CFCs
Chlorofluorocarbons (CFCs) were previously seen as wonder chemicals of the 20th century. Developed in the United States in the 1920s by Thomas Midgeley, they soon became very popular as refrigerants, for making plastic foam and as aerosol propellants. CFCs have a useful combination of physical properties. They are very stable, non-toxic and non-flammable. Unfortunately their chemical stability also means that they destroy stratospheric ozone, in some cases for well over a hundred years before their removal from the atmosphere, although this was not known when they were developed.
Halons
Halons, which contain bromine, are very effective in putting fires out. Their most useful characteristic is that they can be used where both people and machinery are present, without doing any damage to either. They have become widely used in computer rooms, museums, on ships and aircraft, for general office fire-protection and for industrial applications. The two main halons are halon 1301, used in fixed systems, and halon 1211, used in portable fire extinguishers.
Carbon Tetrachloride
Carbon Tetrachloride was first used in the early 1900s as a fire extinguisher, but because of its toxicity it was never widely adopted. It has since been used as a solvent particularly in the manufacture of synthetic rubber, the production of pesticides and pharmaceuticals, and the production of CFC 11 and CFC 12 where the substance itself is actually destroyed.
1,1,1 Trichloroethane
1,1,1 Trichloroethane (methyl chloroform) is a versatile, all-purpose solvent used for its powerful solvent used for its powerful cleaning properties,non-flammability under normal conditions and low toxicity. It was introduced in the 1950s as a substitute for carbon tetrachloride in some applications and is used for cleaning metal parts during the manufacture of equipment.
HCFCs
Hydrochlorofluororcarbons (HCFCs) were developed as an interim replacement for CFCs. They break down more readily in the lower atmosphere, so that little of the chlorine they contain reaches the stratosphere. HCFCs are considered necessary in some applications in the short to medium term, to help users to move rapidly away from the use of CFCs; they have some ozone depleting potential, but damage done by HCFCs is between one-fiftieth and one-tenth of that done by the same amount of the major CFCs.
Methyl Bromide
Methyl bromide is a powerful fumigant used to destroy pests found in soil, structures (such as flour mills, aircraft or ships), products (such as cereals) and for plant quarantine purposes. There is, at present, no single alternative to methyl bromide. There is scope, however, to reduce the amount of methyl bromide used by changing application practices, using substitutes where possible and reducing the frequency of treatments.