Experimental study on the effects of exhaust vent layout on plug-holing for ceiling central smoke extraction in road tunnel fires

Abstract

In this study, a series of reduced-scale experiments are performed to study the phenomenon of plug-holing induced by ceiling central smoke extraction in road tunnel fires. By changing the side length of the vent perpendicular to the longitudinal direction of a tunnel (vent width), the heat release rate and the area of the ceiling extraction vent, the influencing factors for the occurrence of plug-holing are analysed. The experimental results show that increasing any of the three aforementioned factors can increase the smoke exhaust flow rate corresponding to the occurrence of plug-holing. The experimental results are then compared with the results obtained by previous research, and it is found that the previous research is no longer applicable with respect to the change in the vent width. On this basis, we propose a modified Froude number to predict the occurrence of plug-holing, considering the influence of vent width. The critical value corresponding to the plug-holing for the newly proposed Froude number is a constant having a value of 4.71 (Frc = 4.71), regardless of the variation in the abovementioned three influencing factors. The results can be used as a reference for the design of ceiling central smoke extraction in road tunnels.