This part of IS0 4589 specifies methods for determining the minimum concentration of oxygen, in admixture with nitrogen, that will support combustion of small vertical test specimens under specified test conditions. The results are defined as oxygen index values. Methods are provided for testing materials that are self-supporting in the form of vertical bars or sheet up to IO,5 mm thick. These methods are suitable for solid, laminated or cellular materials characterized by an apparent density greater than 100 kg/m3. The methods may also be applicable to some cellular materials having an apparent density of less than 100 kg/m3. A method is provided for testing flexible sheet or film materials while supported vertically. For comparative purposes, a procedure is provided for determining whether or not the oxygen index of a material lies above some specified minimum value. Oxygen index results obtained using the methods described in this part of IS0 4589 can provide a sensitive measure of the burning characteristics of materials under certain controlled laboratory conditions, and hence may be useful for quality control purposes. The results obtained are dependent upon the shape, orientation and isolation of the test specimen and the conditions of ignition. For particular materials or applications, it may be necessary or appropriate to specify different test conditions. Results obtained from test specimens of differing thickness or by using different ignition procedures may not be comparable and no correlation with flammability behaviour under other fire conditions is implied. Results obtained in accordance with this part of IS0 4589-2 must not be used to describe or appraise the fire hazard presented by a particular material or shape under actual fire conditions, unless used as one element of a fire risk assessment that takes into account all of the factors pertinent to the assessment of the fire hazard of a particular application for the material. NOTES 1 It may not be possible to apply these methods satisfactorily to materials that exhibit high levels of shrinkage when heated, e.g. highly oriented thin film. 2 For assessing the flame propagation properties of cellular materials of density < 100 kg/m3, attention is drawn to the method of IS0 3582:1978, Cellular plastic and cellular rubber materials - Laboratory assessment of horizontal burning characteristics of small specimens subjected to a small flame, for testing horizontal burning characteristics