Foam fire extinguishers can be used on Class A and B fires. They are most suited to extinguishing liquid fires such as petrol and diesel and are more versatile than water jet extinguishers because they can also be used on solids like wood and paper.

The foam extinguishes liquid fires by sealing the surface of the liquid, preventing flammable liquid vapour from reaching the air and starving the fire of fuel.

They are not suitable for free flowing liquid fires.