AIVC 11772 Cha~ CURRENT ISSUES, ALTERNATIVE CONCEPTS, AND DESIGN CRITERIA FOR SUBWAY VENTILATION SYSTEMS Paul C. Miclea ICF Kaiser Engineers, Inc., Oakland, California ABSTRACT their homes to their places of work, shopping centers or entertain­ ment locations in large metropolitan areas, in particular, are the With the growing urban population and the concern for traffic principal reasons for a continuous demand for more and more congestion and pollution (emissions control), public transportation transit systems. is becoming more and more attractive to both city dwellers and Whatever innovations will be brought to the design and con­ managers. To gain access to the central area of the city, the sub­ struction of mass transit systems, one thing is sure: the systems way remains the most viable alternative, despite its higher cost need to move more people, more rapidly, and more safely. Sys­ when compared to above ground or elevated transportation systems. tems will be above ground where possible, but the competition for There are relatively few regulations and criteria for subway space, together with the need to suppress noise pollution will ventilation, particularly when compared with mine ventilation. The cause some of the new traffic to be diverted generally under­ main document that provides guidance and general recommenda­ ground (e.g., under cities, rivers, airports, etc.). tions for subway ventilation and environmental control is the Sub­ Urbanization brings a scarcity of available land for new trans­ way Environmental Design Handbook, published in 1976 (2nd portation corridors. In addition, the price of land in large metro­ edition) by the U.S. Department of Transportation, Office of Re­ politan areas, coupled with the interference of new corridors with search and Development. Many of the subway systems in exist­ the already congested street traffic and gridlock, makes the sub­ ence today have been designed and built with ventilation features way transit system a viable alternative. adequate for normal train operation, but their design does not New subway systems are currently under construction or on consider stringent criteria for such emergency conditions as a the drawing boards for many large or emerging metropolises - train fire in a tunnel. The National Fire Protection Association's among them: Athens (Greece), Bangkok (Thailand), Cairo Standard for Fixed Guideway Transit Systems known as NFPA (Egypt), Copenhagen (Denmark), Sao Paolo (Brazil), Taipei (Tai­ 130 as well as the ASHRAE Handbook - HVAC Applications wan), Tel Aviv (Israel). (1995) provide specific design and operation requirements for Existing subway systems in other large (and still growing) met­ subway ventilation systems. Some of the existing, old subways ropolitan areas are becoming overcrowded, and the need for ex­ are upgrading their ventilation systems to comply with the new tending the network as well as for increasing the speed (and con­ regulations. sequently the ridership) is always a top priority for operators. Al­ The ability of a particular ventilation system design to provide most all existing subways are currently extending their systems, adequate ventilation during normal and emergency conditions can e.g., Hong Kong, London, Moscow, New York, Paris, San be evaluated using computer modeling and simulation tech­ Francisco's BART, Seoul, Tokyo, Toronto. niques. A train fire will cause a sudden change in the tunnel ven­ To illustrate the order of magnitude in public transit, see the tilation pattern by adding an unsteady and fast-growing source of statistical data for several subway systems around the world (from heat. The hot air and gasses created by a fire will tend to flow Jane's Urban Transport Systems, 1991) in Table 1 on the follow­ uphill, possibly against the normal flow, producing a "backlayering ing page. effect." To prevent this effect from happening, enough ventilation Moscow's "Metropolitan• carries nine million persons a day, must be provided and the governing criterion to establish the re­ followed by Tokyo Metro with eight million, Mexico City and Paris quired airflow is called "Critical Velocity." with five million each, New York City, Hong Kong and Seoul with Several software packages are available for special applica­ only 3.5 million each while London is far behind with just 2.5 mil­ tions on tunnel and station ventilation as well as to model the lion passengers every day. spread of smoke and heat in case of a major tunnel fire, using For suburban mass transportation, several high speed rail Computational Fluid Dynamics. projects are under construction or on the drawing board all around This paper presents the current issues in subway ventilation, the world. Most of them include long tunnels and challenging as shared by the public transit community around the world, to­ ventilation systems. gether with modern alternative design concepts vis-a-vis the more Under construction is a major subway-like project in London: stringent emerging Fire-Life Safety criteria. Examples of recent the Heathrow Express (HEX), between Paddington Station in studies and ventilation systems design are provided. London's west end and Heathrow airport, scheduled to open in 1998. This express subway line will have a km of new railway INTRODUCTION tunnels and two major underground stations. Another interesting project, not a subway but requiring major The population growth in general combined with current urban ventilation capability is the Channel Tunnel Rail Link, from the development around the world and the need to move people from Channel portal in Kent to the St. Pancras Station in downtown 64 PROCEEDINGS OF THE 6TH INTERNATIONAL MINE VENTILATION CONGRESS CURRENT ISSUES, ALTERNATIVE CONCEPTS, AND DESIGN CRITERIA FOR SUBWAY 65 Table 1. spread of smoke and bot gases from the fire into the periods at temperatures up to 52°C evacuation path (and prevent the backlayering effect). Suburban Ball Me!rQ Leag!h Critical velocity is a site-specific value based on tunnel Ventilation Design Concepts for New Subway Systems MelrQ eQp!Jla!iQD MelrQ Bidera (•) ~ (km) geometry, beat release rate, psychrometric conditions of (mlns) (mlns/yr) .BlQm ("") (mlns/yr) ventilating air, and tunnel grade at the location of the fire; The most effective ventilation system in tunnels would be a 170 The maximum air velocity along the egress route should transverse system which would allow smoke removal close to the Mexico City 20.0 1,550 302 45 be less than 10 mis. source, thus allowing the passengers to escape safely along the Sao Paolo 16.0 635 422 117 For station fires the ventilation system should provide uncon­ tunnel in both directions in case of a fire. Such a system, how­ Seoul 13.5 1,007 170 443 taminated air along station entrances and non-pressurized emer­ ever, is very expensive since it involves the installation of extract New York 13.3 1, 136 8,182 219 gency exits. Similar to tunnels, the maximum air temperature in ducting in the crown of the tunnel and, consequently, enlargement Tokyo 11.9 2,541 511 551 the evacuation route should be less than 60°C. of the tunnel cross sectional area. The longitudinal system where Paris 10.2 1,552 1,365 223 Criteria for Emergency Fans. NFPA 130 requires that emer­ the smoke is driven along the tunnel, away from fire and from Moscow 9.9 2,741 1,486 gency fans be designed with redundant power supply from two passengers, thus enabling them to escape into the oncoming Bombay 9.2 550 406 power feeders from two separate sources (i.e., separate traction fresh air flow, is much less expensive [9]. London 6.7 785 117 power substations or separate utility substations). In addition, Implementation of the ventilation system for new subways var­ Hong Kong 5.5 1,066 fans should be fully reversible and satisfy the following conditions: ies from country to country, and sometimes from city to city. In Fans, their motors, and all related components exposed • Metro includes subway, regional metros, light rail, and tramway . order to design a ventilation system capable of moving air in the to the ventilation airflow must withstand a temperature of Suburban rail includes conventional "heavy" and interurban commuter passenger rail most convenient direction to protect passengers and provide ac­ 250°C for a period of at least one hour cess for fire-fighters, the following concepts and design options .\ Local fan motor controllers should be separated from are most common: London. Out of a total length of 108 km, approximately 27 km will there must be a basis or criteria to check for compliance. For ventilation airflow by a one-hour fire-resistance-rated S!atiQn fans, In this concept, fan plants are attached to the be in tunnels; the longest tunnel, in London, will have twin bores normal conditions, the ventilation system should maintain accept­ separation station, most often at the end of the platform, or 10 to 20 m inside of 18 km in length. The link will allow high speed trains of up to able environmental conditions for passengers and personnel as Airflow induced by emergency fans should meet critical the tunnel. The shafts are designed to operate as blast/relief 300 km/hr. well as suitable operation of equipment and installations. In case velocity criteria in either supply or exhaust vents during normal operation (to alleviate the pressure of the in­ Special precautions must be taken to reduce the effect of a fire of fire in a tunnel or in an underground station, the emergency Discharge and supply air openings to the fans should be coming trains) and also as fan shafts (by closing the dampers on or of release of toxic substances in very long tunnels, such as the ventilation system must be able to control the direction of move­ at a sufficient distance apart or other measures should the relief section of the shaft).