Development for revision of ISO 817 – Evaluation method of self-decomposition reactivity of nextgeneration refrigerants –
HydroFluoroOlefin (HFO) refrigerants are attracting significant attention as next-generation refrigerants due to their exceptionally low Global Warming Potential (GWP) and superior thermal properties. However, certain ethylene-based HFOs exhibit self-decomposition reactivity, which poses potential risks of compressor rupture if such reactions occur inside the refrigeration cycle. Comprehensive safety evaluations are necessary for practical application, yet ISO 817 (Refrigerants - Designation and safety classification) currently specifies only flammability and toxicity, not self-decomposition reactivity (refrigerant stability). Conventional refrigerants used so far do not exhibit self-decomposition reactivity, and there is no standardized evaluation method for the reaction. In this report, developments to revise ISO 817 to include refrigerant stability classification are discussed. Self-decomposition reaction occurs when energy, such as an electric spark, is applied to the refrigerant in highpressure and high-temperature environments. Therefore, for evaluation, the refrigerant to be tested is sealed in a reaction vessel at high pressure and high temperature, and energy is applied by an ignition source inside the vessel. The ignition source is particularly important, and previous research has shown that reactivity changes depending on the type of ignition source. For international standardization, reproducibility and simplicity of testing are also required. Additionally, controlling the amount of energy input to the refrigerant is an important aspect. After investigating existing standards and similar tests, the Fusing Wire and Discharge Method was developed for those reasons. In this method, a fine metal wire (Fusing Wire) is placed between electrodes spaced about 1mm apart, and voltage is applied. When current flows, the Fusing Wire heats up and melts due to Joule heat, causing arc discharge between the electrodes. The phenomenon of melting and discharge was investigated under different gas types, gas pressures, and temperature conditions using this method. Furthermore, the self-decomposition reactivity of next-generation HFO refrigerants was evaluated.