Sodium bicarbonate is used in most dry fire extinguishers. When dispensed, the products absorb heat, decompose to form fire smothering carbon dioxide, and release free radicals which interrupt the flame chain reaction mechanism. Potassium bicarbonate is commonly utilized in industrial applications, as it decomposes at the higher temperatures found in grease and chemical type fires.
The essential factor in extinguishing fires is excluding oxygen by the safest and most effective means. Dry sodium bicarbonate extinguishers are useful in fighting four classes of fire:
- Class A: Fires of ordinary combustible materials including wood, paper and cloth.
- Class B: Fires in flammable liquids
- Class C: Electrical equipment fires
- Class D: Fires resulting from burning metals.