[townsend]

i deal with this at work, since i do commercial air conditioning and deal with cfc, hcfc, and hfc refrigerants. you'd be suprised how often no matter what you do to get all the refrigerant out of a system before brazing or soldering, you still get a little pocket bubble or something of vapor that all of a sudden decides it wants to go poof and decompose into phosgene when doing hot work. when i did residential, a 30-year mechanic was replacing a compressor in a small condensing unit and nearly died from the reefer vapor being released from the oil when he was brazing, which decomposed into phosgene when it came out of the joint and was exposed to the open torch flame.