Experimental study of opening location affecting the delay time of backdraft

Abstract

Backdraft is a special phenomenon in fire research because of its explosive consequence and the occurrence of uncertainty. The delay time of occurrence has been of interest in recent years as this influences the safety and efficiency of firefighting. This paper investigated the location of the opening and whether it affects the delay time of the backdraft. Results show that the location of the opening dramatically dominates the delay time. The hot/cold air mixing path and instantaneous localized fire ignitions determine the delay time. A ‘curtain-like’ effect for the backdraft time delay was observed. The lower opening demonstrates about 50–70 % delay time compared to the upper and middle locations. In the presence of identical fire conditions and door closure control, the extended flammable gas dilution resulting from the upper opening does not significantly impact the onset of backdraft. Hence, the effective volume above the ignition location determines the delay time of the backdraft. Furthermore, the choice of chamber material is a crucial factor influencing the likelihood of backdraft occurrence. Utilizing a material with enhanced cooling capacity reduces the probability of backdraft. This provides insight into the firefighting and intervention tactics when ventilation-restricted compartment fire occurs.