The ISO 4589-3 standard is an oxygen index test method for the combustion performance of plastics at high temperatures. It applies to solid, laminated or porous materials with apparent density (pb) ≥ 100 kg/m ³, and to porous materials with a partial density below 100 kg/m ³. The test assesses the combustion characteristics of the material by igniting the specimen in an oxygen-nitrogen mixture and measuring the minimum oxygen concentration required to support combustion. The method also covers the testing of flexible sheets or films and defines the flammability temperature (FT), which is the temperature at an oxygen index of 20.9%, for determination below 400 ° C. This standard provides a scientific basis for the fire performance evaluation of plastic materials in high temperature environments, and is an important tool for material research and development, quality control and security evaluation.