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?

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    \$\begingroup\$ Does experience from SCA bouts count for such an answer? \$\endgroup\$ Commented Oct 10, 2018 at 12:29
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    \$\begingroup\$ @KorvinStarmast It would, as SCA has some quite nice safety regulations \$\endgroup\$
    – Trish
    Commented Oct 10, 2018 at 15:46
  • \$\begingroup\$ Please use only the answer section to post answers. (See the FAQ.) \$\endgroup\$ Commented Oct 11, 2018 at 14:58

4 Answers 4


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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    \$\begingroup\$ "enough to cause frostbite if it touches the skin" - For a sustained duration in a single spot, yes. However that's actually less likely to occur than it seems due to the fact that the solid CO2 will begin to vaporize the instant it touches anything as warm as a person. You can safely 'hold' a small piece of dry ice in your bare hands, even, so long as you don't let it sit in one spot. \$\endgroup\$
    – aroth
    Commented Oct 10, 2018 at 14:07
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    \$\begingroup\$ "Humans can't breathe this gas, and a fire extinguisher aimed at people would work by replacing the oxygen nearby those people with unbreathable CO2." - It's a bit more serious than that; CO2 is actually toxic to humans. Key quote: "Concentrations of 7% to 10% may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour." \$\endgroup\$
    – marcelm
    Commented Oct 10, 2018 at 23:00
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    \$\begingroup\$ @marcelm the exact wording is actually not a toxic gas but an asphyxiant gas. However, the key point is it can kill you in 10% or lower concentrations. \$\endgroup\$
    – Nelson
    Commented Oct 11, 2018 at 0:43
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    \$\begingroup\$ @Nelson I chose to ignore the fact that CO2 is not classified as toxic by the GHS (and in fact I'm puzzled by that classification), as CO2 can kill without displacing oxygen. The passage I quoted shows this, as does this piece from a page on asphyxiation: "If carbon dioxide is used, controlled atmosphere killing is not the same as inert gas asphyxia, because carbon dioxide at high concentrations (above 5%) is not biologically inert, but rather is toxic and ..." ... \$\endgroup\$
    – marcelm
    Commented Oct 11, 2018 at 16:19
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    \$\begingroup\$ ... Additionally, low concentrations (0.5%) for extended periods of time can have measurable effects on humans (again from the Wikipedia page on CO2), so I'm really hesitant to call CO2 non-toxic, regardless of what the GHS says. The point is, CO2 can be pretty bad, even if oxygen is not displaced, so I think we should warn the OP (and others) of that. And "toxic" seems to describe it fine to me ;) \$\endgroup\$
    – marcelm
    Commented Oct 11, 2018 at 16:21

In answer to your question on the safety of using a CO2 extinguisher as a breath weapon effect at a Live Roleplaying Event: NO, for exactly the reasons stated in the other answers - extreme cold, hypoxia, and CO2 poisoning. I don't think your insurers would be too pleased about that particular course of action, either.

From the point of view of a someone who rigs effects for a large system, what you probably want instead is a portable smoke machine. These can be hired relatively inexpensively, and use a water-based smoke-fuel to provide the effect. If you're technically inclined, you can even make one yourself.

The other way - slightly less directed, but I have seen used as poison clouds at events - is a smoke grenade such as one you might get for use at an Airsoft shoot.

Both of these should be covered under your event insurance.

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    \$\begingroup\$ Can a smoke machine be rigged to sort of 'shoot' smoke in a direction like an extinguisher would? \$\endgroup\$
    – Sava
    Commented Oct 10, 2018 at 15:08
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    \$\begingroup\$ Absolutely. I use a variety of machines for the effects I rig - mainly the fixed appliances, but these do shoot smoke in a cone unless diffused by something in the way. They're exactly the same type of machine you get giving smoke at concerts, funfairs and clubs, so are also safe to use at fairly close range - a couple of feet. I still wouldn't blast someone in the face with it. :) \$\endgroup\$ Commented Oct 10, 2018 at 15:24
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    \$\begingroup\$ As a brief thought, you might want to warn any asthmatics at your event that you will be using smoke effects, but it's less likely to cause as many problems as CO2 - Out of the few thousand who attend the events, I'm only aware of a couple who don't get on with the smoke effects. \$\endgroup\$ Commented Oct 10, 2018 at 15:27
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    \$\begingroup\$ I think you should add that smoke machines/grenades can cause problems for people with asthma or other respiratory issues. If you use them, there should definitely be a warning so people with sensitivities know to avoid those activities. \$\endgroup\$
    – Ethan
    Commented Oct 10, 2018 at 19:28
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    \$\begingroup\$ "In answer to your question on the safety of using a CO2 extinguisher as a breath weapon effect at a Live Roleplaying Event: NO" NO is even worse than CO2. \$\endgroup\$ Commented Oct 11, 2018 at 18:52

DISCLAIMER: I am not a medical or safety professional.

They can be very dangerous

I would not recommend doing this. CO2 Fire extinguishers present 2 basic hazards.

Cold Burns

Do Not Touch the horn (the part that sprays CO2) when spraying a CO2 Fire extinguisher. The horn of a CO2 fire extinguisher becomes extremely cold during use, and can cause cold burns if skin comes into contact with it.

Additionally, while the CO2 rapidly warms once it is clear of the extinguisher, it is very hazardous at close range. You are spraying rapidly-evaporating dry ice out of this thing, which will cause cold-burns.

They displace oxygen.

This is the greater risk. The way a CO2 Fire Extinguisher works is that it pushes all of the oxygen in an area away, replacing it with CO2, thereby smothering the fire. This is obviously a problem, because humans need to breathe oxygen.

Based off this, here are two safety pointers if you do decide to point one of these at a person.

  1. Only use in a large, extremely well-ventilated area. Ideally, outdoors. In a confined space, a CO2 Fire extinguisher can lower the oxygen content of the space far enough to cause asphyxiation
  2. Do not sustain the spray for more than a few seconds at a time. Even in a well-ventilated area, the space that the extinguisher is spraying will quickly have too little oxygen to sustain a person. Sustained spraying can suffocate a person.

IMPORTANT: The CO2 continues traveling even after it is no longer visible as a cloud. Just because you can't see that you're spraying someone or something doesn't mean you aren't.

As an addition (with thanks to @supercat), CO2 is hazardous on its own, even in concentrations less than those required to leave a person hypoxic. If at any point, the air reaches a 10% concentration of CO2 or greater, the CDC qualifies that as 'Immediately Life Threatening.'


I would not, personally, recommend doing this.

But if you do, do so only in a very large and well ventilated space, stay several feet away from anyone while using it, and never spray for more than a few seconds at a time.

  • 21
    \$\begingroup\$ For another example of people not realizing the dangers of simple asphyxiants, pouring liquid nitrogen in a pool creates a cool fog effect but can cause swimmers to pass out and fall into a pool and possibly drown. \$\endgroup\$ Commented Oct 10, 2018 at 13:52
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    \$\begingroup\$ Minor nit: CO2 does not cause asphyxiation by displacing oxygen, but rather by triggering respiratory spasms when atmospheric concentrations exceed blood concentration. This is why spacecraft and submarines need CO2 scrubbers in addition to an oxygen supply/generator. \$\endgroup\$
    – supercat
    Commented Oct 10, 2018 at 15:52
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    \$\begingroup\$ @supercat It will, that's the point of a fire extinguisher. It does also act as a coolant, but the main point is for it to displace enough oxygen so fire doesn't spread. CO2 does indeed cause breathing problems in humans, but so does a lack of O2 caused by CO2 displacing it. \$\endgroup\$
    – Cubic
    Commented Oct 10, 2018 at 16:06
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    \$\begingroup\$ @Cubic: According to OSHA, displacing 5-20% of the oxygen in a space will cause symptoms of hypoxia in someone engaged in physical exertion (presumably significantly faster at 20% than 10%). The CDC classifies a 10% concentration of CO2 is immediately life threatening. The concentration CO2 required to put out fires is sufficient to displace too much oxygen to sustain life, but CO2 can be rapidly fatal in concentrations below that. \$\endgroup\$
    – supercat
    Commented Oct 10, 2018 at 16:12
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    \$\begingroup\$ @Malandy: No, because without the CO2 they wouldn't immediately pass out or start gasping for air; they would proceed into the room, start feeling weird, and eventually black out before realizing that there was no oxygen. Our bodies can't actually detect a lack of oxygen in the air, but they do detect excessive CO2. \$\endgroup\$ Commented Oct 11, 2018 at 3:51

Use a water spray gun

Both CO2 and smoke have issues with displacing air and risking suffocation or frostbite. Water, on the other hand, doesn't displace air, is almost completely safe to use on both humans and the things one would normally wear at a LARP event, can easily be cleaned up and gives a good indication of who is hit by a spell effect (check who is wet). It's also environmentally safe and cheap to use, can be used without electricity and has a cheap solution for those that really don't want to get hit by it (a rainproof coat or plastic sheet).

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    \$\begingroup\$ Upvoted for the positive suggestion, but in most indoor situations large amounts of water can be problematic as well. Furniture and carpet often has padding that can soak up lots of water and then mildew, or components that can be damaged by water like wood or leather. \$\endgroup\$
    – T.E.D.
    Commented Oct 11, 2018 at 14:27
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    \$\begingroup\$ Or bubbles! Bubble guns are also fun :3 \$\endgroup\$
    – Tezra
    Commented Oct 11, 2018 at 17:48
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    \$\begingroup\$ "Water, on the other hand, doesn't displace air" Well, technically ... \$\endgroup\$ Commented Oct 11, 2018 at 19:00
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    \$\begingroup\$ LARP costumes and accessories usually do not really like water... \$\endgroup\$
    – Sava
    Commented Oct 11, 2018 at 20:59
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    \$\begingroup\$ @borjab - I realize torch is commonly used in certain areas (Britain for starters), but since this is about fantasy LARPing, you should probably say flashlight instead... \$\endgroup\$ Commented Oct 11, 2018 at 23:26

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