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At high temperatures (for example open flames and glowing metal surfaces), R-12 and R-22 can decompose to form ____.

A phosgene gas.

Phosgene may also be produced during testing for leaks of older-style refrigerant gases. R-12 and R-22 were formerly leak-tested by a small gas torch with a sniffer tube and a copper reaction plate in the flame nozzle of the torch. If any refrigerant gas was leaking from a pipe or joint, the gas would be sucked into the flame through the sniffer tube and would turn the color of the gas flame to a bright greenish blue. In the process, phosgene gas would be created due to the thermal reaction. No valid statistics are available, but reports suggest that numerous refrigeration technicians suffered the effects of phosgene poisoning due to their ignorance of the toxicity of phosgene produced during such leak testing. Electronic sensing of refrigerant gases phased out the use of flame testing for leaks in the 1980s.

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