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Carbon monoxide poisoning


Carbon monoxide (CO) is a clear and odourless toxic gas. It does not irritate the eyes or respiratory tract. Odour is therefore an inadequate means for preventing carbon monoxide poisoning.

When a person inhales carbon monoxide, the gas enters their blood and interferes with oxygen intake. This damages tissue and can be extremely dangerous to health.

The  effects of carbon monoxide poisoning vary according to the following:

  • Quantity of carbon monoxide in the air
  • Length of a person’s exposure to gas
  • Person’s sensitivity to the effects of carbon monoxide
  • Person’s state of health
  • Repeated exposure over time.


It is important to understand that carbon monoxide poisoning can only occur if a person is in the presence of a source of the gas.

In fact, the symptoms of carbon monoxide poisoning are often difficult to recognize because they resemble symptoms of other health problems.

You can suspect carbon monoxide poisoning when:

  • One or more people are in a place where there is a source of carbon monoxide
  • These people experience symptoms
  • Symptoms diminish or disappear when people are no longer in contact with carbon monoxide (for example, when people leave the area, the area is ventilated, the source of carbon monoxide is shut down or moved).

Therefore, it is very important to know what to do when you have symptoms.

Symptoms of carbon monoxide poisoning vary according to the intensity of the exposure.

The main symptoms of a light poisoning are:

  • Headache
  • Fatigue
  • Nausea
  • Vomiting

Symptoms of a moderate poisoning are:

  • Dizziness
  • Fatigue
  • Chest pain
  • Problems with vision
  • Difficulty concentrating

Symptoms of a severe poisoning are:

  • Problems coordinating movement or muscle paralysis, which prevent the person from leaving the premises
  • Loss of consciousness

What to do when you show symptoms in the presence of a source of carbon monoxide, or when a carbon monoxide alarm goes off

A carbon monoxide alarm is a device that can detect the gas.

If you or someone you’re with shows symptoms of posioning, whether the carbon monoxide alarm goes off or or not:

You need to think first of all about your own safety and the safety of other people present in the same situation as you.

  1. Leave the premises and go outside
  2. Dial 9-1-1 or call the Centre antipoison du Québec (poison control centre) at 1-800-463-5060
  3. Leave the door open when exiting the premises in order to completely ventilate the place
  4. Wait for the authorisation of a firefighter before returning inside even for a few minutes

If you do not have symptoms of poisoning, but your carbon monoxide alarm goes off:

  1. If possible, quickly turn off the fuel supply
  2. Head outside
  3. Call 9-1-1
  4. Leave the door open when leaving the premises to ventilate the area completely
  5. Wait for a firefighter's authorization before returning indoors, even for a few minutes
  6. Do not use your fuel-burning appliances until they have been checked by a qualified person if you suspect a malfunction.


It is necessary to consult a physician to treat carbon monoxide poisoning.

Administration of high levels of oxygen is the standard treatment. If the person’s condition is more serious, the physician may prescribe hyperbaric oxygen therapy. For this treatment, the person is placed in a closed chamber in which they receive pressurised oxygen.


Severe poisoning can cause permanent effects.

The following effects can appear during a period of 2 to 40 days after poisoning, even if treated:

  • Chronic migraines
  • Neurological disorders that can cause problems with coordination of movement
  • Memory and behavioural problems
  • Mood swings: irritability, verbal aggressiveness, violence

Severe carbon monoxide poisoning can also lead to a coma and death within minutes.

Protection and prevention

Only a carbon monoxide alarm can detect the gas and warn you.

When the alarm goes off, knowing what to do is important. To find out more on this, go to the What to do when you have symptoms or a carbon monoxide alarm goes off section.

For information on the types of detectors, their installation and their maintenance, see the Carbon monoxide detectors page.

To properly protect yourself, take precautions to prevent carbon monoxide poisoning.

People at risk

Everyone is at risk of being poisoned by carbon monoxide. However, the risk is higher for the following:

  • People with chronic heart disease, anemia or respiratory problems
  • People 65 years of age and older
  • Children less than 2 years of age
  • People who smoke

Pregnant women and their fetuses. Carbon monoxide poisoning increases the risk of fetal death and developmental disorder

Special conditions

In Québec, carbon monoxide poisoning is a reportable disease.

Cases of carbon monoxide poisoning must be reported to public health authorities by a physician or laboratory. This will enable us to carry out investigations to better protect public health.

Last update: November 23, 2023


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