One-dimensional analysis for optimizing smoke venting in tunnels by combining roof vents and longitudinal ventilation

A hybrid mode that combines both longitudinal ventilation and natural roof venting is proposed for thermal and smoke control in tunnel fires. This hybrid strategy creates safe environments at the upstream side of the fire and shortens the smoke spreading distance at the downstream side, if the longitudinal ventilation and roof smoke venting are well cooperated. It is advantageous to the urban traffic tunnels that are adjacent to other underground facilities. The pressure rise of the longitudinal ventilation system and the geometrical parameters of the roof vents are the two key factors affecting the effectiveness of the proposed hybrid mode. The heat and smoke convection patterns under this hybrid mode are investigated with both a one-dimensional hydraulic analysis method and numerical simulations. The simulation results demonstrate that the smoke can be exhausted by the roof vents downstream of the fire, and thus, the gas temperatures downstream of the vents can be significantly decreased. The maximum deviation between the theoretical smoke exhaust rate and simulation result is approximately 17%, indicating the analytical model and numerical simulation results are in good agreement. The one-dimensional analysis method and the equations associated with it can be directly used to optimize the design parameters. (C) 2016 Elsevier Ltd. All rights reserved.