Carbon dioxide (CO2) extinguishers contain a mixture of liquid and gaseous carbon dioxide (a non-flammable gas). CO2 is normally a gas at room temperature and pressure. Inside the extinguisher, it must be stored under high pressure to make it a liquid. When you release the pressure, the gas expands rapidly and makes a huge white jet.

Carbon Dioxide is heavier than oxygen so it starves the fire of oxygen. It destroys the fire triangle in two other ways: it smothers the oxygen and, when it turns from a liquid back to a gas, it "sucks" in a massive amount of heat from its surroundings (the latent heat of vaporization), which cools whatever you spray it on by removing heat.

CO2, a clean gaseous agent which displaces oxygen. They are suitable for Class B & C fires. They are NOT intended for class A fires, as the high-pressure cloud of gas can scatter burning materials. CO2 is not suitable for use on fires containing their own oxygen source, metals or cooking media. Although it can be rather successful on a person on fire, its use should be avoided where possible as it can cause frostbite and suffocation.

What the A B C ratings mean on Fire Extinguishers


Fire extinguishers with a Class A rating are effective against fires involving paper, wood, textiles, and plastics. The primary chemical used to fight these fires is monoammonium phosphate, because of its ability to smother fires in these types of materials.


Fire extinguishers with a Class B rating are effective against flammable liquid fires. These can be fires where cooking liquids, oil, gasoline, kerosene, or paint have become ignited. Two commonly used chemicals are effective in fighting these types of fires. Monoammonium phosphate effectively smothers the fire, while sodium bicarbonate induces a chemical reaction which extinguishes the fire.


Fire extinguishers with a Class C rating are suitable for fires in “live” electrical equipment. Both monoammonium phosphate and sodium bicarbonate are commonly used to fight this type of fire because of their nonconductive properties.

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