Guide to Dry Powder Extinguishers
Dry powder extinguishers smother the fire rather than reduce temperature. This is why fires sometimes reignite after using dry powder. The substance forms a barrier between the fuel and oxygen, starving the flames and bringing it under control.
When you need the extinguisher, start by removing the safety pin. This breaks the seal. If you’re tackling an electrical fire remember to turn the mains power supply off first if possible.
Which fires CAN you use dry powder extinguishers on?
Dry powder is mostly used on organic materials – including wood, coal, fabrics, cardboard, paper and textiles. They’re also good at fighting flammable liquids like paint and petrol, flammable gases such as liquid petroleum and electrical fires under 1000 volts. There is a specialised extinguisher designed to fight flammable metal fires too.
Which fires CAN’T you use them on?
ABC rated extinguishers contain ammonium phosphate. This is great for tackling flammable gas fires but isn’t practical. If there is water nearby the ammonium will mix with it to create phosphoric acid, which can seep into the smallest of gaps and cause lasting damage.
Don’t use ABC on sensitive (and expensive) electrical equipment such as computers, scientific equipment and switch installations unless you lack a more suitable extinguisher (i.e. CO2).
Avoid chip pan fires (or indeed anything involving cooking oils), electrical fires over 1000v, fires in enclosed spaces (because you can inhale the powder) and fires involving flammable metals (unless you’re using a specialist extinguisher).
Why should you use dry powder?
Because they can be used on loads of different fires. They also work really fast. Thanks to the blanket method, fires can quickly be choked of oxygen and suppressed. Specialist dry powder extinguishers are also the only type capable of dealing with flammable metal fires.
Why shouldn’t you?
While these extinguishers act quickly, they don’t reduce the temperature of the flames, risking the chance of reignition. They’re also messy. While this is the last thing on your mind when you’re fighting fire, dry powder can leave behind expensive damage. It also obscures vision and causes nasty breathing problems, meaning you can’t use them indoors.
Who uses dry powder extinguishers?
Thanks to their strictly outdoor permit, dry powder is usually used on garage forecourts, buildings with large boiler rooms, LPG plants and welding and flame cutting businesses. If you’re looking to protect your office, hotel or anything with an enclosed space, dry powder extinguishers aren’t for you.
What kind of powder is used?
ABC: A combination of ammonium or mono-ammonium phosphate and other powders. This is the general-purpose extinguisher – able to fight class A, B and C rated fires. It’s also the cheapest.
BC: This is a sodium bicarbonate-based powder and was the most common variant before ABC came along.
Monnex: This is a potassium bicarbonate compound which is really effective at fighting petrol and oil-based fires. Monnex is pricey compared with ABC and BC.
Class ‘D’: These are more specialist powders intended for flammable metal fires.
What sizes do dry powder extinguishers come in?
Extinguishers come in a variety of sizes dictated by weight, ranging from 1 kg to 9 kg.
How long do they last?
This depends on the manufacturer – but it ranges from 3 to 12 years. As a rule of thumb, you should have rechargeable extinguishers tested and recharged every 6 years and non-rechargeable ones replaced every 12 years. Check the tag (usually found at the base) for the expiration date and instructions.
What colour are they?
Dry powder extinguishers have a blue label. Unsurprisingly, this should state ‘powder’. There should also be an extinguisher ID sign nearby.