Workplace engineering control for sulphur dioxide, an acid gas

Sulphur dioxide [also called sulfur dioxide and SO2] is a colorless gas or liquid with a strong odor.

It can be produced by the burning of coal, the source of most sulphur dioxide released into the environment.2

Because it can be inhaled in the general environment, much of the research on sulphur dioxide’s effect is concerned with people who have asthma.

Limited occupational studies

Information on SO2 toxicity frequently relates to the effect of peak air pollution episodes rather than the long-term exposure that might be experienced by a worker.1

However, SO2 is a hazard found in many and varied workplaces. Case reports cited in the SO2 recommendation by the Scientific Committee on Occupational Exposure Limits included paper manufacture, smelters and steel mills, aluminum manufacture, carpentry, maintenance, mining, refrigerant manufacture and wine making.1

SO2 toxicity 

SO2 can affect the body if it is inhaled or comes into contact with the eyes or skin. It may cause severe breathing difficulties and may cause a person to stop breathing. Exposure of the eyes can cause a loss of vision.3

SO2 rapidly forms sulfurous acid on contact with moist membranes of the human body. High concentrations may lead to paralysis of the respiratory system and fluid accumulation in the lungs, known as pulmonary edema.

If exposure is combined with certain particulates, the negative effects of SO2 can be increased.3

SO2 has not been found to cause cancer in humans.3

Permissible exposure limit (PEL)

NIOSH recommends workers’ exposure to SO2 be limited to 2 ppm (parts per million) (5 mg/m3) TWA (time weighted average) over an 8-hour shift.

For short periods of time, the recommended exposure limit varies:5

Emergency Exposure Guidance Level [EEGL], expressed as a span of time

SO2 ppm

10 minutes


30 minutes


60 minutes


24 hours


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1Recommendation from the Scientific Committee on Occupational Exposure Limits for Sulphur Dioxide, updated December 2009

2Sulfur Dioxide, Wisconsin Department of Health Services

3Occupational Health Guideline for Sulfur Dioxide, OSHA

4Sulphur dioxide, CAS No 7446-095

5Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs) – Sulfur dioxide