The LWF Blog

Facilities Management & Fire Safety – Fire Extinguishing Equipment – Part 4

January 26, 2017 12:06 pm

In our blog series for those people who work in Facilities Management and have responsibility for fire safety, we have been looking at the various types of fire extinguishing equipment that can be found in many premises. In Part 3, we looked at the use of water extinguishers on fire and in Part 4, we are going to discuss the use of foam extinguishers.


There are two main types of foam fire extinguisher – Fluoroprotein foam and Aqueous film-forming foam (abbreviated to AFFF).


The first type – Fluoroprotein foam – is designed for use on Class B fires, which are those fires involving flammable liquids such as petrol, paraffin and oil. AFFF is the more commonly used extinguisher and is suitable for use on both Class A (solid materials such as paper, wood, plastic) and Class B fires.


Both types of foam work on flammable liquid fires by smothering the flames. The foam creates a barrier between the fuel and the air. As fire needs fuel to grow and air to burn, it is unable to continue to burn. In cases where AFFF extinguishers are used on Class A solid material fires, the smothering effect still applies, but it also serves in adding to the wetting/cooling of the fuel surface.


The size and weight of foam extinguishers is similar to water extinguishers, although AFFF extinguishers are also available in the slightly smaller and lighter 6L versions. In terms of fire efficiency, a 6L AFF extinguisher can achieve the same ‘A’ fire rating as a 9L extinguisher. As mentioned in Part 3, the extinguishers are available in both stored pressure or gas cartridge type, but as both are operated by the user in the same way (trigger mechanism), an understanding of the differences is probably not required by a casual user.


While Fluoroprotein foam extinguishers and AFFF extinguishers are both designed for use with flammable liquid fires, they are not practical for use on running flammable liquid fires and nor should they be used in cases where there is live electrical equipment. Some AFFF spray extinguishers are incapable of conducting an electric current down the foam discharge from the canister, but even in that case, the damp surfaces upon which the person using the extinguisher must stand can pose a danger if it were to come into contact with live electrical equipment.


The use of either of these types of extinguisher on a flammable liquid fire not only douses the flames and provides a coating which expands, but assists in stopping the release of fumes into the breathable atmosphere.


In Part 5 of this series, we will look at Powder Fire Extinguishers and Carbon Dioxide Extinguishers. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact Peter Gyere in the first instance on 0208 668 8663.


Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.


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