Dry powder extinguishers are rated for use on which class fires?

• A. Class A
• B. Class B
• C. Class C
• D. Class D

Answer: (D)

Dry powder extinguishers that are designed for metal fires carry a Class D rating. Metal fires involve combustible metals such as magnesium, titanium, sodium, or potassium, which don’t behave like ordinary fuels and can react violently with water or many other extinguishing agents. The metal-specific dry powder coats the molten metal, forming a crust and absorbing heat, which isolates the metal from oxygen and slows the burning. Because of this specialized action, only extinguishers with a Class D designation are appropriate for these fires. Other extinguishers aimed at common fires (A, B, or C) aren’t effective for metal fires and can even worsen the situation.