The LWF Blog
Facilities Management & Fire Safety – Fire Extinguishing Equipment – Part 5February 1, 2017 10:16 am
In this recent blog series for those who work in Facilities Management and who have a responsibility for or interest in fire safety, we have been looking at fire extinguishing equipment and its use in fire situations. In Part 4, we looked at the use of foam extinguishers and in Part 5, we will move on to look at powder extinguishers.
In previous blogs we have explained the nature of Class A and Class B fires, but to reiterate, Class B fires are those fires involving flammable liquids such as petrol, paraffin and oil. Class A fires involve solid materials such as paper, wood, plastic.
A powder extinguisher may be suitable for use on both Class A and Class B fires, but that is dependent upon the extinguishing medium contained within. The majority of powder extinguishers are made to be multi-purpose and so can safely be used on both types of fire. The suitability for a type of fire is printed on the extinguisher canister using the labels A, B, C etc. with a small pictogram.
A standard fire extinguisher will contain several kilograms of powder agent with an expulsion mechanism which may be stored pressure or gas cartridge based, as with foam extinguishers.
The gross weight of a powder extinguisher is likely to be less than that of water or foam and is often between 5kg and 10kg in weight, with a range of discharge of around 5m. While a lay person can easily comprehend the reasons that water might work to extinguish a fire, powder is a more complex notion, but we can assume that the process involves chemical inhibition and the imposition of a thermal load.
A powder extinguisher is capable of a very rapid knockdown of flame and the performance ratings for such extinguishers are correspondingly high on Class A and Class B fires. Powder extinguishers can also be effective against running flammable liquid fires, where indicated as appropriate.
The application of a powder agent on a fire, however, does not cause it to cool and there is no method of preventing re-ignition, should the fire continue to smoulder after the flames have been extinguished.
It should be noted too that powder extinguishers can be used on electrical equipment, but this is likely to cause damage to the equipment itself, so should only be provided for use in those cases where the equipment itself does not need to be saved or is a secondary concern.
In part 6 of this series, we will begin to look at the effects of carbon dioxide extinguishers and their potential for use within your premises. 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.