Which Class of fire extinguisher is used for ordinary combustibles such as wood and paper, typically using water-based agents?

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

Answer: (B)

Fires involving ordinary combustibles are best tackled by cooling the fuel below its ignition temperature. Class A extinguishers use water-based agents to absorb and remove heat from materials like wood and paper, rapidly lowering their temperature and stopping the flame from continuing. The cooling action is the primary way these extinguishers work, making them ideal for these fuels. Other classes are designed for different fuels: for example, extinguishers for flammable liquids, electrical fires, and metals use different agents and mechanisms. So, for ordinary combustibles such as wood and paper, the appropriate class is Class A.