Assisting Underground Railway Safety
Temperatures on a vertical cross-section along the platform after 3 minutes
In recent years, following the fires at Kings Cross Underground station and in the Channel Tunnel, transport authorities have been acutely aware of the need to ensure provision of adequate means for evacuation and escape for passengers in an underground train or station in the event of fire. With these considerations in mind, the Rome underground railway system recently upgraded the ventilation arrangements on one of its lines. On detection of a fire, emergency fan procedures are activated so as to increase the flow of ventilating air along the relevant tunnels, with the aim of providing fresh air to passenger escape routes.
The consultancy D'Appolonia SpA of Genova commissioned Flowsolve to simulate a number of train-fire scenarios in tunnels and station on the Rome system, to confirm the adequacy of these new ventilation arrangements. The study was managed by STA, Societa Transporti Automobilistici SpA, on behalf of the Municipality of Rome, VII Department.
Scenarios considered included simulations of fires originating on trains in sub-surface and deep-bored tunnels and stations. Each fire was simulated as a heat source, increasing to several megawatts and subsequently decaying, located within the burning carriage. The model simulated the development of the fire plume within the carriage, the egress of hot air and smoke out of the doors, and subsequently the escape of hot air through the roof when the latter collapses. The collapse of the roof allows the fire plume to extend into the upper part of the tunnel. In some cases this was shown to substantially modify the local ventilation pattern, with the supply of cold fresh air being forced beneath the hot plume, creating a pressure disturbance which propagates at a speed comparable with the velocity of the forced ventilation air.
The various scenarios considered had different smoke extraction arrangements, the efficiency of which could be determined as an outcome of the model simulations. A particular feature of the predictions was that for a deep-bored station tunnel, roof-level smoke extraction was shown to be very efficient in removing the drifting hot air and smoke before this could cause problems for passenger escape.
In the case illustrated above, one of the carriages of a train at a station platform has been ablaze for 3 minutes. The plots show temperature contours on a vertical cross-section along the platform (the vertical scale has been increased by a factor of three for clarity). It is clear how the draught of ventilating air improves the possibility of passenger escape.
