Underground fixed guideway system has become an important solution to alleviate over-crowded population problems , especially in urban areas. During the planning stage, the station and the underground tunnel formed an enclosure which necessitated environmental control in order to facilitate thermal comfort and safety in case of fire. In this study, SES program has been utilized as a tool in evaluating the performance of the tunnel ventilation system under normal, congestion , and emergency operation modes, using an actual railway underground project as an example. Conclusions has been drawn that safety criteria can be met successfully, following the SES simulation results with recommendations made to facilitate successful ventilation modes.

ABSTRACT Three-dimensional modeling on the aerodynamics of airflow and diffusion of air pollutants in a longitudinal-ventilated traffic tunnel was carried out. The model takes ventilation fans, traffic flow rate, speed, emission factor and piston effect of moving vehicles into consideration. Turbulent flow and dispersion of gaseous pollutants in road tunnels were solved numerically using the finite volume method. Traffic emissions were accordingly modeled as banded line sources along the tunnel floor. The effects of fan ventilation, roughness and piston effect of moving vehicles on the air flow and pollutant dilution are examined. Concentrations of gaseous pollutants CO, NOX, SO2 and THC (total hydrocarbons) at three axial locations in the tunnel, together with traffic flow rate, traffic speed and types of vehicle were measured. Case study was conducted on the Cross-Harbor Tunnel and the Chungcheng Tunnel in which on-site measurements of traffic flow were also conducted concurrently to provide traffic emission data to the tunnel environment for numerical simulation and comparisons. The aim of this study was to understand the spatial variation of air pollutants generated by traffic emissions and evaluation of ventilation performance and piston effect of moving vehicles on dilution of air pollutants in these tunnels. The results show that the major emission sources of CO are passenger cars and motorcycles, while major emission sources of NOx are trucks. Pollutants convect downstream with the wind generated either by longitudinal ventilation fans and/or moving vehicles, thus causing increasing pollutants concentrations with increasing downstream distance. The piston effect of moving vehicle alone can provide 64% ~ 85% increase of wind speed in Chungchen Tunnel and 13% ~ 20% in Cross-Harbor Tunnel. When all fans are on, showing 185% ~ 328% and 120% ~ 182% increases in Chungchen Tunnel and Cross-Harbor Tunnel, respectively. The piston effect of moving vehicle alone can provide 14% ~ 32% dilution of air pollutants in the Chungcheng Tunnel. The piston effect of moving vehicles is compounded with ventilation fans, showing a 47% ~ 66% dilution effect when all fans are on. For the Cross-Harbor Tunnel, the piston effect of moving vehicle alone can provide 9% ~ 23% dilution of air pollutants and 36% ~ 74% dilution effect when all fans are on. The results reveal that cross-sectional concentrations are non-uniformly distributed and that concentrations rise with downstream distance. When all fans were turned off, wind speed in tunnels would be considered as constant, and gaseous pollutants concentration agree with linearly alone the tunnel.

Fire is a complex phenomenon including many parameters. The nature of fire makes it a very dangerous and hazardous. For many reasons the number of tunnels are increasing on earth and fire safety is one of the major problem related to tunnels. This makes important to predict and understand the behavior of fire, i.e., heat release rate, smoke movement, ventilation effect etc. The literature includes many experimental and numerical analyses for different conditions for tunnel fires. This study investigates pool fire of three different fuel sources: ethanol, gasoline and their mixture for different ventilation conditions, different geometries and different amounts. Combustion gases and the burning rates of the fuel sources are measured and analyzed. The numerical simulation of the cases is done with Fire Dynamics Simulator (FDS), a CFD code developed by NIST.