Refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. Most of the gases in refrigeration plants have adverse environmetal effects and could be dangerous for humans. Some of them, used in the past, with chlorine compounds, are today totally banned with the European Community and can be used only in recycled form:

CFCs: ( R11, R12, R113, R114 and R115) are fully halogenated hydrocarbon compounds with chlorine that have a strong impact on the ozone layer and high Global Warming Potential (GWP). Consequently, the use of these products is subject to legislation. This includes a sales ban in Article 2 (developed) countries from 1996, and Article 5 (developing) countries from 2010, in accordance with the Montreal Protocol.

HCFCs: (R22, R123, R401A, R401B, R402A, R402B, R408A, andR409A) are the second generation of fluorine based gases, the original replacements for CFCs. They are incomplete halogenated hydrocarbon compounds with chlorine that impact on the ozone layer less than CFCs. The use of HCFCs is being phased out as part of global legislation, such as the Montreal Protocol.

HFCs: are (incomplete) halogenated compounds that do not contain chlorine and thus do not affect the ozone layer. However, HFCs have a significant impact on global warming, so emission must be minimised.  The use of HFCs is regulated by the Kyoto protocol.

HFO:  are the fourth generation of fluorine-based gases. The first HFO, jointly developed by DuPont and Honeywell, is HFO 1234yf. HFO refrigerants are categorised as having zero ODP (Ozone Depletion Potential) and low GWP and so offer a more environmentally friendly alternative to CFCs, HCFCs and HFCs.

Refrigerants such as Ammonia (R717), Carbon Dioxide and non-halogenated hydrocarbons do not deplete the ozone layer and have no (ammonia) or only a low (carbon dioxide, hydrocarbons) global warming potential. They are used in air-conditioning systems for buildings, in sport and leisure facilities, in the chemical/pharmaceutical industry, in the automotive industry and above all in the food industry (production, storage, retailing).
One of the most promising alternatives is CO2 (R-744)., as it is non-flammable, non-ozone depleting and has a global warming potential of 1.

There are a number of rules and regulations that needed to be followed, depeding on type of applications and refrigerant used. Some of the most important, related to refrigerants, are listed below:
European Parliament and Council Regulation (EC) No. 842/2006 (effective from July 2006),  concerns HFCs and other fluorinated greenhouse gases, but not Ammonia or Carbon dioxide.
EN378: in general, most coutries have their own statute for the design, installation and control of refrigeration. For European Community and EFTA countries, these are now harmonized in EN 378 Regulation.