FDS simulation of smoke backlayering in emergency lay-by of a road tunnel with longitudinal ventilation

This paper investigates smoke movement and its stratification in a lay-by of a 900 m long road tunnel by computer simulation using Fire Dynamics Simulator. The lay-by is located upstream of the fire in its vicinity. The influence of lay-by geometry on smoke spread is evaluated by comparison with a fictional tunnel without lay-by. Several fire scenarios with various tunnel slopes and heat release rates of fire in the tunnels without and with the lay-by are considered. The most significant breaking of smoke stratification and decrease of visibility in the area of the lay-by can be observed in the case of zero slope tunnel for more intensive fires with significant length of backlayering. Several other features of smoke spread in the lay-by are analysed as well. The parallel calculations were performed on a high-performance computer cluster.

Exploring the Feasibility of Ventilation without Shafts for an Ultralong Subsea Tunnel in the Bohai Strait Channel

The Bohai Strait Channel (BSC) is a strategic infrastructure project connecting the Shandong Peninsula and northeastern China. One challenge related to building the BSC tunnel portion is that ventilation shafts cannot be constructed due to certain limitations, which leads to a barrier for ventilation design. To explore the feasibility of ventilation without shafts, we first compare the tunnel ventilation design methods in China and the European Union. We also present the development process of emission standards, base emission rates, and design concentration values. Then, a new ventilation calculation for the BSC tunnel with reference values from the World Road Association (PIARC) is presented. The results show that the longitudinal ventilation design without shafts is feasible under normal traffic conditions when adopting values designed by PIARC under both the Chinese method and the European method. Furthermore, the influence of new energy vehicles and the necessity of ventilation rate on ventilation design are discussed. We suggest considering new energy vehicle fire situations and ignoring the ventilation rate for BSC tunnels. We hope to provide a strong reference for the ventilation design of BSC tunnels and for the improvement of relative ventilation codes in China.

Numerical Simulations on the Extinguishing Effect of Water Mist System with Different Parameters of Longitudinal Ventilation in Curve Tunnel Fire

Once a fire occurs in a long curve tunnel, the mixing of hot smoke flow and cold air leads to turbulence due to the curvature’s impact. This phenomenon results in a greater thermal pressure difference at the fire source and a substantially greater temperature field than in the straight tunnel. The longitudinal air flowing along the wall loses a lot of velocity in the curve tunnel due to the massive wall friction. Under the same fire extinguishing conditions, the curve tunnel and straight tunnel have different requirements for longitudinal ventilation. Factors such as tunnel curvature, longitudinal ventilation operation time, and ventilation velocity were all evaluated in order to investigate the influence of longitudinal ventilation parameters on the fire extinguishing effect of water mist in the curve tunnel. The fire extinguishing effect of water mist coupling with longitudinal ventilation in the curve tunnel is studied by numerical simulation, and the recommended values of ventilation operation time and ventilation velocity in the curve tunnel with the participation of the water mist system are given. The results show that (1) the fire extinguishing effect of water mist decreases with the increase of curvature under longitudinal ventilation and (2) fire prevention effect is best when water mist and longitudinal ventilation are used in the curved tunnel, and the ventilation velocity should be greater than 2 m/s.