What Is a Fire Extinguisher?

A fire extinguisher is a portable device used to control or put out a small area of a fire. It consists of a pressure-held container filled with a chemical agent that is discharged by turning a handle at the top. The agent smothers the flames by excluding oxygen and interrupts the chain reaction that causes fires to continue burning. Located in easily accessible areas, these devices can save lives and property.

A fire is a dangerous event that can spread rapidly, and people should evacuate the scene as soon as they are able to do so safely. It is important to have a plan for evacuation in place and to make sure that everyone understands where fire extinguishers are located. Fire extinguishers should be kept in easy-to-reach locations, but should not be stored too close to items that could get thrown around by the force of the extinguisher’s operation.

There are many different types of fire extinguishers, and they can be classified by their ANSI or UL ratings. The rated capacity indicates the size fire that the extinguisher is capable of fighting. A class A extinguisher can be used on ordinary combustible materials such as wood, paper, cloth and rubber, while a class B fire extinguisher is effective against flammable liquids like grease, gasoline, solvents, paint and oils.

Dry chemical extinguishers (class A, B and C) use stored pressure to discharge a chemical agent that interrupts the fire’s chain reaction and stops it from spreading. The agent also absorbs moisture from the surface of the flame, preventing it from re-igniting. The earliest units used potassium bicarbonate, but the current agents are a mixture of sodium carbonate and additives including a silicone polymer to prevent moisture absorption and caking.

Foam (class B) extinguishers use an aqueous film-forming foam to create a seal over the fuel that excludes oxygen. This type of agent is usually blue/red in color. Aqueous foams are aspirated (mixed with air in a branch pipe) or nonaspirated (sprayed directly onto the fire). The latter type can be used on liquid fuels such as gasoline and kerosene. Foams also can be used on polar solvents like alcohol.

Water (class A) extinguishers dispense water at high pressure to smother the fire. They are not suitable for electrical fires, which should be dealt with by an electrical deluge system.

Graphite powder (class D) extinguishers contain a finely ground, dust-like, conductive metal such as graphite that smothers hot burning metals by conducting heat away from the fire. This type was originally developed for magnesium fires, but it will work on other metals as well.

Halon (class B) extinguishers dispense a gas that inhibits the fire’s chemical reactions. It was the first gas to be produced commercially for this purpose. However, new production of halon has been discontinued in the US due to its ozone-depleting effects. Older cylinders can still be used, but must be recycled when empty.

All fire extinguishers that store a pressurized chemical must be inspected monthly for damage, proper pressure and broken seals. A mandatory annual inspection is also performed, and it is required that the cylinder be completely removed from service, emptied, inspected and refilled every 6 years.