What breaks down to form poisonous gas in the presence of flames?

• A. Halogenated refrigerants
• B. Hydrocarbon refrigerants
• C. Ammonia
• D. Water

Answer: (A)

When halogenated refrigerants are exposed to flame, their chemical bonds break down and halogen-containing gases are released. The chlorine and fluorine in these refrigerants can form toxic gases such as hydrogen chloride and hydrogen fluoride, and in some conditions even phosgene (a highly poisonous gas). This makes halogenated refrigerants far more hazardous in a fire than other types. Hydrocarbon refrigerants mainly burn to produce carbon dioxide and water, and only with incomplete combustion do they form carbon monoxide, which is dangerous but not the characteristic breakdown product of halogenated types. Ammonia is itself toxic, but the specific dangerous gas formed from flames with halogenated refrigerants is the halogen-derived products like phosgene, which is why this option is the best answer. Water does not form a poisonous gas in typical fire conditions.