## 4 Conclusions  
To address the inability of photoelectric smoke detectors to detect black smoke introduced in the same concentration as the white smoke used to control the detector's sensitivity, the optical characteristics of the smoke of various colors generated inside the detector chamber were analyzed. For this purpose, a light-scattering chamber (LSC) was constructed to have the simplified shape of the chamber of a photoelectric smoke detector. It contained one light-emitting unit, a light-extinction measuring unit (0\({}^{\circ}\)), and a scattered-light-receiving unit (11 angles, from 15\({}^{\circ}\) to 165\({}^{\circ}\) at 15\({}^{\circ}\) intervals). Filter paper, kerosene, and polyurethane (PU) were used as combustibles for smoke generation. The methods of analysis and the main results were as follows. To investigate the distribution of the optical properties of smoke particles flowing into the LSC according to their color, three post-processing analysis criteria were applied to the measured light extinction and light scattering signals. Specifically, the asymmetry ratio--representing the ratio of forward scattering to backward scattering angles--was applied. In addition, in order to consider the single scattering albedo (SSA), which is affected by smoke color, the light extinction signal caused by the complex action of the light source and smoke particles was also considered. Figure 11: Comparison of results according to criterion III for the combustibles inside the chamber. The smoke particle size was roughly evaluated by examining the distribution of the scattering ratio, which was generated from each combustible material through a graph of the same scale as the cross-section inside the LSC. The relationship between the scattering angles and their initial values was examined first, because not all initial values measured by the light sensors were set identically. In addition, the slope was derived by applying a criterion according to the type of combustible used, and to confirm the relationship between the optical properties of the smoke particles, the data were re-established by applying a zero reset to ensure data validity. The scattering signals were measured at all scattering angles for combustibles producing representative smoke colors, and were then analyzed using the analysis criteria. We found that it was possible to distinguish kerosene by using the asymmetry ratio at \(15^{\circ}/165^{\circ}\), and the results also suggest a way to distinguish between filter paper and kerosene by using a specific section of the values for \(15^{\circ}/0^{\circ}\) and \(150^{\circ}/0^{\circ}\). When the specifically presented sections were applied in combination, a probabilistic indicator was presented to determine what color the smoke particles were in combustibles if the processed data were not included in the section. In summary, light scattering distribution data were processed for reliability through repeated experiments for specific criteria and angles, and indicators (the ranges) were presented by which smoke colors could be distinguished probabilistically. This preliminary study has confirmed the interaction between smoke and a variety of variables. For the first step, the correlation between light and smoke particles was analyzed. As a follow-up study, it is expected that the operating characteristics of smoke detectors will be developed if an algorithm for distinguishing the light-scattering characteristics of various combustibles is prepared. Conceptualization, C.-H.H. ; methodology, H.-Y.J. and C.-H.H. ; validation, H.-Y.J. and C.-H.H. ; formal analysis, C.-H.H. ; investigation, [PERSON]-Y.J. and C.-H.H. ; resources, C.-H.H. ; data curation, H.-Y.J. ; writing--original draft preparation, H.-Y.J. ; writing--review and editing, C.-H.H. ; visualization, H.-Y.J. ; supervision, C.-H.H. ; project administration, C.-H.H. ; funding acquisition, C.-H.H. All authors have read and agreed to the published version of the manuscript.