Most fire extinguishers are rated for use with a specific class (or combination of classes) of fires. Some extinguishers, sometimes called universal fire extinguishers, work on several classes of fire.
Classes and Categories
Fires are categorized according to the type of fuel that is burning. Class A fires involve wood, paper and similar common materials. Class B fires involve flammable liquids, such as gasoline, grease or oil. Class C fires are those involving electric equipment, such as common appliances. Class D fires involve combustible metals, such as magnesium.
Each category of fire has unique attributes that must be taken into account. Class C fires, for example, pose the risk of electric shock, and putting out the fire with water is dangerous. For this reason, extinguishers are clearly marked to indicate the class(es) of fire on which they are safe to use.
Multiclass fire extinguishers, also called universal fire extinguishers, are generally rated for Class A, B and C fires. Class D fires are sufficiently different from the others that their extinguishing methods are not combined with the others, and a Class D-specific extinguisher is needed. Because Class D fires are rare under normal circumstances, a standard type ABC extinguisher is recommended for most homes and businesses.
Using a Multiclass Extinguisher
Though designed to combat different types of fires, different types of fire extinguishers are designed to operate similarly, regardless of the class rating. Pull the pin from the extinguisher's handle. Stand about 8 feet from the fire and point the extinguisher nozzle at the base of the fire. Squeeze the handle lever slowly, sweeping the spray from side to side.