Analysis of Air Flow inside the Compartment under Backdraft Conditions using Solid Combustibles

Abstract

Backdraft is a phenomenon of explosive combustion that occurs when fire in a state of smoldering due to the lack of oxygen grows as the air is admitted after opening the entrance door or window. In this study, a reduced compartment was produced to simulate a backdraft. In an actual site, the fire was generated by solid combustibles, and hence, wood pieces were used to generate the backdraft in this study. Twenty-seven thermocouples were installed inside the compartment. One side of a wall consists of polycarbonate and the interior of the compartment was monitored using a camera. An additional fire simulation was performed using a fire dynamics simulator for in-depth analysis of the phenomena inside the compartment. In the experiment, the air flown into the compartment through the vent opening turned the smoldering fire of solid combustibles into the flaming fire, which led to the ignition of flammable gas inside the compartment. Next, the propagation of the flame was first directed upwards to the combustibles, then towards the center, and ultimately to the exterior. This phenomenon was observed in the analysis of the compartment holding a homogeneous flammable mixture. The results of the analysis showed that the flammable mixture on the interior was released to the exterior because of the rise in the internal pressure caused by flame propagation. Consequently, as the internal flame was propagated to the exterior, the mixture was ignited. Thus, the phenomenon of backdraft in the case of compartment fire was shown to occur as follows. First, the air flown in via the vent opening was elevated to the upper part of the compartment by the smoldering heat on the interior. Next, the flame led to the ignition of the flammable mixture formed on the upper part.