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Foam fire extinguishers are one of the most common types of fire extinguisher. Generally used for fires involving flammable solids and liquids, they are also known as AFFF foam extinguishers or spray foam extinguishers.

Foam extinguishers can be used on:

  • Class A fires – combustible materials: caused by flammable solids, such as wood, paper, and textiles
  • Class B fires – flammable liquids: such as petrol, paint or spirits
  • Electrical fires – electrical equipment: such as computers and photocopiers IF the extinguisher has passed the 35kv conductivity test.

The 35kv conductivity test is an additional safety measure designed to safeguard people who accidentally use a foam fire extinguisher to extinguish an electrical fire. Using a foam extinguisher on an electrical fire always poses the risk of electric shock.

Foam extinguishers should never be used on the following fire types:

  • Class C fires – flammable gases: like propane and butane
  • Class F fires – cooking oils: such as olive oil or butter. Typically a chip-pan fire

Identifying a Foam Fire Extinguisher

Foam fire extinguishers have a cream coloured label stating ‘FOAM’. It should also have a sign above or next to the extinguisher that states ‘Foam Extinguisher’.

Foam fire extinguishers come in foam sizes:

  • 2 litre
  • 3 litre
  • 6 litre
  • 9 litre

How Foam Fire Extinguishers Work

Foam extinguishers work in two ways. Firstly, they are mainly water-based so work in much the same way as a water extinguisher. When the foam comes into contact with the flames, it cools the temperature down dramatically, taking away the heat element required to keep a fire burning. Secondly, foam extinguishers contain ‘Aqueous Film Forming Foam’ (hence AFFF extinguishers).

AFFF works by smothering a fire and sealing in the flammable vapours. This effectively prevents the fire from re-igniting. It is also effective in tackling flammable liquid fires by creating a barrier between the surface of the liquid and the flames.

When to Choose a Foam Fire Extinguisher

Because foam extinguishers can be used on both Class A and Class B fires, they are more commonplace than water extinguishers. Most business premises have foam fire extinguishers, and they are commonly paired with a CO2 extinguisher in order to tackle electrical fires, covering all fire risks within a building.

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