Final answer:
Aqueous Film Forming Foam (AFFF) extinguishers are designed for Class B fires involving flammable liquids, utilizing a fluorinated solution that forms a barrier to extinguish the fire. The solution's surfactants reduce the surface tension of water, allowing it to blanket the burning material.
Step-by-step explanation:
Aqueous Film Forming Foam (AFFF) extinguishers are specifically designed to tackle fires involving flammable liquids such as petrol, diesel, and other organic liquids. This is commonly referred to as a Class B fire in fire classification. The AFFF extinguisher utilizes a fluorinated solution that can spread over the surface of the burning liquid. The key property of AFFF is its ability to form a barrier between the fuel and the oxygen, effectively stopping the fire. This is achieved through the addition of surfactants, which are surface-active agents that reduce the surface tension of water, allowing the foam to blanket the fire.
In the past, AFFF was also used for fires involving foaming plastics and was once recommended for use with dry-cleaning solvents, however, this is no longer recommended. Over the years, particular attention has been given to creating extinguisher systems that effectively combat large-scale industrial fires where flammable liquids are a significant risk.