Types of fires

 1.    Class A fires occur in wood, rubber, paper,

cloth and most plastics. The most effective type

of extinguishing agent is one using water, or

solutions containing large concentrations of water,

because the ‘‘quenching-cooling’’ effect reduces

the temperature of the burning material below its

ignition temperature. Fire extinguishers suitable for

this type of fire are designated with a classification

of “A” on the label.

2.    Class B fires occur in flammable or combustible

liquids, such as petroleum products and greases.

A “blanketingsmothering” effect of an agent that

excludes oxygen or inhibits the chemical chain

reaction is most effective. Extinguishers labeled

“Class B” employ carbon dioxide, dry chemical,

Halon or foam.

3.    Class C fires involve electrical equipment. The

extinguishing agent must be non-conductive.

Carbon dioxide, dry chemical and Halon are

the normal types used for electrical fires.

4.    Class D fires involve combustible metals such as

aluminum, magnesium, zirconium and titanium.

The use of water and some other conventional

types of extinguishing agents are ineffective and

may cause a violent reaction. These fires can

be extinguished with specially prepared agents.

Where this hazard exists, extinguishing agents

with a D-class rating should be provided.