[RPG] Is a CO2 fire extinguisher safe to use indoors to represent offensive magic or breath weapons in LARP


In short: my friend, who is also a LARP organizer, has come up with the idea of representing breath weapons and some kinds of offensive weapons (those that are represented by a "cone template" in many games) via a CO2 fire extinguisher.

CO2 is basically just compressed air. However, I have experience of using it for cleaning purposes, and I know that it becomes extremely cold. So, I cannot be sure about its safety.

So, is one safe to use indoors? If the answer is yes, what safety measures do I need?

Best Answer

CO2 extinguishers are not safe to use on people or in a room full of people.

Exit temperatures of the CO2 is -52°C in gaseous form and -78°C in snow form, enough to cause frostbite if it touches the skin. If that happens, it is recommended to remove most of it without rubbing it in and then seek medical advice.

It can also cause respiratory problems, especially among person who already have some troubles such as asthma, because the CO2 is not “basically just compressed air”—it's compressed carbon dioxide, and the fire extinguisher works by replacing the oxygen in the area to put out the fire. A CO2 fire extinguisher aimed at people would work by replacing the oxygen nearby those people with CO2.

This gas is an asphyxiant and extremely dangerous for humans even in low concentrations for any sustained period. This would include anyone having a CO2 extinguisher used on them. Symptoms are debilitating and range up to and including death. This is even when there is otherwise sufficient oxygen present: CO2 alone will cause these symptoms. From a USA EPA report (source 2):

At concentrations [of inhaled CO2] greater than 17 percent, such as those encountered during carbon dioxide fire suppressant use, loss of controlled and purposeful activity, unconsciousness, convulsions, coma, and death occur within 1 minute of initial inhalation of carbon dioxide

The same paragraph continues, but even low concentration exposure has debilitating effects (ibid.):

Exposures to 4 to 7 percent carbon dioxide can result in headache; hearing and visual disturbances; increased blood pressure; dyspnea, or difficulty breathing; mental depression; and tremors

While the risk is low when used outside, it is recommended to always open doors and windows wide if it's been used indoors to evacuate the CO2 and bring in fresh air.


  1. INRS file on fire extinguishers (PDF, in French). INRS = l’Institut national de recherche et de sécurité pour la prévention des accidents du travail et des maladies professionnelles2. In English it is the French National Research and Safety Institute for the Prevention of Occupational Accidents and Diseases3.
  2. Carbon Dioxide as a Fire Suppressant: Examining the Risks, by the US Environmental Protection Agency
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