Studies On The Simulation Of Contact Smoke Detection In Large Space Fire

The recent studies of simulation of large space fire are mainly emphasis on the movement of smoke flow. And according to the temporal and spatial distribution of fire thermal parameters, the performance evaluation and design of detecting systems are carried out. However, for the contact smoke detection, such operation separates the detecting system from fire scenario without considering the interactions of each other. On the basis of introducing detector models into fire simulation platform, the combination of fire analysis information and detector models is realized in this paper. A simulating strategy aiming at the whole detecting process is established respectively based on 2 smoke characteristic parameters: mass concentration and size distribution.Relying on the fire simulation platform of FDS, the parameter calibration methods for spot-type and air sampling smoke detectors were proposed with considering of their respective working characteristics: time-lag effect and diluting effect. Therefore, the conversion of smoke characteristic parameters from fire scenarios into detector's sensing chambers is realized.Early fire analyses of Peking University'gymnasium were carried out, and some typical phenomena of large space fire was obtained with the simulation of plume shapes and smoke movements including 13 conditions subordinated to 3 fire source locations.Based on the smoke mass concentration, numerical wind tunnel experiments and ASPIRE2 program were adopted respectively to model the process of smoke entering the sensing chamber of 2 kinds of detector products: JTY-GD-1109A spot-type detector and VESDA-LaserPLUS air sampling detector. On the basis of FDS fire simulation of Peking University'gymnasium, the performance evaluation of the 2 detector products were presented based on the alarm threshold of obscuration. The analysis results show that the spot-type smoke detectors fail to detect small fires; while the effect of air sampling detection is significantly influenced by the arrangement of pipe networks. The assembled sampling, which combines ceiling and vertical pipes, can overcome the adverse effect of thermally stratified environments, and have high coping ability in various fire situations, especially for small fires.Based on the smoke size distribution, the time evolution of smoke particle spectrum with varying coagulation rate was obtained by combining numerical calculation of fire thermal parameters and the Moment solution of Brownian coagulation equation. With the predicted evolution of smoke particle spectrum parameters in different fire scenarios, the influencing factors were discussed. And furthermore, a practicable operating suggestion aiming at large space fire is proposed that the time evolution of smoke particle spectrum caused by Brownian coagulation can be neglected in detecting positions where remote from the fire origin. Thus, the initial values when the smoke particles leaving the near-zone of the fire origin can be adopted to convert the time history of smoke mass concentration into size distribution in the detector's sensing chamber. Finally, on the basis of optical simulation by Mie model, a preliminary simulating strategy of the whole detecting process is proposed on a more microcosmic level.