What part of the fire triangle is affected by a dry powder fire extinguisher?

Answer 1

It used to be thought that foam blanketed burning substanecs from the air, smothering the fire, and so the side of the fire triangle removed would be "oxygen". Recent research suggests that, whilst smothering plays a small part in foam's effectiveness, its main value is to reduce the transfer of vapours from the burning substance to the flames. In this way, it acts to prevent fuel reaching the flames, and so extinguishes by starvation. Foam also contains about 96% water, and so will cool burning substances below their ignition point. Summary: foam attacks all three sides of the fire triangle, but its main action is to reduce the flow of fuel from the surface of the burning substance to the flames. Note that many science teachers still follow the incorrect information in textbooks which states that foam "smothers" a fire (e.g. excludes oxygen). The UK Manual of Firemanship (official guide for UK firefighters), and the Royal Navy's technical firefighting handbook both provide evidence for the "starvation of fuel" mechanism. In case of a dispute, you could point out that nowadays, all foam (from extinguishers and larger foam generators / branchpipes) is made of a detergent solution that is blown full of air: a blanket of air bubbles wouldn't be particularly effective in simply smothering a fire, but the fact that the bubbles are made from detergent solution allows the foam to spread in a thin flim over the surface of the fuel, stopping the flow of vapour. Modern developments of this theory include the design of afff (aqueous film-forming foam) concentrates which are even more effective at "filming" over a burning substance.

Answer 2

It depends upon the type of extinguisher and the type of fire.

Water, for example, removes heat and also increases the ignition temperature of adjacent wet fuels, essentially "removing" fuel from the triangle.

Carbon dioxide, foam and Halogen extinguishers remove the oxygen.

Class D extinguishers change the chemistry in the fire TETRAHEDRON to stop the chain reaction within burning metal fires.

Answer 3

Dry Powder extinguishers contain a chemical that reacts with the

fire to exclude oxygen.