How do multipurpose dry chemical agents prevent rekindling of Class A fires?

How do multipurpose dry chemical agents prevent rekindling of Class A fires?

• A. By cooling the fuel
• B. By absorbing heat
• C. By removing oxygen
• D. By forming a crust over the fuel

Answer: (D)

The main idea is that rekindling is prevented when the dry chemical forms a crust on the burning solid. When the powder blankets Class A fuel, it adheres to the surface and creates a crust that isolates the fuel from air and slows heat transfer back into the material. With the hot surface shielded, the fuel can’t sustain ignition once the flame is out. The powder’s flame-suppressing action also helps, but the critical factor for stopping rekindling is that protective crust. Other options describe cooling or starving the flame in ways that aren’t the primary mechanism for dry chemical extinguishing.