Accurate predictions of the activation time for smoke detectors using a fire simulation is are required to ensure the reliability of the RSET (Required Safe Egress Time) calculation in the process of PBD (Performance-Based Design). The objective of this study was to enhance the accuracy of input parameters for the numerical models of smoke detector based on the FDS. To this end, a Fire Detector Evaluator (FDE) developed in previous studies was improved. The uniformities of flow and smoke inside the FDE were improved and accurate measurements of the obscuration per meter (OPM) related to detector operation were also performed through a decrease in the forward scattering of smoke particles. The input parameters using the improved FDE showed a significant difference from the previous FDE quantitatively. In particular, a larger difference was found in a photoelectric detector compared to an ionization detector. Considering that the operating conditions of smoke detectors are affected by the detector type, combustibles, smoke particulars, and color, the database (DB) on the input parameters for various detectors and combustibles should be built to improve the reliability of PBD in future studies.
The obscuration thresholds for various smoke detectors and combustibles, required as an input parameter in fire simulation, were measured to predict the accurate activation time of detectors. One ionization detector and nine photoelectric detectors were selected. A fire detector evaluator, which can uniformly control the velocity and smoke concentration, was utilized. Filter paper, liquid fuels, and polymer pellets were employed as smoke-generation combustibles. The nominal obscuration thresholds of the considered detectors were 15 %/m, but the ionization detectors activated at approximately 40 %/m and 16 %/m, respectively, on applying filter paper and kerosene. In contrast, the reverse obscuration thresholds were found quantitatively according to the combustibles in the photoelectric detector. This phenomenon was caused by differences in the color of the smoke particles according to the combustibles, which is explained by single-scattering albedo (ratio of light scattering to light extinction). The obscuration thresholds for liquid fuels (kerosene, heptane and toluene) as well as fire types of polymer plastic pellets were also measured for several photoelectric detectors. A database of obscuration thresholds was thereby established according to the detector and combustible types, and it is expected to provide useful information for predicting more accurate detector activation time and required safe egress time (REST).
It is necessary to predict the activation time of fire detectors accurately to improve the reliability for evaluating the required safe egress time (RSET) in performance-based fire safety design. In this study, problems of the plunge test, which is widely applied in assessing fire detectors, were examined through experiments and numerical simulations. In addition, a new shield-cup test method was proposed to address these problems. A fire detector evaluator (FDE) developed in a previous study was applied to ensure measurement accuracy and reproducibility. During the plunge tests, a significant measurement error was observed in the activation time of the smoke detector because of the rapid flow change when the detector was input. However, during the shield-cup tests, slight changes occurred in the flow inside the FDE when the detector as exposed to smoke. In conclusion, the proposed shield-cup test method is expected to be useful for evaluating the response characteristics of fire detectors more accurately in simulated fire environments.
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