These type of fire extinguishers are ideal where both A & B class fire risks exist. AFFF (Aqueous Film Forming Foam) is particularly suited to class B fires caused by the combustion of materials that liquify such as petrol, oils, fats, paints and tar.
These extinguishers are also known AFFF extinguishers because they contain Aqueous Film Forming Foam in addition to water. The cooling power of water is combined with AFFF which smothers and seals flammable vapours. This means that this type of fire extinguisher is capable of tackling both Class A & B fires. The AFFF helps prevent the fire from re-igniting after it has been initially put out. Another benefit is that the contents of these specific extinguishers are not toxic.
An extinguisher such as this should be chosen for properties where there is a variety of fire risks such as warehouses, factories, garages, and similar buildings.
The use of this type of extinguisher depends on the type of fire you are dealing with: