The principle on which extinguishers work is based on the nature of fire. When a flammable substance is heated to a certain temperature, called the ignition point, or kindling temperature, the substance combines with oxygen from the air and bursts into flame. Usually the fire raises the temperature of adjoining substances to their ignition points. Then the blaze spreads.
Since fuel, oxygen, and heat must be present in order to have fire, one or more of these three elements must be removed or reduced to extinguish a fire. If the heat is reduced by cooling the substance below the kindling temperature, the fire goes out. The cooling method is the most common way to put out a fire. Water is the best cooling agent because it is low in cost and usually readily available in quantity.
Another method of extinguishing fire is by eliminating or diluting the oxygen. This is usually done by smothering or blanketing the fire. Some substance that is not readily combustible is used to cover the fire. Sand, foam, steam, or a nonflammable chemical may be employed. A blanket or rug may be used to cover and smother a small blaze.
A third method is called separation. This method involves removing the fuel, of combustible material, from a fire. In forest fires, for instance, the trees may be cut away leaving a fire lane in which the spreading flame can find no fuel. Explosives may be employed to block oil-well fires.
Fires in wood, paper, cloth, and similar common materials are called Class A fires. These materials usually form glowing coals, which help to sustain the fire. Such fires can be stopped most readily by cooling with water or watery solutions. Water has the advantage of usually being plentiful and cheap.
Blazes in flammable liquids such as gasoline, oil, or grease are termed Class B fires.. The material and the fire would float and spread if a stream of water were used on the flames. Such blazes are smothered; that is, oxygen from the air is cut off.
fires those in charged electrical equipment should be put out by an agent which does not conduct electricity.
Certain combustible metals, such as magnesium, titanium, potassium and sodium. These metals burn at high temperatures and give off sufficient oxygen to support combustion. They may react violently with water or other chemicals, and must be handled with care.
It is natural for a person to use the extinguisher located nearest to a fire which makes it essential that the correct type and size be placed in close proximity to a potential hazard. The most current issue of NFPA-10 should be consulted for minimum recommended fire extinguisher types, placement and travel distances. Your local extinguisher distributor is professionally qualified and equipped to help you evaluate and implement these recommendations. Or your local Fire Department can assist you.
All new fire extinguisher nameplates have the USE symbols shown (older extinguishers will have A B C letters or combinations of these letters). Anyone who might be expected to use a fire extinguisher should be familiar with the USE symbols which identify the classes of fire on which it may be used. The International Sign System red slash, if present, indicates a potential hazard to the user if the extinguisher is used on that particular class of fire. Absence of a class symbol simply means that the extinguisher is not recommended as particularly effective for that class.
Extinguishers should be installed in plain view, above the reach of children, near escape route, and away from stoves and heating appliances.
Before you begin to fight a fire, make sure that:
