What is Class A fire and the recommended extinguishing method?

• A. Flammable liquids; use foam.
• B. Electrical fires; use CO2.
• C. Metals; use water to create steam.
• D. Ordinary combustibles like wood and paper; extinguish with water to cool and smother.

Answer: (D)

Class A fires involve ordinary combustibles like wood, paper, cloth, and similar materials. The most effective way to fight these fires is with water. Water has a high heat capacity and high heat of vaporization, so when you apply it, it absorbs a large amount of energy as it heats and turns to steam. That energy absorption lowers the fuel’s temperature below its ignition point, stopping the flame from continuing. Water also soaks the material, helping to smother the fire by removing the heat that drives the combustion process.

Foam is more suited to surfaces involving flammable liquids, where a blanket helps prevent vapors from reigniting. CO2 is great for electrical fires or confined spaces because it displaces oxygen and is nonconductive, but it doesn’t cool the fuel as effectively for ordinary combustibles. Fires involving metals require specialized dry powder extinguishing agents, not water, due to chemical reactions that can occur with water.