Influence of the Shaft Structure on Natural Smoke Extraction Efficiency in Tunnel Fires

Abstract

The vertical shaft which can discharge fire smoke through the driving force of stack effect, is an effective natural smoke extraction method to control tunnel fire smoke and extend the available personnel evacuation time. Its natural smoke extraction efficiency would be affected by many factors such as the shaft structure. In order to search the optimum shaft structure, a series of tunnel fires with five kinds of shafts (the common shaft, 45 degree angle shaft, shaft groups, shaft with rectangular hood and board-coupled shaft (BCS)) are simulated by Fire Dynamic Simulator (FDS). Results show that the optimization design of the shaft structure, to a certain extent, can improve the smoke extraction efficiency, which are BCS shaft, shaft groups, 45 degree angle shaft, shaft with rectangular hood and common shaft respectively from large to small. There into, the smoke extraction efficiency of the BCS shaft can reach 70% due to the diversion and deflection of the smoke flow by BCS baffle, while the smoke extraction efficiency of ordinary shaft is 49%. Next the smoke extraction efficiency of shaft group can reach 57%, which makes the suction and penetration less likely to occur and directs the flow of fire smoke.