CAW National Council 4000
Occupational Health and Safety

Hazardous Substances:  Ozone

Ozone (O3) is a highly reactive, colour less or bluish gas with a pungent “electric spark” odour. It is the major pollutant in
photochemical smog (brown haze). Most ozone is produced in the environment when ultraviolet radiation in sunlight reacts with
emissions from motor vehicles and industrial pollutants in the air. Ironically, it is the ozone in the upper atmosphere that protects us
from ultraviolet radiation. Chlorofluorocarbons (CFCs) are destroying the ozone in the upper atmosphere. Unfortunately, ozone
produced at ground level does not rise to the upper atmosphere. At ground level, ozone is destructive to human health, agricultural
crops, trees and structural materials.

In the workplace, sources of ozone include photocopiers, electrostatic air cleaners, high-voltage electrical equipment, bleaching
processes, waste treatment processes, mercury vapor lamps, electric arc welding and leakage into aircraft cabins at high altitudes.

Short-term Effects

Ozone can injure various body organs, but it is particularly damaging to the respiratory system. It is a strong irritant that affects the
eyes, throat and lungs, causing painful irritation, coughing and difficulty breathing. Ozone has been shown to cause acute
pulmonary edema (fluid in the lungs) in animals, indicating that the same thing may happen to humans.

Long-term Effects

Hospital admissions due to acute respiratory diseases such as asthma increase when the ozone level exceeds 80 parts per billion,
for example on days where air pollution is heavy. Ozone is believed to be the second most important cause of lung disease (the
most important cause being fine particulate matter, which comes from smoking, second-hand smoke, vehicle exhaust and wood

Animal experiments show that ozone causes many other kinds of adverse health effects, including reduced fertility, birth
abnormalities, biochemical changes, decreased immune system response, respiratory system tumors in mice, growth of nodules in
the lungs of monkeys and genetic damage and mutations in bacterial, animal and human cells. The results from animal studies raise
concerns that similar injuries may happen to people.


Enclose process
Local exhaust ventilation
Reduce smog by insisting on lower emissions from vehicles
In smog-polluted urban areas, avoid doing aerobic outdoor exercise during the peak ozone hours (late morning and afternoon.)


ACGIH TLV 0.1 ppm (0.2 mg/m3).

Ontario Ambient Air Quality Criterion 0.08 ppm (0.165 mg/m3).
British Columbia Air Quality Index “Poor Air Quality” Level 0.08 ppm
U.S. National Ambient Air Quality Standard 0.12 ppm
U.S. Smog Alert 0.2 ppm
Smog Emergency 0.5 ppm

Source:  CAW Health, Safety & Environment Department