I have read this thread after being gone...In most of the fires involving this refrigeration system its not the fault of the propane per se. The fatal sequence of events goes like this...
(1) The lit propane increases the pressure of the hydrogen/ammonia in the mixture as a normal part of operation
, then (2) in a boarder line tube fracture/weakened wall due to corroson a pin hole leak begins in the weakened steel wall of the condenser tubing.
(3) The refrigerant mixture escaping becomes the fuel and the accelerator fuel,
(Note) the heat from a hydrogen fuel source rivals that of an acetylene source at plus 3000 degrees F.
The flash point is completely transparent, if it explodes its shock wave is 5 times faster than sound. If you hear it you have already been burned.
are harmless in modern designs, most occur just sitting there harmlessly and never reach an ignition source.
Its one big reason one must never travel on propane using the refrigerator.
The ABC chemical extinguisher would do nothing on this fuel source...a Halon ( now banned) or a CO2 unit might dampen and cool it enough to keep it from re-lighting once smothered, as would water be better as heat must be subtracted not just oxygen
... Its not safe to be near this type of fire without special equipment.
The ammonia could be rapidly released in a way that makes the burns from the fire pale in comparison when mixed with steam...or worse yet respiratory failure become a result of inhalation.
The point I am making is the ignition source was already there and operating properly, its the pressure behind these other fuel sources that was the problem, both the hydrogen and the ammonia oxidize too rapidly for human intervention to avoid in a trailer without much prior preparedness..
When inspecting the system prior to start up in an old system look for the tell tale signs of ammonia corrosion, or a bubbling of the "paint", pitting or a rough texture to the condenser coils.
I believe by the very rapid onset of the fire and the aggressiveness of its quick penetration that the leak occurred spontaneously in concurrence with the ignition source being a normal flame...Its very rare...there have been recalls on some models on this issue recently.
All these reasons are the WHY the unit is service in a static free pure nitrogen environment with a special automatic fire suppression system.
Are these systems safe?
Yes they are by the numbers...its when the unusual happens
that all this stuff works against you so quickly...
Gasoline engines are safe mostly too, but a leaking tank and a wool sweater have burned down a few fueling stations or two as well...
As long as the physics
are addressed your safer than driving on holiday per 100,000 cars traveling...fear that more.
I line my refrigerator installs with firewall fiberglass matte, it buys about 3 to 5 minuets time so the fire breaks out of the coach outer wall, not into the coach occupied space...the glass will fail, it only buys time.
A cheap $27.00 dollars U.S.
Hope this helps.
Happy Camping Again, Safe Trails Always.