Effect of heat release rate and exhaust vent settings on the occurrence of plug-holing during tunnel fires with two-point extraction ventilation

This paper investigated the plug-holing phenomenon in the tunnel fire with two-point extraction ventilation based on a reduced-scale tunnel model. The effect of the heat release rate (HRR) and extraction vent settings, i.e. the area and aspect ratio (a ratio of the width to the length), on the occurrence of plug-holing was addressed experimentally and theoretically. Experimental results show that the exhaust volumetric flow rate of the occurrence of plug-holing increases with the growth of the HRR and aspect ratio. Besides, with the extraction vent area rising, the exhaust volumetric flow rate of plug-holing improves. However, when the extraction vent area is larger than a certain value, the hot smoke cannot fill the entire extraction vent and may adhere to the upstream of the extraction vent, which is different from the plug-holing. Finally, an empirical equation was developed to predict the occurrence of plug-holing with various HRRs and extraction vent settings based on a proposed modified Froude number in this paper. Research outcomes can provide constructive references for the current design of the point extraction ventilation in tunnel fires.