A Guide to Dry Powder Fire Extinguishers
Dry powder extinguishers, depending on which powder is used, can be used on:
- Class A: Ordinary combustibles (wood, paper, cloth, rubber and plastics)
- Class B: Flammable liquids (petrol, oil, spirits and grease)
- Class C: Flammable gases (gas, propane and hydrogen)
- Class D: Burning metals (sodium, manganese, aluminium, etc)
- Class E: Electrical fires
How to identify them
Dry powder extinguishers are easy to identify with their blue label and white writing. However, you’ll also need an accompanying dry powder fire extinguisher sign
Types of dry powder
As the name implies, dry powder fire extinguishers use dry powder as their extinguishing agent.
There are several types of dry powder:
- ABC: Suitable for class A, B and C fires, and can be used on electrical equipment
- M28: For metal fires, excluding lithium
- L2: For all metal fires, including Lithium
- BC: Suitable for class B and C fires
- Monnex: Potassium bicarbonate-urea based, developed for class B and C liquid and gas fires
How they work
Dry powder extinguishers work by spraying a very fine powder over a fire, forming a layer that eliminates the source of oxygen.
Dry powder extinguishes fires quickly, but extra precautions need to be taken to prevent re-ignition.
Vehicle and car fire extinguishers
ABC dry powder fire extinguishers are the only ones suitable for use on vehicle fires.
Your automobile is filled with gas, oil and flammable upholstery; a dry powder extinguisher can tackle all of these fires and is safe to use on electrical appliances.
Legally, all commercial vehicles must have a minimum of 1 x 2kg dry powder fire extinguishers. Depending on the goods they carry, other extinguishers will be required, too.
ABC dry powder fire extinguishers can be used on electrical fires.
Generally, CO2 extinguishers are the only ones recommended for use on electrical fires, but this is because the carbon dioxide won’t damage electrical equipment. ABC dry powder extinguishers can also be used on electrical appliances, but the powder agent can damage them.
This is because ABC dry powder contains ammonium phosphate, which can react with any water present to form phosphoric acid. This is corrosive and can seep into even the slightest cracks in equipment.
Two types of dry powder can be used on metal fires, which are M28 and L2.
M28 fire extinguishers spray a fine sodium chloride powder onto metal fires (excluding lithium). M28 powder is especially effective on alkali metals, such as sodium, potassium, magnesium.
L2 lithium fire extinguishers can also be used to fight metal fires. Unlike M28 powder extinguishers, they’re also effective on lithium fires.
Neither of these agents will put you at risk of receiving a thermal shock when you use them on metal.
Benefits of Monnex dry powder
Monnex dry powder is suitable for class B and class C fires. Monnex is known for being a powerful agent as it can achieve a higher fire rating for class B and C fires than standard ABC or BC powders.
However, if you are going to use this extinguisher, bear in mind that it isn’t suitable for class A fires.
ABC rating – what does the number mean?
You will notice that in standard ABC fire extinguishers
, there is normally a number next to the letters. For instance, you may see ‘ABC 20’ or ‘ABC 70’.
It basically tells you what proportion of the main agent your dry powder extinguisher contains. For instance, commonly, ABC powder extinguishers’ main agent is monoammonium phosphate (MAP).
A higher MAP indicates a more efficient agent; you will generally find that extinguishers with a higher number also have a higher fire rating.
However, this does not mean you should always opt for a higher MAP.
While they may be better at extinguishing fires, the agent may also be more harmful when inhaled. So if the risk is low, opt for a lower MAP.
Only use them on small fires
Dry powder extinguishers are typically used to control and tackle small fires.
It’s not a good idea to use them on fires that are out of control; the powder emitted can obstruct your vision and can be harmful when inhaled.
Do not use them in enclosed spaces
If you use dry powder extinguishers in enclosed spaces because the powder released can cause breathing difficulties. To keep yourself protected, keep breathing apparatus near your dry powder extinguishers, and avoid using them in tight, enclosed spaces.
How do they react with other extinguishers?
Another aspect to consider is the way dry powder extinguishers react with other fire extinguishers.
Dry powder and water mix to form a corrosive substance that causes damage to electrical appliances, so they shouldn’t be used with water (H2O) fire extinguishers
It’s also important to make sure you know whether your powder extinguisher is foam compatible.
For more information on other fire extinguishers click here