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Types of Fires

Fires are divided into four classes according to the type of combustible substance.

Class “A”. Fires involving solids such as wood, paper, and most plastics are fires of class “A”.

Class “A” fires is almost the only type that concerns people. Water is the most effective, the cheapest, and the most easily applied extinguishing agent for Class “A” fires.

Class “B”. These are fires of organic liquids such as gasoline, fuel oil, benzene, and acetone. Such fires became important with the advent of the petroleum industry and other modern chemical processing industries.

These fires can be controlled by removing the air with a blanketing agent, such as a carbon dioxide or a water based foam. Water in the form of high-pressure fog is an effective extinguisher, but conventional water streams are unsuitable because they spread the fire.

Class “C”. Class “C” fires is any fire in which energized electrical equipment is involved. Because of the hazard of electric shock, any extinguishing agent may be used, that does not form electrically conductive paths, including high pressure water fogs. Aqueous foams are not suitable.

Class “D”. Fires fueled by sodium, magnesium, and other reactive metals or their reactive compounds, such as sodium hydride, compose this class. These fires are best controlled by removal of air by a blanket of unreactive powder, such as sodium chloride or graphite. Carbon dioxide, sand, and water cannot be used either to blanket or to cool metal fires because these substances are a source of oxygen for these fires.

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