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Firefighter Guidance Note: Carbon Dioxide Hazards

Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. For further information please see full disclaimer.


Firefighters may be exposed to the hazard of carbon dioxide in the course of their work.


At high concentrations, carbon dioxide can displace oxygen in the air, depriving the body of oxygen. This can cause unconsciousness. Carbon dioxide also acts as a strong central nervous system depressant.

Actions for employers

Employers should:

  • incorporate the principles set out in this guidance note into their standard operating procedures/operating guidelines
  • consider consulting with their joint health and safety committee or health and safety representative when developing procedures/guidelines

Carbon dioxide

Here are some basic facts about carbon dioxide, or CO2:

  • CO2 is a colourless and odourless gas that cannot be detected by human senses
  • the main route of CO2 exposure is through inhalation
  • at high concentrations, CO2 is considered an asphyxiant because it can displace oxygen in the air
  • it is a strong central nervous system depressant
  • liquid CO2 is stored at extremely low, or cryogenic, temperatures – direct contact with the liquid or cold vapors can chill or freeze the skin

A lack of oxygen can lead to various symptoms, such as:

  • rapid breathing
  • rapid heart rate
  • clumsiness
  • emotional upset
  • fatigue
  • nausea and vomiting
  • collapse
  • convulsions
  • coma
  • death

Symptoms occur more quickly with physical effort due to the increased rate of inhalation.

Exposure locations

Historically, CO2 was typically delivered in pressurized cylinders to businesses serving carbonated beverages or draft beer.

Large volumes of cryogenic liquefied gas may be contained in a Dewar - a double-walled flask of metal or silvered glass with a vacuum between the walls, used to hold liquids at well below ambient temperature. These Dewars can be located either inside or outside the building and are refilled from a delivery vehicle.

CO2 systems can be found in commercial and industrial establishments, including brew-your-own-beer and wine establishments.

Response considerations

Occupants may report CO2 alarms as carbon monoxide alarms. Self-contained breathing apparatus (SCBA), should be used to investigate.

When responding to a location where CO2 is stored, be alert to the possibility that CO2 may be leaking from the delivery systems. Wear appropriate personal protective equipment including gloves and SCBA.

Possible exposure signs to be alert for include:

  • more than one victim with the symptoms listed above
  • unconscious victims located in unventilated spaces
  • CO2 alarms sounding
  • reports of leaking CO2 from occupants

If a CO2 leak is suspected, consider the following measures:

  • put on SCBA and begin ventilating the building
  • positive-pressure ventilation to remove CO2, especially from below-ground areas, because of the high vapour density
  • remove victims from the hazard area immediately, provide supplemental oxygen and contact emergency medical services
  • if safe to do so, shut off, isolate or move the leaking cylinder or Dewar while wearing structural firefighting gear, including gloves and SCBA
  • if it is not safe to shut off, isolate or move the leaking cylinder or Dewar, withdraw and treat the scene as a hazardous materials incident
  • contact the supplier and the Technical Standards and Safety Authority in all cases of CO2 leaks
  • make sure the area is safe, by testing for the presence of CO2, before permitting occupants to re-enter

Applicable regulations, acts and standards


  • Occupational Health and Safety Act
    • clause 25(2)(a) for providing information and instruction to a worker
    • clause 25(2)(d) for making workers aware of hazards
    • clause 25(2)(h) for taking every precaution reasonable to protect workers
  • Ontario Regulation 833 - Control of Exposure to Biological or Chemical Agents
    • section 4 for the short term exposure limit for CO2 of 30,000 parts per million and the time weighted average for CO2 of 5,000 parts per million, as set out in the 2013 ACGIH Table

Disclaimer: This web resource has been prepared to assist the workplace parties in understanding some of their obligations under the Occupational Health and Safety Act (OHSA) and the regulations. It is not intended to replace the OHSA or the regulations and reference should always be made to the official version of the legislation.

It is the responsibility of the workplace parties to ensure compliance with the legislation. This web resource does not constitute legal advice. If you require assistance with respect to the interpretation of the legislation and its potential application in specific circumstances, please contact your legal counsel.

While this web resource will also be available to Ministry of Labour inspectors, they will apply and enforce the OHSA and its regulations based on the facts as they may find them in the workplace. This web resource does not affect their enforcement discretion in any way.