Which foam application method is used for an un-ignited pool of liquid fuel located below a facility tank wall?

The bank down method is the correct choice for applying foam to an un-ignited pool of liquid fuel located below a facility tank wall. This method entails directing the foam onto the pool of fuel from a safe distance, allowing the foam to flow down and blanket the surface of the liquid. The foam forms a protective layer that prevents vaporization and ignition while also suppressing flammable vapors.

The effectiveness of the bank down method lies in its ability to cover a larger area efficiently, creating a barrier between the fuel and the surrounding environment. This is particularly important in scenarios involving facility tank walls, as it helps to contain the hazard and protect the facility structure from potential ignition sources.

Other methods, such as the fogging method, may disperse the foam but are less effective for covering expansive surfaces like large pools of liquid fuel. The pouring and direct attack methods may not provide the necessary coverage or effective vapor suppression in situations where the fuel pool is spread out or located in a sensitive area. Thus, the bank down method is the most appropriate technique for effectively managing this specific fire ground scenario.