Ordinary dry chemical extinguishers are rated for which fire classes?

• A. A
• B. B and C
• C. A and B
• D. A, B and C

Answer: (B)

Understanding extinguisher ratings helps you know what fires a particular agent can handle. Ordinary dry chemical extinguishers release a powder that interrupts the chemical reactions happening in a flame and blankets the fuel surface. This makes them effective for Class B fires, where flammable liquids are involved, by smothering the flame and limiting vapors. They’re also suitable for energized electrical equipment (Class C) because the dry powder is non-conductive and won’t create a path for electricity. They aren’t rated for Class A ordinary combustibles, so their effectiveness on wood, paper, and textiles isn’t guaranteed in the same way, which is why the rating is limited to B and C.