The LWF Blog

Fire Safety for Facilities Management Personnel – Fire extinguishing appliances – Part 220

September 25, 2023 11:00 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 219, LWF discussed foam portable fire extinguishers. In part 220, we talk about powder fire extinguishers and their usage.

Powder fire extinguishers come in different types which are most suitable for certain classes of fire.

A standard dry powder fire extinguisher can be used on solids such as paper, wood and textiles (Class A fire); flammable liquids like petrol, diesel and paint (Class B fire); flammable gases e.g. methane, butane (Class C fire) and electrical fires up to 1000v. Many powder fire extinguishers are known as Powder ABC fire extinguishers to help identify which types of fire they may be used on.

Specialist dry powder fire extinguishers are also available which would be suitable for fires involving flammable metal and lithium (L2 powder extinguisher) or all other flammable metals (M28 powder extinguisher).

Dry powder fire extinguishers are not for use with cooking oil fires, electrical fires over 1000v, any fire in an enclosed space or for fires involving flammable metals unless the specialist dry powder fire extinguishers are provided as noted above. The powder can be harmful if inhaled, so they should be used only in open, outdoor or very well-ventilated areas.

A dry powder fire extinguisher may contain several kg of agent. The expulsion method is often stored pressure or gas cartridge. Overall, these extinguishers tend to be lower in weight than a water or foam extinguisher and the range of discharge is around 5 metres.

The in-depth means by which the powder emitted extinguishes fire is complex and involves chemical inhibition and the imposition of a thermal load. In layman’s terms, however, it provides a barrier between the fire and the source of fuel which usually puts out the fire. Re-ignition is possible, however, and so appropriate caution should be used. These extinguishers do not have a cooling effect and therefore smouldering may continue.

Powder fire extinguishers may be effective on running flammable liquid fires and on live electrical equipment under 1000v, but it should be noted that the powder may cause extensive damage to electronic and electromechanical equipment.

In part 221 of this series, LWF will begin to look at carbon dioxide fire extinguishers. 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.