Fully halogenated chlorofluorocarbons (CFCs) contain only chlorine, fluorine and carbon and have a high ozone depleting potential. Similar compounds, which are not fully halogenated and contain hydrogen, in addition to chlorine, fluorine and carbon are called hydro chlorofluorocarbons or HCFCs. The presence of hydrogen in HCFCs reduces their persistence in the atmosphere and they have a less destructive effect on the ozone layer. Chemicals containing fluorine, carbon and hydrogen but no chlorine or bromine are known as hydro fluorocarbons or HFCs. The HFCs are currently being developed as CFC substitute that do not damage the ozone layer. One commonly used measure of a compound's ozone destroying capacity is its ozone depletion potential (ODP). It provides a useful basis for estimating the ozone depletion potential of various chemicals relative to CFC-11, which has an ODP of 1.0.s.

CFCs and related chemicals have been used in a wide variety of products since the 1930s when CFC-12 began replacing ammonia and sulphur dioxide as primary coolant. CFCs are used in refrigerators as primary coolant and till now have been a crucial ingredient in refrigeration and air conditioning units. They are used to make soft and rigid foams for furniture, cushions, mattress, packaging, building insulation material, computer cabinets, tennis racket, steering wheels, etc. Other CFCs are used as solvents, propellants in aerosol and as a fire extinguisher (halons) in fire fighting equipment. Two other chemicals that significantly damage the ozone layer are carbon tetrachloride (CTC) and methyl chloroform (MCF). CTC is used as a feedstock in production of CFC-11, CFC-12 and many pesticides, as a solvent in manufacture of synthetic rubber and dyes, as a metal degreaser, and as a dry cleaning agent. Methyl chloroform is used mainly as an all purpose industrial solvent for vapour degreasing operations and cold degreasing of fabricated metal parts, etc.

Substitutes for Ozone Depleting Substances (ODS)
Searching of substitutes for these seemingly indispensable chemicals began in 1987 with the signing of Montreal Protocol. Under the aegis of UNDP, a Technology Panel was established drawing knowledge of 110 experts from 22 countries, which reported on substitutes for ozone depleting substances. The Panel recognized that the CFC substitutes should not be toxic in nature and these should not contribute to global warming. Based on the available substitutes, the time schedule for phase out of CFCs has been worked out

As a short-term measure, one of the available alternatives is to use HCFCs, which destroy ozone to a lesser extent. To replace chlorine-containing substances, several substitutes have been developed while research is on to find other substitutes. As of now, the most viable compound to replace CFC-12 is HFC-134a. For foam blowing HCFC-22, HCFC-141b and HFC-123 are some of the substitutes. In fire fighting sector, there is no substitute for Halon. Some of the alternatives are dry chemical powder and CO2. In Aerosol sector, hydrocarbons, dimethyl ether, compressed CO2, N2 and N2O can be sued as substitutes for propellants. The alternative aerosol system includes finger and trigger pumps, mechanical pressure dispenser, etc. The currently available alternatives in sterilization sector are steam sterilization, ethylene oxide, carbon dioxide etc.

Among the HCFC and HFC alternatives only HCFC-22, HCFC-142b, HFC-152a AND HFC-134a are currently available and can be made available in large quantities at relatively short notice. Halon replacement chemicals are not at the same stage of development as CFC replacements for refrigeration, solvents and other applications.