2 May
2005
2 May
'05
10:30 a.m.
Subject: Re: OT Don't read this (was Re: Altair MBL source)
From: shoppa_classiccmp at trailing-edge.com
Date: Mon, 02 May 2005 13:12:33 -0400
To: cctalk at classiccmp.org
Halon does not absob Oxygen. It is an Oxygen displacement that is
also heavier than air. In a closed room if enough is introduced
under pressure (typically) it will push out all air (Oxygen too)
leaving an unbreathable and incombustable mix. Because computer
rooms are largely closed any major air displacement is dangerous
for the users inside.
A bunch of years back I was working at a pharmaceutical plant doing
controls. While I was in a HEPA closed filling room some dolt fired
up a Freon (R12) system used to pressurize the containers without
checking to see if the lines were properly capped. Those 75GPM
pumps were pushing liquid Freon that initially I thought was Glycol
for cooling. It took only a few seconds for the Freon to vaporize
and reduce the breathable air to nil by displacement. In the few
seconds it took to evaluate what's going on and get out I was
quite hypoxic. My boss was extremely upset with the dolt. I spent
many months after that doing lockout/tagout training and used
that case as the what can happen.
Halon and Freon are similar in that they are "non toxic",
incombustable and generally electronics friendly in the gas form.
But life is only supported by Oxygen, anything else while not toxic
is not breathable without causing hypoxia.
Allison
Apparently the whole area gets flooded with halon
(sp?) to quickly absorb
any oxygen from the air, so if you hang about ......
"Absorb any oxygen" is a bit harsh. Halon is pretty good at stopping
things from burning but it doesn't make it impossible to breathe. It's
not the most healthy thing to breathe but in the 80's and earlier a
very common demo of halon extinguishers had the salesman in a halon filled
booth, demonstrating how all fires go out, while happily breathing the
stuff.
Now, CO2 oxygen-displacement extinguishers, that's a different story.
Tim. 
2 May
2 May
10:43 a.m.
[Halon] In a closed room if enough is introduced under
prssure it
will push out all air leaving an unbreathable and incombustable mix.
Also a bit extreme. I've been in two complete and unwarned (the
electronic pre-alarm sounding system was never activated because the
contractors directly operated the release valve) halon dumps and
the resulting mix was quite breathable. We did open the closed doors
and air out the room (which requires a lot of effort as we're deep
underneath Washington DC) of course, and the fire department came
and helped in this. Others here may want to testify as to the
resulting brain damage that I suffered but I generally think I'm doing
just fine :-).
A halon dump in a control center environment is quite impressive. Most
of the celing tiles flew loose, loose papers on the console were blown
everywhere, and for maybe ten seconds after the dump there was zero
visibility.
I'm not sure how other halon installations elsewhere work, but ours
have a pre-alarm system that is supposed to warn occupants to get out
for some number of seconds before the dump. There are also switches
by the door (deadman style) that will let you hold off the dump. So
clearly breathing the stuff isn't the healthiest idea in the world. But
it's not quite as totally lethal as you and others would imply.
Tim.
2:04 p.m.
shoppa_classiccmp at trailing-edge.com wrote:
Also a bit extreme. I've been in two complete and
unwarned
(the electronic pre-alarm sounding system was never activated
because the contractors directly operated the release valve)
halon dumps and
the resulting mix was quite breathable.
Indeed. That was a "selling point". Unlike the earlier
"oxygen displacement" systems (like CO2) which work by
pumping in enough stuff to dilute the oxygen to a level
below that at which it will sustain a fire (and life ...),
halon works by interfering only with the actual combustion
process. So it only needs a 4% or 5% (or thereabouts)
concentration. The idea was to set the system up so that
it would very rapidly dump enough halon in the room to
ensure that the 4% conc. was reached rapidly, at which
point flames would (supposedly) be snuffed out. You were
supposed to be able to breathe this level of halon without
being affected and the oxygen around you would still be there
(unless you were burning, I guess :-)). Of course, rapid
decompression of enough halon to cope with even a smallish
room is obviously going to result in a rapid inrush of gas
and a very rapid drop in temperature. That means a bunch
of stuff flying everywhere and an instant "thick fog".
Still, at least you'll probably be alive (albeit possibly
unconcious on the floor if hit by something) when someone
decides to wander in and rescue you. With a CO2 dump
you'd be dead in the minute or two that it would take
or someone outside to go through the "oops, what was that?
Was anyone in there. I can't see a thing. Ooh what's Bill
doing lying down in that mist" routine!
I do remember the demo of the guy in a transparent,
large diameter pipe smoking a cigarette as the halon
(a slowly increasing concentration) was turned on.
At about 5% the cigarette, went out - the man continued
to breathe without difficulty. At some point (film or
installation technician - I forget) there was a warning
that prolonged exposure to halon at certain levels (about
8%+ sticks in my mind) was considered to be a health risk.
So hanging around after a halon dump was very much _not_
recommended.
I wonder what people use in computer rooms for fire
extinguishing these days. (That is, those people who
don't still have stocks of pre-ban halon ... which
is now presumably worth much more than its weight
in gold)? I'd just like to know for future planning
purposes :-)
Antonio
--
---------------
Antonio Carlini arcarlini at iee.org
2:29 p.m.
At 10:04 PM +0100 5/2/05, Antonio Carlini wrote:
I wonder what people use in computer rooms for fire
extinguishing these days.
I'm experimenting with a product called Inergen. Similar idea to
others in the past: reduce the oxygen concentration to a level where
fire cannot be sustained yet people can still function. The Inergen
formulation is some combination of nitrogen, argon, and carbon
dioxide. Big sales point is no CFCs or ozone depletion (the reason
Halon was discontinued in the US).
We've installed the system for our main data center. Have not had
the mandatory dump for the fire department yet. Will soon.
John
7174
days inactive
7174
days old
4 comments
5 participants
participants (5)
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a.carlini＠ntlworld.com -
ajp166＠bellatlantic.net -
dundas＠caltech.edu -
geoffreythomas＠onetel.com -
shoppa_classiccmp＠trailing-edge.com