Fire extinguisher is a metal container filled with water or chemicals used to put out fires. Fire extinguishers are portable and easy to operate and can be used to put out small fires before the flames spread.
In the United States, state and local fire laws require that extinguishers be installed in easily seen places in public buildings. Such buildings include factories, schools, stores, and theaters. School buses, boats, and most public vehicles also must have extinguishers.
There are many kinds of fire extinguishers. The kind used depends on the type of fire involved. Fire prevention experts divide fires into four classes—A, B, C, and D—depending on the burning material. Class A fires involve such materials as cloth, paper, rubber, or wood. Class B fires involve flammable gases or such flammable liquids as cooking grease, gasoline, or oil. Class C fires involve motors, switches, or other electrical equipment through which electric current is flowing. Class D fires involve combustible metals, such as magnesium chips or shavings. Most extinguishers are labeled with the class, or classes, of fire for which they can be used.
Class D fires require special extinguishers designed for specific metals. But most other fire extinguishers can be classified, by their contents, as one of four types: (1) water, (2) foam, (3) liquefied gas, and (4) dry chemical.
Water extinguishers
are used to fight only class A fires. Water conducts electric current, and so it must never be used on a fire involving electrical equipment. A water extinguisher is operated by a lever or a hand pump that shoots the water through an attached hose.
Foam extinguishers
are used for class A and class B fires. They contain water and a foaming agent. One type of foam puts out fires that involve combustible liquids by depositing a film between the liquid and the flame.
Liquefied gas extinguishers
may be used on class B and C fires. There are three main kinds—carbon dioxide extinguishers, which contain carbon dioxide gas; halon extinguishers, which contain a gas called halon; and halocarbon extinguishers, which contain any one of four gases called halocarbons. All of these extinguishers have the gas in liquid form under pressure in the container. When the operator squeezes a handle, the liquid flows out of the container and becomes a gas that covers the fire. Liquefied gas extinguishers leave no water or powder. Thus they are the most suitable for class C fires involving delicate electrical equipment that could be damaged by other extinguishers. Large halon or halocarbon extinguishers can also be used to fight class A fires.
Halon has been found to harm the ozone layer in the earth’s upper atmosphere. This layer protects living things from most of the sun’s ultraviolet rays. A 1992 agreement among the major halon-producing nations resulted in a plan for the industrialized countries to stop producing halon by 2000. The plan allowed for the continued use of stored or recycled halon. Halon extinguishers are serviced in a closed recovery system, which prevents the release of halon into the atmosphere. Halocarbon extinguishers were developed to replace those with halon.
Dry chemical extinguishers
are used on class B and C fires. One type, the multipurpose dry chemical extinguisher, also can be used against class A fires. A stored pressure dry chemical extinguisher has a cylinder containing a chemical powder and a gas under pressure. Another type of dry chemical extinguisher stores the gas in a cylinder or cartridge separate from the powder. Before using it, users must enable the gas to flow into the main compartment by turning a valve or operating a lever that punctures the gas compartment.
