Posted by Paul (in NY) on Thursday, April 14, 2005 at 1:49PM :
In Reply to: Re: I have 3 in my home posted by Frank USMC on Thursday, April 14, 2005 at 1:02PM :
Come with different extinguishing chemicals. Typically you have Fire Class B & C Rated Extinguishers and Fire Class A,B,C Rated Extinguishers. The actual method of suppression is by killing the free radicals in the in the flame zone (chemical chain breaking). They do not cut off the available air nor remove the fuel, nor cool the fire. In your fire, the wax was melting, running on the hot stove, constantly out gassing and at the ignition temperature, thus when you killed the flame zone, it would reignite.
Dry Chemical extinguishers Rated for A,B,C class fires contain Mono Ammonium Phosphate as extinguishing agent. This agent also chemically breaks the chain reaction of the fire, BUT it also imparts a sticky effect to the heated Mono Ammonium Phosphate which then tends to cling to the burning surface, with a smothering effect to prevent re ignition.
The same re ignition effect you saw would be present in, for example a car seat burning that a B,C rated Dry Chemical extinguisher was used on. The flame zone would be suppressed quickly, the glowing embers in the seat would reignite.
The consideration for Dry Chemical ABC rated extinguishers and a Pressure Water A Rated is good for the home. A class fire is for example burning paper, rugs, cushions, wood etc. NEVER use a Pressure Water Ext on Electrical Fires.
Do not confuse Dry Chemical Extinguishers with Dry Powder Extinguishers. Dry Powder Extinguishers are Rated for Class D fires, burning metals.
Remember, the old fire triangle is no longer valid. Its now replaced with a 4th side, that being the chemical chain breaking of fire.
Paul
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