This test method provides a procedure for assessing the smoke obscuration caused by the burning of solid materials and assemblies in thicknesses up to and including 1 in. (25.4 mm) where subjected to specific test conditions in a closed chamber. The test is used as a research and development tool only and should not be used as a basis for determining ratings for building codes or other regulatory purposes.
Measurement is made of the attenuation of a light beam by the suspended solid or liquid particles — that is, smoke — that accumulate within a closed chamber. The smoke is due to either nonflaming, pyrolytic decomposition or flaming combustion of a relatively small sample of material. The radiant heat source is an electric furnace. NFPA 270, Standard Test Method for Measurement of Smoke Obscuration Using a Conical Radiant Source in a Single Closed Chamber, has subsequently been developed using an improved-design radiant heat source within the same closed chamber.
Test results are expressed in terms of specific optical density, which is a dimensionless property derived from the measured light transmission and geometric measurements of the chamber and the specimen.
This test is intended to measure and describe the properties of materials, products, or assemblies in response to heat and flame under controlled conditions. It is not intended to describe or appraise the fire hazard or fire risk of materials, products, or assemblies under actual fire conditions.