Difference dry powder and ABC powder extinguishers?

[Guest Harry]

Hi, I found confusing and partly contradicting information about the difference between dry powder and ABC powder extinguishers. Can anyone shed any light on this, please?

Harry

[Tom Sutton]

There Are Three Main Types Of Dry Powder Extinguishers

ABC rated or multi-purpose powder, which contain ammonium phosphate

BC rated extinguishers, containing potassium bicarbonate or sodium bicarbonate (otherwise known as bicarbonate of soda or baking soda!) Some BC rated powder fire extinguishers contain Monnex. The pressurising gas is usually nitrogen

A and D rated graphite powder fire extinguishers are usually used only in Class D fires

Check out http://www.fireextinguisherguide.co.uk/types-of-fire-extinguishers/dry-powder-extinguishers/

[AnthonyB]

Most UK extinguishers contain ABC (General or All Purpose) Powder based on mono-ammonium phosphate & sulphate - usually yellow (but with far east imports you can get blue, green, orange/pink). It is slightly acidic and fuses into a sticky flux when hot (which is how it is effective on Class A solid fires by coating embers) This powder as a result has a high secondary damage potential to delicate items, electronics & machinery. It is non toxic, but mildly irritant.

A small number of aerosol and small automotive extinguishers contain BC (Standard Powder) which is Sodium Hydrogen Carbonate and usually white. It is slightly alkaline (hence it's use in kitchens before the development of wet chemical as it had a slight saponific effect on cooking oils). It does not flux and has less damage potential, is easier to clean and less irritant. It is not effective on deep seated Class A fires as it does not flux around embers.

Specialist BC powders exist for high risk environments (Potassium Bicarbonate "Purple K" and Potassium Allophonate/Potassium Bircarbonate/Urea Complex "Monnex") but these are not found in general use due to cost.

BC & ABC Powders main extinguishing effect is by chemically interrupting the chain of combustion with little appreciable cooling or smothering effect so there is a risk of re-ignition after use and with a Class B fire if you don't extinguish it all in one go the fire can instantly re-flash to it's original size.

Class D fires (flammable metals) have specialist powders, choice dependant on the metal involved - these use Sodium Chloride, Graphite or Copper to absorb heat and flux over the metal allowing it too cool.

Where US terminology is used instead of UK then ABC & BC extinguishers are called Dry Chemical with the term Dry Powder being used only for Class D agents.

[Safelincs]

An excellent article, Anthony! Excellent reading and very clear.

Harry

[green-foam]

 

The glass on the left has ABC powder, and the one on the right is BC powder, you can see that the ABC is slightly yellow

[AnthonyB]

These are all ABC Powder!

[green-foam]

I like those.