Opportunity
Los Angeles is known as a city of drivers, but tens of thousands of LA residents rely on public transportation.
Bulky streetcars known as Yellow Cars once ran to East LA, but service stopped in the early 1960s. In 2004, work began on a six-mile (ten-kilometer) extension of the city’s Gold Line light rail system that would reconnect East LA to the rest of the city.
The Gold Line extension, including eight new stations, was to designed to run from downtown Los Angeles through the neighborhood of Boyle Heights and ending in East LA. Two underground stations, Soto and Mariachi Plaza, featured challenging and unique architecture that required rigorous analysis to demonstrate that they could be ventilated effectively in the event of a train car fire incident.
Naturally occurring methane in the ground had to be vented from the stations and the adjoining tunnels, especially during hours when the piston action of moving trains would be absent. The ventilation system would have to meet the requirements of National Fire Protection Association standard 130 (NFPA 130) and the California Building Code and Los Angeles County’s own Design Criteria.
Solution
In 2005, Mott MacDonald was retained by the Los Angeles County Metropolitan Transportation Authority as a subconsultant to the design-build contractor. We provided analysis, design, and testing services for the ventilation systems at the Mariachi Plaza and Soto stations, and for two miles of twin bore tunnels. We designed the ventilation system to control smoke and heat from a fully engulfed train car fire.
The ventilation at each of the stations is provided by four reversible seven-foot-diameter axial fans that are remotely operated from the Rail Operations Control Center. Four reversible jet fans at the east and west tunnel portals provide additional smoke control.
Mott MacDonald used the Subway Environment Simulation (SES) software to create a network model for the two stations and their tunnels. Using SES, we quantified the piston effect created by moving trains and its impact on customers under normal and congested train operating conditions. In addition, we designed the ventilation system to incorporate gas mitigation and prevent potentially hazardous accumulation of methane.
Computational fluid dynamics (CFD) was used to model three-dimensional air flows and smoke movement and analyze the performance of emergency ventilation systems. The CFD model provided an accurate 3D representation of the aerodynamic and thermodynamic effects at the stations and tunnels. The performance of the ventilation system was validated through physical testing in the stations and tunnels using calibrated air measurement equipment.
Outcome
Our analysis showed that smoke movement would be controlled, providing a tenable egress route for passengers and smoke-free access for first responders in the event of a fire. As part of the testing, Metro arranged for an actual trained to the parked in the tunnels in order to replace conditions that we modeled in the CFD analysis. The tests were carried out in the presence of Metro Operations and the LA Fire Department. This allowed all stakeholders to experience smoky conditions in the tunnels and the influence of ventilation on smoke control.
Through regular meetings and workshop sessions with the LA Metro Fire Safety Department and Rail Operations, we developed a safe and cost-effective ventilation system that satisfied and exceeded NFPA 130 requirements and gained the approval of the LA Fire Department without additional cost. We led the effort to test and commission the tunnel ventilation system to verify system performance and optimized the ventilation mode tables that were implemented by the control-systems contractor.
In November 2009, a train broke through a banner at the East LA Civic Center station to mark the first day of the Gold Line extension. About 75,000 riders helped celebrate with firecrackers, confetti cannons, and mariachi bands.
Yvette Robles Rapose of the Metropolitan Transportation Authority said, “The only thing that’s going to be different between having no train and having a train is that there’s going to be an influx of people coming to the Eastside that have never been there before. They’re going to shop there, they’re going to eat there, and they’re going to provide opportunities that were never there before the train came.”