A carbon dioxide (CO2) fire extinguisher is a firefighting tool that is loaded with pressurized carbon dioxide gas. This gas expands very rapidly when a person deploys the device to smother a fire, limiting the fire's supply of oxygen. Many hardware and home supply stores sell carbon dioxide fire extinguishers and it is also possible to install a CO2 fire suppression system in a facility where it might be useful.
This type of fire extinguisher is suitable for use on class B and C fires. Class B fires involve flammable liquids such as kerosene, and class C fires include electrical equipment. In a fire involving a flammable liquid, the gas can limit the supply of oxygen to the fire when it expands, putting out the fire. For electrical fires, it does the same thing, and because it is electrically nonconductive, there is a low risk of shock.
Class A fires that involve combustible materials are not safe for a carbon dioxide fire extinguisher. The high-pressure gas can actually scatter the materials and make the fire larger. In addition, it might not suppress the oxygen supply long enough to put out the fire. The materials could smolder, and when the gas dissipates, the fire might flare up again. Fire extinguishers should have rating indications to indicate the kinds of fires on which they can be used and it can be helpful for a person to get familiar with the ratings in preparation for a fire.
A typical carbon dioxide fire extinguisher has a hard, horn-shaped nozzle to direct the flow of gas. The operator should be careful, because this gas is extremely cold when it vents from the extinguisher. Chunks of dry ice can form around the rim, and people could develop injuries if they handle the nozzle. It also is potentially dangerous to use such devices in areas that don't have a supply of oxygen for the operator, because he or she could suffocate while putting out the fire.
One advantage of the carbon dioxide fire extinguisher is that it does not leave residue. The gas evaporates and clears the area. This can be important in a location that has expensive electronic equipment, because other suppression devices might damage the equipment. It also can be helpful for other types of fires, after which cleanup might be a concern. A carbon dioxide fire extinguisher should be regularly inspected to make sure that it works, and it can be refilled after use.