Dick:
Halon works by chemically interfering with the combustion
process. Water works by blocking oxygen with a film of water, by
cooling, and by displacing oxygen with steam. CO2 works by displacing
oxygen (and in some cases by cooling). Dry chemical extinguishers are
usually sodium bicarbonate and a delivery system. The bicarbonate
releases CO2 when heated, so it is just a different type of CO2
extinguisher (and a MESSY one at that!).
The problem with Halon is that it interferes with the combustion
both by displacing O2, and by SUBSTITUTING itself for oxygen in
combustion. This in turn creates reaction byproducts that are not
created with water or CO2. My understanding is that these byproducts
were considered to be toxic to humans (HOW toxic, I don't know.) I know
that in a closed room if Halon was used to extinguish a fire, it was
considered to be unsafe to enter the room because of the byproducts.
Halon fell out of favor for this reason ('Course, it was probably safer
than the fire it put out in the first place!)
I suspect that the Halon toxicity issue may have been overblown,
or perhaps more data is now available that refutes the previous concerns
(Remember cyclamate based sweeteners? They cause cancer! Do not! Do too!
Do not!) Years after being banned as unsafe, they were again approved
for use because the original studies were found to be 'unsound' in the
scientific sense, and cyclamates were in fact very safe. Or it is
possible that the Halon used today is chemically modified to address the
original concerns, similar to modifying Freon so that it doesn't deplete
the ozone. <shrug>
Anyway, that's my understanding about the original disappearance
of Halon. Why it has reappeared I don't know, but I can speculate (hey,
I *DID* speculate).
Cheers,
Vance
------------------------------
Cogito Ergo Zoom
(I think, therefore I go fast)
TR6 Web page: http://home.comcast.net/~v.navarrette/
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Sally or Dick Taylor
Sent: February 17, 2005 4:30 PM
To: 6pack@autox.team.net
Subject: Re: Fire Extinguishers....
The subject of fire extinguishers came up on this list a few years back.
I had mentioned that I carry a HALON unit in my glove box, and other
ones in my home and shop are still on the ready. Small, but worthy, and
I knew it worked well on a test fire. I was advised that these were no
longer available, as Halon was banned for some reason.
I still have mine, and now I see Moss Motors sells the Halon type, shown
in their latest catalogue. Anyone know the scoop about the Halon
issues?
Dick
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