Fluorinated refrigerant blends: potential unexpected downsides in flammability

Refrigerant blends are often considered effective solutions to reduce flammability and maintain low global warming potential (GWP). However, this view is not always correct. Fluorinated refrigerants may fail to act as flame retardants when blended with flammable refrigerants. Instead, such blends may lead to more serious fire hazards. In this study, we showed that in most fluorinated refrigerant blends, non-flammable fluorinated components promoted the combustion of the flammable components. For example, when the volume ratio of HFC-134a reaches 0.9, the concentration of HC-1270, HC-290, and HC-600a required for ignition decreases to 49.3 %, 47.6 %, and 50.8 %, respectively. Combustion inhibition occurred only when the non-flammable refrigerant was present at high concentrations or formed the main component of the blend. Even under such conditions, the risk of fire remained due to potential dilution and local concentration variations caused by leakage into the air. This phenomenon is mainly due to exothermic elemental reactions that dominate the fluorine-related reactions during combustion, which increase the net heat release rate and thus promote combustion. The net heat release rates of R-1270/125, R-1270/134a, and R-1270/1216 at 3 vol% non-flammable components are 185 %, 327 %, and 290 % of that of pure HC-1270. These findings help the refrigeration industry recognize the potential risks of refrigerant blends and develop targeted safety standards.