HC-12a, also called ES-12a, OZ-12a, and Hydrocarbon Blend B, is a "drop-in" replacement refrigerant for Freon-12 and to a lesser extent, R-134a. HC-12a is a mixture of hydrocarbons, specifically propane (R-290) and isobutane (R-600a), and is therefore considered nearly non-ozone-depleting when compared to dichlorodifluoromethane (R-12, Freon-12) or 1,1,1,2-tetrafluoroethane (R-134a). The mixture can be used in refrigeration systems designed for R-12. HC-12a provides better cooling than an R-12 system retrofitted to R-134a, with much greater energy efficiency as well. Unlike R-134a, HC-12a is completely compatible with the hoses and oils used in R-12 systems, making the conversion much easier to accomplish. HC-12a is also patent-free due to its non-synthetic nature.
Because of its flammability, it is illegal to replace R-12 with HC-12a in the United States. It is not illegal to purchase HC-12a, or to use it in refrigeration systems that were not originally charged with R-12, except for in certain states that prohibit the use of flammable refrigerants in automobiles.
Some advantages to using the HC-12a mixture over retrofitting to R-134a are cost and labor. Since HC-12a is a "drop-in" replacement, no seals need to be replaced and minimal effort has to be put in to changing the refrigeration system around. Disadvantages to using the HC-12a mixture in R-12 systems is that it is potentially dangerous and is illegal in the United States. The refrigerant used is propane and other hydrocarbons which are flammable. However, it should also be noted that R-134a (and other refrigerants) are just as flammable when mixed with refrigerant oil, yet the quantity of refrigerant and oil in a typical system is so low that the danger in any case is minimal.