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Extinction of Different Classes of Fires

The selection of fire attack method is dependent upon the class of involved fuel. Fuel classification creates a criterion for agent selection because each fuel type has reactions to different agents.

Class "A" combustibles are normally extinguished best by an agent that provides cooling. Water is the best agent to perform this task.

Class "B" combustibles are extinguished best by an agent that utilizes the mechanism of starving, or oxygen deprivation. Agents that fall into this category are gases like carbon dioxide. Class "B" combustibles can also be extinguished by foams and dry chemicals.

Class "C" combustibles are actually class "A" or "B" fuels that have been energized. While they are energized, they cannot be effectively attacked with any agent that is a conductor of electricity. Once the fuel is deenergized, the fuel reverts to its normal characteristics. Usually, the best agent for attack on class “C” fires is a gas or dry chemical.

Class "D" combustibles are extremely difficult to extinguish. The agents best suited for attack on them are those that do not react violently with the material. Dry powders like G — 1 or metal - X are primarily used in this type of fire.

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