Carbon Monoxide Poisoning (AEN-164)

ISU Extension Publication #: AEN-164
Author: Dr. Thomas Greiner, Dept. of Agricultural and Biosystems Engineering
Iowa State University
Date: 7/96

CARBON MONOXIDE POISONING: What is it? What causes it? What to do if you suspect it?

What is Carbon Monoxide?

Carbon monoxide (CO) is a colorless, odorless, tasteless, deadly gas. You can’t see smell or taste it. Carbon monoxide is slightly lighter than air and quickly spreads throughout an entire house.

What causes carbon monoxide production?

Carbon monoxide gas is produced when any fossil fuel is incompletely burned because of insufficient oxygen. During incomplete combustion, the carbon and hydrogen in the fuel combine to form carbon dioxide, water, heat, and deadly carbon monoxide. In properly installed and maintained appliances gas burns clean producing only small amounts of carbon monoxide. Anything that disrupts the burning process or results in a shortage of oxygen can increase carbon monoxide production. Wood, coal, and charcoal fires always produce carbon monoxide, as do gasoline engines.

What kinds of appliances and equipment can produce carbon monoxide?

Any appliance or implement which burns a fossil fuel. Examples include:

  • Gas and oil furnaces, boilers and water heaters
  • Gas, oil, and kerosene space heaters
  • Gas and wood kitchen ranges, ovens and fireplaces
  • Gas lawnmowers, snowblowers, chainsaws, weedeaters, generators and water pumps
  • Cars, trucks, motorcycles, and mopeds
  • Charcoal grills, candles, and gas lanterns
  • Wood, coal and charcoal fires.

What would cause carbon monoxide not to vent to the outside?

These may all cause vent failure:

  • Incorrectly installed venting systems and chimneys
  • chimneys plugged by birds’ nests or tree leaves
  • deteriorating chimney
  • chimneys too short to vent correctly
  • appliances with no venting system
  • house air flow patterns
  • downdrafting


What is downdrafting?

Downdrafting is flow reversal in a vent pipe or chimney. Outside air enters the house through the vent. Hot combustion gases spill into the house. Anything that moves air out of a house and depressurizes the house can cause downdrafting. This includes exhaust fans, any vented heating appliance, fireplaces, even holes in the ceiling. Vents in tight homes are especially susceptible to downdrafting.

What is the best way to reduce the risk of carbon monoxide poisoning?

First, install a carbon monoxide detector. Second, have the heating system inspected yearly by a qualified heating contractor. Third, replace natural draft heating appliances with sealed combustion units specifically designed to operate in new, tight houses. The units use sealed pipes with outside combustion air supplied directly to the burner chamber.

Can an existing carbon monoxide problem be solved?

Appliances must be serviced to eliminate carbon monoxide production. The vent system and chimneys must be inspected, repaired, and replaced as necessary. The house must be checked for depressurization and needed corrections made, such as sealing holes in the upper portion of the house, increasing air flow in the lower levels, shutting off exhaust fans, and closing fireplace dampers.

What are the health effects of carbon monoxide poisoning?

Carbon monoxide symptoms mimic the flu.
Mild exposure produces slight headache, nausea, vomiting, and fatigue. Medium exposure produces a throbbing headache, drowsiness, confusion, and a fast heart rate. Extreme exposure produces convulsions, unconsciousness, heart and lung failure, brain damage, and possible death. Because symptoms mimic so many illnesses, carbon monoxide poisoning often is misdiagnosed. Discuss the symptoms with all the family members.

Why is carbon monoxide so dangerous?

When CO is inhaled into the lungs, it bonds with hemoglobin, displacing oxygen, and forming carboxyhemoglobin (COHb) in the bloodstream. The attraction of CO and hemoglobin is approximately 250 times greater than the attraction between oxygen and hemoglobin. This makes even small amounts of carbon monoxide dangerous.

How much is dangerous?

At very high concentrations, carbon monoxide kills in less than five minutes. At low concentrations, carbon monoxide may take years to affect the body. The U.S. Occupational Health and Safety limit is 50 parts per million (ppm). Carbon monoxide detectors are required to sound an alarm when concentrations are greater than 100 ppm. The time of exposure, the concentration of CO, the activity level of the person breathing the CO, and the person’s age, sex, and general health all affect the danger level. For instance, a concentration of 800 ppm will cause headaches after one hour, but can lead to unconsciousness and death in 2 to 3 hours. Strong physical exertion, with an accompanying increase in the respiration rate, shortens the time to critical levels by 2 or 3 fold.

What should be done for someone suspected of suffering CO poisoning?

Immediately move the person into fresh outside air. Call for medical assistance. Medical treatment depends on the amount of carbon monoxide in the bloodstream. Often oxygen is administered. In severe cases, patients are treated in a pressurized oxygen chamber, a hyperbaric chamber, which quickly and thoroughly forces carbon monoxide from body.

Won’t the carbon monoxide leave the body anyway?

Many hours, even days, may be required for carbon monoxide to be eliminated from the body unassisted. During this time, additional damage can occur.

Can carbon monoxide cause long-lasting damage?

Yes, continued exposure to carbon monoxide can cause permanent brain, nerve, or heart damage. Some people require years of recovery, while others remain permanently incapacitated. If the person lost consciousness they typically will have relapses for several weeks and continue to suffer from headaches, fatigue, loss of memory, difficulty thinking, irrational behavior, and irritability.

What should I do to protect myself from the dangers of carbon monoxide poisoning?

  1. Purchase a carbon monoxide detector.
  2. Have all heating appliances checked every year by a qualified heating contractor.
  3. Replace heating units with direct-vent sealed combustion if the existing heating appliances will not operate correctly in the structure.

For more information request other notes in the Carbon Monoxide series. Agricultural Engineering Notes (AEN’s) are informally published information releases on topics of current concern to Iowans.

Prepared by

Thomas H. Greiner, Ph.D., P.E.
Extension Agricultural Engineer

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