The world’s first underground transit line of London in theyear 1863, was based on steam locomotives that had littlethought on ventilation. Later, ventilation was improved byopenings in the tunnel and removing glazing over the stationroof. However, the average ambient temperature of the tunnelincreased from 14°C (57.2°F) to about 25°C (77°F) in last 150years due to heat of the trains and improper ventilation.

Other cities have learned from London’s mistakes, andensured that ventilation systems are an integral part of newmetro systems. Today, all the modern transportation systemover a certain length, located below the surface in undergroundstructures either based on Road or Rail essentiallyrequires Tunnel Ventilation System (TVS) for the normal operationand the control of smoke during emergency.

There are a myriad of papers and handbooks that arepublished by different associations which provides materialaddressing the issue of tunnel ventilation. The Subway EnvironmentDesign Handbook (SEDH) was the first comprehensivesuch document addressing the ventilation andenvironmental control in transit tunnels and undergroundstations. The PIRAC (Permanent International Association ofRoad Congress) has published several important specificdocuments on tunnel fire safety and ventilation for roadtunnels. The ASHRAE handbook also has a chapter onEnclosed Vehicular Facilities which addresses the tunnelventilation.

The authors are fortunate to have been involved in thestate of the art TVS deployed in the Delhi Mass Rapid TransitSystem in India. The authors feel that though there are countlessdocuments available on TVS, still a comprehensive documentwhich described the TVS along with different componentsfrom the designing and simulation stage to the final commissioningof the TVS is missing.

This paper starts with history of evolution of the TVS andits development for mass rapid transit system. Further, thedetails of TVS deployed by Delhi Metro in underground corridorsand the simulation studies to arrive at the capacities ofTVS are presented. The various components of TVS e.g. TunnelVentilation Fans, Tunnel Booster Fans, Tunnel VentilationDampers, Sound Attenuators, Nozzles, and Air Compressorsare presented along with their construction material, testingand performance requirements and installation particulars.The performance assessment of TVS before the system is beingput in use for revenue operations along with their control andmonitoring from the centralized Operation Control Center(OCC) and at the underground stations are also presented.