Pressurizing CO2 Gas
Carbon dioxide fire extinguishers work by cooling a fire and removing oxygen from the area surrounding the fire. This type of fire extinguisher contains a mixture of liquid and carbon dioxide (CO2), a non-flammable gas. Since carbon dioxide is a gas at room temperature, in order for it to exist in liquid form, the gas must be stored at extremely high pressure. When the pressure is released from the extinguisher, the gas expands, cooling the air and shooting out a white cloud resembling snow. Because the gas is so pressurized, dry ice may stream from the extinguisher or form around the horn when in use.
The cylinders of most carbon dioxide fire extinguishers are made from an aluminum alloy that is heavy duty yet much lighter than extinguisher cylinders constructed from steel. Portable sizes can range from 5 to 20 pounds in capacity, although extinguishers are also available in 50 and 100 pound capacities. A carbon dioxide extinguisher is recognizable as it does not have a pressure gauge on the cylinder.
Carbon dioxide extinguishers are used to put out liquid or electrical fires. These types of extinguishers are labeled as either Class B or Class C extinguishers. A Class B extinguisher is designed for use on fires involving grease, gasoline, oil, kerosene or other combustible and flammable liquids. Class B extinguishers have a numerical rating that indicates the average number of square feet of fire the extinguisher can handle. The higher the rating, the greater the area of fire the extinguisher can put out. Class C extinguishers should be used on fires of an electrical nature typically involving electrical appliances, power tools, outlets, panel boxes or other wiring. Carbon dioxide is non-conductive; therefore, this type of extinguisher is safe to put out an electrical fire. Carbon dioxide extinguishers do not work well on Class A fires involving combustible materials like wood, plastic or paper. Even if you succeed at putting out the flames with a CO2 extinguisher, the fire often re-ignites.
PASS – Pull, Aim, Squeeze, Sweep
To operate a CO2 fire extinguisher, pull the pin located at the top of the extinguisher to release the locking mechanism. This prevents the handle of the extinguisher from being pressed accidentally. Aim the nozzle of the extinguisher toward the base of the fire not at the flames. Stand about 6 or 8 feet away from the fire and then slowly squeeze the lever handle to discharge the extinguisher. Keep a safe distance from the fire. You can always move in closer once the fire begins to go out. Releasing the handle will stop the extinguisher from discharging. While squeezing the handle, sweep the nozzle in a back and forth motion toward the base of the fire. Never point a CO2 extinguisher toward an individual, as the person could suffer frostbite to the face. Even after the fire seems to be out, continue discharging the extinguisher as flames could re-ignite. While most fire extinguishers with a full cylinder will release about 10 seconds of extinguishing power, partially discharged extinguishers contain less extinguishing agent. If you do not think that you can put out the fire with one extinguisher, do not try—the fire may be too much for you to handle alone. If you operate the extinguisher in a confined space, ventilate the area once the fire has been extinguished to get oxygen back into the room. Place the extinguisher on its side when empty.