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Carbon Monoxide


The presence of carbon monoxide (CO) is dangerous in homes, cottages, and work places. There are two basic steps to protecting yourself against carbon monoxide poisoning; the first step is to eliminate or prevent carbon monoxide from entering buildings, and the second is to have at least one CO detector installed in your home or cottage.

This FAQ will help to answer some of your questions about carbon monoxide, and provide tips and recommendations on how to protect your family from carbon monoxide poisoning.

Click here for your Free Safe At Home CO Safety Guide

What is Carbon Monoxide?

Carbon monoxide (CO), sometimes called "The Invisible Killer", is a colourless and orderlous gas. Since it can not be seen, tasted, or smelled, it can affect you or your family without anyone knowing that it is even there. Carbon monoxide can cause serious health problems even at low levels of exposure; it will rapidly accumulate in the blood stream, depleteing the ability of the blood to carry oxygen throughout the body.

Where Does Carbon Monoxide Come From?

Carbon monoxide is a byproduct of the combustion (burning) of fossil fuels such as natural gas, propane, oil, gasoline, kerosene, wood, coal, and charcoal. If properly installed and maintained, most fuel burning equipment (natural gas, propane, and oil) produces very little CO and the byproducts of combustion are safetly vented outside. If anything interferes with the venting process however (such as a bird's nest in the chimney), or results in a shortage of oxygen from reaching the burner, dangerous levels of CO production can rise quickly.

Since burning wood, kerosene, coal, and charcoal produces CO, methods of cooking, heating, or lighting that work through the burning of these fuels should never to used indoors or in any enclosed spaces. In engines that burn gasoline, CO production is at it's highest during the start up of a cold engine. Starting and then idling your car, gas mower, or generator in the garage can be dangerous as the fumes containing CO can enter a home through connecting walls or doorways and can reach dangerous levels quickly.

How Can Sources of Carbon Monoxide be Eliminated?

Prevention is your first line of defence. To eliminate the possibility of CO poisoning, the most important step to take is to try to prevent CO from entering your home. Review the following list for suggestions on how to mininmize the risk of CO in your home.

Before the cold weather sets in, have a qualified technician inspect and clean fuel
   burning appliances yearly to ensure that they are in proper working order.
Have chimneys and vents inspected by a qualified technician yearly  to ensure that there are no cracks, blockages (e.g., bird's
   nests, twigs, old mortar), corrosion or holes.
Check fireplaces for blocked or closed flues.
Before enclosing heating or hot water equipment in a smaller sized room, have a qualified technician ensure that there is adequate
   air flow for proper combustion.
If you have a powerful kitchen exhaust fan or downdraft cooktop, have a qualified technician inspect it to ensure that it's
   operation does not pull fumes back down the chimney.
Never use natural gas or propane stove tops or ovens to heat your home.
Never start a vehicle in a closed garage.  Open the garage door first and pull the car out onto the driveway immediately after
   starting, then close the garage door to prevent exhaust fumes from being drawn back into the building.
Do not use a remote starter when the car is in the garage, even if the doors are open.
Never use propane, natural gas or charcoal barbeque grills indoors or in an attached garage.
Kerosene space heaters should not be used indoors or in a garage. If this is unavoidable, provide a fresh supply of air for
   combustion by opening a window during operation and refuel the unit outside after it has cooled off.
Never run a lawnmower, snowblower, or any gasoline-powered tool such as a weed whipper or pressure washer inside a
   garage or house.
Using fossil fuels for refrigeration, cooking, heating, and lighting inside tents, trailers, and motorhomes can be very dangerous. Be
   sure that all equipment is properly vented outside and use electric or battery-powered equipment whenever possible.
Clean the clothes dryer ductwork and outside vent cover regularly. Blockages such as lint, snow, or overgrown outdoor plants
   can obstruct the ventilation system.
Reduce or eliminate the use of fondue heaters indoors.
If you live close to a roadway with heavy traffic, your indoor air quality may be affected by the outdoor carbon monoxide
   levels, especially during rush hour. CO alarms should not be set off by such levels, but these slightly elevated levels may
   be observable on some types of CO detectors with a digital display.

Are Carbon Monoxide (CO) Detectors Necessary?

The chances of CO poisoning occuring are greatly reduced if the actions above are followed. However, despite your best efforts to avoid CO, unanticipated dangerous incidents may still occur. Installing at least one CO detector in your home is a safety precaution that should not be overlooked or underestimated and in some municipalities, it is the law. Although a detector is your second line of defence, it is most certainly necessary to have one.

What Kind of Detectors Are There and How Do They Work?

There are three basic types of CO sensors — metal oxide, biomimetic, and elctrochemical. While there may be performance differences between these technologies, all detectors are tested and appoved for operation. Generally, the retail cost of a detector will relate to the number of features included and the warranty conditions provided.

Metal-oxide-semi-conductor (MOS)
This was the first method of detecting CO developed. Heated tin oxide reacts with CO and determins the levels of this toxic gas. There is no need to remember to check batteries as these units must be directly connected to the house power. Some models do also offer up to 20 hours of battery backup however.

Biomemetic detectors use a gel-coated disc that darkens in the presence of CO and this colour change causes an alarm to sound. This technology is less expensive and can be battery operated.

A checmical rectaction with CO creates an electrical current that sounds the alarm in this type of detector. These detectors are highly sensitive and offer accurate readings at all CO levels. Most units have a continuous digital display and a memory feature that allows you to check previous CO levels. This technology also offers a fast reset time and most units will sound an alert when the sensor needs to be replaced.

Are There Any Features That I Should Consider While Purchasing a CO Detector?

Most CO dectectors are designed to set off an alarm when CO gas reaches high levels within a short period of time. However, health agencies advise that low-level exposure over a long-term period is also of concern, especially for unborn and young children, the elderly, and those with a history of heart or respiratory problems. 1 Detectors that can display both high and low levels do cost more, but they also offer greater accuracy and more information.

Here are some of the features to consider while purchasing a CO detector:

Look for a detector that is listed with the Canadian Standards Association (CSA) standard. The logo of the testing agency will be
   visible on the product.
If you want to monitor long-term, low-level exposure and short-term, high-level exposure, choose  a detector with a memory feature.
   Although product standards do not allow manufacturers to display very low levels of CO, these units will often monitor and store this
   information. Peak levels, no matter what the concentration level, can be viewed by pressing a button on many models.
Battery-operated units allow for placement in the most convenient location. These devices do require the owner's due diligence
   to replace worn-out batteries however.
Be sure not to connect plug-in units to an electrical outlet that is controlled by a wall switch.
CO detectors do not last forever and in most cases, the expirey date will be printed on the unit. If the sensor's life has expired, or
   there is no expiry dated provided and your detector is more than 5 years old, it should be replaced immediately.

Detector Sensitivity Issues
The Canadial Standards Association (CSA) in Canada and Underwriters Laboratories (UL) in the United States have coordinated the writing of CO standards and product testing. s of 2010, the current standards prohibit showing CO levels of less than 30 ppm on digital displays. The most recent standards also require that the alarm will sound only at higher levels  of CO than previous editions of the standard. The reasoning behind these changes is intended to reduce the number of calls made to fire stations, utilities, and emergency response teams where the levels of CO are not life threatening. This change will also reduce the number of calls to these agencies due to false alarms due to sensor inaccuracy or  the presence of other gases. Consequently, newer alarms will not sound at CO concentration up to 70 ppm which is significantly in excess of Canadian health guidelines.

The true CO concentrations in a house can be provided by a detector with a digital display and a "history" option. A low-level display would be useful for people with existing or suspected respiratory problems or for those that would like to spot evolving problems, rather than waiting for the situation to become serious. Low-level CO detection products are commercially available but they will no tbe CSA or UL certified as these standards currently prohibit low-level displays.

Where Should a CO Detector Be Installed?

Most manufacturers will provide instructions on where to best place their CO detector. Generally, the best place to put a detector is just outside of your bedroom where you will here it while sleeping. Since CO is rougly the same weight as air, it is evenly distributed throughout the room, so a detector can be placed at any height in any location, as long as the alarm can be clearly heard. Additional units could also be installed in other locations throughout the home, such as a child's bedroom. Be sure to check the following list before installing however:

To avoid damaging the unit and reducing the chance of false alarms, do not install CO detectors:

in unheated basements, attics, or garages
in areas of high humidity such as bathrooms
where exposure to chemical solvents or cleaners, including hair spary, deodorant sprays, etc. is present
close to vents, flues, or chimneys
within 2 m (6 ft.) of heating and cooking appliances
near forced- or unforced-air ventilation openings
within 2m (6 ft.) of areas where natural air circulation is low, such as corners of a wall
in places where they may be accidentally damaged, such as an electrical outlet in a high traffic area
where directly exposed to the weather

How Can I Test My CO Detector?

Most CO detectors have a test button that should be pressed once a month, or once per week in buildings where CO levels are of particular concern, to confirm that the device is fully operational. Detectors with a display can be tested with a known source of CO such as the smoke from an incense stick; hold the source of CO about 20 – 25 cm (8 – 10 in.) away and watch the digital display as it responds to the presence of even small concentrations of CO, although the alarm will most likely not sound with this test.

CO detector test kits are also available in most places where CO detectors are sold. These kits provide a vial containing a high level of CO (1,000 ppm) and a plastic tent to house the unit during the test. This test only proves that the detector will sound an alarm when very high levels of CO are present.

What Should I Do If I Hear the CO Detector Alarm?

Do not ignore a CO detector if the alarm sounds. Each alarm should be treated as being serious and should be responded to accordingly. CO detectors are designed to sound an alarm well before a healthy adult would feel any symptoms to the exposure to carbon monoxide. Infacts, the elderly, and those with heart or respiratory conditions are at particular risk and may react to even low levels of CO poisoning.1

Response to an Obvious Source of CO
If you have an obvious source of CO, such as an unvented kerosene heater, and the alarm sounds:

evacuate the building (including pets), seek fresh air outdoors and perform a head count to ensure that all occupants are accounted for
if anyone has flu-like symptoms, call 911 immediately
remove or turn off the source only if you know it is safe to do so, otherwise wait for emergency response personel to arrive
ventilate the house by opening up as many doors as possible from the outside
reset the alarm
do not re-occupy the building until the alarm has ceased
take steps to avoid this situation in the future

Response to an Undetermined Source of CO
If there is no obvious source of CO and the alarm sounds:

evacuate the building (including pets), seek fresh air outdoors and perform a head count to ensure that all occupants are accounted for
if anyone has flu-like symptoms, call 911 immediately; if there are no noticable health problems, call your gas utility, heating
   contractor, or the fire department to have your house tested
if you live in a single-family dwelling: do not ventilate your home or turn off fuel-burning appliances. Also, do not reset the CO
   detector prior to having the home tested. Many serious CO alarm calls have been classified as "false alarms" because the
   homeowner had turned off the equipment and ventilated the home before firefighters or technicians could measure the CO
   levels and locate the source
if you live in an appartment building, duplex, row house, or attached house: do ventilate the building and turn off any fuel-burning
   appliances. In this case, the safety of your neighbours is far more important than trying to locate the source of the CO
if they are identified as being the source of the CO, be sure to have a qualified technician inspect and repair all fuel-burning appliances
do not re-ccupy the house unless those who have tested it have informed you that the danger is over

What Are the Symptoms of Carbon Monoxide Poisoning? 2

Be sure that everyone in your household recognizes the symptoms of CO poisoning:

Mild Exposure
Flu-like symptoms such as headache, runny nose, sore eyes, etc.

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

Elevated Exposure
Unconsciousness, brain damage, death.

Continued Low-level Exposure to CO
While observable symptoms may not be noticable, such exposure should still be avoided.

Table 1 — Carbon Monoxide Concentrations and Their Effects

CO concentrations in
parts per
million (ppm)


0 2

Normal conditions in and outside Canadian houses.


Recommended exposure limit over a 24-hour period. 3


Recommended exposure limit over a 1-hour period. 3


CO detectors are not allowed to sound alarm unless this concentration is maintained for more than 30 days. 2


CO detectors must sound alarm within 1 to 4 hours. 2


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


Slight headache, fatigue, dizziness and nausea after 2 to 3 hours. CO detector alarm must sound within 35 minutes. 4


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


Dizziness, nausea and convulsions within 45 minutes, death within 2 to 3 hours. 4


Death within 1 hour. 4


Danger of death after 1 to 3 minutes. 4

1 Canada. Health Canada, Exposure Guidelines for Residential Indoor Air Quality (Ottawa: Ministry of Supply and Services Canada, 1989).

2 Canadian Standards Association, CAN/CSA 6.19-01: Residential Carbon Monoxide Alarming Devices (Canada: Canadian Standards Association, 2001).

3 Canada. Health Canada, Residential Indoor Air Quality Guideline: Carbon Monoxide (Ottawa: Minister of Health, 2010). Available online at

4 T. H. Greiner, Carbon Monoxide Poisoning (AEN-172) (Ames: Iowa State University of Science and Technology, 1997).

Canada Mortgage and Housing Corporation, Carbon Monoxide.

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