Influence of Ambient Pressure over Natural Smoke Ventilation in Shaft Tunnel Fire

Abstract

This paper aims to disclose the influence of different ambient pressures over the smoke flow and smoke ventilation in the shaft tunnel. For this purpose, numerical simulations were carried out on the shaft tunnel, using Fire Dynamics Simulator (FDS), a computational fluid dynamics (CFD) software package. The results show that: Under the same fire power, the smoke of tunnel fire spread faster and faster, with the falling ambient pressure. The longitudinal temperature curves of tunnel fire have basically the same features, at different ambient pressures. With the increase of ambient pressure, the longitudinal smoke temperature on the roof of the shaft tunnel gradually declines. The declining rate is positively correlated with the proximity to the fire source. Compared with that in small power fire, the roof temperature difference between low pressure and normal pressure is large in large power fire. The CO concentration in the shaft falls with the rise of ambient pressure. The smoke ventilation efficiency is better in the low-pressure environment, which facilitates the ventilation of fire smoke. The increase of fire power enhances the horizontal inertial force of smoke, and reduces the probability of plug holing. In addition, the ambient pressure has a small effect on the shaft smoke ventilation in small power fire.