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January 15, 2003

CO: The Silent Killer at Work

By Sean M. Alvarez, CSP

Referred to in many households as "the silent killer", Carbon Monoxide (CO) is not just a residential hazard. Your workplace could be at risk as well. This month's OSH Basics familiarizes you with a common workplace poisoning hazard which can easily be mitigated.


CO is a common industrial hazard resulting from the incomplete burning of natural gas and any other material containing carbon such as gasoline, kerosene, oil, propane, coal or wood.

During normal combustion, each atom of carbon in the burning fuel joins with two atoms of oxygen - forming a relatively harmless gas called carbon dioxide. When there is insufficient oxygen to ensure complete combustion of the fuel, each atom of carbon links up with only one atom of oxygen - forming a colorless, odorless, tasteless and poisonous gas called carbon monoxide.

While having no detectable odor, CO readily mixes with other gases that do have an odor. So, you can easily inhale carbon monoxide right along with gases that you can smell and not even know that CO is present.

Although present in liquid form under high pressure, carbon monoxide (CO) is most commonly encountered as a gas. This gas is the leading cause of accidental poisoning deaths in America, resulting in more than 1700 suicides and over 500 unintentional deaths every year in the United States, according to the Journal of the American Medical Association (JAMA). An additional 10,000 seek medical attention.


Carbon monoxide is an asphyxiant that exerts its toxic effects by combining with the hemoglobin of the blood. This combination decreases the amount of oxygen that can successfully combine with the hemoglobin and be delivered to the tissues.

Simply put, carbon monoxide takes the place of the oxygen, causing your tissues and organs to suffocate and eventually stop working.


Just about any process or piece of equipment using a flame can become a producer of CO. Forges, blast furnaces and coke ovens all produce CO.

Even basic welding procedures generate the gas. According to the Occupational Safety and Health Administration (OSHA), welding and cutting may produce significant amounts of carbon monoxide. In addition, welding operations that use carbon dioxide as the inert gas shield may produce hazardous concentrations of carbon monoxide in poorly ventilated areas.

Of all CO producers, one of the most commonly overlooked in the workplace is the internal combustion engine. In fact, many injuries and deaths occur from small engines and tools.

Many people using gasoline-powered tools such as high-pressure washers, concrete cutting saws, power trowels, floor buffers, welders, pumps, compressors, and generators in buildings or semi-enclosed spaces have been poisoned by carbon monoxide.

The National Institute for Occupational Safety and Health (NIOSH) provides these examples of such poisonings.

  • A farm owner died of CO poisoning while using an 11-horsepower, gasoline-powered pressure washer to clean his barn. He had worked about 30 minutes before being overcome.
  • A municipal employee at an indoor water treatment plant lost consciousness while trying to exit from a 59,000-cubic-foot room where he had been working with an 8-horse-power, gasoline-powered pump. Doors adjacent to the work area were open while he worked. His hospital diagnosis was CO poisoning.
  • Five workers were treated for CO poisoning after using two 8 horse-power, gasoline-powered, pressure washers in a poorly ventilated underground parking garage.
  • A plumber used a gasoline-powered concrete saw in a basement with open doors and windows and a cooling fan. He experienced a severe headache and dizziness and began to act in a paranoid manner. His symptoms were related to CO poisoning.


According to 29 CFR, Table Z-1, the current OSHA permissible exposure limit (PEL) for carbon monoxide is 50 parts per million (ppm) parts of air as an 8-hour time-weighted average (TWA) concentration.

The Consumer Product Safety Commission reports that health effects from exposure to CO levels of approximately 1 to 70 ppm are uncertain, but most people will not experience any symptoms. Some heart patients might experience an increase in chest pain.

As CO levels increase and remain above 70 ppm, symptoms may become more noticeable (headache, fatigue, nausea, dizziness). Since symptoms of mild exposure to carbon monoxide are similar to the flu, many victims of CO poisoning are misdiagnosed.

As CO levels increase above 150 to 200 ppm, disorientation, muscle weakness, unconsciousness, and death are possible.

Additionally, pregnant women, unborn babies, newborns, people with heart or respiratory problems, and the elderly may be more vulnerable to CO poisoning.


Developing and implementing a Carbon Monoxide Control Program at your workplace should help to minimize CO exposures:

  • Conduct a workplace survey to identify all potential sources of CO exposure.
  • Inspect / establish periodic maintenance schedule and equipment operating guides
  • Educate workers about the sources and conditions that may result in CO poisoning as well as the symptoms and control of CO exposure.
  • Conduct regular air monitoring of employees to determine the extent of the hazard.
  • Install Carbon Monoxide detectors and alarms in areas where potential sources of CO exist.

Employers Should Also:

  • NOT allow the use of or operate gasoline-powered engines or tools inside buildings or in partially enclosed areas unless gasoline engines can be located outside away from air intakes.
  • Substitute less hazardous equipment if possible. Use equipment that allows for the placement of gasoline-powered engines outdoors at a safe distance from air entering the building.
  • Learn to recognize the symptoms and signs of CO overexposure: headache, nausea, weakness, dizziness, visual disturbances, changes in personality, and loss of consciousness. Any of these symptoms and signs can occur within minutes of usage.
  • Always place the pump and power unit of high-pressure washers outdoors and away from air intakes so that engine exhaust is not drawn indoors where the work is being done. Run only the high-pressure wash line inside.
  • Consider the use of tools powered by electricity or compressed air if they are available and can be used safely.
  • If compressed air is used, place the gasoline-powered compressor outdoors and away from air intakes so that engine exhaust is not drawn indoors where the work is being done.
  • Use personal CO monitors where potential sources of CO exist. These monitors should be equipped with audible alarms to warn workers when CO concentrations are too high.

Equipment Users Should Also:

  • Substitute less hazardous equipment whenever possible. Use electric tools or tools with engines that are separate from the tool and can be located outside and away from air intakes.
  • Learn to recognize the warning symptoms of CO poisoning.
  • If you have any symptoms, immediately turn off equipment and go outdoors or to a place with uncontaminated air.
  • Call 911 or another local emergency number for medical attention or assistance if symptoms occur. Do NOT drive a motor vehicle--get someone else to drive you to a health care facility.
  • Stay away from the work area until the tool has been deactivated and measured CO concentrations are below accepted guidelines and standards.
  • Watch coworkers for the signs of CO toxicity.

Each year, several thousands of people at home and at work are poisoned by carbon monoxide. Do not be fooled into thinking that the silent killer is only a residential hazard -- This killer goes to work as well!

Below are some helpful links related to carbon monoxide:

ALERT: Preventing Carbon Monoxide Poisoning from Small Gasoline-Powered Engines and Tools [DHHS (NIOSH) Publication No. 96-118].

OSHA Carbon Monoxide Poisoning Fact Sheet (2 page PDF)

"Protect Your Family and Yourself from Carbon Monoxide Poisoning" US EPA Indoor Air Quality Fact Sheet

Checklist for the Prevention of Carbon Monoxide (CO) Poisoning CDC National Center for Environmental Health

Carbon Monoxide FAQ CDC National Center for Environmental Health

OSHA - Marine Terminals - Carbon Monoxide - 1917.24


Response to a request for information concerning the OSHA standard for carbon monoxide -- OSHA Interpretation - 02/25/1988

MMWR September 20, 2002; 51(37);829-830 - Carbon-Monoxide Poisoning Resulting from Exposure to Ski-Boat Exhaust --- Georgia, June 2002

Carbon Monoxide Poisoning - an Invisible Danger on Houseboats: Protect yourself and others from carbon monoxide poisoning inside and outside houseboats.

Houseboat-Associated Carbon Monoxide Poisonings on Lake Powell -- Arizona and Utah, 2000.MMWR December 15, 2000;49(49):1105-8

National Vehicle Emissions Policies and Practices and Declining US Carbon Monoxide-Related Mortality

FARM SAFETY - Carbon Monoxide: What is it and where does it come from? National Ag Safety Database

NIOSH Warns of Deadly Carbon Monoxide Hazard from Using Pressure Washers Indoors CDC / NIOSH Alert - NASD

CARBON MONOXIDE - Farm Bureau Safety Program PDF

Carbon Monoxide and You - Montana State University Extension. Publication date: February 1983

Outdoor Carbon Monoxide Poisoning Attributed to Tractor Exhaust Morbidity and Mortality Weekly Report (1997) PDF

Carbon Monoxide Poisoning in Enclosed and Semi-Enclosed Worksites Hazard Alert Construction Safety Association of Ontario

Abrasive Blaster Dies of Carbon Monoxide Poisoning
(Taken from Construction Safety Magazine, Construction Safety Association of Ontario, Volume 10, Number 4, Winter 1999/200)

Safeguards Against Carbon Monoxide Risk From Small Gasoline Engines Recommended By NIOSH, Partners - NIOSH Update

FACE-90-30: Carbon Monoxide Kills Three Volunteer Firefighters Inside Well in Pennsylvania - NIOSH News

Carbon Monoxide Questions and Answers - Consumer Product Safety Commission - - CPSC Document #466

Associations of CO with Asthma in Children - CO Headquarters

Carbon Monoxide Exposure: A Syndrome Induced by Chronic CO Poisoning - CO Headquarters - list of symptoms

The Acute CO Poisoning Study of Meigs & Hughes, 1952 - CO Headquarters

Carbon Monoxide Kills Website - Campaign Web Site

Chronic CO Poisoning - CO Headquarters

Copyright © 2003 by WorkCare™ All Rights Reserved

See you next month, editor@osh.net

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Original articles © WorkCare™; Orange, California.