How does foam extinguish flammable liquid fires?

• A. It reacts with the fuel to form a stable solid.
• B. It separates the fuel from the fire.
• C. It absorbs the fuel into the foam matrix.
• D. It cools the fuel to below its flash point.

Answer: (B)

Foam extinguishes flammable liquid fires by forming a stable foam blanket that sits on the surface of the liquid, creating a barrier between the fuel and the air. This layer prevents vapor from escaping and reaching the flame, which interrupts the combustion process. Cooling of the fuel can occur because of the water content in foam, but that cooling is not the primary action here. The idea that foam chemically reacts with the fuel to form a solid isn’t how it works, and foam doesn’t primarily work by absorbing the fuel into a matrix. The key effect is the separation of fuel from the fire, cutting off the oxygen-vapor mix the flame needs.