Foam spray extinguishers (AFFF – Aqueous Film Forming Foam) are best suited for Class B flammable liquid risks where they represent a direct hazard. Foam spray extinguishers are especially suitable for Class B fires involving flammable liquids such as oils, spirits, fats and certain plastics. The blanketing effect of foam spray gives rapid knock down which smothers the flame and thus prevents re-ignition of flammable vapours by sealing the surface of the solution.