Freon

Freon is a registered trade name of DuPont, which it uses for a number of halocarbon products. They are stable, nonflammable, moderately toxic gases or liquids which have typically been used as refrigerants and as aerosol propellants. These include the chlorofluorocarbons (CFs) implicated in ozone depletion, but also include newer refrigerants which typically include instead of  and do not deplete the ozone layer.

History
The first CFCs were synthesized by Frédéric Swarts in the 1890s. In the late 1920s, a research team was formed by Charles Franklin Kettering in General Motors to find a replacement for the dangerous refrigerants then in use, such as ammonia. The team was headed by Thomas Midgley, Jr. In 1928, they improved the synthesis of CFCs and demonstrated their usefulness for such a purpose and their stability and nontoxicity. Kettering patented a refrigerating apparatus to use the gas; this was issued to Frigidaire, a wholly owned subsidiary of General Motors. In 1930, General Motors and DuPont formed Kinetic Chemicals to produce Freon. Their product was dichlorodifluoromethane and is now referred to as 'Freon-12', 'R-12', or 'CFC-12'. The number after the R is a refrigerant class number developed by DuPont to systematically identify single halogenated hydrocarbons, plus there are R numbers assigned for other refrigerants besides halocarbons.

Most uses of CFCs are now banned or severely restricted by the Montreal Protocol as they have shown to be responsible for ozone depletion. Brands of Freon containing hydrofluorocarbons (FCs) instead have replaced many uses, but they too are under strict control under the Kyoto protocol as they are super-greenhouse effect gases. They are no longer used in aerosols, but to date no suitable general use alternatives to the halocarbons have been found for refrigeration which are not flammable or toxic, problems the original Freon was devised to avoid.

Safety
According to their material safety data sheets, CFCs and HCFCs are colourless, volatile, toxic liquids and gases with a faintly sweet ethereal odour. Overexposure at concentrations of 11% or more may cause dizziness, loss of concentration, central nervous system depression, and/or cardiac arrhythmia. Vapors displace air and can cause asphyxiation in confined spaces. Although non-flammable, their combustion products include hydrofluoric acid and related compounds.