Fire-fighting gases (halons) owe their rise to early experiments with gas warfare. The problem has always been a way of combining fire-fighting capability with toxicity. Earlier fire-fighting agents, like CBM (ChloroBromoMethane) were extremely efficient at displacing oxygen from the gases of combustion. The problem was that, in the case of CBM, the by-product was phosgene gas!! This is the same gas that was used in the trenches of WW1. In later years, gases like CTC (Carbon TetraChloride) were used to fight fires. Same problem, though. Good at putting the fire out-but very toxic with the by-product gas. In addition to this, many servicemen used to use the contents of CTC fire extinguishers (usually identified by a corrugated-style body with a pull lever at one end) to dry-clean stains from their uniforms-thus rendering the extinguisher useless in a fire, cos it was empty!! Later still, a red dye was added to the contents, so that it prevented servicemen from repeating this exercise!! Recently, ICI in UK and Duponts in USA developed what was perceived to be the perfect balance between toxicity and fire-fighting capability. They called it BCF (BromoChloroDifluoroMethane.) This proved excellent as a multi-purpose, non-damaging fire extinguisher. It left no mess and dealt with all common fires-including "mixed-risk" fires. Unfortunately, being a CFC it was banned by the Montreal Commission-much to the disgust of the fire industry and the fire brigades. When discharged onto a fire, the resultant gases did not destroy the ozone layer, nor did they cause too much problem with breathing (unless you put a fire out in a broom cupboard!!) Only when it was discharged into air did it create a problem, because there was no chemical reaction with the products of combustion, which effectively neutralised the CFC. Another example of burocratic nonsense triumphing over common-sense.
Edited by FiremanFil (22nd Dec 2011 6:33pm)