Which type of fire is best extinguished with water?

• A. Foam - liquids
• B. Dry powder - liquids, gases, metals and computer labs
• C. CO2 - electrical equipment
• D. Water - wood paper

Answer: (D)

For fires involving ordinary combustibles such as wood and paper, removing heat is the most effective way to stop the flame. Water does that best because it has a high heat capacity and a high heat of vaporization. When applied, it absorbs a large amount of heat and turns to steam, cooling the fuel and the flame zone so the fuel drops below its ignition temperature. That cooling effect directly interrupts the combustion process and helps prevent reignition.

Other extinguishing agents are suited to different fire types. Foam is designed to blanket liquid fuels to separate fuel from air and to provide cooling, but it isn’t as effective for solid fuels like wood and paper. Dry powder is versatile and can interrupt chemical reactions and smother some fires, but it leaves a gritty residue and isn’t as focused on cooling solid fuels as water is. CO2 displaces oxygen and is most useful for electrical equipment fires or enclosed spaces; it’s not ideal for ordinary combustibles because it doesn’t cool the fuel as effectively.

So for wood or paper fires, water’s superior cooling effect makes it the best choice.