The following characteristics should certainly be kept in mind when choosing the ideal refrigerant for a specific application:
Ammonia is a colourless gas with a very sharp odour. Ammonia is strongly caustic and corrosive and the main health effects consist of burns at the sites of direct contact (i.e., skin, eyes, respiratory tract, …). These burns might be serious enough to cause permanent blindness, lung disease, or death due to airway blockage and respiratory insufficiency. Due to its high toxicity, ammonia represents the most frequent cause of accidents. Its dispersion can significantly increase the number of affected people and often requires the evacuation of the neighborhood of the concerned place. Firefighters need special equipment to respond to ammonia accidents.
Hydrocarbons are very flammable but their release will only cause accidents if an ignition source is present. Otherwise, the gas is readily dispersed and the risk is rapidly decreased. For this reason and because the number of installed hydrocarbon installations is not very high, except for very small charge sizes and factory sealed equipments, such as those of domestic refrigerators/freezers, the number of reported accidents is much lower.
CO2 refrigeration units function at higher pressures, which can cause dangerous equipment ruptures and projections of metallic parts at high energy, potentially causing severe physical injuries. In addition, CO2 is harmful when exposed to it for several hours at low concentrations (1 3%). At concentrations above 10% it may cause fatalities due to the lack of oxygen uptake potentially leading to suffocation and asphyxia.
Fluorocarbons used in refrigeration typically display low toxicity characteristics, are non-flammable and disperse rapidly. Their major risk is suffocation and asphyxia due to the lack of oxygen, a risk encountered with any inert gas in confined or non-ventilated areas. The number of fatalities reported is orders of magnitude lower than for ammonia systems, even though there are by far more fluorocarbons systems in use.