Health Canada
Symbol of the Government of Canada

Common menu bar links

Environmental and Workplace Health

Carbon Monoxide

Carbon monoxide is a colourless, odourless gas that reduces the amount of oxygen in the blood. Low levels over long periods of time are dangerous, and high levels can cause unconsciousness and even death. To keep your indoor air clean and healthy, make sure that fuel-burning devices are well vented.

What is Carbon Monoxide?

Carbon monoxide (CO) is a gas that forms whenever you burn fuel like propane, natural gas, gasoline, oil, coal and wood. Because it is colourless, odourless and tasteless, it is hard to detect without a carbon monoxide detector. Carbon monoxide can cause health problems before people even notice it is present.

Sources of Carbon Monoxide That Can Pollute Indoor Air:

  • Fuel-burning appliances such as furnaces, fireplaces, gas stoves and water heaters (especially those that are not properly vented or maintained) or when chimneys are blocked or dirty;
  • Idling vehicles in garages that are attached to homes or buildings;
  • Barbecues, grills, space heaters and other non-vented fuel-burning appliances that are designed for outdoor use; and
  • Tobacco smoke.

What Are the Health Risks?

When you breathe in carbon monoxide, it builds up quickly and combines with the blood to produce "carboxyhemoglobin" (COHb), which reduces the ability of blood to carry oxygen.

The effects of exposure to CO can be very serious:

  • At low levels, symptoms include headaches, tiredness, shortness of breath and impaired motor functions. These symptoms sometimes feel like the flu.
  • At high levels, or if people are exposed to low levels for long periods of time, people can experience dizziness, chest pain, tiredness, poor vision and difficulty thinking.
  • At very high levels, carbon monoxide can cause convulsions, coma and even death.

Health Canada's Residential Indoor Air Quality Guidelines

Health Canada has developed an indoor air quality guideline for carbon monoxide in residences. The guideline sets recommended maximum carbon monoxide levels for two types of exposure:

  • The short-term limit of 25 parts per million (ppm) based on a one-hour average is meant to prevent the immediate health effects that may occur from exposure to CO for a short period of time (e.g. one hour).
  • The long-term exposure limit of 10 parts per million (ppm) based on a 24-hour average protects against health effects that may be caused by repeated exposure to CO over a long period (e,g, over days or weeks).

Health Canada's recommended limits are set to protect people with pre-existing heart problems from extra stress on their heart or lungs due to CO exposure.

The most serious, noticeable symptoms of carbon monoxide poisoning will occur at levels much higher than Health Canada's guidelines.

Carbon monoxide levels in Canadian homes with properly functioning fuel-burning appliances are usually well below the limits recommended by Health Canada.

How Do I Prevent or Fix Problems with Carbon Monoxide?

  • Maintenance is the key! Make sure that all fuel-burning appliances such as furnaces, fireplaces, gas stoves and water heaters are well maintained and working properly. Have your appliances inspected by a professional at least once a year and be sure to use a ventilation hood for gas stoves.

  • Leave it outside! Never use a barbecue indoors, and don't use kerosene or oil lamps in enclosed areas unless they are specifically designed for indoor use.

  • No idling indoors! Don't let vehicles idle in the garage, especially when the garage door is closed. Also, keep the doors between your house and the garage closed.Never run gas-powered lawnmowers, trimmers or snow blowers in the garage.

  • Get a carbon monoxide detector! Purchase a Canadian Standards Association (CSA) approved carbon monoxide detector and place it where you can hear the alarm.

  • No smoking please! Since tobacco smoke is a source of carbon monoxide, don't let people smoke indoors.

Where Can I Get More Information?

Health Canada Resources

Other Government of Canada Resources

Other Resources

Did you know?
Carbon monoxide is odourless and colourless but you can still detect its presence with a carbon monoxide detector.