I worked servicing Halon systems in computer server rooms for years.  It
works by interfering with the combustion process on a molecular level.
It prefers a closed area for "soak time" if the parts are very hot or a
re-flash can occur.  Open areas can just blow the agent away and make it
ineffective.  Halon (and R12) production was stopped many years ago, but
lots of of virgin and reclaimed gases are still available and just as
effective as they were years ago.  They just cost more now due to gov't
taxation to make it cheaper to use alternatives, none of which work as
well with the same amount of agent.  The other agents; FM-200 and R-134
are considered "clean" alternatives but require more agent to do
"almost-as-good" of a job.
   I keep Halon extinguishers around because of all these advantages.
One spray of a dry chem into a running engine means automatic rebuild,
where Halon leaves the equipment ready for re-use with no clean-up
required.

Mike B.

On Fri, Jun 1, 2012 at 5:29 PM, Scott Daniel - Turbovans wrote:

> I can confirm that Halon is awesome.
> I bought some little one pounders for about $ 24 each years ago.
> I had a real opportunity to one..
> it instantly stops fire.
> I don't think it does it by just displacing oxygen either.
>
> I had a couple of inches of gas in a yogurt container , on fire.
> One short instantaneous blast of halon ..like a micro-second.'s worth.
> .
> fire gone, , nothing burnt , over an inch of liquid gas still in the
> yogurt container.
> Slight warping of the yogurt container's plastic is all.
> And no mess to clean up either.
> It was banned or changed due to environmental factors is my
> understanding.