What Is a Fire Extinguisher?

A fire extinguisher is a portable device used to combat small fires, as well as smoke and toxic gases. These devices are commonly found in offices, apartments, factories, restaurants and commercial properties. State and local fire codes, as well as federal standards established by the Occupational Safety and Health Administration (OSHA), generally require that extinguishers in buildings other than single-family dwellings be regularly inspected to ensure they remain pressurized and unobstructed. The NFPA, the National Fire Protection Association, requires that all fire extinguishers be maintained and serviced by qualified technicians annually. These technicians inspect the fire extinguisher to ensure it is working properly and recharge or replace it if necessary.

Fire extinguishers are available in handheld and cart-mounted versions. Handheld models typically weigh between 0.5 and 14 kilograms (1.1 to 30.9 lb) and can be easily carried by hand, while cart-mounted units have wheels and may weigh as much as 23 kilograms (51 lb).

In the United States, the color code of a fire extinguisher indicates the type of fire it is designed to fight. A red cylinder means the device is designed to fight class A fires, which involve organic materials such as paper and wood. A green cylinder signifies class B fires, which involve flammable or combustible liquids, excluding cooking oils and greases. A blue cylinder indicates class C fires, which involve flammable gases such as carbon monoxide and hydrogen.

Fires fueled by electrical equipment—including computers, appliances and switches—are classified as class C fires. The only extinguisher that can effectively fight this type of fire is one labeled with the symbol shown to the left. Class D fires are fueled by metals such as magnesium and lithium, which have unique properties that require them to be treated differently than other classes of fires. Class D fire extinguishers have a low-velocity discharge nozzle that allows the suppressant to be applied without damaging the metal surface.

Most fire extinguishers are marked with a pictogram that illustrates how to use them. Generally, the device is pulled or shook to activate it, then the handle is swung in a sweeping motion across the base of the fire. Once the flames have been swept aside, the person using the extinguisher should stand back to make sure that all fire is out and to determine whether more action is required.

In addition to color coding, a fire extinguisher is also usually labeled with the name of its contents. In addition, some extinguishers have a numerical rating that indicates the size of fire it is capable of fighting.

Fire extinguishers are usually made of stainless steel and aluminum. Some are insulated with a rubber seal to protect the internal pressure gauge and the fire suppression agent. Handheld fire extinguishers are usually painted in a bright red RAL 3000, while cart-mounted models are typically painted in a dark blue or green. Extinguishers that are used frequently, such as in an office building, are often marked for inspection with a barcode so that they can be scanned by the fire department to be checked on a regular basis.