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Carbon Monoxide

Yellow forklift unloading some pallets. Caption: Indoor use of mobile equipment can create unsafe levels of carbon monoxide if the equipment is not properly serviced and maintained and a dilution flow of air is not established.

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 in fruit and seafood 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), natural gas cooking units, and propane-powered floor polishers. Outdoor use of any of this equipment is not usually hazardous but in buildings or enclosed spaces, carbon monoxide can quickly build up to dangerous and even deadly amounts.

Employers must provide training to workers so they understand what carbon monoxide is, how it affects their health and safety, and how hazardous exposure can be prevented. See "Signs and symptoms" table below:

Expand or collapse. Signs and symptoms of carbon monoxide exposure

It doesn’t take much CO to cause problems. Below is a table outlining the general effects of carbon monoxide on healthy adults. Individual susceptibility will vary.

PPM CO
in air
Percent CO in air Symptoms experienced by healthy adults Comments
Less than
35 ppm
0.0035% No effect in healthy adults 35 ppm is WISHA 8-hour average permissible limit
100 ppm 0.01 % Slight headache, fatigue, shortness of breath, errors in judgment  
200 ppm 0.02% Headache, fatigue, nausea, dizziness 200 ppm is Short Term Exposure Limit (STEL)
400 ppm 0.04% Severe headache, fatigue, nausea, dizziness, confusion, can be life-threatening after 3 hours of exposure  
800 ppm 0.08% Headache, confusion, collapse, death if exposure is prolonged  
1500 ppm 0.15% Headache, dizziness, nausea, convulsions, collapse, death within 1 hour Levels greater than 1500 ppm are considered “immediately dangerous to life or health” (IDLH). This is the ceiling limit.
3000 ppm 0.3% Death within 30 minutes  
6000 ppm 0.6% Death within 10 – 15 minutes  
12,000 ppm 1.2% Nearly instant death  

ppm = parts per million

At lower levels, people sometimes mistake the symptoms of CO exposure for the flu, or do not associate their severe headache and nausea with carbon monoxide exposure.

People with heart or lung conditions or other health problems can be more sensitive to the effects of carbon monoxide. In addition the fetus of a pregnant woman can be adversely affected by carbon monoxide she inhales. For this reason WISHA Permissible limits for carbon monoxide are 35 ppm averaged over 8 hours with a 200 ppm ceiling limit.

General Rules

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