Q. Canadian Homebuilt: Fire Extinguishers - Halon

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