Experimental justification on thermal empirical equations for post-flashover compartment fires

Many useful correlation equations derived for estimating the heat release rate for a postflashover room fire were applied in performance-based design. A postflashover room fire is very hazardous as demonstrated by several big accidents in the past few years. The authorities are starting to challenge the use of such equations as fire engineering design tools. Additional justification of the results with experiments in fire hazard assessment is now required. Two correlation equations on heat release rates with gas temperature for postflashover fire are commonly used. One was reported by Babrauskas and Williamson and the other by McCaffrey et al., denoted as BW and MQH equations, respectively. Both equations were justified in this article by reported experimental data. Two sets of reported experimental results on postflashover room fires with transient heat release rates measured by oxygen consumption calorimetry were used. One set was reported by Chow et al. on studying flashover in a compartment fire with gasoline pool fires up to 2.8 MW. The other set was the experimental data on cable fires in a long cavity reported by Hietaniemi et al. Direct comparison indicated that heat release rates estimated using the BW equation are lower than measured values of both sets of the experiments. This point should be watched while applying the BW equation in fire hazard assessment. Better agreement was observed in the equation by MQH. A possible reason is that the empirical constants in the MQH equation were deduced by fitting with experimental data.