Which statement about fires is true?

• A. Removing heat keeps the fuel from vaporizing.
• B. Fires are classified by what type of oxidizing agents are involved.
• C. Water cannot be used to extinguish a Class D fire.
• D. This fuel must be vaporized to burn.

Answer: (C)

Fires involving metals require special handling because many reactive metals react violently with water. Water can cause dangerous reactions, producing hydrogen gas and extra heat that may spread the flame or cause an explosion. That’s why water isn’t used on metal fires, and firefighters use specific metal-fire extinguishing powders that blanket the fuel and cool it without triggering a reaction.

Cooling can slow or stop combustion by lowering the temperature, but saying it always keeps the fuel from vaporizing is too absolute; vapor production depends on reaching the fuel’s vaporization conditions, and not all fires respond the same way to cooling.

Fires aren’t classified by the type of oxidizing agent involved; the standard classifications are based on the fuel type (ordinary combustibles, flammable liquids, electrical, metals, etc.).

Not all fuels must vaporize to burn; some fuels burn in the solid or liquid phase without first forming vapors, so that statement isn’t universally true.