1.1 This International Standard describes a method for measuring the oxygen index of insulating liquids. 1.2 The general principles of this test method as applied to solids are described in ISO 4589. 1.3 This method is generally considered as a method describing one of the combustion characteristics of products. 1.4 This test method is applicable to all liquids, the viscosity of which is lower than or equal to 50 mm 2/s at 40 °C ± 1 °C. WARNING: When burning a liquid, hazardous gases and/or vapours may be evolved. Adequate precaution shall be taken to protect the operator.