Simulation-based design of railway tunnels’ safety assets

Among the railway tunnels’ safety assets, emergency doors are one of the most critical elements in fire safety design, necessary or a quick evacuation to the nearest safe location. At the present state, there is a lack of a comprehensive regulation framework for the design of ventilation systems protecting safety doors from smoke and other byproducts during a fire and the design is normally case-tailored. The search for appropriate design requirements depends on the variability of the main parameters. This paper discusses the simulation of highly critical scenarios for fire generated in mixed traffic railways with passenger couches (10 MW) freight wagons (250 MW). Computational Fluid Dynamics (CFD) and Fire Dynamics Simulator (FDS) are used to define the minimum airflow requirements for an effective operation of the emergency doors, depending on local parameters, such as position of fire, wind, morphology of the tunnel (single or twin). The scenarios include: 1) connected single-track twin tunnels; 2) doubletrack tunnel connected to a dedicated safe chamber. Temperature, pressure, and smoke in the connections are relevant parameters affecting the results, as well as opening and closure conditions for the doors. The extensive simulation campaign carried out demonstrated that the most critical scenario requires a maximum ventilation airflow of about 30 m3/s to protect the doors from smoke and other by-products, when the maximum velocity of wind is 10 m/s. These results pave the ground towards a handbook that should cover a large set of infrastructure and operation conditions and would represent an important step ahead towards recognized standards in railway tunnels design.