ABSTRACT
A successful and effective evacuation procedure is essential to ensure safety in underground environments during a fire event. As such the design of metro tunnels and stations should be made to efficiently minimizing possible consequences to the users.
The main aim is to ensure that a tenable environment remains in place during the evacuation, until the last user of the underground place reaches a safe place. This is achieved through a performance-based risk assessment, combining fire dynamics simulation and passenger evacuation analysis. The risk is evaluated using the fractional effective dose (FED) assessed in the users for the required evacuation time, given a set of critical fire scenarios that are balanced between the worst and the most probable condition. Safety standards enforced worldwide (e.g. NFPA 130), do not provide specific guidance regarding the selection of fire size, fire duration or burning materials, of critical scenarios. This paper defines the detailed critical fire scenarios, after the examination of relevant fire scenarios selected from the whole spectrum of scenarios. These critical fire scenarios are used in the combined fire dynamic and evacuation analysis of a metro train that catches fire and stops in a tunnel. The risk level of the tunnel section geometry for two metro tunnel sections, is initially presented, based on the FDS results. Through the coupled evacuation analysis, the evacuation performance for the two tunnel sections is assessed, based on the fractional effective dose of toxicity, that occupants receive during the evacuation procedure. The number of evacuees affected by the fire products and the level of the fire effect is presented. According to the results of the current paper, the single tunnel section presents significantly higher risk, comparing to the double tunnel, as 30% to 95% of the whole population becomes unable to continue the evacuation procedure by themselves, depending on the fire scenario.
