Carbon Monoxide Awareness

Carbon Monoxide (CO) is known as The Silent Killer because you can't smell it, see it or taste it. But it can harm or kill you. In Ontario, over 65% of all CO deaths and injuries occur in homes.

Most people have heard of carbon monoxide, but awareness is often lacking of where it comes from, how it's produced, its physical symptoms, and what precautions can be taken to ensure it doesn't endanger you. Or worse, kill you.

What you need to know

 What is Carbon Monoxide?
Carbon Monoxide, also known as CO, is a poisonous gas that you can't see, smell or taste. CO is often referred to as the silent killer. 

This odourless gas is produced as a byproduct of combustion when common fuel-burning appliances and equipment that use natural gas, oil, wood, propane and kerosene, don’t get enough air to burn up completely. When this happens, CO can build up, especially in a confined room or space – and this can lead to toxic effects on humans and pets.

Many homes in Ontario have on average 4-6 fuel-burning appliances that produce CO.

 What are the symptoms of CO poisoning?

CO has warning signs by how it affects humans.  CO poisoning causes flu-like symptoms, including:

  • headaches
  • nausea
  • dizziness
  • fatigue
  • burning eyes
  • confusion
  • disorientation
  • drowsiness

CO poisoning makes it difficult for your body to absorb oxygen. In severe cases it can cause brain damage and death. The elderly, children and people with heart or respiratory issues may feel the effects sooner than others. Even small amounts of CO gas can be dangerous.

 What causes unsafe levels of CO?
  Certain fuels can produce unsafe levels of CO gas when they are not completely burned. These fuels include:
  • natural gas
  • propane
  • heating oil
  • kerosene
  • coal
  • charcoal
  • wood

Incomplete burning of these fuels can happen when:

  • Appliances using these fuels are not properly installed or maintained
  • Venting systems are not properly installed or cleaned
  • Chimneys are not properly maintained and cleaned
  • Chimneys are blocked by a nest, snow, ice or other debris
  • Furnaces are not properly vented or have cracked heat exchangers
  • Cars are left running in a garage and the exhaust fumes get into your home
  • Fuel-burning appliances made for outdoor use are used in a closed space such as a tent, recreational vehicle, cottage, workshop or garage
  • Too much air is being consumed by a fireplace or exhausted through kitchen or bathroom fans in a tightly sealed house
 What are the sources of CO?

Fuel-burning appliances are the source of CO. Many homes in Ontario have on average 4-6 fuel-burning appliances that produce CO including:

  • Furnace
  • Gas water heater
  • Gas fireplace
  • Gas stove
  • Gas dryer
  • Gas barbecue
  • Portable generators
  • Fuel-burning space heaters
 What are the signs of unsafe levels of CO?
It is important to know the symptoms and danger signs of unsafe CO levels because this poisonous gas is invisible to us. Danger signs of high CO levels include:
  • Your carbon monoxide alarm goes off
  • Flu-like symptoms
  • A sharp, powerful odour or smell of gas when your fuel-burning appliance turns on
  • Stale or stuffy air
  • The pilot light of your fuel-burning appliance goes out
  • Chalky, white powder on the chimney or exhaust vent pipes
  • Soot build-up around exhaust vents
  • Excessive moisture on windows and walls

 What You Need To Do

 Protecting Yourself and Your Family

The best way to ensure that you and your family are not exposed to carbon monoxide is to eliminate this poisonous gas at the source. Here is a list of Do’s and Don’ts when it comes to CO safety:


  • Do have fuel-burning appliances installed by a professional.
  • Do have all your fuel-burning appliances and vents are inspected annually. Find a registered contractor at
  • Do keep chimneys clear of bird and squirrel nests, leaves, and other debris to ensure proper ventilation
  • Do ensure your furnace and other appliances, such as gas ovens, ranges, and cook tops, are inspected for adequate ventilation
  • Do make sure your fuel-burning appliances have an adequate air supply to prevent a CO hazard
  • Do install a working carbon monoxide alarm near all sleeping areas in your home
  • Do remember to test your CO alarms once a month by pushing the test button on the unit


  • Use portable fuel-fired appliances (i.e., barbeque, heater, stove) inside your house or garage.
  • Operate gasoline-powered engines in confined areas such as garages, basements or boat houses.
  • Leave your car, mower, ATV or other vehicle running in an attached garage, even with the door open.
  • Block or seal shut exhaust flues or ducts for appliances such as water heaters, ranges, and clothes dryers.
 Install a CO Alarm

Only working CO alarms give you the warning of the presence of CO you need to keep your family safe.


  • You are required to have a working CO alarm near all sleeping areas in your home.
  • When choosing a CO alarm, look for the CSA Blue Flame mark and the reference “CSA 6.19-01” – the most up-to-date Canadian standard. This shows that the alarm met recognized standards for safety
  • CO alarms should be installed as per manufacturer’s instructions.


  • Remember to test your CO alarms once a month by pushing the test button on the unit
  • Clean your CO alarms monthly with gentle, soft bristle vacuum attachment. Test after cleaning.
  • CO alarm batteries should be replaced in accordance with the manufacturer’s instructions, at least once a year. If an alarm “chirps” or “beeps” to indicate low batteries, they should be replaced immediately.
  • Remember that CO alarms wear out over time. Check the manufacturer’s instructions to find out when your particular unit should be replaced.
 What should I do if my CO alarm goes off?
  • Leave your home and call 9-1-1 if your CO alarm goes off. CO alarms are designed to alert you when CO is present in your home, but has not yet reached dangerous levels.
  • Even if no one is experiencing symptoms of CO poisoning, be safe and exit your home and call 9-1-1 to have RHFES attend to check your home for CO gas.
 What should I do if I think someone has CO poisoning?
  • Leave your home right away and call 9-1-1 when you or anyone in your family suffers symptoms of CO poisoning or experiences any of the danger signs of unsafe levels of the gas.
  • You will need to let the 9-1-1 operator know your address, whether or not anyone has flu-like symptoms and whether or not everyone has exited the home. This will help them send the correct emergency services to your home.

To learn more about carbon monoxide safety, myths and misconceptions, or to find a qualified contractor, visit