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Fire Safety for Facilities Management Personnel – Fire extinguishing appliances – Part 219

September 18, 2023 11:02 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 218, LWF talked about portable fire extinguishers, particularly water extinguishers. In part 219, we discuss foam portable fire extinguishers.

Foam portable fire extinguishers come in two types:

  • Fluoroprotein foam
  • Aqueous film-forming foam or AFFF

Fluoroprotein foam is the less commonly seen of the two types of foam portable fire extinguisher and is for use on Class B fires. AFFF is much more commonly-used and may be used on Class A or Class B fires.

For clarification, a Class A fire might involve combustibles such as paper, straw, coal, textiles, wood or some plastics – mostly organic materials. Class B fires involve flammable liquids such as alcohol, oil, petrol, diesel, turpentine, paraffin, paint ethanol, grease etc.

The foam of an AFFF extinguisher smothers a fire that involves flammable liquids. The foam forms a barrier between the liquid surface and the surrounding air to ensure no further oxygen can be consumed by the fire.  It works to extinguish a Class A fire in the same way as water would, but the reduced surface tension granted by the additive aids the wetting of the fuel surface.

The size and weight of foam extinguishers is similar to that of water extinguishers, although it is possible to get AFFF extinguishers with 6 litre contents. The efficiency of the 6 litre AFFF extinguisher is such that it can achieve the same Class A rating as a 9 litre water extinguisher.

The extinguishers may be either stored pressure or gas cartridge types.

Although foam extinguishers are extremely effective at the types of fire mentioned above, they are not as helpful on running flammable liquid fires and should not be used in the case of a fire involving live electrical equipment. Some CFFF spray extinguishers are incapable of conducting an electric current down the discharge from the extinguisher, but the damp surface on which the operator is standing could be dangerous to them if they came into contact with live electrical equipment.

In part 220 of this series, LWF will look at powder extinguishers and their uses. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.


While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.

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