Which type of refrigerant is considered most hazardous due to its flammability and toxicity?

Ammonia is regarded as the most hazardous among the listed options due to its flammability and toxicity. When used as a refrigerant, ammonia can pose significant health risks if inhaled, as it is highly corrosive and can cause severe respiratory issues. In addition to its toxicity, ammonia is flammable under certain conditions, especially when in the presence of an ignition source.

While chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) do have environmental concerns, particularly regarding ozone depletion and global warming potential, they do not present the same level of immediate health risks related to flammability and toxicity that ammonia does. CFCs and HCFCs have been phased out in many applications due to their environmental impacts, while HFCs, although less harmful in terms of direct human toxicity, are also not flammable. This reinforces ammonia's classification as a more hazardous refrigerant in terms of both human safety and environmental considerations.