City gas flame lit in the dark

How to detect the presence of carbon monoxide?

Invisible, odourless and toxic, carbon monoxide is a potentially lethal gas resulting from incomplete combustion of a fuel (coal, petrol, wood, butane, fuel oil, natural gas, propane, etc.). The only known technique for detecting carbon monoxide is the use of a carbon monoxide detector.

Is carbon monoxide heavier or lighter than air?

Carbon monoxide is slightly lighter than air: its density is 0.968, while that of air is 1. Normally, it is found in ambient air at a concentration of about 0.2 ppm (parts per million).

Due to its characteristics, CO has a natural tendency to concentrate where the air is most circulated, i.e. the centre of the room.

How to install a carbon monoxide detector?

Although carbon monoxide is lighter than air, it tends to spread evenly throughout the room where it is released. This is why it is recommended that you install your carbon monoxide detector on the wall or ceiling.

To ensure your safetyWe advise you to :

  • Refer to the manufacturer's installation instructions to ensure that your detector is installed correctly.
  • Do not install your carbon monoxide detector in the immediate vicinity of combustion appliances (these may release a small amount of CO when started). This advice also applies to city gas detectors.
  • Do not place your CO detector within three metres of a cooking or heating appliance, or in wet areas such as the bathroom.
  • Place a carbon monoxide detector on each floor of your home, in high-traffic areas and near bedrooms where appropriate.

What is the maximum concentration of carbon monoxide that should not be exceeded?

Dangers and how to protect yourself from carbon monoxide in the home
Source :

The WHO (World Health Organisation) has defined carbon monoxide thresholds that should not be exceeded depending on the duration of exposure. These values serve as a reference for the whole population, including pregnant women, the elderly and people with heart or respiratory diseases (known or unknown).

These values allow do not exceed 2.5 % HbCO in susceptible individuals (HbCO = Carboxyhaemoglobin = a form of haemoglobin that is toxic to the body and consists of haemoglobin and carbon monoxide):

  • 100 mg/m3 (87 ppm) for 15 minutes
  • 60 mg/m3 (52 ppm) for 30 minutes
  • 30 mg/m3 (26 ppm) for 1 hour
  • 10 mg/m3 (9 ppm) for 8 hours

The DDASS of the Bas-Rhin also proposes the following analysis grid in order to set a reasonable threshold for a risk situation:

  • CO concentration > 10 ppm: danger exists, but not immediate.
  • CO concentration between 30 and 100 ppm: immediate danger.
  • CO concentration >100 ppm: evacuate the dwelling.

What are the effects of carbon monoxide poisoning?

Health Information | What are the effects of carbon monoxide poisoning?

The severity of carbon monoxide poisoning results from its binding to proteins containing a heme nucleus, notably haemoglobin (blood). This binding leads to a decrease in the transport and use of oxygen in the blood. The effects are :

  • For low levels of exposure Headache, muscle weakness, hypotension, reflex tachycardia, dizziness.
  • For severe intoxication Immediate severe cardiovascular and neurological disorders.
  • For acute high intensity poisoning Comatose or fatal form at the outset.

Carbon monoxide poisoning can also cause lifelong neurological (e.g. Parkinson's syndrome) and cardiac (e.g. myocardial infarction) sequelae in exposed individuals, as well as serious neurological sequelae and even fetal death in pregnant women (source: