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Technical Tidbit Carbon Monoxide (CO) in the workplace

TT-063 Sources of carbon monoxide in the workplace Carbon monoxide (CO) is a colorless, odorless gas produced by all internal combustion engines including diesel and propane-powered engines. It is also produced by burning wood, paper or plastic products and from welding when carbon dioxide shielding gas is used. Workers can be exposed to carbon monoxide in warehouses and fruit packing facilities where propane-powered forklifts are operated. Exposure can also occur when operating equipment with small gasoline engines such as pressure washers, concrete cutters, water pumps, air compressors and generators at construction sites. CO is also produced from kerosene space heaters (salamanders), from natural gas cooking units and from propane-powered floor polishers. Outdoor use of any of this equipment is not usually hazardous, but in buildings or enclosed spaces such as underground parking garages, carbon monoxide can quickly build up to dangerous and even deadly amounts.

Health effects of carbon monoxide It doesn’t take much CO to cause problems. Below is a table outlining the effects of carbon monoxide on humans.

*PPM CO in air

Percent CO in air





8 hours

Generally accepted maximum exposure allowed in the workplace over an eight hour period



2-3 hours

Mild headache, fatigue, nausea and dizziness.



1-2 hours

Serious headache - other symptoms intensify. Life threatening after 3 hours.



45 minutes

Dizziness, nausea and convulsions. Unconscious within 2 hours. Death within 2-3 hours.



20 minutes

Headache, dizziness and nausea. Death within 1 hour.



5-10 minutes

Headache, dizziness and nausea. Death within 1 hour.



1-2 minutes

Headache, dizziness and nausea. Death within 25-30 minutes.



1-3 minutes


*PPM = parts per million

How to control carbon monoxide exposure The most obvious control measure is to not operate internal combustion engines in enclosed spaces or indoors. If this equipment must be used, plenty of ventilation must be provided. Furthermore, a CO sensing system as a safeguard should be in place. The amount of carbon monoxide produced by propane-powered forklifts can usually be reduced by frequent tuning and maintenance, but constant vigilance is required to keep emissions low. Catalytic converters are also available for forklifts. Sometimes the best solution is to switch to electric forklifts. Electric floor polishers should always be used instead of propane powered floor polishers inside buildings. Extreme caution must be taken in confined spaces such as tanks, manholes, vaults or pipes. Internal combustion engines should never be used in a confined space unless there is absolutely no alternative. In that case, the only protection for workers is supplied air respirators. Carbon monoxide detectors with alarms are useful warning devices for people working in confined spaces, but cannot be relied upon as the only means of protection. Welding in confined spaces where carbon dioxide shielding gas is used can generate enough carbon monoxide to reach dangerous levels. Shielded gas welding should not be done in confined spaces. When providing ventilation to confined spaces, locate the fresh air intake away from operating internal combustion engines, or move the engines moved away from ventilation fans.

Information and data in this document can be found at the Washington State Department of Labor and Industries web site: