Well the dry powder fire extinguisher is pretty much the most effective all round model available on the market today. It is the type of extinguisher most often recommended for use in the home or on a vehicle due to its impressive coverage of multiple fire classes. They generally come as ABC or BC variants and are rated for use on those types of fires. As an added bonus they are safe to use on electrical fires too which is an impressive extension to their usage.
It’s simple to recognise a dry powder extinguisher as they are colour coded for easy identification, they are red with a blue panel.
Certain locations are not suitable for powder extinguishers as when set off they produce a cloud which may obscure people’s vision and make it difficult to find the fire exit. The powder can also cause some breathing problems when inhaled. For this reason they are not used in offices, hotels or other areas which are enclosed and filled with the public such as a school or large shop.
This type of extinguisher comes in three main varieties with the most common being ABC and BC.
The models rated as ABC are multi-purpose fire fighting equipment and the powder contains ammonium phosphate as its main agent. The BC extinguisher has potassium bicarbonate in it which is better known as baking powder or soda in the real world. The powder is forced out under pressure by nitrogen gas normally. There is a specialist third type of powder that is rated for class A and D (metals fires). These contain graphite powder and their use requires specialist training also.
A side effect of powder is that the powder is corrosive to soft metals and also attracts moisture, so if used on electrical products they will pretty much be destroyed and useless. This is because ABC dry powder ammonium phosphate can have a chemical reaction with water and form into phosphoric acid which is a corrosive element. They should only be used on sensitive electrical equipment if there is absolutely no other option to tackle the blaze. This is also why you cannot use a powder extinguisher on an aircraft.
Now for the techie part and an explanation of how the powder extinguisher actually works. Well obviously the powder is an extinguishing agent which is forced out of the extinguisher under pressure by a non flammable gas. The powder then smothers the fire and prevents re-ignition by removing one of the fire causing elements such as oxygen. The sodium bicarbonate element of powder is a very clever addition which fully decomposes at 158 degrees F thus releasing CO2 which helps starve the fire of oxygen.
Worth a mention also is Monnex dry powder which was developed by ICI and is one of the most effective fire fighting agents available today.
Another downside of powder is the fact it is extremely messy, but that’s a small price to pay to save your life. The powder should be cleared up fully after any fire and disposed of correctly. This type of powder extinguisher is used a lot within motor racing as its so effective at tackling a petrol fire and is commonly seen at airports also.
So there you have the full details on a powder fire extinguisher.