Carbon Monoxide Awareness

What you need to know to protect you and your family from this “silent killer”

What is Carbon Monoxide?

It is produced by the incomplete burning of fuels like natural gas, propane, heating oil, kerosene, coal, charcoal or wood due to inadequate air.

Improperly installed or poorly maintained appliances that run on these fuels can create unsafe levels of CO. In enclosed spaces like your home, cottage or vehicle, even a small amount of CO is dangerous.

Carbon monoxide (CO) is a colorless and odorless gas. Because you can’t see, taste or smell it, it can affect you or your family before you even know it’s there. Even at low levels of exposure, carbon monoxide can cause serious health problems. CO is harmful because it will rapidly accumulate in the blood, depleting the ability of blood to carry oxygen. (Exposure Guidelines for Residential Indoor Air Quality, Health Canada, 1989).

What are the Symptoms of CO poisoning?

Exposure to CO can cause flu-like symptoms such as headaches, nausea, dizziness, burning eyes, confusion, drowsiness and even loss of consciousness. In severe cases, it can cause brain damage and death.

Older persons, children, people with heart or respiratory conditions and pets may be more sensitive to it and feel the effects earlier than others.

What Causes a CO Hazard?

  • Fuel-burning appliances, venting systems and chimneys that haven’t been serviced or regularly maintained by a qualified heating contractor
  • A chimney blocked by a bird or squirrel nest, snow and ice or other debris
  • Improper venting of a furnace and cracked furnace heat exchangers
  • Exhaust fumes seeping into your home from a car running in an attached garage
  • Using fuel-burning appliances designed for the outdoors (like BBQs, lanterns, chainsaws, lawnmowers, snow blowers) in a closed area (like a tent, recreational vehicle, cottage, garage, workshop)
  • Combustion gases spilling into a home if too much air is being consumed by a fireplace, or exhausted by a kitchen or bathroom fan, in a tightly-sealed house.

Be aware of these Danger Signs

  • You or others in your family are feeling the symptoms of CO exposure
  • You notice a sharp, penetrating odor or smell of gas when your furnace or fuel-burning appliance turns on
  • The air feels stale or stuffy
  • The pilot light of your gas furnace or other fuel-burning appliance goes out
  • Chalky, white powder forms on the chimney/exhaust vent pipe, or soot builds up around the exhaust vent
  • Excessive moisture forms on windows and walls
  • The carbon monoxide alarm sounds.

How Can I Eliminate Sources of CO in my Home?

The most important step you can take to eliminate the possibility of CO poisoning is to ensure that CO never has an opportunity to enter your home. This is your first line of defense. Review this list to minimize the risk of CO in your home.

  • Have a qualified technician inspect and clean fuel-burning appliances yearly, before the cold weather sets in, to ensure they are in good working order
  • Have a qualified technician inspect chimneys and vents yearly for cracks, blockages (e.g., bird’s nests, twigs, old mortar), corrosion or holes
  • Check fireplaces for closed or blocked flues
  • Check with a qualified technician before enclosing heating and hot water equipment in a smaller room, to ensure there is adequate air for proper combustion
  • If you have a powerful kitchen exhaust fan or downdraft cook top, have a qualified technician check that its operation does not pull fumes back down the chimney
  • Never use propane or natural gas stove tops or ovens to heat your home
  • Never start a vehicle in a closed garage; open the garage doors first. Pull the car out immediately onto the driveway, then close the garage door to prevent exhaust fumes from being drawn into the house
  • Do not use a remote automobile starter when the car is in the garage; even if the garage doors are open
  • Never operate propane, natural gas or charcoal barbecue grills indoors or in an attached garage
  • Avoid the use of a kerosene space heater indoors or in a garage. If its use is unavoidable, provide combustion air by opening a window while operating
  • Never run a lawnmower, snow blower, or any gasoline-powered tool such as a whipper-snipper or pressure washer inside a garage or house
  • The use of fossil fuels for refrigeration, cooking, heat, and light inside tents, trailers, and motor homes can be very dangerous. Be sure that all equipment is properly vented to the outside and use electric or battery-powered equipment where possible
  • Regularly clean the clothes dryer ductwork and outside vent cover for blockages such as lint, snow, or overgrown outdoor plants
  • Reduce or eliminate the use of fondue heaters indoors
  • Remove snow and ice accumulations around intake and exhaust vents for furnaces and appliances.
  • If you live close to a road with heavy traffic, outdoor carbon monoxide levels can affect your indoor air quality, especially during rush hour. Such levels should not set off a CO alarm, but slightly elevated CO levels might be observable on some types of CO detectors with a digital display.

Carbon Monoxide Detectors: Is One Really Necessary?

If you take the actions above, you greatly reduce your risk of CO poisoning. But unanticipated dangerous incidents may still occur despite your best efforts to avoid CO. The installation of at least one CO alarm in your home is a good safety precaution; and, in some municipalities, it is the law. A detector might be your second line of defense, but, it is necessary. You should have one in your home today.

There are performance differences between these detector types. However, changes to the CO standards have resulted in all detectors, regardless of detector type, having to undergo extensive testing. All are certified to operate under different environments (various chemical exposures, different relative humidity, etc.) satisfactorily if they meet the standards.

How Does a CO Detector Work?

There are three basic types of CO sensors – metal oxide, biomimetic and electrochemical. Each is discussed in the chart below. Note, while there may be performance differences between these technologies, all detectors are tested and approved for their operation. The retail cost of a detector will generally relate to the number of features included and its warranty conditions.

Metal Oxide Semi-Conductor (MOS)

The original technology for detecting CO. Heated tin oxide reacts with CO to determine the levels of the toxic gas. Must connect to house power.

No need to remember to check batteries as the unit plugs in

Battery backup is available for up to 20 hours


Gel-coated discs darken in the presence of CO. Colour change sounds an alarm.
-less expensive technology
-can be battery operated


Chemical reaction with CO creates an electrical current, setting off an alarm.
-highly sensitive and accurate readings at all CO levels
-most units come with a continuous digital readout and a memory feature that allows you to check past CO levels
-fast reset time
-most units sound an alert when sensor needs replacing

What Features Should I Look for When Purchasing a CO Detector?

Most CO detectors are designed to give an alarm when CO levels reach a high level in a short time. However, health agencies advise that long term, low level exposure are also of concern, especially for the unborn and young children, the elderly and those with a history of heart or respiratory problems (Health Canada, 1989). Detectors that can display both high and low levels are more expensive; but, they do provide greater accuracy and more information.

Here are some features to consider when purchasing a CO detector:

  • Look for a detector that is listed with the Canadian Standards Association (CSA) standard. The logos of the testing agency will be on the product.
  • Choose a detector with a memory if you want to monitor long term low level exposure and short term, high level exposure. Even though product standards do not allow manufactures to display low levels of CO, these units monitor and store this information. Peak levels, no matter what the level of concentration, can be viewed by pressing a button.
  • Battery-operated units allow detector placement in the most convenient location. However, any battery operated device requires the user’s diligence in replacing worn out batteries.
  • Do not connect plug in units to an electrical outlet controlled by a wall switch.
  • No detectors will operate properly forever. Replace them at least every five years, unless the manufacturer specifies a shorter or longer life.

Eventually, manufacturers may be required to print expiry dates on their CO detectors. This will ensure you are purchasing an up-to-date product with a full sensor life.

Where Do I Put a CO Detector?

Most manufacturers specify where you should locate their CO detector. In general, the best place to put the detector is where you will hear it while sleeping. CO is roughly the same weight as air and distributes evenly throughout a room, so a detector can be placed at any height in any location, as long as its alarm can be heard. Additional units could be installed in several other locations around the home, such as a child’s bedroom; check the list below before installing.

To avoid both damage to the unit and to reduce false alarms, do not install CO detectors:

  • In unheated basements, attics or garages
  • In areas of high humidity
  • Where they will be exposed to chemical solvents or cleaners, including hair spray, deodorant sprays, etc.
  • Near vents, flues or chimneys
  • Within 2 metres (6 ft.) of corners or areas where natural air circulation is low
  • Near forced – or unforced – air ventilation openings
  • Within 2 metres (6 ft.) of corners or areas where natural air circulation is low
  • Where they can be damaged, such as an outlet in a high traffic area
  • Where directly exposed to the weather.

What Do I Do if I Hear the CO Detector Alarm?

Do not ignore the CO detector’s alarm if it sounds. Treat each alarm as serious and respond accordingly.

CO detectors are designed to sound an alarm before a healthy adult would feel any symptoms. Infants, the elderly and those with respiratory and heart conditions are at particular risk and may react to even low levels of CO poisoning (Health Canada, 1989).

Response To An Obvious Source of CO

If your detector sounds an alarm and you have an obvious source of CO, such as an unvented kerosene heater:

  • If anyone is suffering from flu-like symptoms, call 9-1-1
  • Remove or turn off the source
  • Ventilate the house
  • Reset the alarm
  • Do not re-occupy the house until the alarm ceases
  • Take steps to avoid this situation in the future.

Response To An Unknown Source of CO

If your CO detector is sounding an alarm and there is no obvious source of CO:

  • Evacuate the house, including pets and do a head count
  • If anyone has flu-like symptoms, call 09-1-1; if there are no health problems, call your gas utility, heating contractor or the fire department to have your house tested
  • If you live in a single family home: do not ventilate your home, turn off fuel-burning appliances or reset your CO detector prior to someone testing your home*
  • If you live in a duplex, row house, apartment, or otherwise attached house, do ventilate the house and turn off fuel-burning appliances. In this case, the safety of your neighbors is more important that trying to find the CO source.
  • Have a qualified service technician inspect and repair all fuel-burning appliances, if they are identified as being the CO source
  • Do not re-occupy the house unless those who tested the house inform you the danger is over.

* Many CO alarm calls have been classified as “false alarms” because the homeowner has ventilated the home and turned off the equipment before fire fighters or technicians can measure the CO levels and find the source.

Symptoms of CO Poisoning

Be sure that all members of your family know the symptoms of CO poisoning:

Mild Exposure

Flu-like symptoms such as headache, running nose, sore eyes, etc.

Medium Exposure

Drowsiness, dizziness, vomiting. The sense of disorientation and confusion may make it difficult for some victims to make rational decisions like leaving the home or calling for assistance.

Extreme Exposure

Unconsciousness, brain damage, death

Continued Low-level Exposure to CO

While this may not lead to observable symptoms, you should still avoid such exposure.

Testing a Carbon Monoxide Detector

Most CO detectors have a test button that should be pressed once a week to confirm the device is in operation. Detectors with displays can be tested with a known source of CO such as smoke from a cigarette or incense stick. Hold the CO source about 8-10 inches away and watch the digital display respond to the presence of even a small amount of CO. BUT, an alarm will most likely not sound with this test.

There are CO detector test kits available, where CO detectors are sold, that provide a vial of high level of CO (1000 ppm) and a plastic tent to house the unit during the test. This test only proves that your detector will sound an alarm with a very high level of CO.

What Standards Apply to CO Detectors?

The two main industry standards used in Canada are CAN/CGA-6.19. “Residential Carbon Monoxide Detectors,” and UL2034, “Single and Multiple Station Carbon Monoxide Detectors.” Units should bear the approval of one of these standards. Electric powered units should also bear the CSA approval.

In general, current standards require detectors to alarm for 70 ppm within 240 minutes, 150 ppm within 50 minutes and 400 ppm within 15 minutes.

Earlier CO-detector models were designed with different standards. Recent changes to detectors primarily address false alarms common with the older models. Revisions to these standards do not make current carbon-monoxide detectors obsolete.

CO concentration in parts per million (ppm)



Normal conditions inside and outside Canadian houses.


Maximum tolerable indoor concentration over an eight hour period. ¹


Maximum allowable concentration for continuous exposure for healthy adults in any eight hour period. ¹


CO detectors must not sound alarm within 30 days. ²


CO detectors must sound alarm within one to four hours. ²


CO detectors must sound alarm within 10 to 50 minutes. ²


Slight headache, fatigue, dizziness and nausea after two to three hours. CO detector alarm must sound within 35 minutes. ³


CO detectors must sound alarm within 4 to 15 minutes. ²


Dizziness, nausea and convulsions within 45 minutes, death within 2 or 3 hours. ³


Death within one hour. ³


Danger of death after one to three minutes

¹ Exposure Guidelines for Residential Indoor Air Quality, Health Canada, 1989.

² From CAN/CSA 6.19, Residential Carbon Monoxide Alarming Devices, 2001

³ Carbon Monoxide Poisoning, Iowa State University of Science and Technology, AEN-172

Do CO Detectors Require Maintenance?

CO detectors should be maintained in accordance with the manufacturer’s instructions. Keep your air vents clean by vacuuming them occasionally. Test the detectors regularly. In general, units should be tested at least once a month. CO Alarms should be replaced every seven years; or, according to manufacture’s instructions.

Are CO Detectors Required?

The Ontario Building Code requires CO detectors in newly constructed homes with solid fuel burning appliances such as woodstoves and fireplaces.
As of October 1, 2009, CO detectors are mandatory in all North Bay homes, containing a fuel burning appliance and/or an attached garage. (By-law # 2009-16)

how to choose a co detector.