Fire extinguishers contain various compounds, depending on the type, that work by interrupting the chemical reactions that sustain fire. The most common compounds used are carbon dioxide (CO₂), monoammonium phosphate, and sodium bicarbonate.

Common Compounds in Fire Extinguishers:

1. Carbon Dioxide (CO₂):
   • Used in CO₂ fire extinguishers, it works by displacing oxygen around the fire. CO₂ is non-flammable and suffocates the fire by reducing the oxygen supply, which is essential for combustion.
2. Monoammonium Phosphate:
   • Found in ABC dry chemical fire extinguishers, this compound works by coating the fuel and preventing the chemical reactions occurring at the fire’s surface. It is effective for electrical, grease, and other general fires.
3. Sodium Bicarbonate (Baking Soda):
   • Present in some dry chemical extinguishers, it works by releasing carbon dioxide when heated, which helps smother the fire. It is commonly used for Class B (liquid) and Class C (electrical) fires.

Working of a Fire Extinguisher:

A fire extinguisher works by applying a substance that either cools the fire, displaces oxygen, or inhibits the chemical reactions of combustion.

• CO₂ extinguishers are effective for electrical fires and flammable liquids, as they do not leave residue.
• Dry chemical extinguishers (using monoammonium phosphate) work on a wide range of fires (A, B, C) by coating the fuel and interrupting the fire’s chemical reaction.

By removing one or more of the elements in the fire triangle (heat, fuel, oxygen), the fire is extinguished.