A stored-pressure water extinguisher would be best used on which class of fire?

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

Answer: (A)

Water extinguishers work by removing heat from the fuel, cooling it below its ignition temperature. A stored‑pressure water extinguisher is best for fires involving ordinary combustibles—wood, paper, textiles—because the rapid application of water soaks the fuel and cools it quickly, preventing ignition and re‑ignition. They’re not effective for fires from flammable liquids, since water can spread the liquid and spread the flame. They’re not suitable for energized electrical equipment, because water conducts electricity and creates a shock hazard; nonconductive extinguishing agents are preferred there. They’re also not used for metal fires, since many reactive metals can flash or explode when contacted with water. In short, the water extinguisher’s heat‑removal action makes it ideal for ordinary combustible fires.