Obtaining additional smoke characteristics using multi-wavelength light transmission measurements

The characteristics of smoke are highly dependent on the materials undergoing thermal decomposition and the environment in which this decomposition takes place. With the rising complexity in dedicated fire simulation tools, there is a need for increased information on the composition and properties of smoke in order to develop/validate and extend the fire safety engineering community's smoke and visibility prediction capabilities. Today, the most common method for the measurement of smoke production potential used in standardized material/product testing comprises of an optical system that measures the attenuation of a light source, by the smoke, over a known path-length. Based on this measurement, properties related to the overall smoke production potential of a material/product can be derived which are then used for material/product safety classifications. The downside to this method, although dynamic and robust, is that it provides only a measure of the amount of smoke being produced; it does not give any further information about additional characteristics of the measured smoke such as particle sizes. In this study, a method based on differences in the scattering and absorption by smoke of various wavelengths of light is examined. This methodology, which requires both a specific experimental approach and theoretical calculations, may potentially provide supplementary smoke characteristics in addition to smoke production measurements. A numerical optimisation routine is developed using Mie scattering theory that aims, in conjunction with experimental data, to provide estimates of mean smoke particle sizes and particle refractive index; which describes how a particle scatters and absorbs incoming light, both useful parameters for detailed smoke and visibility simulations. Initial numerical results give promising indications for the applicability of the method. The specific design requirements for an experimental methodology requiring the implementation of optical transmission measurements at a number of different wavelength light sources are also discussed, with conclusions, future work and recommendations given. (Less)