WMSL Basic DC Practice Test

Aqueous Film Forming Foam (AFFF) is known for its unique ability to form a vapor barrier. This property is crucial in firefighting applications, particularly for class B fires which involve flammable liquids. When AFFF is applied to a flammable liquid fire, it creates a film that spreads across the surface of the liquid. This film not only suppresses the flammable vapors that can ignite but also cools the fire by forming a barrier that prevents oxygen from reaching the fuel. This vapor barrier is essential for effectively controlling and extinguishing fires, making it a critical characteristic of AFFF.

In firefighting scenarios, especially where fuel sources are present, this property helps prevent re-ignition and delay the spread of fire, ultimately improving safety and response effectiveness.