Jarrett,
<<  Ron, I'm curious if Halon has a place at all in a/c.>>
In a previous life I worked on the fire detection and suppression
systems in a bunch of our vehicles now driving into Fallujah.  At the
time, the Army was looking to replace Halon in engine compartments for
environmental (Ozone depleting) and scarcity reasons.  Halon remains in
all crew compartments because it is/was the only agent that could put
out a fire while not killing the crew at the same time.  All other
agents at that time (~8 years ago) required concentrations that were not
survivable.

I must agree with Rob's comments to Jerry about the ventilation issue.
The cooling fans in these vehicles produce large air flows through the
engine compartments much like we see in our planes.  We performed
countless live fire tests and found that discharging agent with the fans
running was absolutely futile.  The other scary observation is that even
a small fire subjected to that kind of airflow turns into a blow torch.
One would either have to close off the inlets or discharge agent at such
a rate that the minimum concentration was maintain for several seconds.
This also assumes that the ignition and/or fuel sources have been taken
care of.  I don't mean to put a damper on the idea, but it is very
difficult to implement.

In terms of detection.  Any thermal detection must be downstream of the
fire, so you need to know the flow patterns and likely fire locations.
If you miss this flow pattern, you could have an inferno in the engine
compartment with the thermal sensor being cooled by fresh air.   In this
case hot air doesn't rise and flames don't go up. Optical sensors are a
good options if you can't pin down flow patterns.  There are many
flavors out there that range in cost and capability. I have never tried
to obtain any on a retail/individual basis, but it is certainly worth a
try.

Chris Zavatson
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