Q. Canadian Homebuilt: Fire Extinguishers - Halon

wrote in message
...

Portable Halon extinguishers made before 1995 are legal for use.
Aircraft are still allowed to use Halon.
It is illegal to release holon into the environment except for use in
"emergency" fires (ie it is illegal to use for "training" purposes)

This, of course, varies with the country.

IMHO, Halon is not the ideal extinguishing agent for most aircraft fires,
especially in-flight. In order for Halon to be effective, it must be applied
to the fire before anything in the vicinity of the flammable gases becomes
heated to the ignition temperature of the gas, otherwise the fire will
re-ignite as soon as the concentration of the Halon drops below the
percentage needed to interfere with combustion.

Establishing and maintaining the required concentration of Halon is
difficult, if not impossible, in an open space. Even closed environments
such as sealed buildings are difficult to permeate. It is likely impossible
under an aircraft cowling when the plane is moving.

One needs to understand the process by which Halon inhibits fire. The fuel
(usually carbon-based material) has a greater affinity for the Halogens
(Chlorine, Fluorine, Bromine & Iodine) that it does for Oxygen. In the
presence of both Oxygen and a Halon, the fuel will "choose" to combine with
the Halon without the evolution of heat and light - what we call "Fire". If
sufficient Halon is available, all the fuel will combine with the Halon and
the fire will go out.

If the Halon is removed and there is still a source of ignition, the fire
will take up right where it left off.

If you've got a cabin fire, that's a horse of a different smell.

Rich S.

Rich S. wrote:

Establishing and maintaining the required concentration of Halon is
difficult, if not impossible, in an open space. Even closed environments
such as sealed buildings are difficult to permeate. It is likely impossible
under an aircraft cowling when the plane is moving.

I disagree. Have you ever used a Halon fire extinguisher? Back in the
Reagan era when the defense departement had a lot of money and Halon
hadn't yet been restriced, we were given training where we used large
Halon hand extinguishers to put out diesel fuel fires set in pans
outside.

If the Halon is removed and there is still a source of ignition, the fire
will take up right where it left off.

If you've got a cabin fire, that's a horse of a different smell.


With a flood system and a relatively closed space it takes a long
time for the Halon to disapate. Try lighting a lighter in a space
near where halon has been discharged.

Of course, much of what you said also applies to CO2. If the CO2
doesn't cool down the metal (which admittedly it has a higher
capacity to do than Halon), then you have the same (actually larger)
reignition problems.

the key statement is...

"It is likely impossible under an aircraft cowling when the plane is
moving. "

For this application it is a waste of weight, money, and time.

"Ron Natalie" wrote in message
m...
Rich S. wrote:

Establishing and maintaining the required concentration of Halon is
difficult, if not impossible, in an open space. Even closed environments
such as sealed buildings are difficult to permeate. It is likely
impossible under an aircraft cowling when the plane is moving.

I disagree. Have you ever used a Halon fire extinguisher? Back in the
Reagan era when the defense departement had a lot of money and Halon
hadn't yet been restriced, we were given training where we used large
Halon hand extinguishers to put out diesel fuel fires set in pans
outside.

If the Halon is removed and there is still a source of ignition, the fire
will take up right where it left off.

If you've got a cabin fire, that's a horse of a different smell.


With a flood system and a relatively closed space it takes a long
time for the Halon to disapate. Try lighting a lighter in a space
near where halon has been discharged.

Of course, much of what you said also applies to CO2. If the CO2 doesn't
cool down the metal (which admittedly it has a higher
capacity to do than Halon), then you have the same (actually larger)
reignition problems.

On Tue, 19 Jul 2005 15:11:53 GMT, "Cy Galley"
wrote:

the key statement is...

"It is likely impossible under an aircraft cowling when the plane is
moving. "

For this application it is a waste of weight, money, and time.

I remember a "discovery" or "military weapons" show I watched one time
where they were attempting to find a substitute for the Halon based
fire extinguishing system being used on some military jet.

They demonstrated the ability of the Halon system to put out a fire
created by a 20mm cannon hit, under controlled conditions. The
conditions included being in a wind tunnel, or directing high speed
air onto the area to be hit to simulate relatively high speed flight.

The Halon based system did a pretty good job of snuffing the fire out
from the cannon shell hit, even while the flame was being fanned by
the high speed air. Must have been a lot of Halon, I guess.

None of the other types of systems shown seemed to work quite so well.

This all came to be because Halon is a CFC, as is the refrigerant
R-12. They are both similar inert gasses. I recall a demonstration
one time wherein this guy breathed in from a hose of R-12, and then
breathed out over a lit candle. The R-12 settled over the flame and
extinguished it.

As a mechanic back in the 70's, we used to discharge that stuff all
over the place. It didn't matter we were told, it was an inert gas...

Corky Scott

Corky Scott wrote:


This all came to be because Halon is a CFC, as is the refrigerant
R-12. They are both similar inert gasses.

They ARE very stable, but not 'inert gasses'.

Historically 'inert gasses' were a handful of chemical elements,
that in their natural state at room temperature were monatomic
gasses, and which would not form any chemical compounds under
any conditions.

Sometime after the mid 20th century some shortlived compounds of
Neon (and maybe some others) were formed under laboratory conditions.
Consequently, the proper term for these gasses was changed to
'noble' gasses, meaning the were reluctant to combine with other
elements, but not completely inert.

AFAIK 'inert gas' remains as an archaic term synominous with
'noble gas'.

... It didn't matter we were told, it was an inert gas...


I think welders use the term 'inert gas' for any gas that will
not ready with the metal they are welding by whatever technique
they are using. But CFCs/Freons never qualified as 'inert'
even by that defintion.

Oh well, such is the nature of slang.

I remember the screens used to support a beaker over a bunsen
burner. they had a disc of asbestos in the middle so the flame
would not burn through the wire. Bet those were a great source of
airborne asbestos fibers.

--

FF

On 20 Jul 2005 10:43:08 -0700, wrote:

They ARE very stable, but not 'inert gasses'.

I stand corrected, the guy demo'd how to service automotive A/C
systems, I doubt he was a trained chemist. I for sure didn't know
enough chemistry to challenge, or even know the difference. ;-)

I was just impressed that anyone would inhale the stuff.

Corky Scott

Corky Scott wrote:

...

I was just impressed that anyone would inhale the stuff.


I'm impressed also, and not favorably. Although CFC refrigerant
itself is non-toxic, like air from a shop compressor it usually
contains trace contamination by lubricants making it dangerous
to inhale.

Ditto for helium sold to inflate balloons. Sure, you can make
your voice sound funny but you can get chemical pnemonia too.

--

FF

"Ron Natalie" wrote in message
m...
Have you ever used a Halon fire extinguisher?

Yup. I have fought actual aircraft fires using Halon, Dry Chemical (both
"Purple K" and "Super K"), Protein foam, CO2, etc., etc. For a picture, see
http://temp.corvetteforum.net/c4/elw...mp/oysters.jpg or
http://tinyurl.com/csndg . That's me in the middle next to the pilot's
seat. All those little black dots are fresh oysters he was bringing back
from Canada. The white stuff is Dry Chemical - 1,500 pounds of it. It
wouldn't stop the fire until we covered it with foam. Items like the burning
tires would reignite the gasoline behind us after we had moved the hose line
past. Had to replace my bunking outfit after that one - too many burn holes
to repair it.

With a flood system and a relatively closed space it takes a long
time for the Halon to disapate. Try lighting a lighter in a space
near where halon has been discharged.

I spent several years inspecting, discharging and signing off fixed Halon
system in computer rooms, satellite communications buildings, and one
180,000 sq. ft. building for Boeing that I can't even talk about. There are
no areas on a light aircraft which are sealed tightly enough to establish or
maintain a proper concentration of Halon. You can "overkill" a simple pan
fire with a portable extinguisher, but that won't work on an engine
compartment fire when you're in the cockpit.

Halon is a wonderful product, for it's purpose.

Of course, much of what you said also applies to CO2. If the CO2 doesn't
cool down the metal (which admittedly it has a higher
capacity to do than Halon), then you have the same (actually larger)
reignition problems.

Some other factors must be considered with CO2. Being heavier than air, it
tends to settle in a low spot - very important in ship fires. Halon diffuses
throughout the space. I'm not sure how the Latent Heat of Vaporization
compares between Halon and CO2. In either case the cooling capability is a
very minor effect when it comes to extinguishment. If you want cooling, use
water. If you want to secure the area and prevent reignition, use foam.

In a three-dimensional fire such as an aircraft fire, all bets are off. Even
foam may not prevent reignition. Trust me - it is scary to be wading in Jet
A trying to plug a leaking tank when the stream coming from the tank keeps
igniting. Even in a drill. 8-}

Rich S.

Rich S. wrote:
...

Some other factors must be considered with CO2. Being heavier than air, it
tends to settle in a low spot - very important in ship fires. Halon diffuses
throughout the space.

Recalling Avogodro's law, Isn't Halon also heavier than air?
In fact, isn't it heavier than CO2?



--

FF

wrote in message
oups.com...

Recalling Avogodro's law, Isn't Halon also heavier than air?
In fact, isn't it heavier than CO2?

Well, I don't remember. I know it's typically discharged from the high point
in an enclosed space through specially designed diffuser nozzles, so what
you say may be correct. I seem to remember that, like air, it is a
homogenous mixture of gasses and tends to diffuse throughout the atmosphere.
Maybe that's why some are concerned about the "Ozone hole" and Halon
affecting that in the upper atmosphere.

It's been a long time since I've studied any basic chemistry and I didn't
know that much about it then. If different gaseous elements tended to
separate out, wouldn't Nitrogen separate from Oxygen in the atmosphere? But
we know it doesn't. I don't know enough to hold up my side of a technical
discussion based on Avocados. I remember that we used to put sniffers at
different heights inside buildings where we were discharging Halon systems
and would measure the concentration at all levels.

Rich "Getting old is no job for a sissy!" S.