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OSHA Safety Hazard Information Bulletin
on Potential Carcinogenicity of Diesel Exhaust
November 30, 1988
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.
Table 1. -- Limits for occupational exposure to selected components of the gaseous fraction of diesel exhaust; OSHA, MSHA, NIOSH compared __________________________________________________________________________ MSHA PELs* Component OSHA PEL Underground mines __________________________________________________________________________ Carbon dioxide 5,000 ppm (9,000 mg/m(3)) 5,000ppm (9,000mg/m(3)) (C02) 8-hr TWA^ 8-hr TWA; 30,000 ppm (54,000 mg/m(3)). STEL@ __________________________________________________________________________ Carbon monoxide 50 ppm (55 mg/m(3)) 50 ppm (55 mg/m(3)) (CO2) 8-hr TWA 8-hr TWA; 400 ppm (440 mg/m(3)) STEL __________________________________________________________________________ Formaldehyde 1 ppm, 1 ppm (1.5 mg/m(3)). 8-hr TWA 8-hr TWA; 2 ppm, 2 ppm (3 mg/m(3)).STEL 15-minute STEL __________________________________________________________________________ Nitrogen dioxide 5 ppm (9 mg/m(3)). 3 ppm (6 mg/m(3)). (NO2) ceiling 8-hr TWA: 5 ppm (10 mg/m(3))STEL __________________________________________________________________________ Nitric oxide 25 ppm (30 mg/m(3)). 25 ppm (30 mg/m(3)). (NO) 8-hr TWA 8-hr TWA __________________________________________________________________________ Sulfer dioxide 5 ppm (13 mg/m3). 2 ppm (5 mg/m(3)). (SO2) 8-hr TWA 8-hr TWA; 5 ppm (10 mg/m(3)),STEL __________________________________________________________________________ Metal and Nonmetal NIOSH REL mines __________________________________________________________________________ Carbon Dioxide 5,000 ppm (9,000 mg/m(3)) 10,000 ppm (18,000 (CO2) 8-hr TWA; mg/m(3)). 8-hr TWA; 15,000 ppm (27,000 30,000 ppm (54,000 mg/m(3)) STEL mg/m(3)) 10-min ceiling __________________________________________________________________________ Carbon Monoxide 50 ppm (55 mg/m(3)) 35 ppm (40 mg/m(3)) 8-hr TWA 8-hr TWA 400 ppm (440 mg/m(3)) 200 ppm (230 mg/m(3)) STEL ceiling (no minimum time) __________________________________________________________________________ Formaldehyde 2 ppm (3 mg/m(3)) 0.016 ppm (0.020 mg/m(3)) ceiling 8-hr TWA; 0.1 ppm (0.12 mg/m(3)) 15-min ceiling __________________________________________________________________________ Nitrogen 5 ppm (9 mg/m(3)) 1 ppm (1.8 mg/m(3)) Dioxide ceiling 15-min ceiling (NO(2)) __________________________________________________________________________ Nitric oxide 25 ppm (30 mg/m(3)) 25 ppm (30 mg/m(3)) (NO) 8-hr TWA; 10-hr TWA 37.5 ppm (46 mg/m(3)). STEL __________________________________________________________________________ Sulfur dioxide 5 ppm (13 mg/m(3)) 0.5 ppm (1.3 mg/m(3)), 8-hr TWA; 10-hr TWA 20 ppm (52 mg/m(3)), STEL (5 MIN) __________________________________________________________________________ * 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 ___________________________________________________________________________ MSHA PELs Component OSHA PEL Underground Metal & NIOSH REL coal mines Nonmetal mines ___________________________________________________________________________ Respirable 5 mg/m(3) 2 mg/m(3) No Limit No REL dust(*) ___________________________________________________________________________ Respirable 10 mg/m(3) 10 mg/m(3)^ no mg/m(3)@ REL is dust when specific content is to quartz more than 5% of total* ___________________________________________________________________________ Coal tar Not appli- Not Not 0.1 mg/m(3), pitch cable to considered considered 10-hr TWA volatiles diesel relevant relevant (cyclo- (CTPV) emissions. hexane-ext actables). ___________________________________________________________________________ Polynuclear No PEL No PEL No PEL No REL aromatic hydrocarbons ___________________________________________________________________________ FOOTNOTE(*) 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.