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If the fire doesn't kill you the CO2 might
Carbon dioxide is an efficient way of extinguishing some fires... but it can be dangerous if misused.

If the fire doesn’t kill you, the CO2 might – Carbon dioxide sensors and fire suppression

Visit our carbon dioxide section or contact us to find out more about our carbon dioxide sensors, or sign up to our blog for weekly updates about the gas industry.

Carbon dioxide (CO2) has been used in fire extinguishers and fire suppression systems for more than a hundred years. In high concentrations it dilutes oxygen, thus removing one of the three elements of the combustion triangle (the other two being heat and fuel).

It is also cheap, widely available, electrically non-conductive, chemically inert and it leaves no residue. It is the ideal gas for extinguishing certain types of fire.

But (and there’s usually a ‘but’), it can kill you in under a minute.

Fire triangle

Carbon dioxide in a confined space can be fatal

At the minimum concentration necessary for a total flooding fire suppression system, 34%, carbon dioxide presents an immediate hazard to health. (A concentration of 17% to 30% can rapidly cause unconsciousness, coma and death.) Therefore, a fire extinguishing system that puts CO2 into a confined space presents a high risk of suffocation to anyone in the vicinity.

Statistics1 show that in the five decades between 1948 and 2000 there were 62 reported fire suppression incidents worldwide resulting in 119 deaths and 152 injuries.

The hazards of gas release from fire suppression systems can be partly mitigated by the installation of a life safety device, typically a CO2 detector and an audio-visual alarm. These provide an early warning of increasing CO2. However, if the occupants or responders are unfamiliar with the dangers of CO2 then they may still be overcome by the gas.

Note also that most incidents are caused by either accidental system activation or maintenance on or near the fire protection system itself. CO2 poisoning during a fire is very rare.

A tragic incident in May 2008, involving a CO2 fire extinguishing system, resulted in the death of a foundry worker at Sheffield Forgemasters. The employee was working in a cellar when the fire system was triggered, quickly flooding the area with CO2 gas.

The UK Health and Safety Executive later concluded that exhaust fumes from a petrol-driven saw used in the cellar may have triggered a smoke sensor. The sensor would then have automatically switched on the fire extinguishing system, quickly filling the area with carbon dioxide.

Halons versus carbon dioxide

Because of its inherent dangers CO2 has long been under review as an extinguishant gas for fire suppression systems. It was used exclusively until the late 1960s until it began to be replaced by halons. These became the dominant gases because of their safe exposure levels and cheaper delivery systems, but their success was short-lived.

Newly produced halons were subjected to production and import bans from 1994 due to their destructive effect on the ozone layer. Consequently, CO2 systems have increased in recent years2.

Visit our carbon dioxide section or contact us to find out more about our gas detection monitors, or sign up to our blog for twice-weekly updates about the gas industry.

Sources

1Carbon Dioxide as a Fire Suppressant: Examining the Risks, U.S. Environmental Protection Agency, Office of Air and Radiation, Stratospheric Protection Division, February 2000

2Review Of The Use Of Carbon Dioxide Total Flooding Fire Extinguishing Systems, Robert T. Wickham, P.E. August 8, 2003

Author: Paul Smith, Technical Writer.

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8 Comments on If the fire doesn’t kill you, the CO2 might – Carbon dioxide sensors and fire suppression

  1. This is actually really alarming that CO2 is so harmful. I suppose that when I fire is blazing right in front of you, you might not stop to read the label on the extinguisher. It might make more sense to do a massive personal audit on all your gear to make sure everything is in order before an emergency happens. Thanks for alerting me to some of these dangers!

    Drew Harrison | October 7, 2015 at 6:29 pm () ()
    • Thank you for the kind comment Drew – we’re glad that it’s given you some food for thought in regards to fire extinguishers.

      Kate Ingham | October 8, 2015 at 7:10 am () ()
  2. This is very interesting. I was unaware of the gases involved in extinguishing fire. Do you know which type of fire this harmful CO2 gas will put out? I know little about the subject, but I know that I might need something different for electrical fires. Thanks for sharing!

    James Hobusch | October 10, 2015 at 12:28 am () ()
    • Hi James – despite its inherent risks, carbon dioxide gas is a very effective fire extinguishant. It is generally recommended as the best gas to control electrical fires. As long as it is carefully stored and maintained it should not present a hazard.

      However, to provide reassurance to building occupants, a wall-mounted CO2 detector can be installed near the fire extinguishing system to give advance warning of a gas leak. This gives personnel time to exit the area safely and alert the relevant authorities.

      Kate Ingham | October 12, 2015 at 8:12 am () ()
      • Okay, that makes a lot of sense. Thanks for the information on the wall mounted CO2 detector, I will definitely look more into it. Thanks for getting back to me!

        James Hobusch | October 15, 2015 at 4:02 am () ()
        • You’re more than welcome James – if you’d like more information from us about carbon dioxide detection, please let us know.

          Kate Ingham | October 19, 2015 at 10:23 am () ()
  3. It’s important to remember that oxygen is the most essential requirement for the human body to stay alive. You make a great point about how using CO2 in your fire suppression systems does bring an inherent risk for asphyxiation. Talk to a fire suppression specialist to ensure that your system has the proper space, ventilation, and sensors to ensure that it is safe for fire suppression and the people in the building.

    Alex Trodder | February 18, 2016 at 8:47 pm () ()
    • Thank you for the great feedback Alex. Kate

      Kate | February 24, 2016 at 8:18 am () ()

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