Fire extinguishers are offered in different types to tackle any fire. Not all work on every type of fire, and knowing what risk is possible will assist with choosing the right extinguisher. Fire extinguishers are available in seven types: water, foam, carbon dioxide, dry chemical, wet chemical, clean agent and dry powder. Each of these has a fire code that states what type of fire for which it is best. Never use an extinguisher that is not coded for the type of fire you are putting out.
Water and Foam
Water fire extinguishers are used for Class A textile fires. This is paper, wood, straw, coal and other textiles, such as cotton. They are made of water and a compressed gas. The compressed gas propels the water, and various types are used in different brands of extinguishers. The main component of water fire extinguishers is liquid water or potassium bicarbonate. Foam extinguishers are for Type A fires as well, but rather than using water as their firefighting ingredient, various foams are used, such as film-forming fluoroprotein, aqueous film-forming foam or alcohol-resistant foam. Both water and foam extinguishers work by taking away the heat source.
Carbon dioxide extinguishers are effective on Class B and C fires. A Class B fire is a liquid spill, such as oil, paint or petrol. A Class C fire involves electrical equipment. Because carbon dioxide disperses quickly, it is effective only from 3 to 8 feet from the base of the fire. The carbon dioxide is stored as a compressed liquid in the extinguisher, making it the propelling agent also. CO2 extinguishers work by removing oxygen and heat from a fire.
Dry chemical extinguishers are effective on Class B and C fires. Some multipurpose dry chemical extinguishers are effective on Class A fires, but more commonly not. Dry chemical fire extinguishers can contain several chemicals, among them soduim bicarbonate, potassium bicarbonate or monoammonium phosphate. These chemical interrupt the chemical reaction within the fire, putting it out.
Wet chemical extinguishers remove heat from a fire and create a barrier between oxygen and fuel. This is most common in kitchen fires, which are usually Class B. A wet chemical extinguisher contains potassium and either acetate, carbonate or citrate.
Clean agent extinguishers are more commonly referred to as Halon extinguishers. These are not widely used because they were replaced by dry chemical extinguishers. A Halon extinguisher is used in Class B or C fires and works the same way as a dry chemical extinguisher, interrupting the chemical reaction within the fire. A clean agent extinguisher contains Halon and a compressed gas as a propelling agent.
Dry powder extinguishers are effective on metal fires and are commonly referred as a Class D extinguisher. This is because that is the only fire class on which it can be used. A dry powder extinguisher separates oxygen from fuel and removes heat, but in a safer manner than other extinguishers involving metal fires. Class D extinguishers contain sodium chloride as the active ingredient and a compressed gas as propelling force.