HEALTH HAZARD

ADVISORY

HAZARD EVALUATION SYSTEM & INFORMATION SERVICE

California Department of Health Services

Occupational Health Branch

1515 Clay Street, Suite 1901, Oakland, CA 94612 HESIS510-622-4300 • www.dhs.ca.gov/ohb

NOVEMBER 2002 California Department of Health Services • California Department of Industrial Relations

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Diesel Engine Exhaust Diesel Engine Exhaust

Diesel engine exhaust can cause lung cancer. Long-term exposure to diesel

exhaust particles poses the highest risk of any toxic air contaminant evaluated by California’s

Office of Environmental Health Hazard Assessment. On average, long-term occupational

exposures to diesel exhaust are associated with a 40 percent increase in the relative risk of

lung cancer. California’s Air Resources Board (CARB) estimates that about 70 percent of the

cancer risk that the average Californian faces from breathing toxic air contaminants stems

from diesel exhaust particles. Diesel exhaust also causes lung diseases such as asthma, and 

it may damage the immune system, increasing the risk of allergies.

What is diesel exhaust?

Diesel engine exhaust is a mixture of thousands of

different gases and tiny particles. The particles are

most important. They include polycyclic aromatic

hydrocarbons (PAHs) and metals such as nickel and

arsenic (these are known causes of human cancer).

Most diesel particles are small enough to be inhaled

deep into the lungs, where they pose the greatest

hazard. Diesel exhaust contains 20 times more 

particles than gasoline exhaust does. Some of the

main toxic gases in diesel exhaust are nitrogen

oxides, sulfur oxides, and carbon monoxide.

How diesel exhaust

affects your body

CANCER. Diesel exhaust causes lung cancer.

Based on animal tests and dozens of studies of

exposed workers, the lung cancer risk for long-term

highly exposed workers may be large, even when

compared to most other workplace risks.

Health

Hazard

Advisory

LUNGS. Diesel exhaust irritates the eyes, nose,

throat, and lungs. It interferes with lung function.

Diesel exhaust can also affect the immune system,

making people more prone to allergic reactions and

possibly more prone to infectious diseases. Both

lung irritation and allergic reactions can cause 

asthma, or make asthma worse. Asthma is a very

serious disease. Symptoms include shortness of

breath, chest tightness, wheezing, and coughing.

Some experts think that diesel exhaust in modern

city air may be one main reason why asthma is

becoming much more common in big cities.

PREGNANCY AND REPRODUCTIVE HEALTH. 

We don’t know whether diesel exhaust can affect

pregnancy or reproduction in humans. Many tests

have been done in animals, but the results have

been mixed and uncertain. Many tests showed no

effects, but some suggested various effects on 

sperm, ovulation, or fetal development. Some of 

the substances in diesel exhaust (such as PAHs and

carbon monoxide) can harm a developing baby if

exposure is great enough, so pregnant women

should avoid high exposure when possible.
Reducing exposure

By law, employers must provide a safe and healthy

workplace. Here are some things that employers and

workers can do to reduce the amount of diesel exhaust

that workers breathe.

Change the Fuel or the Engine.

Reformulated diesel fuels (with lower sulfur 

and aromatics) or biodiesel fuel can reduce diesel

exhaust emissions.

Natural gas works well in heavy-duty trucks and

buses. It meets all state and federal standards for

the year 2004. Many cities use natural gas vehicles

in their city fleets.

Electricity works best for light or medium trucks

and buses, short runs, and indoor use.

Low-emission diesel engines with exhaust gas 

recirculation, improved fuel injection, and other

improvements burn fuel more efficiently.

Install Vehicle Accessories That Reduce 

or Re-direct Diesel Exhaust.

Exhaust extenders that re-direct the exhaust away

from the operator.

After-treatment devices such as diesel exhaust 

filters and oxidation catalytic converters.

Ventilate Indoor Work Areas.

Place fixed diesel engines in separate, ventilated

areas under negative air pressure.

Use mechanical ventilation systems to pull diesel

exhaust-contaminated air away from workers and

exhaust it outdoors.

Slip exhaust extractor hose attachments on the

tailpipes of vehicles that must idle for long periods 

of time (such as in vehicle maintenance shops).

Run diesel engines outdoors rather than indoors

when possible.

Don’t run diesel engines near the air intake of 

building ventilation systems.

Open doors and windows of work areas to let in

fresh, uncontaminated air whenever possible (but this

is often of limited use).

Ventilate Booths (Toll, Weigh Station, 

Border Inspection, etc.).

Install a ventilation system that flushes the booth

with clean, uncontaminated air.

Use Safe Work Practices. 

Maintain engines to ensure that they are functioning

properly and emitting as little exhaust as possible.

Conduct regular tune-ups and checks to detect 

leaking exhaust.

Reduce engine idling time. Start engines only when

necessary, and turn them off whenever it’s practical.

This is the most effective way to reduce exposure to

diesel exhaust. Exhaust is still being emitted 

whenever engines are idling. Reducing idling time

also saves money on fuel.

Don’t tamper with engines to improve fuel 

economy. It increases diesel exhaust emissions, 

and it’s illegal.

Check the bodies of vehicles. Seal cracks or holes

with weather stripping to keep exhaust from getting

into the cabin.

Increase the distance between you and the source

of the diesel exhaust whenever practical.

Use a respirator only if ventilation and other 

control methods are not effective and feasible

(California Code of Regulations, Title 8, Section

5144).

Participate in Incentive Programs.

For example, the Carl Moyer Program administered

by CARB will help pay for cleaner engines for onroad heavy-duty engines over 14,000 pounds gross 

vehicle weight. Interested persons should contact

their local air district.

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MECHANICS

 Use exhaust extractor hose attachments on tailpipes

to carry exhaust outdoors.

 Run engines only when necessary, preferably 

outdoors.

 Open all windows to get fresh air into the work area.

 Distance yourself from the source of the exhaust.

 Get hands-on training in basic troubleshooting 

and repair skills in the one-day ARB training 

(see “Where to Get Help").

UNDERGROUND MINERS

 Switch to electric vehicles where possible.

 Ensure good ventilation in the work area.

 Install exhaust filtration devices such as exhaust

extenders, disposable diesel exhaust paper filters, 

and catalyzed or uncatalyzed diesel particulate

ceramic filters.

 Do regular maintenance of the intake air cleaner 

or filter to reduce engine emissions.

BUS AND OTHER HEAVY-DUTY

VEHICLE DRIVERS AND OWNERS

 Use vehicles that use natural gas, low-sulfur diesel, 

or other cleaner fuels.

 Use diesel particulate filters.

 Prepare your vehicle to pass the heavy-duty vehicle

inspection program and periodic smoke inspection

program, as well as to meet increasingly tough 

nitrogen oxides and particle emission standards.

 Make sure leased vehicles meet current 

and upcoming regulations.

 Maintain cab integrity.

TOLL BOOTH OPERATORS, TRUCK

WEIGHING STATIONS, AND BORDER

INSPECTION OFFICERS

 Install a fresh-air ventilation system in the booth.

 Increase the distance from the source of the exhaust

when possible.

 Have drivers shut off engines rather than idling for

very long periods.

FIREFIGHTERS (IN FIRE STATIONS)

 Attach fall-away tailpipe exhaust hoses to trucks

while idling indoors.

 Provide fresh air ventilation both to apparatus floor

and to living areas.

 Keep living areas under positive air pressure.

 Weather-strip doors that separate living quarters 

from apparatus floor. Keep doors between apparatus

floor and living areas closed.

CONSTRUCTION AND FARM WORK

 Do regular maintenance on vehicle engines.

 Don’t idle engines any more than necessary.

 Maintain cab integrity.

SPECIFIC WAYS TO REDUCE EXPOSURES 

FOR VARIOUS OCCUPATIONS
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Recommended exposure

limits

Based on the risk assessment performed by Cal/EPA’s

Office of Environmental Health Hazard Assessment,

exposure to 20 μg/m3 of diesel particles over a working

lifetime would create an excess lung cancer risk of one

in a thousand, which is often used as an upper limit of

acceptable workplace risk. HESIS recommends that

exposures be kept below 20 μg/m3

.

The American Conference of Governmental

Industrial Hygienists (ACGIH), a private organization,

has proposed a recommended workplace exposure limit

of 20 μg/m3 of diesel exhaust particles (“elemental 

carbon").

Legal exposure limits

Cal/OSHA (California's Division of Occupational

Safety and Health) sets and enforces limits for 

exposure to chemicals in the workplace. Currently,

there is no Permissible Exposure Limit (PEL) either for

diesel exhaust itself, or for the tiny particles that are

probably the most important part of diesel exhaust.

There are PELs for some other main components of

diesel exhaust, such as carbon monoxide and polycyclic

aromatic hydrocarbons (PAHs), but they do not protect

against the lung cancer risk from diesel exhaust.

The U.S. Mine Safety and Health Administration

(MSHA) limits the amount of diesel exhaust particles

(“total carbon") in underground non-coal mines to 400

micrograms per cubic meter of air (400 μg/m3

). In 2006

this limit will drop to 160 μg/m3

.

State and federal environmental protection 

agencies enforce various laws and regulations to 

minimize diesel emissions. In California, regulations

require use of low-sulfur fuel, reduction of nitrogen

oxides and particles, and use of alternative fuels.

Regulations cover both on-road and non-road vehicles.

These regulations are for environmental protection, not

worker protection. For more information, contact the

California Air Resources Board (see “Where to Get

Help").

The U.S. Environmental Protection Agency limits

the small-particle exposure of the general population in

each region to 15 μg/m3

, as an annual average, not to

exceed 50 μg/m3 during any given 24-hour period.

This environmental regulation, for all particles and not

just diesel particles, is enforced by the Air Resources

Board and does not directly affect the workplace.

Measuring your exposure

If you think you might have significant diesel exhaust

exposure at work, talk to your supervisor and/or your

union. If any worker might be exposed to a substance

at more than the legal exposure limit, the employer

must measure the amount of the chemical in the air in

the work area (California Code of Regulations, Title 8,

Section 5155). An industrial hygienist can measure the

amounts of carbon monoxide, PAHs, and particulates in

your workplace air. You have the right to see the

results of such monitoring relevant to your work (Title

8, Section 3204). It is probably better to measure fine

elemental carbon; there is not yet a legally enforceable

standard for it, but the monitoring results can be 

compared to the recommended exposure limit of 

20 μg/m3

.

Medical tests for exposure

and effects

There is no medical test to measure the amount of

diesel exhaust you've been exposed to. Your body

quickly gets rid of most diesel exhaust gases. Your

lungs also remove the particles, though not as quickly.

HESIS recommends that workers exposed to diesel

exhaust have baseline pulmonary function tests (PFTs).

PFTs measure how well your lungs move air. If you

develop breathing symptoms, comparing a baseline PFT

to follow-up PFTs is important in evaluating your lung

function change. A simple form of PFTs is called

spirometry. Spirometry can be done both before and

after a single work shift to tell whether lung function is

affected by your work. For a worker with breathing

symptoms or an unexplained change in periodic PFTs,

this pre- and post-shift testing can be very valuable.

HESIS can provide a spirometry fact sheet.

You have the right to see and copy your own medical

records, and any records of exposures to toxic 

substances. These records are important in determining

whether your health has been affected by your work.

Employers who have such records must keep them and

make them available to you for at least 30 years after

the end of your employment.
5

DOES YOUR WORK EXPOSE YOU 

TO DIESEL EXHAUST?

Other highly exposed workers include:

 operators of diesel powered engines (such as in trains, trucks, buses, tractors, and forklifts),

 toll booth workers, 

 roadside inspection workers, and 

 workers in some oil and gas production areas, railroad yards, and loading/shipping docks.

Most Americans are exposed to some diesel

engine exhaust, but some jobs involve much

higher exposure. 

The highest exposures are in jobs 

where diesel engines are running

indoors.

These include working...

 as a diesel engine mechanic,

 in bus barns,

 in fire stations, and 

 in mining operations where diesel 

equipment is used.
WHERE TO GET HELP

➤ The California Air Resources Board has

information about emission control technologies,

alternative fuel formulations, air quality regulations,

incentive programs, etc. Contact ARB at

www.arb.ca.gov, 800/242-4450 (statewide) or 

P.O. Box 2815, Sacramento, CA 95812.

➤ The U.S. Department of Energy

Alternative Fuels Data Center at

www.afdc.doe.gov has information on alternative

fuels and vehicles. It also has listings of available

alternative fuel vehicles, links to related websites,

and more than 3,000 documents in its database.

➤ HESIS answers questions about workplace hazards

and has many free publications available.

For information on workplace hazards:

(510) 622-4317. Please leave a message and 

your call will be returned.

For HESIS Publications: (510) 622-4328. Call, or

visit our website www.dhs.ca.gov/ohb, or write to

HESIS, 1515 Clay Street, Suite 1901, Oakland, CA

94612.

• Pulmonary Function Testing Fact Sheet. Explains

how the lungs work and tests that can be used to

identify lung disease.

• n-Hexane Use in Vehicle Repair Health Hazard

Advisory. Helps mechanics identify and prevent

nerve damage from n-hexane-containing brake

and parts cleaners.

• HESIS Publication List. Fact sheets, booklets,

medical guidelines, and technical documents on

workplace hazards including chemicals, repetitive

motion, and infectious diseases. Visit our website,

call, or write for the list.

➤ California Division of Occupational

Safety and Health (Cal/OSHA) investigates

workers’ complaints and answers questions about

workplace health and safety regulations.

Complainants’ identities are kept confidential.

Contact the Cal/OSHA Enforcement District office

nearest to your workplace. They are listed in the

blue government section near the front of your

local phone book under “State Government /

Industrial Relations / Occupational Safety and

Health / Enforcement" or visit their website at

www.dir.ca.gov/DOSH/districtoffices.htm.

➤ Other resources for employees may

include your supervisor, your union, your 

company health and safety officer, your doctor,

or the company doctor.

➤ Cal/OSHA Consultation Service helps

employers who want free, non-enforcement help

to evaluate the workplace and improve the health

and safety conditions. Employers can call 

(800) 963-9424.

➤ Occupational health services can be 

found at:

• UC San Francisco/SFGH Occupational 

and Environmental Medicine Clinic:

(415) 885-7580.

• UC Davis Occupational and Environmental

Medicine Clinic: (530) 754-7635.

• UC Irvine Center for Occupational and

Environmental Health: (949) 824-8641.

• UC San Diego Center for Occupational and

Environmental Medicine: (619) 471-9210.

JANE NORLING DESIGN

Gray Davis, Governor

State of California

Grantland Johnson, Secretary

Health and Human Services Agency

Diana M. Bontá, R.N., Dr.P.H.

Director, Department of Health Services

Steve Smith, Acting Secretary 

Labor and Workforce Development Agency

Chuck Cake, Acting Director 

Department of Industrial Relations

OSP 02 73849