Gary

<I use r-134 which cools marginally and if I thought
es-12 would cool better and I was switching from r-12
I would not worry about the burning issue. >
 It's not the burning per se, it's the explosion that is of concern.

< First of all the amount of gas in comparison to the propane you
are already carrying is small.   It is in a sealed
system without oxygen.   If a leak develops the gas
will dissipate quicky.>
The propane tank is in a specially designed and tested vessel that should
withstand severe impact and pressure rise. The AC system in not designed to
the same DOT/ASME standards - actually not even close. Your right, since
there is no O2 in the system, it won't cause a problem until it leaks out and
mixes with air. For the same reason you wouldn't check your propane tank for
leaks with match.
Small amount is also a relative term How long will 3 lbs of propane last in
your BBQ. What if all of that energy was realsed at once (ie. explosion)?

<If you are going to worry about es-12 you should not
use the propane and for that matter the gas in your
tank which represent a much greater hazard.>

Not so.... see above

These are two totally different types of systems - one designed with all the
appropriate safety measures and one not. Just think about it before betting
yours and some one elses life. Believe me, I wish this stuff were safe, I'd
use it in a heartbeat. Think   "works great, blows up".
John
84 Westaru