East + West
August 01, 2010
Appeared in NFPA Journal
The new AeroTrain transit system is a critical part of the upgrades underway at Washington Dulles International Airport. The system, which began operation in February, connects current and future concourses via an underground tunnel system, and it was important to design the system in a way that provided not only swift and efficient movement of passengers, but also maximized the protection of passengers and first responders in the event of an emergency.
Designing a smoke control system in an underground mass transit setting is a complex proposition. In the case of the AeroTrain system — also known as the Automated People Mover (APM) — the open architecture of the stations added further challenges. To create open and inviting terminals, the Metropolitan Washington Airports Authority (MWAA) decided to forego door enclosures that would separate the concourse level from the station platforms, which were two stories below. That physical connection became a major factor when it came to designing and implementing effective smoke control strategies to ensure safe passenger egress to the concourse level.
Syska Hennessy Group, the consulting engineering firm I work for, became involved with the Dulles AeroTrain project in 2001 when it began working with the architect, HOK, to design the HVAC, electrical, sprinkler, and fire alarm systems for two APM stations, located at either end of the airport’s Concourse B. Syska Hennessy’s mechanical engineering team was involved in the design of the APM stations from the earliest stages of the process, meaning that fire- and life-safety considerations as specified in NFPA codes were part of every design decision, from the concept stage onwards. Working with the architects’ wish list, Syska Hennessy’s engineering team, in collaboration with the Dulles Airport fire marshal and safety committee, developed a set of innovative design solutions, several of which had not been previously used in airport design in the United States.
Designed by Eero Saarinen and inaugurated by President John F. Kennedy in 1962, Washington Dulles International Airport is one of the nation’s great monuments to the early days of air travel. It was the first airport designed with separate buildings to accommodate people and aircraft; passengers were processed in one building, then boarded one of the airport’s “mobile lounges" — a fleet of diesel-powered transport vehicles — that ferried them across the tarmac to their waiting aircraft.
But what seemed forward-looking five decades ago gradually became outmoded and cumbersome. As aircraft became larger and traffic became heavier, Dulles became more difficult and time-consuming for passengers to navigate. The main terminal was expanded, and additional concourses were built in an attempt to handle the greater volume of traffic. The mobile lounges were used as oversized commuter vans to shuttle passengers to the new concourses, and, as the years went by, the aging lounges became symbols of everything that was wrong with Dulles. A 1994 story in The Washington Post, headlined “Where Should the Dulles Mobile Lounges Go to Die?”, began: “Give them five years, maybe 10. But with a lurch and a clunk, Dulles International Airport has begun to ditch its infamous mobile lounges.”
To efficiently transport a growing number of passengers — the airport hosts more than 23 million passengers annually — Dulles officials envisioned an underground people-mover system that would eliminate ground transport and help streamline airport operations.
Such a system was part of the MWAA’s Dulles Development program, or D2, which was launched in 2000. The $3.4 billion initiative included new runways, a control tower, a security plaza in the main terminal, parking garages, and more. The new AeroTrain, which replaced most of the mobile lounges, and its related infrastructure accounted for about $1.5 billion of the D2 budget and was the first step toward modernizing the passenger conveyance component of the facility.
Using NFPA 130, Fixed Guideway Transit and Passenger Rail Systems, which applies to subway systems as a whole, including stations, trains, tunnels, and platforms, and NFPA 92B, Smoke Management Systems in Malls, Atria, and Large Spaces, Syska Hennessy engineers designed the Concourse B APM stations. The final design scheme called for integrating two new AeroTrain stations at either end of the existing Concourse B, adding 15 new gates, and expanding the concourse level from 560,000 square feet (52,026 square meters) to more than 800,000 square feet (74,322 square meters). The West Station covers 152,000 square feet (14,121 square meters) and contains 12 elevators, 10 escalators, and 18 stairwells, as well as concessions and gates at the concourse level. The East Station covers 118,000 square feet (10,963 square meters) and includes four elevators, eight escalators, and eight stairwells. Train tunnels are separated from the station’s platform by glass enclosures. While their designs vary, both stations open to the concourse level above.
This direct connection to the concourse was a concern that had to be addressed effectively and economically. The electrically operated trains and the track bed are the most likely sources of fire in a subway system, and passengers evacuating a train on fire in the station via the train enclosure doors could allow smoke to spread into the concourse above. The designs of the stations necessitated different approaches to fire protection and smoke control. The West Station was designed with a much larger and more open connection to the concourse than the East Station, which is located mostly beneath a mobile lounge crossing and a bridge at the east end of Concourse B. In the West Station, innovative smoke containment barriers were specified to prevent smoke from the subway station from reaching the concourse level. In the event of a fire, deployable smoke barriers made of a fire-resistant cloth composed of fiberglass, stainless steel, and aluminum drop to within 7 or 8 feet (2 or 2.4 meters) from the floor. This creates a physical barrier and ensures that smoke will bank up against the smoke extraction fans at the top of the space.
The curtains also help reduce the opening between the concourse and the station. As they descend, air velocity increases through the egress opening, keeping smoke in the station and out of the concourse. Manufactured by Coopers Fire, these curtains had not been used before in the United States, and the design team had to obtain approval for their use by the airport’s fire marshal and safety committee, which were the authority having jurisdiction.
At the East Station, smoke control is achieved through the introduction of outside air at the escalators, eliminating the need for curtains.
The design of both stations required a complex network of stairs to evacuate the platforms and provide emergency egress from the tunnels. These stairs had to be pressurized due to the stations’ designation as underground buildings. Because of the sheer size and volume of the stair passages, and because of the number of people that could be flowing into and out of the stair doors simultaneously, the team decided to equip the pressurization fans with active pressure control and variable pitch-in-motion fan blades. The resulting system can modulate to maintain positive pressure in the stairs regardless of how many doors are open. It also ensures that the doors are operable and not over-pressurized when few doors are open.
Calculating the most efficient placement and size of the fans used to manage smoke removal was achieved using computational fluid dynamics (CFD) modeling. An algebraic calculation approach to design, fire, and smoke plume analysis resulted in smoke evacuation requirements of nearly 1 million cubic feet per minute (cfm). By using the CFD model and strategically locating the exhaust and makeup air points in the station, the system capacity was reduced to 460,000 cfm. The model was also indispensible for analyzing the location and timing of smoke detectors, the movement of smoke between the tunnels and the station in various tunnel ventilation modes, and the effects of the deployable smoke barriers.
Integration + Suppression
Syska Hennessy worked with the tunnel design team, HNTB Corporation, and the AeroTrain system provider, Mitsubishi Heavy Industries, to develop a fire alarm system. We also worked with all the design teams to identify the manual responses — by a train operator or emergency responder, for example —a nd automatic responses, such as smoke control or the operation of the main sprinkler system, necessary for any given emergency. A fire could occur in a station, a train could catch fire between stations in a tunnel, or a train could simply stop between stations without a fire. Regardless of the emergency, the train operator, who controls traffic remotely, must have all the relevant information at his fingertips to be able to respond appropriately. This meant that all systems had to be integrated and communicate effectively with one another.
The result of our emergency-scenario input was the innovative comprehensive ventilation interface and control system (CVICS), designed by the firm Hatch Mott MacDonald. This integrated system communicates and receives data from the building automation system, the fire alarm system, the train’s traction control system, and the train operator in the command center, and is responsible for supervisory control of the tunnel ventilation system and the station smoke control systems. CVICS identifies an emergency based on the information it receives from those systems and alerts the train operator to a possible problem. The system essentially asks the train operator, “tell me what you know,” and is programmed to take action depending on the answers it receives. The operator can override that action or accept it; CVICS can also act without an answer from the train operator. Meanwhile, the fire alarm system alerts first responders.
Another innovation addressed the difficulty of fighting train fires. Most train fires occur in the traction system in the motors beneath the cars and getting to those fires can be difficult, considering that firefighters can only access a train at either end when it is in a tunnel. In the event of a fire in an AeroTrain station, however, a high-pressure mist suppression system can be activated manually to help fight track and undercarriage fires. The vapor generated by this system can penetrate the tightest spaces, extinguishing fires by cooling, oxygen depletion, and radiant heat absorption.
Ordinary sprinkler systems generate droplet sizes in the 0.04- to 0.2-inch (1- to 5-millimeter) range. By contrast, Dulles’ Hi-Fog system, provided by Marioff Corp., produces water droplets of less than 0.001 inch (0.025 millimeters). The tiny water droplets can penetrate deeply into equipment without doing a lot of damage, since only a small amount of water is used. The limited use of water and the added protection from radiant heat also add to the protection of the firefighters, who no longer have to risk standing in deep water under potentially hazardous conditions. NFPA 750, Water Mist Fire Protection Systems, was used in the design of the high-pressure mist system. Fire suppression systems throughout the stations and concourses were all designed to meet the requirements of NFPA 13, Installation of Sprinkler Systems.
The Dulles project required the integration of multiple system elements and design teams, and the lessons we learned during the design process are being put to use daily in our designs. Syska Hennessy Group recently completed the renovation design for the General Services Administration’s headquarters in Washington, D.C., and systems integration was a major part of the project, where sustainability drove the need for efficient integration of a diverse set of building systems. Lighting control, daylight harvesting, automated blind controls, photovoltaic systems, natural ventilation, and radiant cooling are just a few of the technologies integrated on a single fiber-optic communications system — a prime example of how the integration of architecture and mechanical/electrical systems and controls, at both a physical and electronic level, is increasing throughout our industry.