What unique feature does a foam extinguisher provide when used on a Type B fire?

A foam extinguisher is particularly effective on Type B fires, which involve flammable liquids such as oil and gasoline. One unique feature of a foam extinguisher is its ability to form a blanket over the burning liquid. This foam layer acts as a barrier between the fuel and the air, effectively cutting off the oxygen supply necessary for combustion.

The foam not only suppresses the flames but also prevents the release of flammable vapors from the liquid, reducing the risk of re-ignition. This characteristic makes foam extinguishers highly suitable for managing Type B fires compared to other methods that might not provide such a protective layer or could even exacerbate the situation.