Flammability Properties of R152a versus Hydrocarbons

The refrigerant R134a is in discussion to be banned in Europe for mobile air conditioning (MAC) in passenger cars by limitation of the global warming potential (GWP) of the refrigerant used. Most likely R744 will be the replacement. As alternate refrigerant R152a is proposed [10]. Even though its molecular structure still contains fluorine the global warming potential is an order of magnitude lower than that of R134a. Major drawback of R152a is its flammability. However in case of a GWP limit of 150 R152a is remaining a hydro-fluorocarbon (HFC) subject to re-enforcement of regulation.

A comparison of literature values of the flammability properties of R152a to those of hydrocarbon gases such as methane (R50), ethane (R170), propane (R290) and butane (R600) revealed some differences in ignition limits, ignition temperature and minimum ignition energy. However the flammability properties and specifically the pressure rise of the combustion process are not so much different to approve R152a for automotive air conditioning without further detailed investigations covering cabin, engine compartment and servicing area.

The combustion gas of R152a contains harmful hydrogen fluoride. Risk assessments have to take this fact into consideration.