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I have a scenario where it is likely that one of the PCs will be using a CO2 fire extinguisher as an offensive weapon. I need to come up with how this would work mechanically using Savage Worlds.

Specifically, how would it affect visibility? If sprayed up close, would it effectively blind the target? What would happen to any surfaces sprayed? And above all, how would these things be represented mechanically using Savage Worlds?

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We recently had fire extinguisher training at work. They warned us about the risks involved in exposure to the CO2 -- the main one being frostbite, as the gas is extremely cold under pressure. Frostbite may affect your eyes, with consequences for vision. There is also a risk of asphyxiation if the person can't breathe oxygen while being sprayed with CO2. –  Lowly Minion Apr 16 '13 at 10:08
    
… and here is some medical evidence of what happens when you spray a CO2 extinguisher on someone's bare foot for 30-45 seconds. Not pretty: dermatology-s10.cdlib.org/1509/case_presentations/… "even short contact with carbon dioxide gas can result in severe frostbite injury". –  Lowly Minion Apr 16 '13 at 10:15
    
… and here is a description of what might happen if briefly sprayed by a CO2 extinguisher to create a theatre smoke effect: goaskalice.columbia.edu/i-m-melting-inhaling-carbon-dioxide –  Lowly Minion Apr 16 '13 at 10:20
    
You might want to summarise those links in an full answer. Even without the game system equivalent mechanics, the information is still useful –  Phil Apr 16 '13 at 10:57
    
Will do. Wasn't sure about the etiquette involved. –  Lowly Minion Apr 17 '13 at 1:13
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3 Answers

up vote 11 down vote accepted

To use a CO2 fire extinguisher for general obscurement, I'd suggest having it be in a Cone Template and having the the area sprayed grant "Light Cover", because that's described as "half or less of the target is obscured, which sounds about right for a light, gaseous propellant that moves quickly.

Against humans, I think the easiest thing to do would be to use the blind power and have its trapping be a CO2 fire extinguisher. This gives targets a chance to make an Agility roll at –2 (–4 with a raise). Failure means that they are Shaken and have –2 Parry. If they roll a 1 on the Agility die, they are also at –6 to Trait rolls requiring vision for as long as they are Shaken.

I'd say make the CO2 fire extinguisher a limited use object that can "cast" the blind power on a Cone Template. These things are pretty easy to use, so I'm inclined to make there be no skill roll needed (although you could add one to reflect how accurately you can point it).

Against inanimate surfaces, I'd just include in the description that it lowers the temperature of the surface. There's not really a good mechanical way to model this given the wide variety of materials, so I'd just leave it to the GM to adjudicate what that means.

One thing you could do is add the Cold Trapping. The Fatigue one (Vigor roll or take one level of cold-based Fatigue) makes sense given that using this on a person is dangerous as it could result in frostbite, but the trapping says that range should be halved (not possible with a Cone Template) or power point cost should be doubled. The latter could be achieved by having a low number of uses.

Speaking of how many uses, I'd suggest taking a page Savage Worlds Showdown and just make it a random die roll to see whether they ran out or if there is at least one more shot. Given the Cold Trapping, I'd say roll a d6 after each use and on a 6, it's out (which given that these things last 20 seconds or so, seems about right).

Putting it all together:

CO2 fire extinguisher
A C02 fire extinguisher is designed to quickly extinguish a fire by lowering the temperature and displacing oxygen. It can be sprayed in a Cone Template as an action. Unlike other fire extinguishers, C02 does not leave any residue behind.

In a pinch, it can be used as a weapon. As an action, the wielder can spray the C02 on targets in a Cone Template, effectively using the blind power with the Cold: Fatigue Trapping against them. No roll is needed to activate the CO2 fire extinguisher and so all "arcane skill" rolls are considered successful (with no chance for a Raise). After every use, roll a d6. On a 6, the fire extinguisher has run out of C02 and can no longer be used.

The area sprayed by the extinguisher provides Light Cover (-1 to attack rolls) for all attacks that target an individual inside the Cone Template or on the opposite side of the Cone Template until the wielder's next turn.

The canister can also be used as an improvised weapon. It counts as one size larger when full.

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Add the Cold Trapping? –  David Allan Finch Apr 16 '13 at 11:28
    
Done. Let me know if I ought to modify it. –  Thunderforge Apr 16 '13 at 17:42
    
Nice. I like it. –  David Allan Finch Apr 17 '13 at 10:54
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We recently had fire extinguisher training at work. They warned us about the risks involved in exposure to the CO2 -- the main one being frostbite, as the gas is extremely cold under pressure. Frostbite may affect your eyes, with consequences for vision. There is also a risk of asphyxiation if the person can't breathe oxygen while being sprayed with CO2.

Even brief exposure to CO2 from an extinguisher can have painful consequences. This article describes the general risk involved in using such devices:

Contact with the solid carbon dioxide gas for more than a second or two without proper protection may cause skin injury because of rapid and profound cooling, leading to localized cold injury and cellular destruction. Numbness develops because of inactivation of nerve sensation. Frostbite following exposure to cold gases is an occupational hazard. … Generally, the primary health dangers of carbon dioxide gas are: asphyxiation, kidney damage or coma, and frostbite. Asphyxiation is caused by the release of carbon dioxide in a confined or unventilated area. This can lower the concentration of oxygen to a level that is immediately dangerous for health. Kidney damage or coma is caused by a disturbance in the chemical equilibrium of the carbonate buffer. When carbon dioxide concentrations increase or decrease, causing the equilibrium to be disturbed, a life threatening situation may occur.

It also describes what happened when a football team improvised and used an extinguisher instead of an ice-pack on a player's foot:

A 20-year-old man of good general health was admitted to our burn care unit with frostbite involving the left foot. He told us that the frostbite injury resulted from contact with the fire extinguisher while he was playing football. The patient sprained his ankle and complained of severe pain. His teammates came to his rescue witha cooling spray, from a fire extinguisher. The carbon dioxide gas spray was sustained for a period of 30-45 seconds. Immediately after the exposure, the skin of his foot had gone white and cold. Afterwards, he initially felt numbness, but then increasing foot pain. … The initial physical examination demonstrated second degree frostbite of the left foot.

On this page, an actor asks what the risks would be if she was briefly sprayed by a CO2 extinguisher to create a theatre smoke effect. The answer was that she should not do it because there is a risk of serious injury.

CO2 is naturally present in the air at a concentration of about 0.035 percent. Short-term exposure to CO2 at levels below two percent has not been reported to cause harmful effects, but higher concentrations, like you might be exposed to when sprayed by a fire extinguisher, can affect respiratory functioning. In addition, high concentrations of CO2 can cause the central nervous system to be simultaneously stimulated and depressed, a phenomena that can have dangerous results. Your body responds pretty recognizably when it has had more than its desired dose of CO2. Breathing CO2 concentrations of four to seven percent has been shown to produce headaches, hearing and visual disturbances, increased blood pressure, difficulty breathing, mental depression, and muscle tremors. As CO2 concentration increases, its effects become more dangerous and symptoms occur more quickly — exposure to seven to fifteen per cent carbon dioxide can produce drowsiness, dizziness, and unconsciousness within a few minutes. At 17 to 30 percent CO2, people have experienced loss of controlled activity, unconsciousness, coma, convulsions, and death within a minute. Several deaths have been attributed to exposure to concentrations greater than twenty percent. As you can see, playing around with CO2 could be a risky endeavor, with very little margin for error.

Bear in mind that she was proposing being sprayed on her back by people trying not to injure her. The risks involved when the CO2 is sprayed directly and deliberately into a person's face would presumably be towards the higher end.

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Interesting question!

I would rule that it works as a cone. Outdoors, the visibility would be only slightly reduced in the area (-1 perhaps) and the powder would dissipate after 1d2 rounds. Indoors, it would be worse (-2 perhaps) and stay in suspension for a while, 2d4 rounds. If you like it more realistic, then you would need a few (2-3) rounds to fill the area with all that powder.

Of course, these things run out rather quickly. It holds maybe a 20 seconds charge.

Another way to use it would simply be to rule that its use constitute a trick, as per the tricks rules.

The best way to use it offensively: use it as a club.

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You may be thinking of powdered chemical extinguishers. CO2 extinguishers in the other hand emit colourless gas that leaves no residue—it only makes a cloud because its extreme cold forces air moisture to condense suddenly. –  SevenSidedDie Apr 16 '13 at 4:20
    
+1 for suggesting tricks. –  Hand-E-Food Apr 16 '13 at 5:30
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