Dang!
Wasn't it Phosgene gas the Germans used in WWI?
FYI: some of the refrigerants Freon, etc) are chloronated too.
I am a hazmat technician and teach Weapons of Mass Destruction, and yes, phosgene was used as a chemical warfare agent in WW1.
There are many chlorinated compounds which can decompose under high heat and turn into very toxic chemicals.
One very common source of phosgene is welding galvanized metal.
Basically, when exposing compounds to high heat, it is critical to make sure the chemical being used is intended for that purpose. Unless you are a hazmat technician or an industrial hygienist, it's very difficult to know what the substance will be when heated. Use substances designed for the application you are intending to use.
Also, be very careful of mixing chemicals. Even seemingly harmless chemicals can mix and release extremely toxic gases.
And yes, freon and some other refrigerants will decompose under high heat and release phosgene and other toxic compounds. That is one of the dangers in building fires and one concern regarding the workers at the WTC site following 9-11, where the refrigeration units (air conditioners) here buried in the burning rubble, and may have converted to phosgene.
