Ed Quinn wrote:
>
> Halon is heavier than air and
> displaces the oxygen to prevent fire, but you can't breathe if immersed in
> the gas. I think it was outlawed in Europe as people died from suffocation
> when the halon system in their building went off.
Ed :
I think you may have Halon confused with CO2 here. Halon is
specifically designed to decompose when exposed to the direct heat of
the fire (900F), it only works right where the fire is burning. The gas
that comes out of the extinguisher is (reasonably) safe to breathe, and
does not require a high enough concentration (the target is something
like 2% in enclosed areas) to displace any significant amount of oxygen.
The byproducts formed in the fire are somewhat toxic (but then so are
most combustion products), so it's certainly recommended to leave the
area if you can, but Halon's relative lack of toxicity in an enclosed
area is one of the reasons it's preferred by the FAA. There's a copy of
a relevant FAR (Federal Aviation Regulation) at
http://www.h3r.com/ac2042c.htm
The alternatives are dry chemical, which can cause vision problems and
dizzyiness almost instantly, and CO2 which in concentrations adequate to
extinguish, will cause unconsciousness in a few minutes and death within
20 minutes.
There may be some truth to the ozone story, except that no one has ever
shown a solid, cause and effect link between use of (heavier than air)
chlorinated fluorocarbons at ground level, and the "hole" in the ozone
layer. (Note that ozone concentrations at ground level have generally
increased in industrialized areas.) Nor have they shown that the "hole"
is not a perfectly natural phenomenon, caused by the lack of high energy
radiation in the area.
Randall
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