Fire Reconstruction Research Of Flashover In The Special Confined Compartment

Fire investigation, an important branch in the fire science research, is obtaining more and more attention in the world as an interdisciplinary research. Fire reconstruction is used to determine the most likely development of a fire using a scientifically based methodology. Flashover is a rapidly occurring transitional event in the development of a compartment fire. It can be easily occurred in the specially confined compartment, where ventilation is poor in such limited space. In fire investigation, proper application of flashover analysis can be very valuable tool in unraveling the mysteries of a fire's origin and development, and presenting the theoretical basis for judgment. In this paper flashover is under research from the point of fire reconstruction.The basement of construction of fire reconstruction model is the analysis of material. Especially the thermal degradation of combustible material in solid phase related with the occurrence and development of flashover. First the thermogravimetric evaluation of typical solid combustible material, including nylon and plywood, was studied with thermogravimetric analysis and thermal kintiecs . The kinetics parameters obtained could be used to predict the percentage composition of pyrolysis product under different temperatures, which might indicate the possibility of flashover under certain circumstances. Meanwhile the study could provide the basic data for numerical simulation for flashover reconstruction.The model compartments of different scales were constructed. The experimental reconstruction was done under various experimental conditions, including the height of ceiling, the location of fire source, the ventilation condition, the radius of fire, etc. The critical conditions of occurrence of flashover were studied in such compartment. With the help of two-layer zone model, the change of heat gain and heat loss in the nonlinear dynamics could well explain the development of compartment fire. The wall temperature parameter U_c and the radius of fire were the primary factors in the development flashover. The nonlinear dynamics model could judge the occurrence of flashover and predict the highest stable temperature in the smoke layer.The scale modeling in the process of flashover was studied.The dimensionless control equations of pool fire in compartment were established .Under the analysis of the relation of the plume velocity and the heat release rate, the dimensionless variable of heat release rate was considered to take the leading control effect. This induced the establishment of the scaling rule for the pool fire in a compartment by this constant rate variable of heat release, which could be applied in the design of model experiment.The numerical simulation results in CFAST and FDS were compared with the experimental results by the numerical experiment reconstruction of the flashover in this confined compartment. CFAST was weak in modeling the thermal degradation of fire source and the combustion reaction, which would limit the application of CFAST in fire scene reconstruction. FDS could well predict the development process of compartment fire by modeling the thermal degradation of fire source and the combustion process properly.The feasibility of the application of the empirical model of flashover, the BFD curve method and FDS modeling in the fire scene reconstruction were studied by the full scale flashover test. It showed that the FDS modeling had wide applicability, and BFD's ability to predict the temperature curve of smoke layer and the judgment of the highest temperature for the flashover in compartment were better than FDS. It could be an effective way to estimate the highest heat release rate by McCaffrey's model, resulting in the judgment of the mesh dimension in FDS.