Discrimination Between Fire Smokes and Nuisance Aerosols Using Asymmetry Ratio and Two Wavelengths

Optical smoke detectors are very prone to produce false alarms and cause a great economic loss when exposed to interference particles, i.e. non-fire aerosols. This paper aims to study the discrimination between fire smokes and two common nuisance particles (i.e. dusts and water particles) based on the asymmetry ratio (AR, the ratio of forward to backward scattered light signals). The experiments were conducted using a home-made detector model and the forward- and backward-scattering angle are 45° and 135° respectively. The test process refers to the Society of Automotive Engineers Aerospace Standard 8036A. Fire smokes, standard dusts and water steam/mists were tested in this study. The effect of particles pollution was firstly studied. Due to the pollution of dust particles on the detector model, the forward signal increases significantly, leading to obvious deviation on the asymmetry ratio. Experiments of fire smokes show that a balance response between the soot and smoldering particles can be achieved based on the asymmetry ratio. By comparing the asymmetry ratios of fire smokes and nuisance aerosols, it is found that we can use the short wavelength (i.e. 405 nm) to distinguish the smoldering particles (the ARs range is 6.8–7.6) from nuisance aerosols, and long wavelength (i.e. 870 nm) to separate the soot particles (the ARs range is 2.2–3.5) and as well the cotton smoldering particles (the ARs range is 10.1–10.6) from nuisance aerosols. Moreover, results also show that nuisance aerosols cover wide ranges of asymmetry ratios, i.e. about 3.4–6.1 at 405 nm and 4.2–8.2 at 870 nm. This suggests that further work is needed to help the differentiation of aerosols.