Predicting the flashover occurrence and energy distribution in compartment fires with different boundary materials

Buildings with different wall/ceilings present different burning characteristics, significantly increasing the difficulty in predicting enclosure fire development and spread. In this work, to investigate the mechanism of the influence of boundary conditions on compartment fire dynamics, a total of 54 bench-scale experiments with one quarter dimension of ISO 9705 were conducted with three boundary materials, namely, calcium silicate board, corrugated steel sheet and rock wool sandwich plate; for each boundary material, six different square pans of 80 mm, 100 mm, 150 mm, 200 mm, 250 mm and 300 mm were used to provide different energy release rates of fuel to determine the critical conditions for flashover occurrence and energy distribution in the compartment. Parameters such as the mass loss rate of fuel, temperatures of gas and wall/ceilings surfaces, start time of ejected flame and length of flame ejected from the opening were measured and analysed. It was found that with the identical pan size, flashover is most likely to occur in the compartment of the sandwich panel, and it is most difficult for flashover to occur in the compartment of the calcium silicate board. Among the three boundary conditions, compartments consisting of high thermal conductivity material on the inner surface of wall/ceilings (corrugated steel sheet and rock wool sandwich plate) show higher HRR, compartment gas temperature and inner wall/ceilings surface temperature. Through the experimental data at the pre-flashover stage, the relationships between the HRR, upper gas temperature, fuel pan size, compartment opening, and parameters of the boundary materials were quantitatively established by energy conservation to predict the occurrence of flashover, which is suitable for thermally thin, thermally thick and composite boundaries. Moreover, an energy distribution theory for the transient state was developed to predict the HRR of compartment fires very well under different boundary conditions and fuel loads.