Numerical Study of Longitudinal Ventilation System with Extraction Shaft for Control of Fire and Smoke in Tunnel

Convenient and efficient design of tunnel ventilation system for increased safety in case of fire is required. One of the main purposes of designing a ventilation system is fire and smoke flow control to create a safe passage to escape the travelers. Longitudinal ventilation system, using jet fan and axial fan, is most commonly used in tunnels. But, efficiency of longitudinal ventilation system decreases with increasing the length of the tunnel. In this paper, the effect of extraction shaft combined with a longitudinal ventilation system, in emergency situations, in a relatively long tunnel, has been studied. In a ventilation system with an extraction shaft, the aim is limiting the flow of fire and smoke in the distance between the fire source and the shaft. In this paper, FDS code, which is a computational fluid dynamic model, was used to study the smoke flow and temperature distribution in the tunnel. The effects of changes in parameters such as flow rate of the output shaft, input speed, slope of tunnel, shaft dimensions and heat release rate on temperature distribution under the tunnel ceiling was investigated. Results showed that efficiency of the longitudinal ventilation system using extraction shaft was increased and change of the tunnel slope, and its corresponding change in the direction of smoke flow in the tunnel, was under control. The results also revealed that increasing the outflow cross section of the ventilation shaft does not have much effect on the system performance. Considering this parameter, different scenarios could be defined and possible control of fire and smoke flow could be created