Effects of fire source position on smoke extraction efficiency by natural ventilation through a board-coupled shaft during tunnel fires

Abstract

Experimental studies on the influences of fire positions on the smoke extraction efficiency of a board-coupled shaft (BCS) are conducted in a 1:15 scale model tunnel, and the general condition that the first shaft cannot extract the entirety of the smoke is considered in this study. The results indicate that the BCS with proper board dimensions and installation positions can achieve better smoke extraction performance than the traditional shaft, whether the fire is located beneath the shaft or not. Besides, the advantages of BCS will gradually decrease as the distance between the fire source and the shaft increases. Flow visualisations captured beneath the shaft illustrate different flow patterns as the fire location changes. Based on the one-dimensional theory, an analytical model is developed to analyze the flow process in and around the vertical shaft, and a general formula is derived for predicting the dimensionless volume flow rate in the BCS, which may contribute positive significance in the tunnel smoke control and extraction design.