A _______ fire extinguisher should be used on a diesel electrical fire.

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

Answer: (C)

Diesel is a hydrocarbon fuel, so a fire involving it is a Class B fire. Class B extinguishers are designed for flammable liquids like diesel, gasoline, and oil. They smother the liquid and starve it of vapors, using agents such as dry chemical powder or foam that coat the fuel and prevent re-ignition. Even though electrical equipment is involved, the primary hazard here is the diesel fuel, so a extinguisher rated for flammable liquids is the appropriate choice. Water should be avoided on hydrocarbon fires because it can spread the fuel. The other classes target different hazards—ordinary combustibles, energized electrical equipment, or metals—so they don’t fit this situation as well.