ISO 4589-1:2017 specifies the general requirements for the oxygen index (OI) test which are further described in ISO 4589‑2 and ISO 4589‑3 as follows:
- ISO 4589‑2 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;
- ISO 4589‑3 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 can be used).