An experimental study on plug-holing in tunnel fire with central smoke extraction

A series of fire experiments were carried out to investigate the plug-holing in the road tunnel with central smoke extraction system. The smoke layer height and the temperature under the exhaust vent as well as the velocity in the upstream and downstream are measured and analyzed. The results show that with the increase of smoke exhaust rate, no plug-holing, incompletely plug-holing and completely plug-holing will occur in turn for the smoke layer under the exhaust vent. The height of smoke layer under the vent increases rapidly, while the temperature decreases quickly with the increase of smoke exhaust rate, until they become stable when the completely plug-holing occurs. The velocity difference between upstream and downstream of the vent firstly increases with the larger smoke exhaust rate, and then it starts to decrease in the transitional region of plug-holing. Similarly, it becomes stable when the completely plug-holing occurs. When Fr is<1.2, no plug-holing occurs and when Fr is larger than 1.8, the completely plug-holing occurs. It is transitional state for plug-holing when 1.2 < Fr < 1.8.