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Natural ventilation for Milpitas Station

A study of a California rapid transit station determined that natural ventilation could be used successfully to control smoke during a fire incident.


The Silicon Valley Rapid Transit Project (SVRT) extends the existing Bay Area Rapid Transit (BART) third rail transportation system 16.3 miles (26.2 kilometers) from Warm Springs to Milpitas, San Jose, and Santa Clara.

The first 11.8 miles (19 kilometers) are at grade, elevated, or in trench from Warm Springs to the eastern portal structure near Alum Rock. From there, the system continues 4.5 miles (7.2 kilometers) underground through downtown San Jose, passing through four cut-and-cover stations (Alum Rock, Civic Plaza/San Jose State University, Market Street, and Diridon/Arena), two ventilation structures, and a crossover to arrive at the west portal in Santa Clara. The system then continues at grade to the Santa Clara surface station near the existing Santa Clara Caltrain station.


Mott MacDonald was responsible for the design and construction management of the tunnel segment, interagency coordination, and the project cost and schedule controls for the entire SVRT project. In addition, we provided expertise in ventilation and computational fluid dynamics (CFD) modeling to support the fire/life safety evaluation of the design.

Mott MacDonald was responsible for the ventilation study of Milpitas station. The objective of the study was to evaluate whether tenable conditions of the station could be achieved during a fire incident within the evacuation time by utilizing a natural ventilation design concept, and to decide whether a mechanical ventilation system was required. The tenability criteria are defined in the 2001 California Building Code (CBC) and the 2007 NFPA 130.


After exploring different ventilation strategies for the station, Mott MacDonald used the Santa Clara Valley Transportation Authority's CFD field model approach to assess the wind effects on smoke movement and the performance of the natural ventilation system.

We recommended a design modification to the venting system to help ensure successful natural ventilation for smoke control.

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