On-line determination of the optical properties of particles produced by test fires

The performance of smoke detectors depends largely on the characteristics of the smoke produced in a fire situation. A better knowledge of the properties of the aerosol particles originating in fires will therefore help to improve the performance of existing detectors, reduce the amount of false alarms, and serve as guideline in the development of new measuring techniques. Here, we present a study of the optical properties of the standard EN54 test fires. The measurements were done using the diesel particle scatterometer [Hunt A, Quinby-Hunt M, Sheperd I. Polarized light scattering for diesel exhaust particulate characterization. In: Proceedings of the DOE diesel engine emissions reduction workshop. Castine, MA, 1998; Hull P, Shepherd I, Hunt A. Modeling light scattering from diesel soot particles. Appl Opt 2004;43(17):3433–41.] This instrument measures the angular distribution of the Mueller scattering matrix elements S11S11, S12S12, and S34S34 [Bohren C, Huffman D. Absorption and scattering of light by small particles. New York, USA: Wiley Science Paperback Series; 1983.] with a time resolution faster than 1Hz. The size distribution and the complex refractive index of the particles can then be determined by fitting the data with Mie-scattering calculations. The optical information was complemented with the aerosol size distribution measured using a SMPS system. Our results show that the simultaneous measurement of several scattering-matrix elements can serve as a good discrimination criterion for the different types of fire (flaming and smoldering). In contrast, the type of fire cannot be determined from the size distribution data alone.