What are AFFF's key effects on hydrocarbon fuel?

• A. Releases an air/vapor-excluding film, spreads a foam blanket, drains water/cooling film, and can heal disturbed areas.
• B. Increases vapor release and cause additional burning.
• C. Only forms a film without cooling.
• D. Has no effect on the fuel.

Answer: (A)

AFFF extinguishing effect on hydrocarbon fuels comes from forming a vapor-suppressing foam blanket that cools and seals the surface. The foam blankets the fuel surface, creating a barrier that excludes air and reduces vapor release, which helps prevent reignition. The water content in the foam provides cooling, so the fuel is cooled as the blanket spreads, further suppressing vapors and slowing any potential ignition. The foam film can flow and “heal” disturbed areas, re-establishing a continuous protective layer over irregularities or broken surfaces. This combination—air/vapor exclusion, a spreading foam blanket, cooling from the water content, and the ability to re-seal disturbed areas—is what makes AFFF effective. Descriptions that claim it increases vapor release or burning, or that it only forms a film without cooling, or that it has no effect on the fuel, don’t reflect how AFFF actually works.