Generally speaking, there are five classes of fires as defined at below. Halon fire suppression systems and some of their alternatives are being used quite effectively on the first three, Classes A, B and C. Halon fire suppression systems are not recommended for use on the other two classes, D and K, where specialized agents are usually employed.

Classification of Fires Class Description
A Fires in ordinary combustibles such as wood, cloth, paper, rubber, and many plastics.
B Fires in flammable liquids, oils, greases, tars, oil-base paints, lacquers, and flammable gases.
C Fires that involve energized electrical equipment.
D Fires of combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium.
K Fires that involve cooking appliances with flammable cooking oils and fats, vegetable or animal.

Fire Suppression System Methods of Applying Fire Extinguishing Agents

There are two common methods for applying fire extinguishing agents: (1) total flooding and (2) local application. In addition, there are two rather specialized applications (3) explosion suppression and (4) inerting against explosions and fires. The explosion suppression and inerting applications are not discussed further in this report due to their specialized nature and, relatively speaking, limited market presence.