 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 cause a colour change 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 anecdotal 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.