For prevention of depletion of the ozone layer on the earth and the global warming Fron are strictly limited to use as the refrigerant of refrigeration unit complying with the protocol of the United Nations climate conference on global warming in Kyoto 1997 and of Montreal. This includes the alternative refrigerant R-134a as well as the conventional ones such as CFC. One of the candidates for these substitutes will be the hydrocarbons which have close physical properties with Fron and may provide the solution to the influences to the earth environment. Authors studied the thermal performances of the representative hydrocarbon refrigerants of single component and formulated constituents in comparison with the conventional R-22 and ammonia and proposed the countermeasures for an arrangement against the flammability of new refrigerants from the safety aspect.