1. The role of ventilation

Urban guided transport networks such as metros generally have large underground sections. In these underground sections, in the absence of specific measures, the air could be confined, leading to degraded ambient conditions in normal operation and increased evacuation and fire-fighting difficulties, as shown by the example of the event cited in the introduction [1]. Metro and tramway tunnels built some fifty years ago are therefore equipped with a mechanical smoke ventilation system. Under normal operating conditions, this system is designed to maintain air quality at the required level and provide thermal comfort for passengers in stations and tunnels. In the event of a fire, its role is to extract smoke as far as possible and limit its spread, firstly to protect passengers so that they can evacuate the tunnel, and secondly to facilitate the intervention of emergency services and fire-fighting....