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, 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 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.

Common carbon monoxide sources in workplaces

Propane-powered forklift	Gasoline concrete cutter
Propane-powered floor polisher	Gasoline pressure washer
Propane space heater (Salamander)

 

Examples of actual workplace incidents

We have been fortunate in Washington State to not have a workplace fatality from carbon monoxide exposure for many years. Nevertheless, exposures still occur regularly. Here are examples of some of these incidents:

• In 2003, a farmhand in Skagit county became ill while operation a gasoline-powered pressure in an enclosed basement area... He was treated at a local hospital and released.
• In 2002, several employees working in an unventilated cooler in a vegetable packing facility were treated for carbon monoxide poisoning after a propane-powered forklift was operated in the cooler room.
• In 2002, a veterinary assistant operating a gasoline pressure washer in an enclosed area became ill and was taken to the hospital.
• In 2001, two electricians were overcome with CO poisoning while operating a gasoline concrete cutter in an enclosed room. One of the employees collapsed, the other suffered a severe headache, and dizziness.

Most people recover completely after a carbon monoxide poisoning. But in severe cases, symptoms can persist for many weeks or even months afterwards, or there can be permanent brain damage or damage to the heart.

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.

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.

For more information

• The National Institute of Occupational Safety & Health (NIOSH) has additional information on carbon monoxide from small gasoline engines at http://www.cdc.gov/niosh/topics/co/
• For more information from the Washington Department of Health about carbon monoxide dangers at home go to: http://www.doh.wa.gov/ehp/ts/IAQ/CO_Fact_Sheet.htm
• For more information on the health effects of carbon monoxide go to: http://www.coheadquarters.com/CO1.htm
• Carbon Monoxide Poisoning from Gas Fired Cooking Units in Food Preparation Locations (131 KB PDF)
• See SHARP's Carbon Monoxide web page to learn how to reduce forklift carbon monoxide emissions and to get employee educational materials in English and Spanish.