submicrometer elemental carbon (used as a surrogate for diesel exhaust) in the trucking industry, while generally low compared to some occupational exposures (e.g. miners in enclosed spaces), are measurably higher than background levels measured in residential areas (averaging 3.8 ug/m3 in truck drivers to 13.8 ug/m3 in dock workers). (7) A second study found that average exposures to respirable particulates, adjusted for tobacco smoke, in the railroad industry ranged from 17 ug/m3 in clerks to 134 ug/m3 for locomotive shop workers. Differences in climate, facilities, equipment and work practices were found to affect exposures to diesel exhaust within the railroad industry. (10)

In 1989, the International Agency for Research on Cancer (IARC) concluded that there is sufficient evidence for the carcinogenicity of whole diesel exhaust in experimental animals and that there is limited evidence for carcinogenicity of whole diesel exhaust in humans. IARC classified diesel exhaust as a probable human carcinogen (Group 2A). (6)

In 1994, the Air Resources Board of the State of California released a preliminary draft document on the Health Risk Assessment for Diesel Exhaust. The draft report concluded that the evidence that diesel exhaust is carcinogenic in rats is clearly sufficient and, in humans, the carcinogenic evidence appears to be sufficient. (2)

In 1994, the Environmental Protection Agency (EPA) also released a preliminary draft of a Health Assessment Document for Diesel Emissions. In that document, EPA concluded that on the basis of limited evidence for carcinogenicity of diesel engine emissions in humans, supported by adequate evidence in animals and positive mutagenicity data, diesel engine emissions are considered to best fit the weight-of-evidence for category B1 (considered to be a probable human carcinogen). (3)

The Health Effects Institute's Diesel Working Group published a special report on diesel exhaust in April 1995. This document finds that diesel emissions have the potential to cause adverse health effects including cancer and other pulmonary and cardiovascular diseases. However, the document concludes that the lack of definitive exposure data precludes using available epidemiological data to develop quantitative estimates of cancer risk, and raises questions about the validity of using rat bioassay data to characterize the potential human risk associated with ambient exposure to diesel emissions. (11)

Current Status

There is no OSHA permissible exposure limit (PEL) for diesel exhaust. NIOSH published a Current Intelligence Bulletin on diesel exhaust in 1988, recommending that whole diesel exhaust be regarded as a potential occupational carcinogen and controlled to the lowest feasible exposure level. (1) In 1990, NIOSH published a Risk Assessment, "An Exploratory Assessment of the Risk of Lung Cancer Associated with Exposure to Diesel Exhaust Based on a Study of Rats." The analysis found the excess risk to miners of lung cancer at the upper range of the diesel particulate exposure reported (1.5 mg/m3) to be approximately 1.5 to 3 in 100, but cautions, however, that the risk assessment is based on a number of assumptions with a great deal of uncertainty and should be viewed as an exploratory effort. (12)

In 1982, the Environmental Protection Agency (EPA) implemented emission standards for light-duty and heavy-duty diesel vehicles which have been steadily decreasing due to a phased-in approach. For example, the particle emission standard for heavy-duty diesel vehicles has decreased from 0.6 grams per brake horsepower-hour in 1988 to 0.01 grams per brake horsepower-hour in 1994. (3)

The American Conference of Governmental Industrial Hygienists (ACGIH) recently convened a committee to discuss the setting of a Threshold Limit Value (TLV) for diesel exhaust. As a result, diesel exhaust was placed on ACGIH's Notice of Intended Changes for 1995/1996 ( 0.15 mg/m3 TWA with a designation as a suspected human carcinogen (A2)).

The Mine Safety and Health Administration (MSHA) is currently in the process of developing a proposed rule for limiting the exposure of mine workers to diesel particulate matter. Studies by MSHA and the Bureau of Mines show that miners working in dieselized mining operations are probably the most heavily exposed workers of any occupational group. Also, the use of diesel equipment in underground coal mines is increasing. While after-treatment technology to control diesel emissions is available to reduce some exposures, it is currently not available as off-the-shelf technology for all mining operations. MSHA is holding two workshops in the Fall of 1995 to seek public input into some areas to be addressed by the rulemaking (e.g., measurement and control technology and alternative regulatory approaches).


Diesel exhaust meets several criteria for designation as an OSHA priority. A large number of workers are currently exposed to a very serious hazard, and such exposure is increasing due to the expanding use of diesel equipment. The quality of the data is good; however, additional research and information are needed regarding the methods for monitoring diesel particulates, and the appropriate basis for a PEL (elemental carbon or whole diesel particulate). In addition, available control technology, such as exhaust after-treatment devices and ventilation, can be utilized to reduce employee exposures.

  1. NIOSH (1988). NIOSH Current Intelligence Bulletin No. 50, Carcinogenic effects of exposure to diesel exhaust.
  2. California Environmental Protection Agency, Office of Environmental Health Hazard Assessment (June 1994). Health Risk Assessment for Diesel Exhaust (preliminary review draft).
  3. U.S. Environmental Protection Agency (March and September 1994). Health Assessment Document for Diesel Emission (external review draft), Vols. I-III, EPA/600/8-90/057.
  4. Mauderly, J.L. Diesel Exhaust, Chapter 5, Environmental Toxicants: Human Exposures and Their Health Effects, M. Lippman, Ed., Van Nostrand Reinhold, New York, NY, 1992, pp. 119-162.
  5. Wade JF 3rd, and Newman LS (February 1993). Diesel Asthma, Reactive Airways Disease Following Overexposure to Locomotive Exhaust. Journal of Occupational Medicine (35:2), pp. 151-154.
  6. IARC (1989). International Agency for Research on Cancer, Monographs on the Evaluation of Carcinogenic Risks to Humans, Diesel and Gasoline Engine Exhausts and Some Nitroarenes, Vol. 46.
  7. Zaebst, et al. (1991). Quantitative Determination of Trucking Industry Workers' Exposure to Diesel Exhaust Particles. Am Ind Hyg Assoc J 52(12):529-541.
  8. Steenland, et al. (1992). Exposure to Diesel Exhaust in the Trucking Industry and Possible Relationships with Lung Cancer. Am J Ind Med 21:887-890.
  9. Garshick, et al. (1988). A Retrospective Cohort Study of Lung Cancer and Diesel Exhaust Exposure in Railroad Workers. Am Rev Respir Dis 137:820-825.
  10. Woskie, et al. (1988). Estimation of the Diesel Exhaust Exposures of Railroad Workers: I. Current Exposures. Am J Ind Med 13:381-394.
  11. Health Effects Institute (April 1995). Diesel Exhaust: A Critical Analysis of Emissions, Exposure and Health Effects. A Special Report of the Institute's Diesel Working Group.
  12. NIOSH (1990). NIOSH Risk Assessment "An Explanatory Assessment of the Risk of Lung Cancer Associated with Exposure to Diesel Exhaust Based on a Study of Rats." (Publication No. NTIS PB-91-116-269.)

NOTICE: This is an OSHA Archive Document, and no longer represents OSHA Policy. It is presented here as historical content, for research and review purposes only.