Rail tunnels risk analysis: the effects of infrastructure and fire characteristics

The Italian standard on “Rail tunnel safety” have identified the minimum safety requirements for each type of rail tunnel. This standard also introduces two types of Risk Analysis (Base and Extended) to be performed in order to verify the fullfilment of all safety requirements and to compare the tunnel risk level with fixed acceptability thresholds. In this study a methodology to conduct an Extended Risk Analysis was applied in order to allow to evaluate the heat and toxic gasses concentrations inside the tunnel due a fire on a train coach and to calculate their diffusion and their effects on passengers in function of infrastructure, train and fire characteristics. The used procedure allows to account for tunnel geometric characteristics (section and sidewalks number and width), vehicle characteristics (type of train and number of passengers) and fire event conditions (Heat Release Rate, Heat Release development time, toxic gasses type and concentration). The application of this methodology allows to estimate the saving people likelihood and the number of expected deaths as a function of the distances covered by each passenger depending on different accident scenarios and on evacuation procedures and tunnel characteristics. A sensitivity analysis has been conducted in order to identify the influence of all parameters on passengers evacuation capacity, highlighting the effects of different parameters such as air speed and temperature inside the tunnel. An analysis on different tunnel sections has been conducted in order to identify infrastructure effects on saving people likelihood. This methodology could also be useful as a design tool in order to identify the best design, construction and management options to increase safety levels. It could also be used to define the most effective evacuation procedures for each emergency scenario. In this study the effects of the central footpath in double track sections have been investigated.