Carbon Monoxide Hazards

Published On: March 18, 2024By Categories: Safety, Safety Matters

CO can impact workers quickly, so it is crucial employees know how to recognize its dangers.

By Alexandra Walsh

Carbon monoxide (CO) is a colorless, odorless gas generated by combustion processes such as those found in heating units and internal combustion engines. It can rapidly accumulate—even in areas that appear to be well ventilated—and build up to dangerous or fatal concentrations within minutes.

Examples of workplace sources of carbon monoxide are found all throughout the groundwater industry. Propane- and gasoline-powered forklifts. Temporary heating units. Gasoline-powered pressure washers, compressors, and pumps. Small engines and other tools.

How Is Carbon Monoxide Harmful?

Carbon monoxide is harmful when breathed in because it displaces oxygen in the blood and deprives the heart, the brain, and other vital organs of oxygen. Large amounts of CO can overcome someone in minutes without warning, causing them to lose consciousness and suffocate.

In addition to tightness across the chest, initial symptoms of CO poisoning may include headache, fatigue, dizziness, drowsiness, or nausea. Sudden chest pain may occur in people with angina. During prolonged or high exposures, symptoms may worsen and include vomiting, confusion, and collapse in addition to loss of consciousness and muscle weakness.

OSHA standards prohibit worker exposure to more than 50 parts of CO gas per million parts of air averaged during an eight-hour time period.

Symptoms can vary widely in people. CO poisoning may occur sooner in those most susceptible: young children, the elderly, people with lung or heart disease, people at high altitudes, or those who already have elevated CO blood levels such as smokers.

CO poisoning can be reversed if caught in time. But even if someone recovers, acute poisoning may result in permanent damage to the parts of your body that require a lot of oxygen such as the heart and brain. Significant reproductive risk is also linked to CO.

Immediate Response

If CO poisoning is suspected, promptly taking the following actions can save lives:

  • Move the victim immediately out to fresh air in an open area.
  • Call 911 or another local emergency number for medical attention or assistance.
  • Administer 100% oxygen using a tight-fitting mask if the victim is breathing.
  • Administer CPR (cardiopulmonary resuscitation) if the victim has stopped breathing.

Individuals may be exposed to fatal levels of CO poisoning when a rescue is being attempted. Those attempting to rescue someone with CO poisoning need to be skilled at performing recovery operations and using recovery equipment.

Monitoring Equipment

OSHA permissible exposure levels for CO are measured at 50 parts per million. OSHA standards prohibit worker exposure to more than 50 parts of CO gas per million parts of air averaged during an eight-hour time period.

There are three types of carbon monoxide monitoring devices that are most suitable for determining worker exposure to CO. There are advantages and disadvantages with each device.

Electronic sensing instruments that display a digital readout of carbon monoxide in parts per million are considered by many occupational safety experts to be the most accurate. To ensure accurate results, these devices require routine calibration, but systems have been developed to simplify the calibration process for easier use. Although these instruments can be more expensive, there are lower cost options available.

Colorimetric detector tubes with a hand pump can be used to sample over a time period of about two to 12 minutes with an error factor of plus or minus 25%. These tubes change color when exposed to CO and can be read in parts per million.

This method involves little maintenance. The detector tubes have a limited shelf life (typically 12 to 18 months) and the hand pump should be leak-tested before each use. If the hand pump leaks, the repair usually involves greasing components or replacing rubber gaskets. An annual volume calibration check should also be done.

The third carbon monoxide measuring device is a passive dosimeter tube. They are similar to the detector tubes, except a pump is not used. Carbon monoxide levels are indicated by a color change that reads in parts per million-hours with an error factor of plus or minus 25%.

The passive dosimeter tube is useful for sampling over time periods of several hours and determining time-weighted average exposures. After the seal is broken, the tube can be attached to a worker’s collar. The passive dosimeter tubes also have a limited shelf life (typically 12 to 36 months).

Prevention Best Practices

To reduce the chances of CO poisoning in the workplace, both employers and workers should take the following actions:

  • Do 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. Use of gasoline-powered tools indoors where CO from the engine can accumulate can be fatal.
  • An exception to this rule might be an emergency rescue situation in which other options are not available—and then only when equipment operators, assisting personnel, and the victim are provided with respirators supplying air.
  • Learn to recognize the symptoms and signs of CO overexposure: headache, nausea, weakness, dizziness, visual disturbances, changes in personality, and loss of consciousness.
  • Consider instead using tools powered by electricity or compressed air if they are available and can be used safely. For example, electric-powered tools present an electrocution hazard and require specific precautions for safety.
  • 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 or when exceeding the ceiling limit for CO of 200 parts per million.

Employers should also:

  • Conduct a workplace survey to identify all potential sources of exposure to carbon monoxide.
  • Educate workers about the sources and conditions that may result in CO poisoning as well as the symptoms and control of CO exposure.
  • Always substitute with less hazardous equipment if possible. Use equipment that allows for the placement of gasoline-powered engines outdoors at a safe distance away from air entering the building.
  • Monitor employee CO exposure to determine the extent of the hazard.

Workers should also:

  • Substitute with less hazardous equipment whenever they can. 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 early warning symptoms of CO poisoning.
  • If they suspect any symptoms, immediately turn off equipment and go outdoors or to a place with uncontaminated air.
  • Call 911 or another local emergency number without delay for medical attention or assistance if symptoms occur.
  • Stay away from the work area until the tool in question has been deactivated and measured CO concentrations are below accepted guidelines and standards.
  • Watch coworkers for serious signs of CO toxicity.


Workers can experience a range of effects caused by carbon monoxide poisoning in a variety of work settings with exposures that occurred over different periods of time and with different types of ventilation.

Workers in confined areas with little ventilation can be incapacitated within just minutes. Opening doors and windows or operating fans does not guarantee safety. It is best to have a workforce that is educated in the dangers of carbon monoxide and knows how to perform their job safely.

Alexandra Walsh is the vice president of Association Vision, a Washington, D.C.–area communications company. She has extensive experience in management positions with a range of organizations.

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