Foam extinguishers :  If the burning liquid is in a container the jet should be directed at the inside edge of the vessel or at a vertical surface in order to break the jet and allow the foam to build up and spread across the surface of the liquid (Figure). If this is not possible, the correct procedure is to stand well back (perhaps as far as 6 or 7 m) and to direct the jet with a gentle sweeping movement to allow the foam to drop down and form a layer on the surface of the liquid (Figure). Do not aim the jet directly into the liquid as this will drive the foam under the surface where it will be ineffective in extinguishing the fire and may spread the fire by splashing the liquid on the surroundings.

Figure: Use of foam extinguisher-I. Fig.12.4: Use of foam extinguisher-11.