Types of Fire Extinguishers
It is vital to know what type of extinguisher you are using. Using the wrong type of extinguisher for the wrong type of fire can be life threatening.
Class A extinguishers are for ordinary combustible materials such as paper, wood, cardboard, and most plastics. The numerical rating on these types of extinguishers indicates the amount of water it holds and the amount of fire it can extinguish. Geometric symbol (green triangle)
Class B fires involve flammable or combustible liquids such as gasoline, kerosene, grease and oil. The numerical rating for class B extinguishers indicates the approximate number of square feet of fire it can extinguish. Geometric symbol (red square)
Class C fires involve electrical equipment, such as appliances, wiring, circuit breakers and outlets. Never use water to extinguish class C fires – the risk of electrical shock is far too great! Class C extinguishers do not have a numerical rating. The C classification means the extinguishing agent is non-conductive. Geometric symbol (blue circle)
Class D fire extinguishers are commonly found in a chemical laboratory. They are for fires that involve combustible metals, such as magnesium, titanium, potassium and sodium. These types of extinguishers also have no numerical rating, nor are they given a multipurpose rating – they are designed for class D fires only. Geometric symbol (Yellow Decagon)
Class K fire extinguishers are for fires that involve cooking oils, trans-fats, or fats in cooking appliances and are typically found in restaurant and cafeteria kitchens. Geometric symbol (black hexagon)
Water or APW fire extinguishers (air-pressurized water) are suitable for class A fires only. Never use a water extinguisher on great fires, electrical fires or class D fires – the flames will spread and make the fire bigger!
Dry Chemical fire extinguishers come in a variety of types and are suitable for a combination of class A, B and C fires. These are filled with foam or powder and pressurized with nitrogen.
Class BC – This is the regular type of dry chemical extinguisher. It is filled with sodium bicarbonate or potassium bicarbonate. The BC variety leaves a mildly corrosive residue with must be cleaned immediately to prevent any damage to materials.
Class ABC – This is the multipurpose dry chemical fire extinguisher. The ABC type is filled with monoammonium phosphate, a yellow powder that leaves a sticky residue that may be damaging to electrical appliances such as computers.
Dry chemical extinguishers have an advantage over CO2 extinguishers since they leave a non-flammable substance on the extinguished material, reducing the likelihood of re-ignition.
Carbon Dioxide (CO2) Fire Extinguishers
CO2 fire extinguishers are used for class B and C fires. CO2 fire extinguishers contain carbon dioxide, a non-flammable gas, and are highly pressurized. The pressure is so great that it is not uncommon for bits of dry ice to shoot out the nozzle. They do not work very well on class A fires because they may not be able to displace enough oxygen to put the fire out, thus causing it to re-ignite.
CO2 fire extinguishers have an advantage over dry chemical extinguishers since they do not leave a harmful residue – a good choice for an electrical fire on a computer or other favorite electronic device such as a stereo or television.