1 This part of ISO 5659 specifies a method of measuring smoke production from the exposed surface of specimens of essentially flat materials, composites or assemblies not exceeding 25 mm in thickness, when placed in a horizontal orientation and subjected to specified levels of thermal irradiance under forced ventilation conditions. with or without the application of a pilot flame. This method of test is applicable to plastics and may also be used for the evaluation of other materials (e.g. rubbers, textile coverings, painted surfaces, wood and other building materials). 2 Values of optical density determined by this test are specific to the specimen or assembly material in the form and thickness tested and are not to be considered inherent, fundamental properties. 3 The test is intended for use in research and development and not primarily as a basis for ratings for building codes or other purposes. No basis is provided for predicting the density of smoke which may be generated by the materials upon exposure to heat and flame under other exposure conditions, such as end-use conditions, nor has any correlation been established with measurements derived from other test methods. 4 It is emphasized that smoke production from a material varies according to the ventilation conditions and the irradiance level to which the specimen is exposed. In making use of the results of this method, it should be borne in mind that the results are based on exposure to the specific irradiance levels of 25 kW/m and of 50 kW/m under specific ventilation conditions.