This part of ISO 4589 constitutes a guidance document for the OI test. It provides information to guide the reader in the use of the test procedures described in parts 2 and 3. Part 2 describes a method for determining the minimum volume fraction of oxygen in a mixture of oxygen and nitrogen introduced at 23 °C ± 2 °C that will just support combustion of a material under specified test conditions. The results are defined as OI values. For comparative purposes, a procedure is also provided for determining whether or not the OI of a material lies above some specified minimum value, which is particularly important for quality control purposes. There is also a procedure for the testing of thin films between 20 ¼m and 100 ¼m thickness Part 3 describes methods of carrying out the same determination over a range of temperatures typically between 25 °C and 150 °C (although temperatures up to 400 °C may be used). The results are defined as TI (Temperature Index) values at the test temperature. Part 3 also describes a method for determining the temperature at which the OI of the small vertical test specimens is 20,9 %. The result is defined as the flammability temperature. Part 3 is not applicable to materials having an OI value of less than 20,9 % at 23 °C.