Extinguishing Agents, Foam Proportioning, and Application Techniques
Foam is the primary agent for fuel fires; this domain tests agent selection, proportioning accuracy, and the physical technique that builds and preserves a blanket.
Agents
Water cools but spreads fuel. AFFF and AR-AFFF form a film, work fast, and are used at 3% on hydrocarbons; AR-AFFF is also rated for polar solvents, often 3%/3% or 3%/6%. FFFP adds a protein layer; protein foams are slower and used at 3–6%. Fluorine-free foams are being adopted at many airports because of PFAS concerns and are generally less forgiving in application and burnback. Dry chemical (Purple-K, sodium bicarbonate, ABC) knocks down flame almost instantly but provides no cooling or blanket, so fuel re-ignites; it is best used to buy a rescue window or in combination with foam. Halon 1211 and 1301 have been replaced by clean agents and dry chemical for hand-held use.
Application fundamentals
Foam must land gently. Bank it off a bulkhead or the ground, rain it down, or sweep it across the surface; never plunge a straight stream into a pool - it submerges the foam and splashes fuel. Start upwind and work downwind, keeping a retreat path. For hydrocarbon spill fires, NFPA 11 design work uses an application rate around 0.10 gpm/ft² of solution.
Worked example. A 40 × 60 ft fuel spill is 2,400 ft². At 0.10 gpm/ft² you need 240 gpm of solution; at 3% that is 7.2 gpm of concentrate. A 95 gpm handline is not the tool - a turret is.
Traps. Using standard AFFF on an ethanol-blend fuel; aiming at flame rather than at the fuel surface; letting a dry-chemical knockdown convince you the fire is out.