Ventilation and smoke extraction for metro systems

On January 12, 2015, smoke engulfed the L'Enfant Plaza metro station in Washington, impacting two trains, one of which was unable to reach the station. The event caused the death of one person and poisoned 84 others. An analysis of the causes of this tragedy showed that, after an arcing-type trigger, the filling of the station and subway tunnel with smoke could have been avoided by a better smoke extraction strategy.

The smoke ventilation system is a key factor in ensuring the safety of people in the event of fire in an urban guided transport tunnel. It is also necessary to maintain good thermal conditions during normal operation. Its design and the development of activation scenarios are essential.

Here, urban guided transport systems are understood in the broadest sense, encompassing the metro and the Paris regional express train in urban areas, as well as underground sections of tramway and funicular networks in urban areas.

In France, these steps are governed by regulations, but in order to apply these regulations properly, it is important to understand the physical phenomena and underlying principles. This article aims to do just that. The demonstration is based almost exclusively on French regulations, with a brief digression on standardization in the USA, but the physical principles are of course identical for all countries.

Firstly, the role of ventilation and the main principles involved are explained. French regulations are then reviewed and explained. The various possible tunnel ventilation schemes are then explained, and placed in the wider context of stations and interconnections between lines, showing how design and sizing are carried out. Finally, the principles of scenario-based verification are detailed.