Fire Extinguishers

Sodium bicarbonate is used in most dry fire extinguishers. The products when dispensed absorb heat, decompose to form fire smothering carbon dioxide, and release free radicals which interrupt the flame chain reaction mechanism. Potassium bicarbonate is utilized more in industrial applications because it decomposes at the higher temperatures found in grease and chemical type fires.

Fires are divided into four classes, each requiring special treatment. The essential point in extinguishing all types is exclusion of air from the fire by the most effective means.

Class A includes fires in combustible materials, such as wood, paper and cloth where the quenching and cooling effect of water is effective and most widely used. In the soda-acid extinguisher carbon dioxide is generated within the cylinder at the time of use.

Class B includes fires in flammable liquids where a blanketing or smothering effect is essential. Dry chemical bicarbonate extinguishers are ideal here.

Class C includes fires in electrical equipment. The use of carbon dioxide gas or dry chemical extinguishers is recommended and water should not be used.

Class D fires are the results of burning metals. Powder formulations consisting of graphite or trimethoxyboroxine will extinguish a metal fire; water should not be used.