Newsgroups: sci.military
From: mikew@sr.hp.com (Mike Weihman)
Subject: Re: HALON gas
Date: Sat, 11 Mar 1995 00:41:47 GMT

From mikew@sr.hp.com (Mike Weihman)

There are a lot of misconceptions of halon kicking about... I thought
I'd repost a few of my old postings on the subject, fyi.  This is LONG.



RE: benefits and deleterious effects of halons

"Halon" is a term for halogenated hydrocarbons; that is, a methane or
ethane (etc.) chain in which some of the hydrogen atoms are replaced
by halogens, namely chlorine, bromine, fluorine, and iodine.  (Freon,
on the other hand, is a Dupont trademark for their line of
chlorofluorocarbon refrigerants.)
	

	Halons have some unique properties in firefighting which make
them ideal agents in some situations.  Computer rooms happen to be one
of those situations:


1) Halons are gaseous, and therefore leave no residue on people or
equipment.  Water, and especially dry chemicals, leave behind
materials which can seriously harm electrical equipment, often causing
far more damage than the fire they put out.  Furthermore, halon will
not destroy any paperwork (which might itself be irreplaceable)
present in the room, as would water or dry chemicals.  Halon presents
absolutely no cleanup problem.  (In the post-halon world, water is
being re-examined, with small, local application.)


2) They are nonconductors of electricity, for all intents and
purposes.  If one were to use a water sprinkler in a computer room,
the equipment would have to be shut off first or else might
short-circuit.  In many large installations, this interruption of
power itself would destroy quantities of data that might not be lost
if Halon were used.  For hand extinguishers, this allows use on any
live equipment without danger to the extinguisher operator.


3) They have a low heat of vaporization.  Unlike CO2, halon will not
thermally stress equipment or cause water or ice to condense on
surfaces, when used in flooding systems.


4) They are relatively non-toxic. (Carbon Tetrachloride, which in fact
is Halon 104, is a well known health hazard and is not used in
firefighting anymore.)  Halons in current use include 1211
(Bromochlorodifluoromethane), used in hand extinguishers, and 1301
(bromotrifluloromethane), used in flooding systems.  In their
non-decomposed state, as at the discharge nozzle, and at the typical
concentrations and exposure times for use in firefighting, they are
quite harmless to humans. Halon 1301 is used in concentrations of
5-10% of room air, and at this level it poses no significant threat to
health, either immediately or latently for an exposure of several
hours or less.  (Of course, one would not remain in such an atmosphere
for longer than was necessary.)  My MSDS for halon 1211, which is
slightly more toxic than 1301, lists a suggested TLV (which is an 8
hour time-weighted reccommended maximum exposure for everyday workers)
of 1000ppm (0.1%).  The effects of toxicity are similar to other CFC
solvents: headache, dizziness, etc., up to suffocation, CNS depression
and unconsciousness.

	When brought in contact with fire, though, Halon does produce
more toxic products, such as HBr, HCl, and HF.  (These are actually
the radicals which act as anticatalysts to interrupt the combustion -
see below.)  They are nasty toxins, but would be present in dangerous
quantity only in the context of a large fire, an exceptionally hot
fire, or in a small enclosed space, and only over minutes of exposure.
[A battle tank surely qualifies as a 'small enclosed space'...]  Being
irritants, these toxins provide their own warning of exposure.  One
could reasonably assume that in a fire of this size, the occupants
would already have left because of the heat and smoke present. 

	Halon flooding systems do NOT displace enough air so as to be
a hazard of suffocation.  CO2 systems, by contrast, lower the oxygen
content of the room to a level which supports neither combustion nor
human life.


5) They work.  Halon will extinguish gaseous, liquid and solid fueled
fires in almost any material which one might find in an office, car,
etc.  They will prevent reignition for as long as the gas
concentration is maintained, which by design, is long enough to allow
fire fighting personnel to arrive and effect full control.


It's true that halons do nasty things to ozone.  Halon 1301 is more
than 10 times as damaging, per pound, as are the popular refrigerant
freons.  I think 1211 is even worse.  However, the VAST bulk of the
halon which is released into the atmosphere has been done in the
testing of flooding systems.  Most current and future testing, for
reasons of cost as well as environmental harm, is done with other
methods and/or materials.  I don't believe that the Halon actually
dumped on fires poses a real threat to the ozone, in comparison to the
refrigerants and propellants which are otherwise discharged by
industry... but that point is moot.  In fact, the pollution that they
prevent by extinguishing the fires may be quite significant
environmentally... although I have not seen this considered.

Halons aren't for everything, though.  In many cases, water, foams, or
dry chemicals (none of which are nasty toxins, mind you, although ya
don't want to eat them either) are cheaper and/or more effective.
There are several kinds of "halon alternatives" now in the market
which fit well in certain applications, as well.



>> What's wrong with CO2 fire extinguishers, anyway???

1) They can freeze electronics and cause damage to sensitive materials.

2) They are a suffocation hazard when in firefighting concentrations
(about 60% volume)

3) They are ineffective: CO2 will not easily put out a fire in class A
materials--that is wood, paper, fabrics-- most of what burns in
everyday life.  Further, they are much less effective per mass than
either halons or dry chemicals... especially when container weight is
considered too.




CHEMISTRY OF HALON EXTINGUISHMENT:
	
	I am not a chemist, and so I do not have a really good idea
for what is going on when halon is applied to a fire.  From the looks
of it, real chemists aren't entirely sure, either.  But, here is the
accepted theory in a nutshell::

	A few good references:

	     1) FIRE PROTECTION HANDBOOK, NFPA, 16th ed., 1986, ch.19-2.
		An exceptional book on the subject of fire protection
		in many areas.  This chapter discusses the
		effectiveness and toxicity of halon in qualitative and
		quantitative terms, as it was known at the time.

	     2)	Usenet discussion in sci.physics: "A half-baked idea
		(halon possibility)", which was a discussion of using
		halon in a hydrogen balloon that digressed into an
		examination of halon.


> 
> 	When methane is heated to the point of ignition it absorbs energy
> and produces two free radicals: CH3~ and H~.  The resultant hydrogen
> atoms react with oxygen in the atmosphere to form hydroxyl free radicals,
> OH~.  All of these free radicals possess so much energy that they
> further propagate the reaction, which proceeds in several stages like:
> 
> 	CH4 + OH~ --> H2O + CH3~
> 
> 	CH3~ + O2 --> OH~ + HCHO
> 
> 	HCHO + O~ --> OH~ + H-C=O
> 
> 	H-C=O --> H~ + CO
> 
> 	CO + OH~ --> H~
> 
> 	2OH~ --> H2O + O2
> 
> 	And some of you probably though that burning methane just produced
> water and carbon dioxide as a direct process! :-)
> 
> 	When a Halon agent is heated by the above combustion process, it
> produces ITS OWN FREE RADICALS which compete with those produced by the
> original combustion process.  As an example, bromotrifluoromethane
> (Halon 1301) produces bromine free radicals which combine with the
> hydrogen free radicals to produce hydrogen bromide - which does not
> further decompose.  The hydrogen and hydroxyl free radicals produced
> by combustion are significantly reduced in concentration by combining
> with the halogen free radicals produced by the Halon agent.  Voila! -
> the fire goes out.
> 
> <>  Larry Lippman @ Recognition Research Corp., Clarence, New York
> <>  UUCP:  {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry

[My salute to Larry...a truly sharp and helpful chemist in net-land. -mikew]


	Basically, for the Bromine in Halon 1301, the heat of the fire
separates the halon into radicals:

		CBrF3 --> CF3~ + Br~
 
	The bromine radical then reacts with an afforementioned
hydrocarbon radical:

		CH4 + Br~ --> CH3 + HBr

	The bromine has 'stolen' a hydrogen from the methane, making
the fuel more stable (less flammable).  It produces the toxins Br and
HBr in this process.  Then the HBr reacts with a hydroxyl radical
(also present in the above combustion analysis) as follows:

		OH~ + HBr~ --> H2O + Br~

creating water vapor (nontoxic and stable) and releasing the bromine
for another interaction.  The important thing here is that the free
Br~ is a catalyst only and so is continuously resupplied to the fire
site.  This means that a small quantity of the extinguishant can act
on a much larger supply of fuel and oxidizer.  Generally, the toxins
created by the burning material (not methane!) will be a more
significant hazard than the products of the decomposed extinguishant.

	Also of note is that the whole decomposition process which
allows the smothering of the fire is 'powered' by the heat of the fire
itself (trick!), and so it stops when the fire goes out.


	It's neat stuff... a fire in a room of adequate Halon
concentration could never start!  Halon flooding systems work so fast
and so thoroughly that systems exist for high hazard areas (explosive
atmospheres) which use ultraviolet flame sensors to detect an
explosion starting.  The halon is deluged into the room and actually
STOPS the expanding flame front of the explosion before the pressure
rise destroys the container or room.  (Can you imagine??)

(Hmmm... what a way to enforce no smoking areas ;-) "Hey-why won't my
lighter work?"

	There are limits, though.  It won't work on fuels that contain
their own oxidizer (high explosives, organic peroxides), reactive
metals such as sodium and magnesium, metal hydrides (chemical
incompatibility), or materials that can violently decompose without
oxidizing, like hydrazine and acetylene (no oxidation reaction to
interrupt).  A more common limitation is a limited ability to
extinguish deep-seated class A fires (such as a mattress or a
haystack) in low concentrations.  In these cases the halon will stop
the spread of fire but a cooling agent like water or "wet" water
(reduced surface tension) will be needed to extinguish the smoldering.

	Another fundamental limitation is that it only works when it's
there (profound, huh?)-- it will put out the fire, but if it is vented
or blown away before the burning material cools below the fire point,
the fire will restart.  Thus, a multiagent attack is sometimes
necessary: halon to knock down the flame, and then dry chemicals or
water to keep it under control.  I believe the Navy has used this
method to combat some cargo fires onboard sea vessels.  (expensive
cargo -> expensive protection!)
 

And a final note from the safety guy...
As always, when using any fire extinguisher, remember:

1) Don't use it unless the fire is small enough to handle.
2) Don't use it until everyone is out of the room and out of danger.
3) Never let the fire get between you and your exit.
4) Priority: people before property.


-mike
________________________________________________________________________
Mike Weihman    mikew@sr.hp.com 
                                 
Hewlett-Packard Co.              | HP Fire/Chem/Medical Response Teams     
Microwave Instruments Division   |                                    
1212 Valley House Drive          | Firefighter/EMT-D                  
Rohnert Park, CA 94928  USA      | Rancho Adobe Fire Protection District 
(707) 794-4454                   | Penngrove, CA                     
________________________________________________________________________

From misc.emerg-services 
 From: George Goble <ghg@ecn.purdue.edu>
 Subject: Re: HALON
 Date: 30 Sep 90
 Organization: Purdue University Engineering Computer Network

 In article <27508.2704B95C@stjhmc.fidonet.org>
 Al.Stiebel@f440.n101.z1.fidonet.org (Al Stiebel) writes:
 >Any information yet as to research and development for a
 >replacement for Halon?
 ...
 Great Lakes Chemical, HQ in W. Lafayette, IN has announced a
 replacement for Halon-1211 I believe (think it may be called
 Halon-1508, but not sure). It also seems to work as a refrigerant I
 have heard.  Their phone number is (317) 497-6100 if you want to
 give them a call.
 --ghg



 From: Larry Lippman <larry@kitty.uucp>
 Subject: Re: HALON
 Summary: Halon replacement chemistry...
 Date: 30 Sep 90
 Organization: Recognition Research Corp., Clarence, NY
 ...
 "Halon" refers to a general classification of halogenated aliphatic
 hydrocarbons which are useful for fire suppression applications, and
 does not refer to a specific compound.

 With respect to environmental issues involving CFC's (chlorinated
 fluorocarbons), not all Halons are CFC's.  As an example, Halon-1301
 (bromotrifluoromethane) is not a CFC, and therefore poses no harm to
 the ozone layer.  This does not mean, however, that Halon-1301 is
 without toxicity or other potential harm.

 > Great Lakes Chemical, HQ in W. Lafayette, IN has announced
 >a replacement for Halon-1211 I believe (think it may be called
 >Halon-1508, but not sure).

 Halon-1211 (bromochlorodifluoromethane) is indeed a CFC.  However,
 the above replacement of "Halon-1508" could not be correct, unless a
 singular carbon atom has been discovered with a valence of at least 13. :-)

 Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
 VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
 FAX:   716/741-9635                  {utzoo, uunet}!/\aerion!larry



 From: George Goble <ghg@ecn.purdue.edu>
 Subject: Re: HALON
 Date: 30 Sep 90
 Organization: Purdue University Engineering Computer Networt
 ...
 True, 1301 has no chlorine, but bromine does much more damage to the
 ozone layer. The "Alliance for Responsible CFC use" lists the ODP
 (ozone depletion potential) for Halon-1211 as 3.0 (three times worse
 than Freon-12).  Halon-1301 is a whopping 10.0, the highest of any
 substance I have seen.  Look for nasty taxes on Halons in '91.

 >> Great Lakes Chemical, HQ in W. Lafayette, IN has announced a replacement
 >> for Halon-1211 I believe (think it may be called Halon-1508, but not sure).
 >
 >Halon-1211 (bromochlorodifluoromethane) is indeed a CFC.  However,
 >the above replacement of "Halon-1508" could not be correct, unless a
 >singular carbon atom has been discovered with a valence of at least 13. :-)

 The "1508" was the number printed on the tank and MSDS, the formula is
 still secret since they are still working on a patent I think.  Thanks
 for pointing this out Larry.
 --ghg

Newsgroups: sci.military.moderated
From: Urban_Fredriksson@icl.se (Urban Fredriksson)
Subject: Halon replacements (Was: Re: FAEs)
Date: Thu, 7 Dec 1995 17:34:27 GMT

damian@/etc/HOSTNAME (Damian Kneale) writes:

>Last I checked, combustion stopped pretty much at either 8 or 12 percent
>O2 available (can't remember exact figure, and it's not really important
>for this example).

The upper limit for stopping combustion is 15%.

> Anyway, respiration is effective much below that, so
>suffication isn't a danger.

Not normally, no: At sea level pressure, 10% oxygen
(compared to the normall 21%) corresponds to the oxygen level at 6000 m
altitude and for most people unassisted respiration isn't effective at
that altitude.

But if you want to stop fires and cannot use Halon any
longer, there are ways around that. Increasing the amount
of CO2 stimulates breathing, 2.5-5% is useful.
The Halon replacement I know of consists of injecting large
amounts (40-70%) of a nitrogen/argon/carbon dioxide
mixture, aiming for 12% O2 and 4% CO2, causing no
discomfort or health concerns.
--
 Urban Fredriksson  urf@icl.se  "That afternoon it rained on Earth."