CAW National Council 4000
Occupational Health and Safety

Hazardous Substances:  Diesel Exhaust

Inhalation of diesel exhaust can produce a variety of ill-health effects. If a diesel engine were to run perfectly it would produce only
harmless substances which are found in the normal atmosphere:
nitrogen - 73%

carbon dioxide & oxygen - 13%

water - 13%


The problem is that diesel engines are not perfect combustion machines. Hazardous waste materials are produced such as:

carbon monoxide - 1%
nitric oxide - 1%
nitrogen dioxide - 1%
particulates - 1%
sulfur dioxides - 1%
hydrocarbons - 1%
Other - 1%

It is these byproducts that can damage human health.

The oxides of nitrogen, such as nitrogen dioxide and nitric oxide, are often a major problem.

Nitrogen Dioxide (NO2)

Nitrogen dioxide can affect the body if it is inhaled or if it comes in contact with the eyes or skin. Exposure to nitrogen dioxide may
cause severe breathing difficulties which are usually delayed in onset and which may cause death. Recover may be slow (2 to 3
weeks) with possible relapse and possible permanent damage. Pneumonia may occur. Irritation of the eye, nose, throat and wet
skin may also occur with short term high exposure.

The present ACGIH TLV is 3 ppm (parts per million) but the U.S. National Institute for Occupational Safety and Health (NIOSH)
recommends reducing the limit five times to 1 ppm. Long term effects to levels of NO2 below the legal limit and which do not cause
acute (short term) effects may produce long term lung damage.

Nitric Oxide (NO)

Nitric oxide is less hazardous than nitrogen dioxide. The problu is that it spontaneously turns into the more hazardous nitrogen
dioxide. At high exposures NO reduces the oxygen carrying capacity of the blood which can lead to breathing difficulties.

The ACGIH TLV for NO is 25 ppm.

Carbon Monoxide (CO)

Carbon monoxide is readily absorbed from the lungs into the blood and it reduces the oxygen carrying capacity of the blood. At high
concentrations tissues are starved from oxygen and the person asphyxiates or chokes to death.

Short term effects of high exposure include headaches, nausea, coma and death.

Because the brain and the heart have the greatest need for oxygen, long term exposure to excessive amounts of carbon monoxide
can cause heart disease and impairment of muory, vision hearing and speech. Excess fluid in the lungs, enlarguent of the liver and
adverse reproductive effects are also possible outcomes of CO exposure.

The ACGIH TLV for CO is 25 ppm.

Sulfur Dioxide

Sulfur Dioxide is produced as a result of the sulfur content of diesel fuel. A highly refined fuel has no sulfur content. Sulfur dioxide is
water soluble, turning to sulfuric acid. The bulk of the inhaled sulfur dioxide is absorbed in the upper nose, mouth and throat due to
contact with moist mucous mubranes or tissues.

Short term exposures can lead to lung resistance. Long term exposure can lead to chronic bronchitis. SO2 may assist PAH to
develop cancer.

The ACGIH TLV is 2ppm. The U.S. NIOSH recommendation is ten times lower, 0.5 ppm.

Polycyclic aromatic hydrocarbons (PAH’s)

These complex organic substances include types of PAH’s that cause cancer. They travel on particulate found in diesel exhaust and
are then carried into the lung. Tests taken in Sudbury found cancer-causing PAH’s underground in the Inco mine at levels 6 to 350
times that found in the air in the City of Sudbury.

Diesel Particulate

This is soot or carbon particles. Like charcoal filters they soak up gaseous and non-gaseous material and carry thu into the lungs.

Hydrocarbons (HC)

These are unburned particulates from diesel fuel. They are complex and include aldehydes, ketones, phenols, alkanes and alkenes.

Prevention Methods to Reduce Diesel Exhaust Emissions

  1. Modify fuel (to reduce sulfur content) and fuel-air mixture
  2. Modify engine and fuel injection systu
  3. Add emission control devices such as water scrubbers, ceramic filters and catalytic converters but be cautious as some of
    these devices create more problus than they solve.



There must be sufficient quantities of fresh air supplied. In underground mining this can be provided through an adequate number
of fresh air raises, ventilation ducts cared for and repaired when damaged, and doors closed after a vehicle has passed through.

Work Practices

The above procedures with respect to ventilation must be followed. Diesel engines must be maintained with a proper, regular,
preventive maintenance program.


Monitoring must be carried out regularly. In underground mining if you find an excessive reading you must:

  1. immediately shut down equipment
  2. remove workers to fresh air


Recent evidence has shown that exposure to diesel exhaust can cause cancer in animals. Some studies have also been done which
associate lung cancer in humans with exposure to diesel exhaust at work. As a result of these studies, the U.S. Government
National Institute for Occupational Safety and Health (NIOSH) is now recommending that whole diesel exhaust be regarded as a
potential occupational carcinogen (cancer-causing agent).

1986 Publication

In 1986 NIOSH published a document evaluating potential health effects of occupational exposure to diesel exhaust in underground
coal mines. The study concluded that among workers exposed to diesel exhaust, eye irritation and reversible lung problus were in
evidence. It is noted that while “a casual connection between exposure to whole diesel exhaust and cancer” would be plausible
because of the variety of harmful substances found in diesel exhaust, to that date no studies had been done to see if there was a

Recent Animal Studies

Animal studies are used to determine whether substances are likely to cause ill-health in human beings. Mammals such as mice and
rats are quite similar to human beings in their reaction to harmful substances. We can thus predict what substances are likely to
harm humans without conducting medical experiments on human beings.

In 1986 and 1987 five studies have been done by medical researchers to determine the link between exposure to diesel exhaust
and the development of cancer.

1. Heinrich (1986)

Heinrich and his team of researchers exposed mice, rats, and hamsters to the exhaust from a 1.6 liter Volkswagen engine. An
increase in lung cancers was found in rats exposed to unfiltered diesel exhaust at amounts of 4 mg/m3 of particulate but no
increase was found in those exposed to filtered exhaust. Mice developed lung cancer when exposed to either filtered or unfiltered
diesel exhaust while hamsters did not.

2. Mauderly (1987)

The Mauderly researchers in 1987 exposed male and fuale rats to the unfiltered exhaust of a 5.7 liter Oldsmobile engine. Lung
cancer rates increased with an increased rate of exposure to diesel exhaust from 3.5 mg/m3 to 7.0 mg/m3 of particulate. The rate of
tumor incidence rose rapidly late in the exposure regimen.

3. Brightwell (1986)

Back to the Volkswagen engine for the Brightwell study. Hamsters again were lucky with no increase in tumor incidence. Rats
however developed tumors when exposed to unfiltered diesel exhaust in both intermediate (2.2 mg/m3) and high exposures (6.6
mg/m3). No particulate in the filtered exhaust produced no increase in tumors.

4. Ishinishi (1986)

Cell changes but no tumors were found in rats exposed to unfiltered exhaust from a light duty, 1.8 liter, 4 cylinder swirl chamber
diesel engine. Increased lung cancer tumors were however found in rats exposed to 4 mg/m3 of particulate from a heavy duty 11
liter, 6 cylinder direct injection unfiltered diesel engine. The same engine filtered produced cell changes but no statistically significant
increase in lung tumors.

5. Iwai (1986)

Various lung and other types of tumors were found in rats exposed to unfiltered diesel exhaust with 4.9 mg/m3 of particulate from a
2.4 liter diesel engine. Tumors and malignant lymphomas of the spleen, through no lung cancers were found in rats which were
exposed to filtered diesel exhaust.

Human Studies

Most human studies have not shown a conclusive link between exposure to diesel exhaust and the development of lung cancer. The
reasons for this lack of conclusive evidence have been incomplete information on the extent of exposure, insufficient time from first
exposure to allow for the appearance of exposure-related cancer, and the presence of other things that cause lung cancer such as
asbestos, smoking and ionizing radiation.

In 1987 however a U.S. study was released which indicated an increased risk of death from lung cancer among railroad workers
exposed to diesel engine uissions. The Garshick study collected the death certificates for 87% of the 15,059 deaths reported to the
U.S. Railroad Retiruent Board. Taking out the lung cancer increases expected from exposure to asbestos and cigarette smoke, a
statistically significant increase in lung cancer was found among workers aged 64 or younger at time of death who had worked in a
job with diesel exposure for 20 years. No such increase was found in older workers because they had retired shortly after the
transition from steam to diesel-powered locomotives and had thus not been exposed to much diesel exhaust.


The animal studies in rats and mice confirm an association between the development of cancer, especially lung cancer, and
exposure to whole diesel exhaust. Limited studies of workers suggests an association between occupational exposure to diesel
engine exhaust and lung cancer. The consistency of these findings suggests that a potential occupational cancer hazard exists in
human exposure to diesel exhaust.

Tumor creation is associated with diesel exhaust particulates. Limited evidence indicates that the gaseous part of diesel exhaust
may cause cancer as well.


NIOSH recommends that “the probability of developing cancer should be decreased by minimizing exposure. As prudent public
health policy, uployers should assess the conditions under which workers may be exposed to diesel exhaust and reduce exposures
to the lowest feasible limits”.

The above information on cancer and diesel exhaust is taken from “Carcinogen Effects of Exposure to Diesel Exhaust” published by
the U.S. Department of Health and Human Services, Public Health Service, Centres for Disease Control, National Institute for
Occupational Safety and Health, 1988.


Diesel Exhaust - ACGIH TLV 0.15 mg/m3 (proposed 1995/96) (0.1 ppm)

Source:  CAW Health, Safety & Environment Department