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ISSUE NO. 78 DECEMBER 2014 A technical journal by Parsons Brinckerhoff employees and colleagues http://www.pbworld.com/news/publications.aspx

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INTRODUCTIONGlobal Perspectives on Tunnel SystemsJohn Munro, Kate Hunt, Steven Lai, Argun Bagis .............3

FIRE AND LIFE SAFETYSubway Tunnel Cross-Passage Spacing: A Performance-Based ApproachWilliam D. Kennedy, Justin M. Edenbaum, Mia Kang, Kirk G. Rummel ...................................................................10

A Note on Fixed Fire Fighting Systems in Road TunnelsAnna Xiaohua Wang, Norman Rhodes ...........................13Fixed Fire Fighting Systems in Road Tunnels – System IntegrationMatt Bilson, Sal Marsico ...................................................16 Fire-Life Safety and System Integration: The Functional Mode TableMatt Bilson, Andrew Gouge ..............................................19

VENTILATION SYSTEMSUsing Quantified Risk Assessment to Inform Ventilation System ResponsesKate Hunt ...........................................................................23A Risk-Based Approach to Jet Fan OptimisationAnthony Ridley ...................................................................26Cost-Effective Ventilation System for a Light Rail Transit ProjectSilas Li, Andrew Louie .......................................................30Meeting the Challenges of Smoke Duct Fan Selection for Australian Road TunnelsChris Chen ..........................................................................34 Analysis Considering the Conversion of an Existing Road Tunnel Transverse Ventilation System to Transit UseJesse Harder, Andrew Louie, Vamsidhar Palaparthy, Silas Li ..................................................................................37

Long Road Tunnels and Portal Emission Control

Argun Bagis, Duncan Saunsbury .....................................41Merging Emergency Ventilation System Sound Power and Pressure Drop CalculationsMichael MacNiven .............................................................44 Cost-Effective Power Supply Scheme for Tunnel Booster Fans in Long TunnelsCC Cheung, Steven Lai .....................................................48 Air Purification System for a Road Tunnel ProjectCathy Kam, Chris Ma, Steven Lai ....................................51

PRESSURE TRANSIENTElimination of Portal Flares Kenneth J. Harris, Bobby J. Melvin, Steve Gleaton .........52Comparison of 3-D and 1-D CFD Simulation Approach for Aerodynamic Effects in a HSR Tunnel System Dicken KH Wu, Rambo RB Ye ...........................................55

CLIMATE CHANGE AND RESILIENCYRailway Cooling Challenges Mark Gilbey ........................................................................60

Dynamo – Enhancing Tunnel Ventilation Modelling Jolyon Thompson ...............................................................63

ASSET MANAGEMENT AND PROGRAM SUPPORTAsset Management Database for the Brooklyn Battery Tunnel Ferdinand Portuguez, Debra Moolin .................................67

COMMUNICATIONS / POWER AND ELECTRICAL SYSTEMS SCADA System Security for Two UK Road Tunnels Peter Massheder ...............................................................71CCTV Design for a US Road TunnelRyan Williams ....................................................................73 How Alternating Current Interacts with Direct Current in the Shatin to Central Link Traction Systems in Hong Kong – A Quantitative Approach Sam Pang ...........................................................................76

CONSTRUCTION AND REHABILITATIONTunnel Inspection Basics for Mechanical and Electrical Systems James Stevens, Mark VanDeRee ......................................81 Tunnel Sump Construction Savings Through Drainage System Design Modification Kevin Stewart .....................................................................86

LIGHTINGThe Modernization of Tunnel Lighting and Controls: Technology, Challenges, and Cost of Implementing a Tunnel LED Lighting SystemChristopher J. Leone, Jonathan T. Weaver,Kimberly Molloy .................................................................89

SES AND MODELINGEvaluating Freeze Protection Needs with CFD Raylene C. Moreno ............................................................92Computational Modeling as an Alternative to Full-Scale Testing for Tunnel Fixed Fire Fighting Systems Kenneth J. Harris ...............................................................96 Latest Enhancements to the Subway Environment Simulation (SES) Program Andrew Louie, Tom O'Dwyer, Silas Li ............................ 100Use of Building Information Modelling (BIM) on Road Tunnels and Metro Projects YF Pin, R. Ashok Kumar, Steven Lai .............................. 102

Call for Articles ............................................................. 104

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Introduction: Global Perspectives on Tunnel Systems

For decades, Parsons Brinckerhoff has been at the fore-front of providing innovative tunnel systems solutions to our clients. In 1973 at the First International Sym-posium on Aerodynamics and Ventilation of Vehicle Tun-nels in Canterbury England, attended by representatives from 26 different countries, a paper was presented on the Subway Environmental Simulation (SES) program co-developed by the late William D. Kennedy. That paper led directly to a contract for the design of an extension to the Hong Kong Metro and, out of that project, Parsons Brinckerhoff’s Hong Kong office was established. Over 40 years later in 2015, Dr. Norman Rhodes of Parsons Brinckerhoff will chair the 2015 16th International Sym-posium on Aerodynamics, Ventilation, & Fire in Tunnels to be held in Seattle.

Advances in tunnel systems have evolved to account for a changing world, and Parsons Brinckerhoff’s response has been to ensure that we are both anticipating and responding to these changes and challenges as they oc-cur and that we continue to provide innovative and robust solutions to our clients.

Responding to the challenges of climate change, and the resiliency needed to adapt to a rapidly changing climate, or providing sustainable energy and environ-mental solutions require advances in existing tunnel system technologies and new technologies. Examples of this could be the design of a sustainable LED light-ing solution for the Queens Midtown Tunnel in New York or using groundwater to cool the rising temperatures in the London Underground tunnels (see Mark Gilbey’s article in this issue).

Parsons Brinckerhoff remains at the forefront of the provision of tunnel safety system solutions and their continued improvement as technology evolves. Our un-derstanding of fire behavior and development in tun-nels has increased considerably as a result of testing

programs such as the Memorial Tunnel Fire tests1 in West Virginia, led by Parsons Brinckerhoff, and more recently the Runehammer fire test program in Europe. This has allowed us to develop more focused strate-gies that address individual tunnel fire sizes and spe-cific risks. For example, Parsons Brinckerhoff designed a tunnel fire suppression system for the Doyle Drive tunnel project in California. The recently opened Airport Link tunnel in Australia has emergency exits with built-in voice messages to guide users to safety in the event of a fire incident.

Although systems technology has advanced significantly over the years, we must keep asking: What will the needs be for future tunnel owners, operators, and users and how do we develop our tunnel systems to respond to those needs?

The imperative to provide resiliency in our designs and to ensure that our designs are also energy efficient and sus-tainable are what drives our solutions. Parsons Brincker-hoff has become a charter member of the Institute for Sustainable Infrastructure to affirm our commitment to the underlying principles of sustainable infrastructure, as well as the specific, evolving practices that characterize sustainable solutions. Our tunnel systems designers are trained in sustainability assessment.

We also need to keep researching and innovating. Our 2014 William Barclay Parsons Fellowship winner, Anna Wang of our tunnel systems team in New York, is devel-oping a model to predict the interaction of fixed fire fight-ing systems on tunnel fires. The outcome of this work will be used to achieve more efficient designs leading to considerable cost savings for our clients. (See Anna Wang and Norman Rhodes’ article in this issue.)

Finally, we need to recognize that smart or connected road and rail vehicles are a rapidly developing part of our

1See “Pioneering New Technology: PB’s Innovation in M&E Analysis and Design,” (Network #34, Spring 1996) for three articles on the Memorial Tunnel Fire Ventilation Test Program, at the time the most comprehensive full-scale fire ventilation testing undertaken.

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present and future. Parsons Brinckerhoff is involved in a program to evaluate connected vehicle technol-ogy. The potential for connected vehicles to interact with tunnel systems is limitless. Imagine a tunnel ven-tilation system that automatically regulates its airflow based on the number and type of vehicles travelling through the tunnel or a deluge system putting out a vehicle fire without waiting for a tunnel operator to re-spond to the emergency.

Tunneling Overview in the United Statesby John Munro, New York, NY, US, +1-212-465-5588, munroj@pbworld.com

Standards such as NFPA 130, ‘Standard for Fixed Guide-way Transit and Passenger Rail Systems,’2 or NFPA 502, ‘Standard for Road Tunnels, Bridges, and Other Limited Access Highways,’ have been a cornerstone guiding the design of tunnel systems for the last few decades. In many countries, these have been used as the de-facto international standards shaping the design of tunnel so-lutions globally.

In the United States, Parsons Brinckerhoff has been cen-tral in shaping the direction of both NFPA 130 and NFPA 502 through active committee participation and chair-manship. Perhaps the most significant development in recent years is the change from purely prescriptive standards to standards that allow performance-based approaches. For example, NFPA 130 states: ”Nothing in this standard is intended to prevent or discourage the use of new methods, materials, or devices, provided that sufficient technical data are submitted to the authority having jurisdiction (AHJ) to demonstrate that the new method, material, or device is equivalent or superior to the requirements of this standard with respect to fire performance and life safety.”

The change from prescriptive to performance-based designs has led to a situation where designers can exercise a greater level of flexibility and innovation in providing solutions for our clients. For example, previ-ous standards prescribed a fan inlet temperature that had to be met without regard to the actual temperature that a fan inlet may experience in a fire. The current standards require that designers analyze the actual fan inlet temperatures that would be experienced for the type of fire that could be realized in relation to the spe-cific rolling stock for that system. Another example is

described in “Subway Tunnel Cross-Passage Spacing: A Performance-Based Approach,” by Kennedy, Edenbaum, et al, which shows that the spacing of cross-passages, the width of walkways, and the width of cross-passages all have an effect on the simulated evacuation time from a train stopped in a tunnel.

Performance-based design challenges designers to more accurately define inputs and parameters, and thus create more accurate models. As with any engineering design, the more accurately you can define and analyze the situation, the less conservative the design and, hence, more value is provided to our clients.

An example of Parsons Brinckerhoff adding value for our clients by more accurately defining design inputs is in the area of analyzing design fires. Historically, de-sign fires were prescribed, often conservatively, based on limited information at the time. The advancement of analysis tools, such as computational fluid dynam-ics (CFD), coupled with better research data, allows us to much more accurately define the design fire which is a major criterion in tunnel system design. CFD and risk analysis were used on recent projects to determine the fire curves for the projects, ultimately leading to a cost-effective design. (See “Cost-Effective Ventilation System for a Light Rail Transit Project,” by Silas Li and Andrew Louie.)

As alternative procurement and delivery methods, such as design-build, become more frequent in the US, perfor-mance-based tunnel systems design can play a central role in providing value. Design-build projects are essen-tially outcome-based and innovation plays a central role in defining their success. The flexibility of performance-based design not only allows but encourages innovation, making it an ideal design methodology that is suited to design-build projects. On recent projects, we have been using the latest fire modeling and heat transfer tech-niques to refine tunnel structure thickness requirements due to fire effects. Reducing structural thickness can reduce construction cost and delivery schedules.

In addition to the design and construction of new tun-nels, such as the recently opened Port of Miami Tunnel, there is an increasing focus in the US on aging infra-structure. MAP-21 (the Moving Ahead for Progress in the 21st Century Act of 2012) includes funding for contin-ued improvement to tunnel conditions that are essen-tial to protect the safety of the traveling public. Parsons Brinckerhoff has continually developed and refined our

2NFPA 130 (2014) and NFPA 502 (2014), National Fire Protection Association, www.nfpa.org

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techniques, including using the latest inspection and as-set management technologies, to efficiently assess ex-isting tunnel infrastructure (see articles by Stevens and VanDeRee; and by Portuguez and Moolin). Following the assessment, our performance-based methodologies are used to develop innovative upgrades that provide a level of safety equivalent to code-compliant solutions and that minimize or eliminate interruptions to tunnel operations.

High speed rail projects frequently involve long tun-nels and long distances between stations. Parsons Brinckerhoff can draw on global and local experience to provide solutions for unique challenges such as analyzing the pressure waves associated with high speed trains (see article by Wu and Ye) and providing cost-effective tunnel ventilation and fire and life safe-ty strategies to accommodate the extended egress distances of long tunnels.

Tunnelling Overview in the United Kingdom, Europe, and the Middle East by Kate Hunt, Godalming, UK, +44 (0)1483 528966, huntk@pbworld.com

The UK’s tunnelling market has seen substantial and rapid growth in recent times, with more tunnels predicted in the near future for the rail, metro, road, and utilities networks.

The 1990s saw a number of significant new tunnelling projects including the opening of the Limehouse Link tunnel (road – 1993), the landmark Channel Tunnel (rail – 1994), the Jubilee Line Extension (metro - 1999) and, more recently, the High Speed 1 tunnels (high speed rail – 2007), the Lower Lea Valley utilities tunnel (2012), and the long-awaited Hindhead Tunnel (road - 2011). The Docklands Light Railway added new tunnels as part of the Lewisham (rail – 1999) and the Woolwich Arsenal extension (rail – 2009). The Crossrail project, a new com-muter line railway running East/West below Central Lon-don, is also in construction.

In addition, significant investment has been made to refurbish, upgrade, and improve a number of key road tunnels around the UK including the Hatfield and Bell Common tunnels (on London’s M25 orbital motorway), the Mersey tunnels (Liverpool), Tyne Tunnel (Tyneside), Saltash Tunnel (in the South-West), and refurbishment is ongoing or planned for the North Wales Coast Road tun-nels and the Brynglas Motorway tunnel (South Wales).

Alongside this infrastructure investment, Transport for London’s metro operator, London Underground, has been investing heavily in replacing the fleet and increasing the service levels on all their lines. Parsons Brinckerhoff has a long and ongoing history of assisting London Underground in these works. Looking to the future, we are working to-wards the construction phase of High Speed 2, linking London with Birmingham and on to the North East and Scotland; phase 1 of the route alone features a dozen new high speed rail tunnels ranging in length from just 500 metres (1640 feet) to an impressive 13 kilometres (8 miles). Other tunnel-related rail projects in the plan-ning stages include the Northern line extension to Batter-sea, the Bakerloo line southern extension, and Crossrail Phase 2. In addition, further tunnelled crossings of the River Thames are being considered, along with a number of urban road tunnels on the periphery of London.

However, the investment in the UK’s tunnels market was small in comparison to the enterprising projects under-taken in Scandanavia, Istanbul, the Middle East, and Is-rael. A new fixed link between the countries of Sweden and Denmark was opened in 2000: the Øresundsbron linked the metropolitan areas of Copenhagen in Den-mark and Malmö in Sweden via a combined rail and road link consisting of the 8 kilometre long (5 mile) Øresund bridge and 4 kilometre (2.4 mile) Drogden tunnel. Simi-larly, the Marmaray Crossing in Istanbul (opened in 2013) successfully negotiated the Bosphorus Strait - one of the busiest shipping lanes in the world - to connect the Euro-pean and Asian parts of the old city via a 1.5 kilometre (.9 mile) immersed tube tunnel – the world’s deepest at 60 metres (196 feet) below sea level.3

Meanwhile, in the Middle East, more than $279 billion worth of projects were being planned or underway in 2012. A high proportion of these are in the transport sector, including metro schemes for Abu Dhabi, Cairo, Doha, Jeddah, Kuwait, Riyadh, and Tehran.

Similarly, designs for the proposed metro in Israel’s Tel Aviv urban district continue to be developed, with the construction phase drawing nearer. At the same time, plans for a high speed rail line from Tel Aviv to Jerusalem are being developed.

Many of our past and current projects involve technical in-novations, or cutting edge techniques to address clients’ unique challenges. Whether we are providing strategic ad-vice to operators (see the “Railway Cooling Challenges” article by Mark Gilbey in this issue), leading discussions

3For 18 articles on many aspects of this multidisciplinary project including 5 articles on tunnel mechanical and electrical systems, see “Linking Two Continents: The Marmaray Project,” Network #65, June 2007, pp 1-58.

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with the UK’s Climate Projections group (UKCP), develop-ing a new toolset such as DYNAMO to address a devel-oping market (see Dr. Jolyon Thompson’s article in this issue, a version of which won the 2014 Parsons Brinck-erhoff Emerging Professionals Technical Paper competi-tion), developing sustainable designs through the use of innovative cooling techniques such as groundwater cool-ing or embedded liners, using the latest risk-based tech-niques to optimise designs and operations (see articles in this issue by Kate Hunt and Anthony Ridley), or intro-ducing world-class high speed rail to the UK, our team of engineers is at the forefront of innovation.

Parsons Brinckerhoff continues to retain its high profile in tunnel systems capability through many of the major proj-ects being undertaken. Parsons Brinckerhoff’s in-depth knowledge and internationally renowned global team is able to deliver technical excellence to clients across all geographies and all sectors. As we engage with WSP, the challenge in the Europe, Middle East, and North Af-rica regions is to enhance our service offering across a broader range of sectors, to embrace the many exciting opportunities available, and to continue to provide our clients with the technical excellence they rightly expect of Parsons Brinckerhoff.

Tunneling Overview in Asia by Steven Lai, Hong Kong/Singapore, +852-2963-7625 / +65-6589-3661, lai.steven@pbworld.com

Parsons Brinckerhoff has a rich history of working on major tunnel projects and designing innovative solutions for tunnel systems in Asia. Some of these designs, con-cepts, and challenges are presented below.

Closed systems and platform screen doors. In the 1970s, Parsons Brinckerhoff introduced an energy ef-ficient closed system for the first metro in Hong Kong thereby providing a comfortable air-conditioned station environment for passengers. Then in late 1970s, with the availability of a more advanced signaling system for accurate train stopping positions, Parsons Brinckerhoff introduced the platform screen door (PSD) system for the first metro in Singapore and has continued to be involved in this design for other metro systems in the region (e.g., Japan, India, Mainland China, Taiwan, Thailand, and Viet-nam). A PSD system can provide a more comfortable and less dusty environment inside the station, for example, 25 degrees C instead of 28 degrees C (77 degrees F

instead of 82 degrees F), a reduction of air velocity at the platform edge and staircases, and a lower noise level.

Better land use and increased carrying capacity. Parsons Brinckerhoff provided engineering design support in the conversion of an elevated metro line to an underground metro line in Taiwan, resulting in better land use and a better interchange (transfer) arrangement with other met-ro lines. Parsons Brinckerhoff is also assisting various clients in increasing the capacity of existing metro lines through extending the catchment area, modification of roll-ing stock, and reducing headway of the trains. Subway En-vironment Simulation (SES), computational fluid dynamics (CFD) modeling, and evacuation models have been used to study the impact of these methods on the environmental control systems (ECS) and the fire and life safety systems in stations and tunnels and to assist clients in establish-ing cost-effective design schemes.

Fire engineering approach. Since the mid 1990s, a performance-based fire engineering approach has been widely used to analyse the heat release rate from a train, the tenable environment along the evacuation path, etc. Parsons Brinckerhoff has adopted this approach for proj-ects in Hong Kong, Taiwan, and Singapore, and was rec-ognized with an award for innovation for the design of a station with an atrium in Shanghai. Parsons Brinckerhoff has also assisted metro companies in the integration of individual operations control centers (OCC) for existing lines and new lines in the region.

Pressure transient from high speed trains. The high speed trains in Taiwan and Mainland China travel at 300kph (186mph) or even greater speeds. The pressure transient created by high speed trains can create issues for the passengers inside the trains, stations, and areas around ventilation shafts and tunnel portals. Parsons Brinckerhoff has developed various mitigation schemes which have been used to resolve the pressure transient issues in the Hong Kong Airport Express Railway, Taiwan High Speed Railway, West Rail in Hong Kong, several metro systems in mainland China, and Express Railway Link in Hong Kong. (See article by Dicken Wu and Rambo Ye in this issue.)

Parsons Brinckerhoff’s work on road tunnels includes: • design of the 2km (1.2 mile) Cross Harbour Tunnel in

Hong Kong in which a transverse ventilation system was used;

• design of a longitudinal ventilation systems for road tunnels in Singapore with the use of the critical veloc-ity concept;

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• minimizing the tunnel construction cost of the 3.9km long (2.4 mile) Tate’s Cairn Tunnel in Hong Kong with the use of construction shafts as permanent ventilation adits, which also resulted in early completion of this design-build project;

• design of the 2km long (1.2 mile) Western Harbour Crossing in Hong Kong with optimized mechanical and electrical (M&E) services and ventilation ducts. This re-duced the overall immersed tube tunnel cross-section and resulted in construction cost savings; and

• design of an Air Purification System (APS) for the Central and Wanchai Bypass project in Hong Kong in order to pro-duce cleaner air at the tunnel portals and the ventilation buildings. This system has been applied to various road tunnels in order to achieve a better environment. (See ar-ticle by Cathy Kam, Chris Ma, and Steven Lai in this issue.)

New challenges in tunnel systems. Nowadays, excep-tionally long tunnels with large cross-sectional areas and/or multi-purpose tunnels create new challenges to engineers. Parsons Brinckerhoff has participated in the following design of tunnel systems for several spe-cial tunnel projects in China:

• the 18km long (11 mile) Zhong Nam Shan Tunnel with very long ventilation shafts, more than 500 meter (1640 feet);

• the 6km long (3.7 mile) Chongming road tunnel which links Shanghai to the out-lying Chongming Island and has an upper deck for vehicular traffic and a lower for the metro line;

• the 2km long (1.2 mile) Fuxing East Road Tunnel in Shanghai which also has an upper deck and a lower deck both of which are used for vehicular traffic; and

• the Macau Sai Van Bridge which has an upper deck used for vehicular traffic and an enclosed lower deck used for light rail operation (normal condition) and ve-hicular tunnel operation (during typhoon conditions).

Value engineering and cost effective design. Parsons Brinckerhoff has developed various value engineering schemes and creative approaches to achieve cost effec-tive design for our clients and provide a better environ-ment for the people. These schemes include: • the use of combined ventilation shafts instead of indi-

vidual ventilation shafts to reduce the constraint on the station planning and the size of aboveground structures (Suzhou metro);

• the use of a centralized chilled water system to reduce the overall spatial requirement and result in a more en-ergy-saving system (Tsuen Wan Line in Hong Kong);

• the use of higher voltage to supply the power for tun-

nel ventilation equipment in long tunnels to reduce the cable cost and overall spatial requirement, as described in an article by CC Cheung and Steven Lai in this issue (Airport Express Line in Hong Kong, Cheung Ching Tun-nel in Hong Kong);

• sharing of tunnel ventilation fans for different lines (Tai-wan Nankong Extension);

• use of Saccardo nozzles to replace numerous jet fans (West Rail in Hong Kong, KPE in Singapore);

• use of tunnel cooling systems for long tunnels to reduce the number of ventilation shaft structures (Tsuen Wan Line in Hong Kong); and

• the use of water mist systems to cool down long vehicu-lar tunnels (Chongming road tunnel in Shanghai).

Apart from the above, with the use of CFD modelling, Parsons Brinckerhoff has designed and developed cost-effective ventilation systems for various cable tunnels in Hong Kong, Singapore, and Mainland China.

Building Information Modelling. To increase productivity and provide a better visualization of complicated engi-neering solutions to stakeholders, Parsons Brinckerhoff is the first company in Hong Kong to use building infor-mation modelling (BIM) for the tunnel systems of a road tunnel project. Parsons Brinckerhoff is also the first com-pany in Singapore to use BIM for designing the mechani-cal and electrical (M&E) systems in a metro project, and has also used BIM for a cable tunnel project in Singa-pore. (See article by YF Pin, R. Ashok Kumar, and Steven Lai in this issue.)

Tunnelling Outlook in Australia and New Zealandby Argun Bagis, Sydney, AUS, 61-2-9272 5435, bagisa@pbworld.com

Australia’s population is projected to grow significantly by 2050, with Sydney, Melbourne, and Brisbane identified as cities where the majority of this growth will take place. Ac-cordingly, the development of road and rail infrastructure has been at the forefront of the Australian government’s priorities and has resulted in the construction of a num-ber of strategic road tunnels, and the safeguarding of rail corridors, primarily on the eastern coast of Australia.

There are a significant number of tunnelling projects in the works for the latter half of this decade. Funding has already been approved for most of the nine new tunnels

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currently being planned along the east coast of Austra-lia, with the west coast expecting some movement as well with the planning of an extension to the existing metro system.

In addition, the Australian government is focused on shifting the transportation of freight from road to diesel rail. This raises the need to upgrade existing rail infra-structure as well as to develop new rail routes to relieve the already congested east coast rail network. Rail proj-ects linking the city of Brisbane with Melbourne over a new inland rail path, the extension of this rail path to the Port of Brisbane, and the Maldon to Dombarton rail link in New South Wales are initiatives that have been brought to the forefront of infrastructure spending. Tun-nel ventilation and fire & life safety are key aspects in the successful delivery of these projects.

Figure 1 provides both a summary and a forecast for the tunnelling sector in Australia, from 2003 through to 2023. As is evident from the graph, the outlook for tun-nel projects from 2014 onward is looking very positive, and there will be a strong need for specialist engineer-ing services, such as in tunnel ventilation. Brisbane, QLD in particular became (and continues to be) a ma-jor centre for tunnelling construction in Australia, with the construction of the M7 Clem Jones Tunnel (Clem 7), Airport Link and Northern Busway, and Legacy Way (still under construction) road tunnels. Parsons Brinck-erhoff has been involved in the detailed design work on many unidirectional traffic tunnels. Chris Chen’s article on “Meeting the Challenges of Smoke Duct Fan Selec-

tion for Australian Road Tunnels” describes the unique fan duty requirements for this type of tunnel ventilation system, employing a combined longitudinal and distrib-uted smoke extraction ventilation (smoke duct) system for fire emergencies.

In New Zealand, the Waterview Connection for Auckland’s Western Ring Route is the largest road project ever un-dertaken in the country, including a 2.5-km long twin-tube tunnel with three lanes in each tunnel. Parsons Brincker-hoff is a member of the Well-Connected Alliance which is both delivering the project, and operating and maintaining the facility for 10 years after the opening. Kevin Stewart’s article on “Tunnel Sump Construction Savings through Drainage System Design Modification” describes how this DBOM project structure gave all parties an interest in cost-effective design for both construction and maintenance.

Parsons Brinckerhoff has diversified into non-traditional road and rail tunnel services. The re-development of ex-isting rail stations, provision of post construction servic-es to tunnel operators, and even mine ventilation have been markets where Parsons Brinckerhoff has delivered successful outcomes. Other examples of technical chal-lenges include:

• The planning and design of longer tunnels which is gain-ing momentum in Australia. A reduction in vehicle emis-sions, traffic fleet composition, and recent innovations in ventilation plant design have enabled the design of tunnel lengths to be almost double that of existing Aus-tralian tunnels, with fewer intermediate tunnel ventila-

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Melbourne Rail Link (VIC)

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East-WestLink (QLD)

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BrisbaneUnderground (QLD)

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Toowoomba Range Second Crossing (QLD)

Lane CoveTunnel (NSW)

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North-South Bypass Tunnel (QLD)

Legacy Way (QLD)

Airport Link (QLD)

CityLink Western (VIC)

East-West LinkEastern Section (VIC)

03 05 07 09 11 13 15 17 19Source: BIS Shrapnel, ABS DataYear ended June

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East Link (VIC)

M5 East (NSW)

M4 East (NSW)

North West Rail Link (NSW)

Forrestfi eld Airport Rail Link (WA)

M1 to M2Link (NSW)

Figure 1 – Major road and rail projects with tunnel components (value of work done)

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Steven Kam-Hung LAIDirector, Infrastructure, China RegionHong Kong

Kate Hunt Service Leader, Tunnel Ventilation & Fire Engineering (RMS), Rail & TransitGodalming, UK

John MunroDirector, M&ENew York, NY, US

tion plants. There are currently three tunnels in the early design phase with lengths expected to be in the 8-9 kilometre (5-5.6 mile) mark.

• The current Australian policy to limit emissions at tunnel portals (see the article on “Long Road Tun-nels and Portal Emission Control” in this issue) con-tinues to be a major factor in increased energy use in Australian road tunnels.

• The relatively hot Australian climate, principally in mid to north Australia, has made the effects of climate change a key consideration in the design of tunnel ventilation systems, particularly in relation to rail tun-

nels. Climate projections beyond 2030 and 2050 are now commonly used for the design of tunnel ventila-tion systems.

Overall, the future demand for tunnel ventilation and tun-nel systems in Australia looks strong, with funding for major road and rail tunnel projects already confirmed. The challenge remains to fully utilise Parsons Brincker-hoff’s capability outside of the traditional concept phase by taking on leading roles in the detailed design, con-struction, and operation phases, as on the Victoria Park Tunnel and the Waterview Connection projects.

Argun Bagis Principal Engineer, Tunnel SystemsAustralia, New Zealand

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Subway Tunnel Cross-Passage Spacing: A Performance-Based Approachby the late William D. Kennedy; Justin M. Edenbaum, Toronto, Canada, +1-917-225-6314, Edenbaum@pbworld.com; Mia Kang (formerly of Parsons Brinckerhoff); and Kirk G. Rummel (formerly of Parsons Brinckerhoff)

The US National Fire Protection Association's Standard 130, "Fixed Guideway Transit and Passenger Rail Sys-tems," requires that tunnel-to-tunnel cross-passages shall be spaced a maximum of 800 feet (244 meters) apart. No guidance is provided on how the actual spacing should be determined. Intuition says that the spacing should vary with the length of the train, the number of passengers on board the train, the walkway width, the design fire scenario, etc. This paper presents a performance-based approach for calculating cross-passage spacing for downstream emergency evacuations from the fire site, and discusses NFPA 130 compliant methodologies for reducing the num-bers of cross-passages required. The performance-based calculations include the use of computer software for ana-lyzing and comparing exiting strategies. The simulations account for the geometry of a bored tunnel.

IntroductionBased on earlier emergency ventilation studies, it was concluded that the maximum cross-passage spacing should be such that those downstream of the fire could evacuate to a point of safety within the time that it takes for the floor of a train car to burn through (which leads to flashover of the entire train car).

This leads to the conclusion that increasing the car-floor burn-through time would allow greater tunnel-to-tunnel cross-passage spacing and possibly reduce costs. This is suggested in NFPA 130 (Section 8.5.1.3.2(1)). Another possibility is wider walkways or cross-passage doors to speed passenger movement away from the fire site.

It also leads to the inference that an interior or post-flash-over fire should not be allowed to stop a train in a tunnel. Driver override should allow the movement of the train to the nearest station even if a passenger activates the emergency brake. The analysis for this paper assumes that this is the circumstance and that the only fire that will stop a train in a tunnel is a below-car fire that critically damages the propulsion system or derails the train.

Physical Scenario for Computer ModelPhysical scenarios are simulated using computer mod-eling to predict the evacuation times for passengers downstream of the fire site to reach a point of safety. Seven cross-passage spacings, ten walkway widths, and one passenger load were analyzed. The computer model accounts for the unique geometry of a bored tunnel by considering shoulder space requirements. The simula-tion results provide sample engineering information to develop a sample of cost-effective alternatives without compromising safety.

The physical scenario for modeling is selected to be typi-cal of a heavy- or main-line rail passenger system. The results of this type of analyses are affected by many spe-cific project factors. Therefore, the results provided in this paper MUST NOT be directly applied to any projects. See Figure 1 for data used.

A number of assumptions were made in the model in or-der to be conservatively safe and simulate a reasonable worst case situation, such as:

William D. Kennedy, an internationally recognized expert in tunnel ventilation, died in June 2012. During a 46-year career with Parsons Brinckerhoff, he was instrumental in the development of tunnel ventilation systems for road and rail tunnels worldwide. His reputation in tunnel ventilation was recognized in March 2012 by the International Symposium on Tunnel Safety and Security, which awarded him its 2012 Achievement Award, citing his “long and illustrious career in ventilation engineering of tunnels” and calling his lifetime body of work “a shining example of wedding practice and theory in the design of tunnels.”

This abstract is condensed from a paper that was originally prepared for the 2006 APTA Rail Conference and has been updated to reflect the current 2014 version of NFPA 130.

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• The location of the fire is in the middle of the train. • The to-be evacuated train has a fire that is aligned with

a cross-passage.• A population of rail passengers consists of typical

“commuters” with a range of demographics and walking speeds. (When the given walkway is wide enough, the model allows faster individuals to over-take slower walkers.)

• The fire scenario was assumed to be:- Time 0 minutes, fire ignition;- Time 5 minutes, fire reaches below-car fire heat

release rate;- Time 10 minutes, fire stops train; and- Time 15 minutes, evacuation begins.

Therefore, when calculating the minimum car-floor burn-through time required, 10 minutes (15-5) should be added to the evacuation time. This does not include any allowance for modeling accuracy.

The emergency exiting analysis was done using the computer program SIMULEX1, which simulates the emer-gency exiting of people. The program algorithms for the movement of individuals are based on real-life data and predict realistic flow of people. It simulates the escape movement of each person instead of using a mathemati-cal formula for uniform flow rates and average speeds of groups of people. This program is well-validated and has been used to model rail system emergency evacuations for a number of years2.

The evacuation method was assumed to be all doors open to the walkway with movement to the nearest cross-pas-sage downstream or adjacent to a stopped car. The pas-sengers were considered to reach a point of safety after reaching 10 feet (3048 mm) inside of the cross-passage.

Bored Tunnel GeometryCross-passage spacing is particularly important in bored tunnel construction where cross-passages have to be mined in poor soil. Costs to construct each cross-pas-sage in this situation can be high. The SIMULEX model inputs are adjusted for a bored tunnel construction. This leads to the concept of “Constructed Width” vs. “Effec-tive Width.” Constructed Width is the actual width of walk-way on the ground. Effective Width refers to the width entered into the SIMULEX model to accurately simulate the evacuation, relating to factors such as walkway width at shoulder height and the natural inhibition of walking near the edge of an empty track.

Figure 2 presents the results of the simulations for 250 people per car and seven cars being evacuated.

Some observationsThese observations are based on the sample data and should not be directly applied to other projects.

• Clearly the spacing of cross-passages has a significant impact on evacuation times. For the assumed data, any evacuation times required to be lower than 30 minutes, with train capacities in this study range, and with reason-able walkway and cross-passage widths, require spacing of cross-passages significantly shorter than the 800 foot maximum in NFPA 130. Other variables such as walkway or cross-passage width would also have an impact.

• There are significant benefits of wider walkways and wider cross-passage doors at cross-passage intervals above 700 feet or so. This is because the wider walk-way after the train allows faster passengers to overtake slower passengers. In general, wider walkway widths help evacuation scenarios when the spacing has cross-passage doors that are not adjacent to the train and

1"SIMULEX Users Manual"; 1998, Integrated Environmental Solutions, Limited; 141 St. James Road, Glasgow G4 0LT, Scotland.2William D. Kennedy, Norris A. Harvey, and Silas K. Li, “Simulation of Escape from Rail Tunnels Using SIMULEX,” American Public Transportation Association (APTA), Boston, Massachusetts, June 2001.

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Figure 1 – Evacuation Scenarios

X= Cross Passage Spacing (200, 300, 400, 500, 600, 700, and 800 feet) (61, 91, 122,152, 183, 213, to 244 meters)

W= Constructed Walkway Width (36, 38, 40, 42, 44, 46, 48, 50, 52, and 54 inches) (914, 965, 1016, 1067, 1118, 1168, 1219, 1270, 1321, to 1372 mm)

Downstream

Under-Car Fire

Upstream595' (181 m)

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are located far away from the end of the train. Under these circumstances, wider walkways can be considered as an alter-native to shorter cross-passage spacing.

• In the scenario adopted for analysis, it is obvious that shorter cross-passage in-tervals (in the range of 200 to 500 feet) result in one to three cross-passages adjacent to the train immediately ac-cessible as soon as the evacuees move onto the walkway. Because the train can discharge passengers at a greater rate than they can exit through cross-passag-es, the effect of wider walkways in these shorter intervals is minimal.

• While not immediately apparent from the data shown, the effect on evacuation times due to varying passenger travel speeds is significant, again, at the lon-ger intervals; of interest where continuous movement is occurring as opposed to the accumulated conges-tion immediately next to the train that dominates the shorter spacing cases. Thus, if performing analysis around cross-passage spacings that are beyond the train, careful attention must be given to the model inputs for evacuation speeds.

• Finally, the model examines the paths of evacuation up to the point of safety - the cross-passage. A close examination of the dynamics of the evacuation paths suggests that a project-specific application might want to consider the entire evacuation path—to whatever ends: a rescue train, a station platform, the opposite bore trackway, etc. The effects of the complete path should be modeled to study if there is an adverse af-fect of the evacuation in the non-incident tunnel. At a minimum, such analysis could suggest appropriate instructional and training emphasis.

ConclusionA performance-based approach for estimating evacua-tion times downstream from a tunnel fire site and mini-mum car-floor burn-through times has been presented. It allows the trade-off among cross-passage spacing, car-floor burn-through time, and walkway and cross-pas-sage door width. For existing systems with fixed cross-

passage locations and widths, this approach could be used to select car-floor burn-through times when cars are retrofitted or new rolling stock is ordered. For future designs, this approach could be used to develop a cost analysis combining cross-passage spacing and widths, car-floor burn-through time, and walkway width; possibly increasing the cross-passage spacing beyond the NFPA 130 maximum of 800 feet (244 meters).

RecommendationAfter peer review this approach could be used to devel-op an enhancement to NFPA 130. This enhancement, in relating cross-passage to other project characteristics, could provide a more logical basis for cross-passage spacing that could be greater or lesser than the current 800-foot requirement (244 meters).

William D. “Bill” Kennedy was instrumental in the development

of tunnel ventilation systems for road and rail tunnels worldwide

and he led the development of the Subway Environmental Sys-

tem (SES) software program, widely considered the standard tool

for the analysis and design of transit systems.

Justin Edenbaum is a Supervising Mechanical Engineer in the

Toronto office of Parsons Brinckerhoff specializing in tunnel ven-

tilation and fire life safety.

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Figure 2 –Time vs. Width

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A Note on Fixed Fire Fighting Systems in Road Tunnelsby Anna Xiaohua Wang, New York, NY, US, +1-212-465-5756, wangx1@pbworld.com; and Norman Rhodes, New York, NY, US, +1-212-613-8861, rhodesn1@pbworld.com

IntroductionHistorically, the disappointing results of the Ofenegg Tun-nel fire tests (1965, Switzerland) had a negative impact on sprinkler application in tunnels. The tests, which employed pools of aircraft fuel, led to the view that visibility was much reduced by the sprinkler systems and hot steam was generated that could cause scalding at long distances from the fire. The steam production also displaced smoke more quickly causing temperatures to be higher than with-out sprinklers. After extinguishment the fuel continued to evaporate, reaching critical concentrations within about 20 minutes. Subsequent deflagrations occurred that created air velocities of up to 30 meters per second.

It was the impact of this experience that was reflected in the World Road Association (PIARC) recommendations which, between 1983 (World Road Congress in Sydney) and 2004, consistently advised against the installation of fixed fire fighting systems (FFFS) in road tunnels, and this position was reflected in US standards.

One of the factors that maintained this attitude against the application of FFFS in tunnels was the fire sizes gen-erally used. The fire sizes chosen on which to base the design were relatively small—20 to 30 MW—typical of a bus or truck fire. Such fires were regarded as man-ageable and ventilation systems were sized to control smoke for such events.

Several severe road tunnel fires - the Mont Blanc Tunnel (France/Italy, 1999), the Tauern Tunnel (Austria, 1999), the St. Gotthard Tunnel (Switzerland, 2001), and the Fre-jus Tunnel (France/Italy, 2005) - resulted in loss of life, injury, and infrastructure damage that were far more ex-tensive than if they had occurred on surface roadways. These fire incidents demonstrated that fire sizes could be much larger than 20-30 MW and completely changed the perception of the design fire size. Since then the maximum design fires utilized in tunnel design have in-creased as much as tenfold in some cases. These re-

cent incidents have emphasized the need for further im-provement to be made in tunnel fire management; the FFFS is one technique that is actively being promoted.

Types of FFFSSeveral types of FFFS have been used in road tunnels worldwide:• Sprinkler/spray (water deluge) systems, based on dense

water jets consisting of large-size droplets;• Water mist systems, based on very fine water droplets;

and• Foam water suppression systems.

Water sprinkler type FFFS have been installed in road tunnels of significant length for many years in Japan and Australia. Tunnels that have water deluge fixed fire fight-ing systems installed can also be found in the United States, Norway, Canada, and Sweden. These have been found to be effective in preventing fire spread and en-hancing cooling of the tunnel structure. In 1999, two fires occurred in the underwater tunnels of the Tokyo Metro-politan Expressway and the FFFS helped control the fires so firefighters could approach and eventually extinguish the fires. The deluge system in Sydney Harbor Tunnel in Australia is reported to have worked well during a van fire in 2004. Another example is the Burnley Tunnel fire in 2007; the deluge system was activated quickly and this was deemed by firefighters to have kept the fire under control. Based on this experience, and the development of alternative types of FFFS, PIARC re-evaluated its posi-tion with regard to FFFS and at the same time the Europe-an Community undertook research programs to examine fire suppression and the impact of larger design fires.

Several relevant European research programs, including UPTUN (Multinational European Research Project) and the SOLIT (Safety of Life in Tunnels) Project, have dem-onstrated through independent tunnel fire tests that, with early activation, high pressure water mist systems can be effective in controlling potential 200 MW solid fuel fires

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and 200 MW diesel oil pool fires. The water mist systems have been installed in the A86 tunnel in Paris, the M30 tunnel in Madrid, the Roertunnel and the Tunnel Swalmen in the Netherlands, and other tunnels in Europe.

Therefore, FFFS are now increasingly being considered in the design of tunnel systems worldwide. This position is also reflected in changes to the recent NFPA 502 and PIARC documentation.

Choosing a Fire Suppression SystemChoosing the type of fire suppression system for a road tunnel is not an easy decision to make. Some of the dif-ferent aspects of the systems are as follows:

Water Sprinkler Fire Protection SystemThe water sprinkler fire protection system (see Figure 1) has existed for over 100 years and is a commonly used and reliable technology; deluge water sprinkler systems are the common FFFS in Australia and Japan. The system performs very well for Class A (solid fuel) fires, but is con-sidered to be less suited for Class B (liquid fuel, oil) fires or where "splashing" of the fuel is to be avoided.

Water Mist Fire Protection SystemCompared to the water sprinkler system, the water mist system (see Figure 2) generates much smaller water droplets and therefore has advantages in promoting more efficient gas-phase cooling and uses 2 to 3 times less water for road tunnels (depending on the system used). Both the water mist and water vapor system can measurably reduce radiant heat flux to objects near the fire - this helps firefighters approach the fire and provides better conditions for evacuation. However, be-cause the system contains fine water particles, it may be less efficient in cooling or wetting the fuel surfaces; therefore, the system is less efficient to combat solid fuel fires compared with the water sprinkler system.

Fixed Foam-Water Fire Suppression SystemsFixed foam-water fire suppression systems may be an-other alternative to combat tunnel fires. A foam agent is especially suited for the control and extinguishment of flammable and combustible liquid-type fires. There are two types of foam-water fire suppression systems pro-posed for road tunnels:• the foam-water sprinkler system (see Figure 3); and • the compressed air foam (CAF) system (see Figure 4).

The use of the foam-water sprinkler system against die-sel pool fires was investigated in the Memorial Tunnel

in West Virginia by Bechtel/Parsons Brinckerhoff. The foam-water sprinkler deluge system has been installed in several tunnels in Seattle, Washington. The com-pressed air foam (CAF) system has been tested in road tunnels in the Netherlands. For both types of foam-water suppression systems, corrosion protection is required for the storage tanks and the pipe systems, and the system can be costly in the long run because of the cor-rosion problem associated with the use of foam agents.

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Figure 3 – Schematic of a foam-water sprinkler system

Figure 1 – Water sprinkler nozzles in the tunnel

Figure 2 – Water mist nozzles in the tunnel

NozzlesAlarm CheckValve

ProportioningController

Main ControlValve

Water Supply

Piping Network

BladderTank

Figure 4 – Schematic of a compressed air foam (CAF) system

Piping Network

Releasing Controller

AirMixing Chamber

CAF Generation

CAFNozzles

Water

Foam Concentrate

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For longer tunnels, the use of foam-water fire suppres-sion systems may be challenging:

• for the foam-water sprinkler system, the delivery time of the foam may be too long as the foam tanks have to be installed at the tunnel portals and it may take time for the foam to reach the fire if the fire is located in the middle of the tunnels; and

• for the CAF system, additional mechanical rooms need to be installed at specific intervals of length in the tun-nels which increases the initial capital cost of the instal-lation of a CAF system.

ConclusionThe FFFS is also being considered in road tunnels to re-duce the size of the ventilation system required. When authorities prepare to permit all types of traffic, such as dangerous goods or heavy goods vehicles, to cope with in-creasing economic activities, mitigation options that can combat 200 - 300 MW fires would be necessary for tun-nels, as recommended by NFPA 502 and most European standards. Without FFFS, large fires (such as 200 - 300 MW) dictate the need for a very powerful ventilation sys-tem, increasing space requirements and adding signifi-cant cost. In addition, FFFS, unlike a ventilation system, can provide benefits for firefighting, tunnel system protec-tion, and operational continuity.

Although the benefits of FFFS are clear, many design issues remain, such as: the reduction in the design fire size with the inclusion of the FFFS and the subsequent reduction in venti-lation requirements; the impact of the FFFS on the structural protection system; the performance of the FFFS under op-erational conditions that have not been tested in the tunnel fire experiments; and the impact of the FFFS on the overall tunnel safety concept and operation procedures.

The most reliable method available to date for those un-solved design questions is full-scale testing, but that is extremely expensive and impractical for new or existing tunnels. A computational fluid dynamics (CFD) fire mod-eling approach is an alternative and holds great promise once a reasonable correlation between numerical simu-lations and full-scale tests has been achieved.

References• Haerter, “Fire Tests in the Ofenegg-Tunnel in 1965”,

International Symposium on Catastrophic Tunnel Fires, Boros, Sweden, November 2003.

• PIARC 2008: Road Tunnels: An Assessment of Fixed Fire Fighting Systems.

• UPTUN, Fire development and mitigation measures, Work Package 2 of the Research Project UPTUN, 2008.

• Starke, H., “Fire Suppression in Road Tunnel Fires by a Water Mist System – Results of the SOLIT Project”, Fourth International Symposium on Tunnel Safety and Security, Frankfurt am Main, Germany, March 17-19, 2010.

• Water Mist Fire Suppression Systems for Road Tun-nels, Final Report, The SOLIT Research Project, 2007.

• NFPA 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways, 2014 Edition, Nation-al Fire Protection Association.

• Huijben, Ir. J.W., “Tests On Fire Detection Systems And Sprinkler in a Tunnel,” ITC Conference Basel 2-4, December 2002.

• Liu, Z.G., Kashef, A., Lougheed, G., Kim, A.K., “Chal-lenges for Use of Fixed Fire Suppression Systems in Road Tunnel Fire Protection”, NRCC -49232, Sup-pression & Detection Research Applications – A Technical Working Conference (SUPDET 2007), Or-lando, Florida, 2007.

• Quenneville, R., “The Emergence of CAF Fixed-Pipe Fire Suppression Systems”, Fire & Safety Magazine, Spring, 2006.

• Memorial Tunnel Fire Ventilation Test Program, Test Report (section 8.10), Massachusetts Highway Depart-ment, by Bechtel/Parsons Brinckerhoff, Nov. 1995.

• Lemaire, A.D. and Meeussen, V.J.A., “Effects of Water Mist on Real Large Tunnel Fires: Experimental Deter-mination of BLEVE-risk and Tenability during Growth and Suppression”, Rept. 2008-Efectis-R0425, Efectis Nederland BV, June 2008.

• Grant, G., Brenton, J., Drysdale, D., “Fire Suppression by Water Sprays,” Progress in Energy and Combustion Science 26 (2000), 79-130.

• Tunnels Study Center (CETU), "Water Mists in Road Tunnel," State of knowledge and provisional assess-ment elements regarding their use, June 2010.

• NFPA 15, Standard for Water Spray Fixed System for Fire Protection, 2007 Edition, National Fire Protection Association.

Dr. Anna (Xiaohua) Wang is a Principal Technical Specialist in

Parsons Brinckerhoff’s New York office.

Dr. Norman Rhodes is the Technical Director of the Parsons

Brinckerhoff Mechanical/Electrical Technical Excellence Center.

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IntroductionFires that occur in road tunnels can grow rapidly and reach very high heat release rates. As a result, road tunnels are designed with mitigation technology and procedures to help reduce the detrimental effects that can occur.

The main goals of the mitigation measures are to:• Provide a tenable environment for motorist evacuation;• Assist firefighters with their operations; and• Maintain the structural integrity of the tunnel.

A fixed fire fighting system (FFFS) is one type of mitiga-tion measure implemented to help achieve these goals. The major components of the FFFS include water deliv-ery infrastructure (pumps, pipes, valves, and nozzles – divided into separate zones for water delivery) and also components for water removal (drainage, pumps, pipes, water treatment).

A FFFS is typically installed to help reduce the fire growth rate and air/smoke temperature, which helps to prolong occupant tenability and provides structural protection. Proper integration of the FFFS with other tunnel fire-life safety systems is essential to achieve the FFFS goals.

The first important question in FFFS integration is wheth-er or not the tunnel has a full-time operator. In many tun-nels with FFFS, a full-time operator is present. In this ar-ticle the integration question is considered in the context of a full-time operator being present, but it is noted that if an operator is not present there will be different integra-tion considerations. Tunnel systems and functions that require particular attention for integration with a FFFS, with full-time operator present, include:• Closed circuit television (CCTV);• Ventilation systems;• Egress provisions;• Drainage;• Fire alarm systems, control systems, heat detection

systems; and• Traffic and operations.

Poor system integration can lead to a reduction in FFFS performance and fire safety.

System Integration with Fixed Fire Fighting SystemsCCTVActivation of the FFFS at an early stage of a fire incident is the best way to assure optimal performance, and this is

Fixed Fire Fighting Systems in Road Tunnels – System Integrationby Matt Bilson, New York, NY, US, +1-212-465-5510, bilsonm@pbworld.com; and Sal Marsico, New York, NY, US, +1-212-465-5576, marsicosa@pbworld.com

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Figure 1 – Example of good CCTV and FFFS integration

179

Plan view of roadway:

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Fixed camera

Deluge zone/ventilation zone

Tunnel wall

Traffi c and airfl ow

Linear heat detector

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Zone N178 is in the foreground

Zone N179 is in the background

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typically accomplished through manual activation by the tunnel operator. The tunnel operator relies on the CCTV system to assist in identifying the fire location, as the CCTV system would typically detect smoke or stalled traf-fic well before a heat detector senses the fire. Once the fire has been located, the operator activates the corre-sponding FFFS zone. It is imperative that operators can easily and accurately identify the fire locations. Figure 1 provides an example of effective design integration be-tween a CCTV and FFFS system. The figure shows an example of good systems integration with camera locations relative to their proximity to FFFS zones. Placing a camera within a zone, instead of at zone boundaries, may generate confusion for the operator be-cause, instead of the CCTV image showing the start of a zone, the image would be starting halfway along the zone, requiring the operator to cycle through views to confirm the location. VentilationThe ventilation system in a tunnel is used to direct heat and smoke away from the egress path by producing a lon-gitudinal tunnel air velocity flow in one direction (longitu-dinal ventilation); extracting the heat and smoke through vents along the tunnel (transverse ventilation); or a com-bination of the two.

The air velocity can cause water in the FFFS’s water deliv-ery region to shift away from the active zones. Computa-tional fluid dynamics (CFD) results in Figure 2 show an example of the extent of water delivery drift for a longi-

tudinal ventilation system. In this example, activation of both the FFFS zone where the fire is located and one zone upstream mitigates drift effects. Careful zone ac-tivation can mitigate the effect of drift and provide as-surance that water will reach the target. Jet fans near the FFFS zone should be activated only if necessary. In the region near a jet fan’s outlet there will be high velocity relative to the average velocity of the tunnel, which will exacerbate the water delivery drift.

Egress ProvisionsEgress points (e.g., exit doors to escape passages) are generally positioned equidistant from each other along the tunnel and should be placed at the ends of the FFFS zones and not within active FFFS zones where egress may be hindered by visibility reduction, noise (the active FFFS is in fact very loud), physical restric-tion, and psychological stress. Placing egress points at the ends of a FFFS zone contributes to more stream-lined egress. Firefighters using these egress points to enter the tunnel could experience significant disorien-tation if entering an active FFFS zone, thereby slowing their subsequent response.

DrainageDrainage is another aspect to consider when installing an FFFS. In some systems, the very large flow rates of water mean that not all of the FFFS water will be cap-tured at the drains within the zone of discharge, and practically there may be few design options to achieve this. The travelling fuel can create a risk of fire spread since the water can transport the fuel away from the

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Figure 2 – Example of FFFS and tunnel ventilation integration-CFD results

Extra water due to zone overlap

Application criterion is 8 kg/m2 in one minute

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Water overshooting zone of application (overshoot by up to 15m)

Water not reaching entire zone of application (up to 5m of a zone missed)

Plan view of tunnel water accumulation at roadway level

FFFS Zone

30m (100 ft.)30m (100 ft.)

AIRFLOW

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fire site. The fuel draining away from the fire site would be unshielded by vehicles and so it will typically be sup-pressed, if it is burning, prior to exiting the FFFS zone. Flame traps in the drainage system are sometimes used to prevent a secondary fire moving through the drain pipe network.

Fire Alarm Systems, Control Systems, and Heat DetectionRoad tunnels can be fitted with automatic and/or manu-ally activated FFFS. In a manually operated system, op-erators are provided with a CCTV system to identify the fire location, so that they are able to activate the FFFS in the appropriate zone(s), as described above. In some instances a back-up automatic activation system is pro-vided. This system typically uses a linear heat detector (LHD) to identify the fire location. Once the LHD signal is received at the control panel, a countdown timer activates. If no response is made by the operator within the allotted time, the FFFS is deployed.

The LHD is an addressable sensing cable which can de-tect absolute temperature or rate-of-rise, with each detec-tion zone coincident with a specific FFFS zone. In the case of an automated response, the following items support good system integration:

• FFFS and LHD zones are to be coincident.• The FFFS should activate in the first LHD zone to detect

heat and the adjacent zone upstream.• Any further LHD activations must not trigger any addi-

tional FFFS zone activations (as explained below).

The system must be programmed such that the opera-tor can override an automated response if necessary. Automated systems are capable of executing ineffective responses, so it is up to the operator to make the final operational decisions. For example, in a tunnel, heat will travel over a large number of FFFS zones and trip the LHD

in zones remote from the incident. If all of these zones were to discharge water, there may not be enough water capacity available in the incident zone to suppress the fire (a FFFS can be feasibly designed with enough water supply capacity to feed two or three zones). Conversely, the fire can propagate or the operator may need to correct their choice, which means the operator needs to have the abil-ity to shut zones off and start others.

Traffic and OperationsAfter a fire is identified, traffic must no longer be allowed to flow into the tunnel. In unidirectional traffic, the vehicles downstream of the fire are expected to exit the tunnel while those upstream are expected to stop (a common assumption in tunnel fire-life safety design).

The system must be designed so that the FFFS is never activated over live traffic. An activated FFFS will reduce motorist visibility and vehicle traction, which increases the chance of a vehicle collision and exacerbates the emergency, or worse still, creates an unsafe situation (see Figure 3).

ConclusionAn FFFS is a useful fire safety tool for a road tunnel. Good integration of the FFFS with other tunnel systems and func-tions, using the principles outlined above, assists in bring-ing to fruition its purported benefits for tunnel fire safety. In addition to the engineered systems, it is important that the tunnel operator is well-trained and that tunnel systems are well-maintained to assure good performance.

Matt Bilson is a Principal Technical Specialist in the field of

tunnel ventilation and fire-life safety in the New York office of

Parsons Brinckerhoff.

Sal Marsico is a Mechanical Engineer in the field of tunnel

ventilation and fire-life safety in the New York office of Parsons

Brinckerhoff.

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Figure 3 – Effect on visibility due to FFFS

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Fire-Life Safety and System Integration: The Functional Mode Tableby Matt Bilson, New York, NY, US, +1-212-465-5510, bilsonm@pbworld.com; and Andrew Gouge, New York, NY, US

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IntroductionA fire or other emergency situation in a tunnel environ-ment can be a serious threat to human life and the in-frastructure. One of the main tasks of the fire-life safety (FLS) engineer is to develop a response strategy to manage or prevent such events. The strategy will fre-quently rely on many sub-systems such as ventilation, lighting and signage, traffic management, alarms, op-erator responses and coordination, and communication with emergency services agencies (e.g., the fire depart-ment). The harmonious and correct operation of the sub-systems is essential to protecting life and infrastructure during an incident; clear and concise system integration is needed to achieve this goal.

Integration is not a new concept as exemplified by the “V” diagram (see Figure 1) which is a well-known con-cept in systems engineering. However, FLS relies on more than just systems integration; it is also necessary to combine the emergency incident plans with the de-sign concepts and operator training. The concept of the

Functional Mode Table (FMT) is proposed herein as a tool to assist in this exercise.

The FMT, in principle, is a high-level computer program for tunnel operation during a given emergency scenario. It is a matrix of instructions that spells out in a detail how each sub-system must respond for a given emergency incident.

It is based on an incident type, the means of detection, and the sub-sys-tem responses required (see Figure 2).

The goal of the FMT is to assure that all major players in the tunnel’s fire-life safety – the FLS engineer, the imple-mentation engineers, the operator, and emergency services workers – will work to a common framework, thereby improving implementation, commis-sioning, training, thereby maximizing the probability of a favorable outcome if an emergency occurs. Subsequent system responses for an incident can be pre-programmed using the FMT, reducing the complexity and burden placed on the tunnel operator.

Figure 1 – The “V” diagram and the Functional Mode Table relationship

Time

Detail

The functional mode table is set out between Concept and

Requirements/Architecture phases. It is then used at every

level of the process.

Implementation

Operation and Maintenance

System Verifi cation and Validation

Integration Testand Verifi cation

Concept

Requirements and Architecture

Detailed Design

INCIDENT ANDMODE ID

DETECTION METHODS AND

LOCATION

SUB-SYSTEMRESPONSES

Manual

Automatic

Escalation Modes

Traffi cDevices

Communications

Lighting/Signs

Ventilation

Fixed Fire Fighting System

Incident ID (as per the operator’s incident

response plans)

Figure 2 – Functional Mode Table concept outline

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Case Study – An Urban Road TunnelTo illustrate the FMT concept, a virtual case study of an urban road tunnel several kilome-ters long is used. For the present discussion the tunnel is taken to have the following prin-cipal system features:

• Unidirectional traffic;• Longitudinal ventilation;• Egress points at 200 meter spacing (to an

adjacent tunnel);• CCTV system;• Fixed fire fighting system; • Communications (phones, public address),

lighting, traffic controls; and• Full-time tunnel operator.

The ventilation system plays a major role in life-safety, directing smoke downstream of the fire so that people upstream are protect-ed (see Figure 3). However, the ventilation system alone will not necessarily produce a favorable outcome; a successful outcome needs several provisions to operate correctly. During a major incident, ventilation operation is only one of several important steps that need to be taken, as explained in Table 1.

Overcoming Operational Complexity – The FMT and a One Button ResponseTable 1 outlines a number of sub-systems required to operate during an emergency, and a major tunnel will typically have a full-time and well-trained operator. However, it is not reasonable to expect the operator to manually perform all of the actions required for the following reasons:

• Operators are typically not engineers and therefore not versed in tunnel systems design.

• During an emergency an operator’s capacity to perform sophisticated system adjustments may be limited by the enormous flow of information among the operator, the motorists, and the emergency agencies. An operator’s attention becomes focused on specific events and as a result may fail to take into account the broader situation, a condition referred to as “attention tunneling”.

• Emergencies do not occur frequently and so the operator has limited practice at performing the required actions.

• Emergency situations are high stress events within the control room. Designers of the systems need to be mindful of the possibility for an operator to “lock up” which could further delay the correct response.

Figure 3 – Road tunnel fire-life safety concept

Table 1 – Sub-system response for a road tunnel fire

Jet fans are usedto direct smoke downstream

Egress: back upthe tunnel and via exit

Traffi c upstream is told to stop

Fire Traffi c drives out ofthe tunnel downstream

System Response Sub-systems available

Operator Activate sub-systems and adjust response as incident progresses, contact fi re department and other emergency services, and deploy staff where possible.

Human-machine interface.

Traffi c management

Stop vehicles upstream of the fi re and have vehicles downstream exit the tunnel.

Lane use signs, signals, portal barriers, and variable message signs.

Ventilation Direct smoke downstream of the fi re, away from people upstream.

Jet fans and axial exhaust fans.

Lighting Provide direction to exits, assist with exit identifi cation.

Low-level lights, door strobes, tunnel lights, and door identifi cation lights.

Detection and alarms

Identify incident, and then initiate and direct evacuation.

Radio rebroadcast, tunnel public address, variable message signs, CCTV,and heat detectors.

Fixed fi re fi ghting system

Activate system in the correct location.

Valves and pumps, and CCTV for identifi cation.

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System integration and programming of the control system to automate much of the incident response is required for the essential actions to take place. It is critical that the responses required with each sub-system for defined emergency scenarios have a simple yet methodical procedure. The FMT provides this procedure. It is the connection among the fire safety engineer, the programmers developing the con-trol system’s detailed automatic routines, the system hardware, and the tunnel operator (see Figure 4). The FMT also forms a critical link at the design level (see Figure 5).

Given the number and complexity of tunnel systems, the burden on the tunnel operator needs to be minimized. If the operator has “too many clicks” to initiate at his/her interface, it will slow the response and increase the chances of errors. In the “one button response” the systems are configured in a way that, once the opera-tor provides essential information, a pre-programmed response is enacted. The FMT provides a framework for this and a simple example is provided in Table 2.

Generating a one button response requires that all stake-holders in the emergency response system are aware of the realistic information available during an emergency situ-ation and the order of actions to be taken. As fire-life safety engineers, it is our responsibility not only to define the spec-trum of data and available actions, but also to define the data with language, terminology, and structured presenta-tion that is easily communicated and understood by other stakeholders. This task is challenging but not out of reach.

For example, with a well-designed FMT and incident re-sponse plan, during a fire in a road tunnel the opera-tor would need to answer some basic questions at each stage in order to then activate the physical tunnel sys-tems. Table 3 provides a simplified account of the re-sponse stages, questions, and system actions.

The outline of questions in Table 3 minimizes the amount of information that the operator must give, thus reduc-ing the time it takes for a response and maximizing the chances that the correct system actions will be taken and all the essential sub-systems will be activated.

Figure 4 – Functional Mode Table links Figure 5 – Functional Mode Table design links

Operator Emergency Services Occupants

FUNCTIONALMODE TABLE

Incidents andResponse Plans

Systems(Detection, Alarm,

Egress, Traffi c Light, Lighting, Ventilation)

FUNCTIONALMODE TABLE

ControlSystemDesign

Fire-LifeSafety andVentilation

Concept Design

MechanicalDesign

ElectricalDesign

Table 2 – Functional mode table example (showing a limited number of incidents and devices)

ID Comment

Detection Devices Traffi c Devices – Incident Tunnel Egress Devices Ventilation

Manual Auto Escalationmode

Upstream from

incident

D’stream from

incidentPortal Lights, PA,

VMS Jet fans

1 Suspected fi re CCTV Heat

sensor Mode 2 Stop traffi cExitwith

cautionStop traffi c N/A

On,emergency

mode

2 Confi rmed fi re Operator N/A N/A Stop traffi c

Exitwith

cautionStop traffi c

On,egress mode

On,emergency

mode

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The operator may need to make adjustments later, pos-sibly manual adjustments, but with this framework the initial response and activation of critical systems for fire-life safety are certain.

The example presented assumes an automated control system that will activate all appropriate systems. However, in preliminary discussion with tunnel operators that work with antiquated or ill-equipped control systems, a similar approach can be taken with the use of clearly defined hard-copy instructions. In summary, the format, language, and terminology of the FMT are critical for operator interpreta-tion and response in an actual emergency situation.

Fire-Life Safety StandardsNFPA 502: Standard for Road Tunnels, Bridges, and Other Limited Access Highways 2014 edition requires that a road tunnel have an emergency response plan, developed by the agency responsible for operating the tunnel. The standard requires that the plan state how the various systems will operate for a given incident. The FMT paradigm encourages a one-to-one match be-tween the emergency response plan incidents used by the operator, and the subsequent incidents used by the system developers in the system programming. This can have significant advantages for an integrated response between the operator and the system programmers be-cause both parties are working to the same terminology.

In addition, NFPA publishes a standard that is pertinent to the role of the FMT. NFPA 3: Recommended Practice for Commissioning and Integrated Testing of Fire Protection and Life Safety Systems, outlines a systematic approach

for the owner and the design team to provide documented confirmation that fire protection and life safety systems function as intended. The standard addresses the pro-cedural concepts of fire-life safety system commission-ing and also provides direction on the integrated system tests—tasks with which the FMT can assist.

ConclusionA well-integrated tunnel system will provide better func-tionality at all stages of a project including planning, implementation, commissioning, training, and operation. The FMT is a tool to assist with integrating the key stake-holders in the tunnel system design process including the operator, the designer, people who use the facility, the implementation staff, and emergency services. One of the greatest advantages of the approach is that it can be used to simplify the operator’s actions during an emergency, thereby improving the chances of a favorable outcome and greatly contributing to public safety.

As a leading consultant in fire-life safety engineering, Parsons Brinckerhoff is well placed to improve the deliv-ery and perception of fire-life safety training and opera-tion within tunnels for our clients. The FMT can help to achieve this and provide a safer road or rail facility.

Matt Bilson is a Principal Technical Specialist in the field of

tunnel ventilation and fire-life safety in the New York office of

Parsons Brinckerhoff.

Andrew Gouge is a Senior Controls Engineer in the field of tunnel

ventilation and fire-life safety. He left Parsons Brinckerhoff in

2014 to pursue an MBA.

Table 3 – Operator response concept – “one button” concept

Stage of response Operator inputs (to generate the “one button” response)

Pre-programmed system actions once incident confi rmed (via the Functional Mode Table programs)

Initial – suspected fi re in roadway

1. What kind of incident?

2. Where is the incident (camera ID)?

3. Confi rm incident?

Operator has provided enough information, and the system can now simultaneously execute commands to operate the many sub-systems.

Activate radio rebroadcast message warning people.

Activate emergency ventilation mode.

Close tunnels to traffic, change traffic signals and messaging in tunnel to tell people to stop if they are upstream of the fire.

Secondary – evacuation required Is evacuation required?

Activate messaging, public address and radio rebroadcast to require evacuation.

Activate lighting to guide people and warn vehicles in the other tunnel.

Tertiary – fi xed fi re fi ghting required Is fi xed fi re fi ghting needed? Activate the system based on the incident location determined

from the camera ID or linear heat detector zone.

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AbstractThe tunnel ventilation system for the metro line described in this article was designed in the late 20th century. It provides comfort cooling and smoke control and was based on a fixed block signalling system that allowed only a single train in any ventilation section. Commercial pressures to enhance timetable capacity resulted in a signalling upgrade to train-based control (“moving block” signalling), which permits up to three trains to simultane-ously occupy a ventilation section. The client wished to understand the risk impact of this change and in particu-lar how the ventilation system should now be operated to best effect in the unlikely event of a tunnel fire.

Parsons Brinckerhoff performed a comparative quantita-tive risk assessment (QRA), using available fire frequency data, to understand the impact of the ventilation system operation on the level of risk. This article describes the work and presents our findings.

Review of available fire frequency and consequence dataThe client had comprehensive data covering fire events on its network over the past 20 years. Of the 7,291 re-cords reviewed, 384 related to the line on which we were working and only 18 related to the area of interest.

Electrical arcing initiated the majority of the relevant fire events, at 175 (45.6 percent); arson accounted for 32 fires (8.3 percent); overheating equipment a further 22 (5.7 percent); and the remainder had a variety of causes, or were listed as “other/unknown”.

The data demonstrated that the operator experiences a modest number of fire events, the vast majority of which are small events that are managed by day-to-day opera-tional staff with minor to insignificant consequences for passenger and staff safety.

We concluded that fires could be categorised broadly as:

• “Small” in-car fires (up to around 200kW) – “common arson events” using readily available materials such as newspapers and unlikely to cause a major fire;

• “Small” undercar/track/tunnel fires;• “Large” in-car fires (greater than 1MW) – “determined

arson events” involving a quantity of accelerant and suf-ficient to cause a major conflagration (thankfully, to date no such event has occurred on the network); and

• “Large” undercar/track/tunnel fires.

The QRA analysisA set of event trees was developed, using known initiat-ing events and with various possible outcomes shown on different branches. The significant inputs were as follows:

• Frequency of initiating fire event (small or large fire, in-car or undercar/track/tunnel);

• Number of trains in section (1, 2, or 3);• Train reaches next station (yes/no);• Ventilation mode selected (remain in comfort cooling,

switch off, select optimum smoke control mode, select sub-optimal smoke control mode);

• Smoke control achieved (yes/no);• Smoke ingress into passenger compartment (yes/no);• Driver controls passengers (yes/no);• Passengers remain on train (yes/no); and• Protection implemented for evacuating passengers

(yes/no).

The probability of each outcome was determined in con-sultation with the client. Some were easy to define, such as the number of trains in a single ventilation section (33 percent probability of each possibility under new signal-ling system), while others required more detailed con-sideration, for example the probability of smoke being drawn into the passenger compartment.

The client’s own modelling team undertook computer analyses to determine whether smoke control would be achieved with multiple trains in a ventilation section.

Using Quantified Risk Assessment to Inform Ventilation System Responsesby Kate Hunt, Godalming, UK, +44 (0)1483 528966, huntk@pbworld.com

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These analyses suggested that critical velocity1 would be met with two trains in section but if three trains were present, critical velocity would be lost at the incident train but achieved at the non-incident trains due to cool-ing of the smoke along the tunnel length. The probabil-ities agreed are shown in Figure 1 above. Four event trees were then constructed and the resulting relative risk levels were reviewed.

Results of the QRAFigure 2 shows the impact on each scenario of leaving the ventilation in a comfort cooling mode (no change), switching it off, setting it to a non-optimal mode, and set-ting it to the optimal smoke control mode. Note that with a moving block signalling system, the following trains could be close to the train in front (around 25 metres apart). The train positions shown in Figure 2 are not in-tended to convey an accurate location for each train.

Shaded results show an appreciable increase in risk due to the ventilation configuration selected. The worst case outcome for a small fire was essentially the same for all ventilation configurations: operating the ventilation sys-tem gave no material benefit, regardless of the number of trains in the ventilation section. However, there was no disadvantage in using it. Therefore, since staff may not

know whether a fire is “small” or “large”, the ventilation response derived for large fires was considered accept-able for small fires as well.

For large fires, the presence of additional trains has a marked effect on likely risk level. For a single train event, there is a modest benefit in operating the ventilation sys-tem in the optimal mode (although for a fire near the centre of the train, even the optimal mode may incur a large loss of life). When there are multiple trains in a sec-tion, however, the impact of using the optimal ventilation mode offers a substantial benefit for a large fire incident, even if critical velocity is lost over the incident train.

Conclusions and recommendationsThe comparative QRA proved an important tool for deci-sion making. The structured event trees allowed various ventilation options to be tested and the clear outcome guided changes to maximise safety on this railway. It showed that the optimal smoke control mode gave a sig-nificant benefit for large in-car and undercar fires, with the greatest benefit when there are multiple trains in the ventilation section. For small undercar fires, using the op-timal smoke control mode also gave a fractional benefit, since it reduced the tendency for smoke ingress into the incident train.

1Critical velocity – the air flow required to prevent smoke from moving upstream of the fire location.

Event Small in-car fi re Large in-car fi reSmall under-car /

tunnel fi reLarge under-car /

tunnel fi re

Trains in section (1, 2, or 3 max) 33.3% 33.3% 33.3% 33.3%

Train reaches next station(not immobilised)(IT = incident train),AT = adjacent train,

TT = third train)

IT 99.8%AT 99.8%TT 99.8%

IT 99%AT NullTT Null

IT 95%AT NullTT Null

IT 66.5%AT NullTT Null

Change of ventilation mode(4 modes)

(No change, Off, Optimal smoke control mode,

Other smoke control mode)

25% 25% 25% 25%

Critical velocity achievedIT = 10% or Null

AT & TT = 50% or Null

IT = 5% or 50%

AT & TT = 5% or Null

IT = 10% or Null

AT & TT = 50% or Null

IT = 5% or 50%

AT & TT = 5% or Null

Smoke ingress into passenger compartment Null

IT = Null

AT & TT 0% or 100%as appropriate

As appropriate

IT as appropriate

AT & TT 0% or 100%as appropriate

Driver effectively controls passengers (client data) 96.367% 96.367% 96.367% 96.367%

Passengers remain in situ 85% 85% 85% 85%

Protection implemented for evacuation 96.7% 96.7% 96.7% 96.7%

Maximum fatalities per incidentIT = 3AT = 0TT = 0

IT = 1400AT = 1050TT = 700

IT = 3AT = 0TT = 0

IT = 1400AT = 1050TT = 700

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Figure 1 – Probabilities and consequences used in the QRA event trees

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When there is one train in a ventilation section, the op-timal smoke control mode should be determined based on the fire location along the train and the driver’s in-tended direction of evacuation. When there is more than one train in the ventilation section, trains in front of the incident train should be driven forward at low speed, out of the ventilation section. The preferred direction of ven-tilation should then be forward, to avoid passing smoke

over the trains that follow. Figure 3 summarises the recommended actions.

Kate Hunt is the Tunnel Ventilation & Fire Engineering Service

Leader for the UK. She has over 20 years’ experience in the

design and analysis of tunnel ventilation systems and in develop-

ing operational strategies for tunnel ventilation systems for road,

rail, metro, and cable tunnel applications.

Figure 2 – Impact of differing ventilation responses to various scenarios

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Figure 3 – Table of recommended actions

Number of trains in section Incident train condition Recommended actions

1 Incident train can move to next stationMove train to next station using any driving mode.Evacuate train and respond to fi re incident at station.

1Incident train cannot move (incident train immobilised or platform not available)

1) Establish driver’s intended evacuation direction.2) Use optimal smoke control mode to move smoke in opposite direction.3) Evacuate train and respond to fi re incident in situ.

2 or more Incident train can move to next station

1) Use optimal smoke control mode to move smoke forward, and2) Move train(s) in front to the next station at low speed, and3) Move incident train to next station using any driving mode. Evacuate train and respond to fi re incident at the station.4) Move or evacuate trains behind the incident on a case-by-case basis.

2 or moreIncident train cannot move (incident train immobilised or platform not available)

1) Use optimal smoke control mode to move smoke forward, and2) Move train(s) in front to the next station at low speed, and3) Evacuate train and respond to fi re incident in situ.4) Move or evacuate trains behind the incident on a case-by-case basis.

Results: Worst case average numberof fatalities per 1000 years

ScenarioNo

ChangeSwitch

OffNon-

OptimalOptimal

“Small” in-car fi re (common arson event)

2.34 2.60 2.60 2.60

“Small” undercar/track/tunnel fi re

26.35 29.27 30.90 30.90

“Large” in-car fi re (determined arson event)

1.21 1.27 1.27 0.46

“Large” undercar/track/tunnel fi re

29.24 30.78 32.49 4.28

Results: Worst case average numberof fatalities per 1000 years

ScenarioNo

ChangeSwitch

OffNon-

OptimalOptimal

“Small” in-car fi re (common arson event)

2.34 2.60 2.60 2.60

“Small” undercar/track/tunnel fi re

26.35 29.27 30.90 30.90

“Large” in-car fi re (determined arson event)

118.97 125.23 125.23 0.46

“Large” undercar/track/tunnel fi re

98.35 103.53 105.24 4.28

Results: Worst case average numberof fatalities per 1000 years

ScenarioNo

ChangeSwitch

OffNon-

OptimalOptimal

“Small” in-car fi re (common arson event)

2.34 2.60 2.60 2.60

“Small” undercar/track/tunnel fi re

26.35 29.27 30.90 30.90

“Large” in-car fi re (determined arson event)

197.48 207.87 187.88 0.68

“Large” undercar/track/tunnel fi re

144.42 152.02 153.73 8.58

Direction of travel

criticalvelocity

met

criticalvelocity

met

criticalvelocity

met

Direction of travel

criticalvelocity

lost

criticalvelocity

met

criticalvelocity

met

Direction of travel

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A Risk-Based Approach to Jet Fan Optimisationby Anthony Ridley, Godalming, UK, +44(0)1483-52-8661, Anthony.ridley@pbworld.com

IntroductionIn addition to providing adequate air quality and maintain-ing temperatures within acceptable limits, tunnel venti-lation systems need to be designed to move smoke in the event of a fire with a ‘good’ level of confidence. Wind and other meteorological forces can negatively affect the performance of the ventilation system, but for how much wind force should the system be designed?

Parsons Brinckerhoff’s UK tunnel ventilation team is working on a large railway project with a number of tun-nels, so it was important to answer this question confi-dently and with a solid basis. Risk analysis was used as a tool to help the decision-making process.

This article focuses on the optimisation of a range of rail tunnels that would utilise jet fans to provide smoke con-trol in the form of longitudinal ventilation. Longitudinal ventilation prevents smoke from back-layering, providing a tenable evacuation environment upstream of the fire. In total, seven tunnels with lengths ranging from approxi-mately 500 metres to 3 kilometres were analysed.

The optimisation was carried out after an initial design phase where the tunnels were found to be sensitive to atmospheric wind. At that stage of the design, questions still remained as to whether the wind force that was be-ing designed for was reasonable. We based the design on a 1 percent probability of exceedance in any year, but should it be 10 percent, 1 percent, 0.1 percent, or something different?

The design included an assumption that the jet fan nearest the fire was inoperable. In the emerging design, approximately one jet fan per portal was required to overcome the wind forces, two jet fans were required to control the smoke, and one standby/redundant jet fan

was provided to handle other random failures. A further question arose as to the probability of both a high wind and a failed jet fan. Was the investment in the redundant jet fan warranted? A quantitative risk analysis was there-fore undertaken to understand the acceptability of this risk of removing the redundant jet fan.

The combination of a fire in the tunnel, a high wind force, and a failure of one of the required jet fans might lead to the back-layering of smoke within the tunnel. Back-layering occurs when the ventilation flow rate is not high enough to meet ‘critical velocity’1 (CV). The critical velocity will depend on factors such as the fire heat release rate and tunnel gradient. The consequences associated with providing less than critical velocity required evaluation.

MethodologyAn event tree was generated to consider the probability of various scenarios (see Figure 1). Each branch or scenario of the event tree had an overall predicted event frequency and consequence assigned. This was subsequently used to estimate risk.

A tunnel fire frequency rate was estimated through inter-pretation of statistical data from the UK’s Railway Safety and Standards Board. Various probabilities were then assigned to each scenario.

Each event path required an evaluation of consequenc-es to passengers. The consequence analysis was bro-ken down into two constituent parts:

• Bulk-flow simulations were undertaken using the Sub-way Environment Simulation (SES)2 software for three representative tunnels. This provided information about the tunnel air flow rate for every different configuration of ventilation mode, train location, fire heat release rate,

1Critical velocity – the air flow required to prevent smoke from moving upstream of the fire location.2Subway Environmental Design Handbook. Volume II. Subway Environment Simulation Computer Program (SES). Part 1. Prepared by Parsons Brinckerhoff as part of a joint venture for the U.S. Department of Transportation, in 1975.

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ventilation direction, and wind force that was tested. From this, average percentage of critical velocity was determined for each combination of tunnel, ventilation mode, and wind condition.

• A 3-D analysis was then performed on a character-istic short tunnel section using the Fire Dynamics Simulator (FDS) software. The evacuation model was enacted within the software which allowed the co-incident location of the smoke and passengers to be predicted. These simulated the evacuation of 1,100 passengers within the tunnel with different fire heat release rates and air flow rates. Predicted effects or consequences to passengers during the evacuations were recorded based on the Fractional Effective Dose (FED) method, but adjusted for these simulations to also account for the effects of irri-tant gasses. The simulations were undertaken for different airflow rates to allow the outcomes to be mapped to the SES simulations.

ResultsThe results of the consequence analysis can be seen in Figure 2.

It is evident that for the larger fires simulated there is al-ways a base equivalent fatality rate of approximately 55 persons. This represents the inherent consequence in-volved with longitudinal ventilation systems; there is a risk that passengers may be located downstream of the fire location. To minimise passenger numbers downstream of the fire, the ventilation direction is decided by the fire lo-cation. To model a condition where an “average” number of passengers were downstream of the fire, the fire was set to be a quarter of the length down the train. As the percentage of critical velocity achieved reduces, the back-layering of the smoke advances. This process is illustrated in Figure 3. The jump in the predicted number of equivalent fatalities from 55 to 250 as seen in Figure 2 was due to the back layering of smoke past an upstream passenger exit (illustrated by scenario C in Figure 3).

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Figure 1 - Event tree (dotted arrows represent uncompleted branches of the tree, only one complete branch is fully shown)

7MW

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Risk analysisThe UK rail industry has acceptance criteria for the probability of injury for individuals as well as methods to evaluate the so called ‘societal risk’ that can oc-cur for low-frequency high-consequence events such as tunnel fires.

The risk to an individual passenger was predicted to be 1 in 240,000,000—orders of magnitude lower than the broadly acceptable limit of 1 in 1,000,000 in the UK.

Societal risk was evaluated using frequency/severity (FN) curves where the value plotted on the y-axis is the cumulative frequency of experiencing N (passenger

fatalities). These are assessed graphically and were compared to the current national railway risk profile of the UK railway (see Figure 4). The FN risk should be below this line.

‘System failure’ points on the bottom right of the FN graph represented scenarios where the ventilation system had suffered complete failure. The points were slightly higher than the baseline risk of the UK railway. The majority of this risk was predicted to be due to the calculated human error in operating the ventilation system correctly in the event of an incident. Figure 5 shows an FN plot where the element of human error has been removed. This suggests a strong benefit in providing a fully automatic control system.

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Figure 2 - Predicted relationship between percent of critical velocity achieved and total passenger fatalities and weighted injuries for different fire magnitudes.

Figure 3 - Illustration of evacuation scenarios: a) CV is achieved, b) CV not achieved but no additional passenger fatalities (60-100% CV), c) CV not achieved and resulted in additional passenger fatalities (<60% CV).

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b) CV not achieved but no additional passenger fatalities (60 - 100% CV)

c) CV not achieved and resulted in additional passenger fatalities (<60 % CV)

a) CV is achieved

Walkway TrainTrain/Tunnel exit Fire

Untenableconditions

Evacuationroute

Ventilationdirection

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ConclusionsIt was concluded that the fire hazard could be managed so far as is reasonably practicable with the proposed ventila-tion approach of using the spare jet fan to also overcome wind forces. There was no strong case for adding further jet fans to reduce the risk. Eighteen (18) jet fans were eliminated from the ventilation system design, potentially saving many millions of pounds.

It was also concluded that if efforts were made to reduce the human factor from the operation of the ventilation system, the societal risks attributed to the higher conse-quence events could be significantly reduced.

Anthony Ridley is a Graduate Tunnel Ventilation Engineer in Go-

dalming. He joined the tunnel ventilation team two years ago

after completing his MEng in Aeronautics at Durham University.

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1.E-07

1.E-06

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Fatality Weighted Injuriesshort tunnels societal risk UK railway societal risk 2013

Figure 5 - Societal risk with the removal of human error from the operation of the ventilation systems.

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short tunnels societal risk UK railway societal risk 2013

Wind risk

Inherent Longitudinal risk

System failure

Figure 4 - Breakdown of societal risk profile of three representative tunnels.

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Cost-Effective Ventilation System for a Light Rail Transit Projectby Silas Li, New York, NY, US, +1-212-465-5217, lisilas@pbworld.com and Andrew Louie, New York, NY, US, +1-212-631-3767, louiea@pbworld.com

1Fire Dynamics Simulator (FDS) Version 5.5.3, 2010, (CFD Software), Building and Research Laboratory, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Stop 8600, Gaithersburg, MD 20899-8600, USA.

2NFPA 130, "Standard for Fixed Guideway Transit and Passenger Rail Systems", 2010 Edition, published by the National Fire Protection Associa-tion, 1 Batterymarch Park, Quincy, MA 02269-9101, USA, August 2009.

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An underground light rail transit system project in the US includes two new stations and connecting tunnels of 3.3 miles in length (5.28 kilometers) that require emergency ventilation to provide a tenable environment along the egress path in the event of a train fire.

The cut-and-cover station is a center island platform that is 395 feet (120 meters) long. Each train consists of four cars. The platform level is served by two sets of escala-tors, one at each quarter point of the platform, that lead up to the mezzanine level. From the mezzanine level, two stair/escalator combinations lead up to two separate entrances at the street level. In addition, enclosed emer-gency exit stairways located at both ends of the platform lead to exits at grade level (see Figure 1). Due to the similar design of both stations, only one station ventila-tion analysis is presented here.

Original Ventilation ConceptFigure 2 shows the airflow schematic for the original ven-tilation concept with two ventilation systems:

1. Station ventilation system - The intent of the station ventilation system design is to exhaust smoke and hot gases from a fire on a train stopped at the station. The smoke would rise up into the atrium and the station ventilation system would extract the smoke near the top of the atrium via the station ventilation dampers. The station ventilation system includes four bi-direc-tional fans each delivering 100,000 cfm (50 m³/s).

2. Tunnel ventilation system - The intent of the tunnel ventilation system design is to exhaust smoke and hot gases from a fire on a train stopped in the tun-nel between stations or between the station and portal. The tunnel ventilation dampers are located near the ends of the station platforms to extract the smoke before it enters the station public area. The

tunnel ventilation system includes four uni-direction-al fans each delivering 250,000 cfm (125 m³/s).

The original station design consists of ventilation fan plants located directly over the trainways at the ends of the station platform. There is a large atrium in the middle of the station where station ventilation dampers connect the station ventilation fans to the atrium area via damp-ers in the fan room level walls. At the ends of the station, there are tunnel ventilation dampers located in the ceiling of the trainway that connect the trainway region to the tun-nel ventilation fans.

Modified Ventilation Concept with Station Ventilation Fans EliminatedA computational fluid dynamics (CFD) analysis was per-formed to determine if the four station ventilation fans can be eliminated by re-configuring the tunnel ventila-tion fans and associated ducts and plenums so that the tunnel ventilation fans can exhaust smoke and hot gases from a tunnel fire or from a station fire (Figure 3). The design requirements precluded the need to de-sign for simultaneous station and tunnel fires.

The CFD analysis used to model the station, fire, and ventilation system was a software package FDS1. The ventilation criteria is to maintain a tenable path of egress from the incident train to a point of safety for at least six minutes, which is the maximum time it should take passengers to evacuate from the platform to a point of safety2. The design fire for this station is a 13.2 MW fire that follows a medium growth rate fire curve and reaches peak fire heat release rate at 17.7 minutes. The average soot yield of the fire is 0.1245 kgsoot/kgfuel burnt. The fire properties used are representa-tive of the light rail vehicles. The ventilation system is served by four fans, two fans at each end of the sta-tion, each fan delivering 250,000 cfm (125 m³/s). The

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Figure 1 - Section View of Station

Figure 2 - Airflow Schematic for Original Ventilation Concept

Street Level

Mezzaninie Level

Platform Level

Fan Room Level

To Outside

Ventilation Shaftto Outside Ventilation Shaft to Outside

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Station Ventilation Fans (typ.)

Mezzanine

Station VentilationDampers (Typ)

Tunnel Ventilation Fans (typ.) Tunnel VentilationDampers (typ.)

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TunnelVentilation System

StationVentilation System

To Outside

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To Outside

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Ventilation Shaft to Outside

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Station Ventilation Dampers (typ.)

Ventilation Fans (typ.) Tunnel VentilationDampers (typ.)

TunnelVentilation System

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To Outside

Mezzanine

Figure 3 - Airflow Schematic for Modified Ventilation Concept

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Figure 4 - Comparison of Visibility at Platform Level

fans are activated two minutes after the fire starts, and reach full operational capacity after 180 seconds.

Figure 4 shows the CFD results at the platform level, 8.2 feet (2.5 meters) above the platform for a fire ignited on a train stopped in the station. The simulation results for the original ventilation concept and the modified venti-lation concept are shown in comparison. Only the con-tours of visibility are shown, as that is the controlling

criterion. Un-shaded regions are within the visibility cri-teria, while regions that are shaded violate the criteria.

The result of the CFD analysis shows that the modified ventilation concept performs just as well as the origi-nal ventilation concept for the critical first six minutes during passenger evacuation. It outperforms the original ventilation concept when the fire has reached its maxi-mum fire heat release rate. This is due to the increased

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ventilation capacity of the tunnel ventilation fans over the station ventilation fans.

ConclusionThe CFD results were presented to the ‘authority having jurisdictions’ (AHJ). The AHJ approved the modified venti-lation concept with the elimination of station ventilation fans. The modified ventilation design saved approximate-ly US$6 million in mechanical and electrical costs, in ad-dition to lowered maintenance costs due to less equip-ment. Additional savings were realized by the elimination of fan room space and ventilation shafts.

The CFD analysis also provided insight into key station design elements that impact the effectiveness of the ven-tilation system. For this type of station, the large atrium functions as a smoke reservoir and locating the smoke

extraction dampers near the top of the atrium is effective in removing smoke from the station during the evacuation period. In addition, locating the tunnel ventilation damp-ers at the ends of the station is effective in preventing the spread of smoke from a tunnel fire to the station.

Andrew Louie is a Professional Associate in Tunnel Ventila-

tion who has worked on tunnel ventilation projects for Parsons

Brinckerhoff for the past 9 years across the US and England.

He is currently one of the main developers of the SES program.

Silas Li is Manager of the Parsons Brinckerhoff US Tunnel Venti-

lation Analysis Group and chairman of the NFPA 130 ventilation

task group. He has 29 years of experience in the design and

simulation modeling of fire/smoke management and ventilation

systems for numerous projects involving transit, rail, and road

tunnels in seven countries.

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Meeting the Challenges of Smoke Duct Fan Selection for Australian Road Tunnelsby Chris Chen, Sydney, AUS, +61 2 9272 5082, chenc@pbworld.com

IntroductionParsons Brinckerhoff has been involved in the detailed design work on some recently completed major Austra-lian road tunnels. A number of these unidirectional traf-fic tunnels, including the M7 Clem Jones Tunnel (Clem 7), Brisbane’s Airport Link Tunnel, and Legacy Way (un-der construction), employ a combined longitudinal and distributed smoke extraction ventilation (smoke duct) system for fire emergencies. This type of system can re-sult in unique tunnel ventilation fan duty requirements. This article describes the challenges and analysis ap-proaches to account for a wide range of parameters that can affect the fan requirements, including:

• fire location in the tunnel (distance to fans); • fire heat release rate; • thermal losses; • tunnel section and grade at the fire site; and • duct leakage.

Fan selection will be based on achiev-ing multiple fan duties (airflow and pressure capacities), and analysis is required to ensure all parameters are accommodated.

Combined Ventilation DesignThe longitudinal ventilation system provides air flow at or above the criti-cal velocity upstream of the fire to prevent smoke from backlayering, and the smoke extraction system captures smoke downstream of the fire site. The longitudinal ventilation is primarily achieved by in-tunnel jet fans. The jet fans can operate with active controls (with a tunnel air ve-locity feedback system) to achieve a predetermined critical velocity. Ex-

cess longitudinal flow needs to be avoided to contain the smoke at the fire incident site (i.e., no overshoot).

The smoke extraction system is provided to protect oc-cupants downstream of the fire during congested traffic conditions. This is achieved by opening sets of smoke dampers located immediately downstream of the fire. A specific mass of air flow has to be exhausted from the tunnel. This mass flow equates to the volume of air at ambient conditions required to prevent backlayering of smoke upstream of the fire and overshoot downstream of the fire. Values for this air volume flow are typically on the order of 3 metres (10 feet) per second and 1 metre (3.3 feet) per second respectively. This value is also known as the critical velocity, determined by CFD modelling and/ or empirical equations.

Figure 1 shows the typical configuration of this longitu-dinal ventilation and smoke extraction system. In order

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Figure 1 - Typical configuration of a longitudinal ventilation and smoke extraction system

Smoke duct Open dampers

Path 1 with ductpressure loss P1a

Path 2 with ductpressure loss P2a

Case A: 50% and 50% split of total airfl ow at pressure loss of P1a=P2a

≥ 1m/s (3.4ft/s)

Smoke duct Open dampers

Path 1 with ductpressure loss P1b

Path 2 with ductpressure loss P2b

Case B: 30% and 70% split of total airfl ow at pressure loss of P1b=P2b

≥ 1m/s (3.4ft/s)≥ Critical velocity

≥ Critical velocity

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to minimise the smoke duct size, extraction is in the upstream and downstream direction in the duct. For ex-ample, Path 1 is the travel path of exhausted smoke and air mixture from the open dampers in the smoke duct near the fire location, to the exhaust fan upstream of the fire. This article focuses on fan selection using this type of configuration.

Fire size, location, and thermal effectsThe fire size (heat release rate) and location of the fire in a tunnel are major factors in determining the required extraction, the smoke duct system pressure, and the fan duty. Dependent on project requirements, by increasing design fire size, a higher critical veloc-ity of air needs to be supplied to prevent backlayering of smoke. Additionally, for fires located in larger cross sectional areas of the tunnel, or in caverns where there are traffic off/on ramps diverging/merging with the mainline tunnel, the critical velocity may still need to be maintained. Both of these factors will require a larger air flow volume and hence increased smoke duct system capacity. The fan selected must accommodate these multiple capacities.

Determining the fan capacity can be further complicated by the need to allow for varying air densities due to different fire sizes and heat losses. As the air is being heated at the fire site, the volume expands and density decreases. As the hot smoke travels along the smoke duct, heat transfer cools the smoke and the air density increases. Due to this, the fire size and location along the tunnel affects the pressure loss along the duct and the density of the air to be handled by the fans. For multiple extraction locations (i.e., different fire locations in the tunnel) this effect must be accounted for in the analysis to ensure the required extraction is achieved.

Smoke duct and damper leakageA road tunnel smoke duct is not completely sealed. When the duct is in extraction mode it is at a lower pres-sure than the adjacent roadway, causing leakage of air between the tunnel roadway and the smoke duct. The air leakage occurs via cracks, construction tolerances, and gaps in closed dampers and duct slabs. Leakage is dependent on duct pressure and construction quality (i.e., there is no single leakage rate figure).

As an example, an increase of around 10 percent in air flow was estimated for a typical construction of “non-sealed” smoke duct for every 1000 metres (~3300 feet) of length for a particular configuration. The amount of damper leakage can be estimated via damper specifica-tions and the expected local duct pressure. It needs to be noted that it is difficult to accurately estimate the impact of civil construction tolerances during the design stage of a project. Conservative estimates are often ap-plied. The leakage effect both on flow rate and on duct pressure loss along the duct distance is shown diagram-matically in Figure 2.

Design and AnalysisThe analysis to be undertaken on a smoke duct config-uration has a number of elements. A numerical analy-sis can be used to account for incremental air leakage and air density changes along the duct, with simplified heat transfer models under steady state conditions. The results give a prediction of the required fan duties to achieve the air extraction mass flow rate at the fire site. This needs to be determined at multiple extrac-tion locations.

As an example, Figure 3 shows a “flow split” between the two smoke extraction paths, Path 1 and Path 2, for a given fire size at two different fire locations (Case A and Case B, refer to Figure 1). Identical fan properties are used for both paths.

• Case A is for a fire located roughly at the aerodynamic midpoint between the extraction fans. By definition the airflow split is 50 percent between each end. In reality this may not occur exactly at the geometric tunnel mid-point, and depends on the upstream and down-stream characteristics of the tunnel and the smoke duct. The important element is that the pressures are approximately equal on either side of the flow extraction point, regardless of fan sizes at each end of the path. DE

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Figure 2 - Effect of air leakage in ducts for both pressure and flow

Duct Distance (length)

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• Case B shows a fire located closer to the end of Path 2. In this example case, the pressures are approximately equal as the length of the airflow of Path 2 is decreased compared to air flow of Path 1.

Together, Case A and B show that the fan duty varies con-siderably with the fire location. Given that the required extraction will change with differing fire sizes and other locations, many fire locations will need to be assessed in order to determine the maximum flow and pressure the fan has to service.

The resulting fan duties for the two cases are shown parametrically in Figure 4 and show that the fan duty points vary considerably even when only two fire lo-cations are considered. When assessing, many loca-tions will need to be considered along with the varying fire size. The analysis is an iterative process. This will determine a range of fan duty limits. Practically, the final fan selection is based on the need for the fans to cover all possible fan duty points that may be encountered during operation. The fans ultimately selected will generate flows in excess of the required flows for many cases which will need to be considered and accounted for. Generally for smoke extraction du-ties, excess of design performance requirements is not an issue.

ConclusionThe process of sizing smoke ducts and determining the smoke extraction fan requirements is technically chal-lenging, involving factors from many tunnel design disci-plines, interactions of thermodynamics and fluid dynam-ics, and physical constraints. Fan requirements for the smoke extraction system are based on the possible fan duty points the system will encounter during operation.

Designs undertaken by Parsons Brinckerhoff have dem-onstrated the viability of smoke extraction systems for long road tunnels, by determining the necessary fan re-quirements and smoke duct requirements to achieve the required capacity. The design analysis and research the team has undertaken will benefit future smoke extrac-tion system designs for long road tunnels, by ensuring that the installed systems can perform to their intended purposes and capacities. However, the actual perfor-mances of such systems are also dependent on the constructor’s final system design, the equipment sup-pliers, and the installer’s performance based on their project contractual obligations. The completed smoke extraction systems installed in the Clem7 and Airport Link tunnels are currently in service.

Chris Chen is a Mechanical Engineer who has worked on vari-

ous road and rail tunnel projects, including Airport Link in Bris-

bane, as part of Parsons Brinckerhoff’s tunnel systems team

in Australia.

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Figure 4 - Fan duty curve with different flows

Flow rate (volume/time)

Case BPath 1

Pa

Pb

Case APath1 & 2

Case BPath 2

Potential Fancurve for coveringall duty cases of 30% to 70% of total airfl ow

70%fl ow

50%fl ow

30%fl ow

(Two identical fans)

Pressure (force/area)

LegendRequired duties

Fan curves

System curves

Figure 3 - Flow split and duct pressure loss

Flow rate split (%)

Pressure (force/area)

Case BPath 2

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Case A

Case B

P1a=P2a

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Analysis Considering the Conversion of an Existing Road Tunnel Transverse Ventilation System to Transit Useby Jesse Harder, Sacramento, CA, US, +1-916-567-2512, harderjl@pbworld.com; Andrew Louie, New York, NY, US, +1-212-631-3767, louiea@pbworld.com; Vamsidhar Palaparthy, New York, NY, US, +1-212-465-5521, Palaparthy@pbworld.com; Silas Li, New York, NY, US +1-212-465-5217, lisilas@pbworld.com

In 1927, the first fully transverse tunnel ventilation sys-tem was commissioned for the Holland Tunnel in New York (see Figure 1). Until that time, tunnels had been ventilated only by longitudinal airflow systems.

Longitudinal ventilation systems provide airflow along the tunnel axis at a velocity sufficient to prevent smoke back-layering during fire emergencies, allowing safe egress in one direction (into the fresh airflow). Fully-transverse ven-tilation systems utilize separate supply and exhaust air ducts extending the length of the tunnel to provide fresh air into the tunnel at the roadway level and to extract heat, emissions, and smoke out of the tunnel near the ceiling. Transverse ventilation limits smoke spread to an area near a fire by extracting smoke generated through openings in the exhaust air duct, allowing safe egress away from the incident in both directions.

Ole Singstad (Barclay, Parsons and Klapp 1917-1918) was the engineer responsible for developing the revolu-tionary Holland Tunnel ventilation system. At the time, ventilating such a congested vehicle tunnel was thought to be impossible, but the completed Holland Tunnel ven-tilation system would not only work, it would set the stan-

dard for fully transverse ventilation sys-tem design for many decades to come.

Today, road tunnels throughout the United States and the world contain transverse ventilation systems. Traditionally, road tunnel ventilation systems have been de-signed to meet contaminant level criteria. In the decades since the Holland Tunnel ventilation system was designed, mean-ingful reductions in vehicle emissions have been realized due to advancements in automotive technology, and fire science has advanced significantly leading to a greater understanding of fire size and de-velopment. As a result, the design para-digm for tunnel ventilation systems has

shifted over the past century from emissions control to a stronger focus on smoke control during fire emergencies.

Considering Road to Rail Tunnel ConversionAs rail transit systems continue to expand in an effort to offset heavily congested roadways, and with limited available right of way in populous metropolitan regions, some rail transit extensions are converting portions of existing roadways and road tunnels to passenger rail use (see Figure 2). In Seattle, Washington the Sound Transit East Link Extension project has proposed the conversion of existing Interstate I-90 center roadway and associated

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Figure 1 - Full-scale Model Section of the 1927 Holland Tunnel in New York

Figure 2 - Transit Route in median of congested interstate

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center tunnels into a light rail transit (LRT) trainway con-necting Seattle to Bellevue (see Figure 3).

In 2013, Parsons Brinkerhoff performed extensive ven-tilation analysis in support of the East Link project fi-nal design, investigating the ventilation system design for two existing road tunnels in the Seattle area, the Mount Baker Ridge Tunnel and the Mercer Island Lid Tunnel. The analysis specifically considered modifica-tions to the existing fully-transverse road tunnel ventila-tion systems to determine the feasibility of reusing it for the new LRT trainway.

Existing East Link Tunnel VentilationThe Mount Baker Ridge Tunnel and the Mercer Island Lid Tunnel each consist of a fully-transverse ventilation system with a central fan plant located above the tun-nel near the mid-point. The Mount Baker Ridge tunnel is 3,478 feet (1060 meters) long and has air ducts along each side of the roadway, while the Mercer Island Lid tunnel is approximately 2,900 feet (884 meters) long with air ducts arranged above the roadway, separated from the roadway by a suspended ceiling. The ventila-tion airflow is evenly distributed along the tunnel length through small ports spaced at regular intervals.

Investigating the Reuse of a Transverse Ventilation SystemIn 1993, the Memorial Tunnel Fire Ventilation Test Pro-gram (MTFVTP) began conducting full-scale fire tests in an abandoned road tunnel to evaluate the ability of several ventilation system types to manage smoke and temperature. The tunnel ventilation systems were tested across a range of fire sizes. Sound Transit East Link proj-ect design criteria specified a medium t-squared (time squared) growth rate fire curve with a peak heat release rate (HRR) of 13.2 MW. Comparing this fire size and smoke generation rate with the ventilation performance

for 10 and 20 MW fires from the findings of the MTFVTP, it would appear that some variation of extraction ventila-tion could control the smoke generated. However, road tunnel ventilation systems, like those considered for re-use in the East Link extension, were designed to the 100 cubic feet per minute per lane foot criteria. In MTFVTP findings, this criterion was not sufficient for many emer-gency fire scenarios.

The existing road tunnel ventilation system for each East Link tunnel consists of three fans for supply and three fans for exhaust ventilation. Parsons Brinckerhoff’s ven-tilation analysis specifically considered the re-use of the exhaust ventilation fans for the new LRT trainway. The analysis utilized computational fluid dynamics (CFD) to investigate the performance of several system types:

• Single Zone Exhaust System – Steady State Run: use the existing system to exhaust from the entire length of tunnel (supply fans off). The existing system failed due to smoke spread (see Figure 4). The tunnel width and existing fan capacity limited the effective-ness of the extaction system.

• Two-Zone Exhaust System – Transient Run: use the existing system to exhaust half of the tunnel by clos-ing isolation dampers at the tunnel midpoint (sup-ply fans off). The existing system failed to control smoke spread at 6 minutes (see Figure 5). Smoke spread was limited, but not contained to the imme-diate area at the fire car due to wind forces and extraction port locations.

• Point Extraction System - Close all existing exhaust ports and install new openings, 160 square feet (14.9 square meters) with motorized dampers every 250 feet (76.2 meters) on-center creating a point extract system where the three closest dampers to the fire are opened, and the exhaust fans extract the smoke through the open dampers (see Figure 6). This system controlled smoke for the duration of egress (8 minutes) with increased fan capacity, but was rejected due to the rigorous structural analysis required and potential seismic retrofit work.

• Four-Zone Extraction System - Close all existing exhaust and supply port openings. Convert the supply duct into a second exhaust duct and effectively subdivide the system into 4 zones. Install isolation dampers to direct all exhaust ventilation to a single incident zone. Create large openings, 240 square

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Figure 3 - Simulation of the proposed East Link Extension along I-90 across the Homer M. Hadley floating bridge

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Figure 4 - Single Zone Exhaust System

Limit of smoke spread allowed for extraction systems

East Portal

Ext. Coeff

West Portal

Figure 5 - Two-Zone Exhaust System

Limit of smoke spread allowed for extraction systems

Ext. Coeff

Close all exhaust portsExhaust Damper 2Exhaust Damper 1 250 feet

Fire Car

Figure 6 - Point Extraction System

Exhaust Openings (typ.)

Motor-OperatedDamper Connectionto Fan Plant (typ.)

Exhaust Duct

Supply Duct

Zone 1

Zone 2 Zone 3

Zone 4

East Portal West Portal

Figure 7 - Four-Zone Extraction System

12 Jet Fan Operating

Longitudinal Ventilation DirectionWest Portal

Figure 8 - Longitudinal System

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feet (22.3 square meters) in the suspended ceiling to extract smoke and hot gases from the incident fire zone (see Figure 7). This system controlled smoke spread for the duration of egress (12 minutes) with increased fan capacity, but the option was rejected due to concerns about the structural impact on the existing tunnel.

• Longitudinal System (Jet Fans) – install 14 jet fans (12 fans operating - analysis considered 1 fan out of service and 1 fan out due to fire) along the tunnel walls providing longitudinal ventilation and protecting the egress path indefinitely (see Figure 8).

ConclusionConverting an existing fully-transverse road tunnel ven-tilation system to transit use is feasible but presents many challenges to the designer. Based on CFD analy-sis of the East Link tunnels for the stated fire size, the following parameters significantly affect the ventilation system performance:

• Wind speed (normal to the portals) – This was the primary parameter contributing to smoke spread along tunnel length for the extraction system analysis;

• Extraction points – The existing ventilation port size and spacing significantly limited the extraction capacity nearest the fire car;

• Tunnel Width – Extraction airflow velocities across the tunnel cross-section were non-uniform and diminished opposite the ports; and

• Fan Capacity – Fan size was limited by maximum allowable airflow velocities in the ducts and at the egress walkway.

Fully-transverse road tunnel ventilation systems were designed to provide distributed transverse air flow evenly along the length of the tunnel. Such a design works

well for controlling air quality during times of congested traffic, where automobiles fill the tunnel from portal to portal and contaminates are evenly distributed. In road tunnels, parameters such as wind speed improve air quality by purging the tunnel pollutants.

For transit tunnels, where emergency fire conditions drive the design, extraction ventilation systems must effectively control smoke and heat to a very limited area near the fire car under worst-case conditions. Existing fully-transverse ventilation systems can be modified, allowing the extraction capacity to be directed nearest the fire source, but such modifications require structural analysis of the tunnel and may not be able to control smoke spread for fire sizes greater than 10MW. The EastLink tunnel ventilation analysis led Parsons Brinckerhoff to recommend a longitudinal system that resulted in significant cost savings over the preliminary design.

Jesse Harder is a registered Mechanical Engineer specializing in

transit facilities. He is experienced in the design and construction

of mechanical and fire life safety systems and has served in key

roles on large transit extensions.

Andrew Louie is a Professional Associate in Tunnel Ventilation. He

has worked on tunnel ventilation projects for Parsons Brinckerhoff

for the past 9 years across the United States and England.

Vamsidhar (Vamsi) Palaparthy is a Mechanical Engineer and has

been involved in the design and analysis of ventilation systems

for various major vehicular and subway tunnels.

Silas Li is Manager of the Parsons Brinckerhoff US Tunnel

Ventilation Analysis Group and chairman of the NFPA 130

ventilation task group. He has 29 years of experience in the

design and simulation modeling of fire/smoke management and

ventilation systems for transit, rail, and road tunnels.

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Long Road Tunnels and Portal Emission Controlby Argun Bagis, Sydney, AUS, +61-2-9272 5435, bagisa@pbworld.com; and

Duncan Saunsbury, Sydney, AUS, +61-2-9272 1419, saunsburyd@pbworld.com

The use of longitudinal tunnel ventilation in road tunnels is arguably the preferred method for modern tunnels, in particular for those classified as ‘long tunnels’, with lengths generally over 1500 metres (4921 feet). How-ever, the use of longitudinal ventilation often brings with it the need to control portal emissions, especially for tun-nels located in urban or residential areas.

In a longitudinal system the concentration of pollutants in the tunnel air generated by vehicles transiting the tun-nel increases continuously from the entry portal to the exit portal (refer to Figure 1). Ideally, the tunnel air would need to be captured prior to exiting the tunnel, and discharged with sufficient dispersion so as to meet ambient air quality limits at the nearest sensitive receptors. This typically requires the ability to control the tunnel airflow so that a net inflow of fresh air is able to be maintained through the exit portal against the traffic direction, generally at a steady-state inflow velocity of between 0.5 – 2.0 metres per second (1.7 – 6.6 feet per second), depending on the aerodynamic characteristics. Consequently, the installed capacity of the tunnel ventilation system may not be driven by air quality demands, but rather by the need to control the piston-driven airflow generated by vehicles.

Parameters such as the maximum design traffic speed and the proportion of heavy goods vehicles become more critical when designing for portal emission control. Figure 2 provides an overview of a typical longitudinal ventilation system with portal emission control and point extraction prior to the exit portal.

The dilution air that is required to maintain in-tunnel pol-lution limits is introduced into the tunnel through the en-try portal(s) and extracted via the exhaust system, just prior to the exit portal(s). Depending on the traffic flow and tunnel length, the quantity of airflow generated by the piston effect can be in excess of this dilution air, which would need to be extracted by the exhaust system, with

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Figure 1 - Emission concentration along tunnel

Figure 2 - Point extraction for portal emission control – fully reversible jet fans shown

Fresh Air Fresh AirPiston Effect

Reversible Jet Fans

ExhaustSystem

Unidirectional traffi c

Exit P

ort

al

En

try P

ort

al

Vitia

ted

Air

Reversible Jet Fans used to reduce or to augmentpiston effect induced tunnel air fl ow

Net positive fresh air infl ow into exit portal

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longer tunnels requiring greater exhaust capacity. Figure 2 schematically shows the location of the exhaust system within the context of the tunnel and associated ventilation equipment. The capacity of the exhaust system needs to be sufficient to capture both the main tunnel airflow and the additional fresh air inflow through the exit portal.

Aerodynamic efficiencies can be improved by augmenting the exhaust system capacity with jet fans within the tun-nel to control tunnel and portal airflows (see Figure 3).

In a unidirectional tunnel the aerodynamic drag of the vehicles moving in one direction creates a piston effect which generates air flow in the direction of traffic. In a simple longitudinal ventilated tunnel without portal emis-sion control, the piston effect is utilised with the jet fans augmenting the flow when required. When portal emis-sions are to be controlled, jet fans are often utilised to retard the traffic piston effect along the length of the tun-nel, to reduce the required extraction system capacity just prior to the exit portal. The number of jet fans needed to operate at any one time is dependent upon a number of factors including the ventilation system exhaust rate, the traffic speed, the fleet vehicle profile, the tunnel geometry, and the capacity of the jet fans.

Generally, the relationship between the ventilation system exhaust rate and the number of jet fans required to main-tain a portal inflow is an inverse one, such that higher exhaust rates require fewer jet fans to operate.

Designing for portal emission control can be complex due to the dynamic effects of real world traffic. The piston ef-fect from moving vehicles often dominates the tunnel aero-dynamics, particularly during peak vehicle flow at maximum design speed. The ventilation system often has to operate

throughout the day in order to maintain control of portal emissions and therefore the system operating cost is an important consideration during the design phase.

Mid-tunnel exit rampsPortal emission control becomes more complicated and challenging when mid-tunnel exit ramps are introduced into the tunnel alignment creating an additional exit portal. A dedicated exhaust point incorporated prior to the addition-al exit portal would require an additional exhaust plant and ventilation outlet near the exit ramp, or a complex arrange-ment of ductwork/adits, that connect the exhaust point to the main ventilation plant. Apart from additional cost impli-cations, this has the potential to create unwanted environ-mental issues and community response.

The use of jet fans to control the airflow in the ramp should also be considered. The jet fans would be used to gener-ate sufficient reverse airflow (against the flow of traffic) in the ramp to overcome the piston effect generated by the vehicles and induce a net positive inflow of air through the exit portal. Although controlling the ramp flows in this manner can introduce additional challenges for the con-trol of the system as a whole, it is widely regarded as a practical and cost effective solution to an otherwise tech-nically and environmentally challenging problem. This is particularly the case where peak traffic flow is limited to a small number of hours per day. The ramp length must be sufficient to accommodate the installation of the minimum number of jet fans required to achieve the reverse flow. In addition, the introduction of airflow from the ramp back into the mainline tunnel would increase the concentration of pollutants and the mini-mum required exhaust capacity of the main ventilation plant, which would need to be accounted for. Additional jet fans may be required to operate within the mainline tunnel sections to augment the ramp airflow control.

Short-term dynamic effectsIn order to ensure that portal emission control is main-tained, it is also important to consider the short-term transient effects that fluctuations in the traffic volume, profile, or speed can have on the portal inflow condition. The tunnel exit section is typically short in length with the air within that section having a relatively low inertia mak-ing it susceptible to short-term fluctuations due to traf-fic. A short-term increase in the number of heavy goods vehicles travelling through the tunnel in a convoy could generate a piston effect sufficient to not only reduce the portal inflow but also create an outflow condition.

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Figure 3 - Example of jet fans in a road tunnel

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Short-term effects can be managed by maintaining a relatively high portal inflow condition, although this could result in relatively high operating costs. An inflow condi-tion of approximately 1.0 metre per second (3.3 feet per second) should be sufficient for most cases; however, depending on the specific project design parameters, an inflow condition as low as 0.5 metres per second (1.7 feet per second) may also be acceptable.

A complex tunnel geometry also could affect portal emission control. The bifurcation of an exit ramp after the ventilation exhaust point (as shown in Figure 4) can make it difficult to control portal emissions, especially if the exhaust point is located at the side of the tunnel, rather than the top. The bifurcation creates two separate exit portals with a large tunnel cross section just prior to the bifurcation.

An inflow will need to be maintained for both exit ramps; however, due to interconnectivity, they can be particularly susceptible to short-term fluctuations in the volume of traffic exiting either ramp. Analysis has shown that a higher portal inflow condition of approximately 1.5 – 2.0 metres per second (4.7 – 6.6 feet per second) could be required in order to maintain an acceptable portal in-flow condition for bifurcated exit ramps. The inflow of air through each exit portal can be achieved independently of the bifurcation geometry, the traffic flow, and the physical location of the exhaust point within the tunnel, provided that the mainline jet fans are utilised to assist in the con-trol of the airflow. An increased portal inflow condition does, however, increase the fan capacities, which could be compensated for by reducing the cross-sectional area of the portal openings.

Wider considerationsIt has been shown that there are engineering solutions available for the control of emissions through tunnel exit portals. However, we recommend that a holistic approach be taken prior to committing to a portal emission control ventilation strategy and that it not be carried out in isola-tion from other disciplines.

The use of jet fans to control in-tunnel airflow and ex-haust fans to extract the air from the tunnel is a relatively costly strategy, considering that the fans may be required to operate on a 24-hour basis, depending on the traffic and air quality limits. The decision to go ahead with por-tal emission control should be undertaken with support from air quality assessment, dispersion modelling, power demand, and future climate change projections on power cost, carbon emissions, community consultation, and whole-of-life assessment.

Relaxing portal emission control during off-peak, shoul-der, and night time operation should also be considered, provided that portal emissions are monitored, ambient air quality limits strictly observed, and community consulta-tion and subsequent buy-in is obtained.

Argun Bagis is a Principal Mechanical Engineer at Parsons

Brinckerhoff, with over 18 years’ engineering experience,

primarily in the transportation infrastructure industry.

Duncan Saunsbury is a Mechanical Engineer with over 3 years

of experience specialising in tunnel ventilation, fire, and life

safety. Originally based in the UK, he has worked on tunnel

projects worldwide including in the US, Europe, Middle East,

Australia and New Zealand.

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Figure 4 - Plan view of bifurcation of an exit ramp

Exit Ramp

Exi

t Por

tal

Exi

t Por

tal

ExtractionSystem

Traffi c Flow

Air Flow

Exit Ramp

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Merging Emergency Ventilation System Sound Power and Pressure Drop Calculationsby Michael MacNiven, Sacramento, CA, US, +1-916-567-2542, macnivenmc@pbworld.com

Introduction/OverviewThis article describes a methodology that simultaneously calculates sound and pressure levels for very large tun-nel emergency ventilation systems and explains how this methodology benefits the ventilation design process. This method was used on the Sound Transit Northgate Link Light Rail Extension Project (NLLREP) in Seattle, Washing-ton for the ventilation design strategy for two underground stations (Roosevelt and U-District stations) and the con-necting bored tunnels.

Traditionally on many tunnel projects, sound and pressure loss calculations have been done separately. The primary solution to sound mitigation is to add silencers, which use sound absorbing materials, and geometrical features to at-tenuate sound waves in the airstream. This adds length to the duct system and often creates more pressure loss, which leads to larger fans and additional sound genera-tion. Therefore, the relationship of sound and pressure is best understood when simultaneously calculating their val-ues. The combined calculation (of the sound and pressure) of the longer silencers determines if the sound meets the environmental regulatory requirements while determining the additional impact on fan horsepower.

The traditional approach of adding longer silencers to solve sound problems often does not take advantage of the contribution that the system duct work can provide in sound mitigation. A significant proportion of unwanted sound could be mitigated by ductwork system effects in a beneficial way.

This methodology provides insight that enables the engi-neer to quickly identify problematic areas within the sys-tem, and adjust key parameters such as fan room layout, attenuator size, and duct geometry that would otherwise negatively impact the final design. Knowing how sound and pressure considered together can be made to opti-mize the cost, mechanical advantage, station footprint, or noise mitigation can be a beneficial tool.

The NLLREP stations and connecting tunnels required a ventilation system in the event of a train fire emergency. The ventilation strategy chosen was to be a “push/pull” extraction system as shown in Figure 1.

For this system to work effectively, the fans must be lo-cated on either side of the potential fire hazard. The fans can then work in unison to create airflow in one direction with one station fan in exhaust and the adjacent station fan in supply, thereby meeting the required velocity and

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Figure 1 - Ventilation scheme

RooseveltStation

U-DistrictStation

South Bound Tunnel

North Bound Tunnel

SouthEmergency

VentShaft#1

Fan Damper(TYP)

Reversible EmergencyFan (TYP)

EMFN-7

EMFN-6

NorthEmergencyVentShaft #2

SB Portal

fromNorthgateStation

NB Portal

fromNorthgateStation

NorthEmergency

VentShaft

TrackDamper

(TYF)

EMFN-1

EMFN-2

EMFN-5

EMFD-3

EMFN-4

Push/Pull Push/Pull Push/Pull

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flow rate to control the smoke in the tunnel. The total pressure loss must be considered in combination with the air flow to determine the required fan motor power needed to move air through the system. NLLREP ventilation system fans were sized based on the resistance losses from the tunnel portal to the exit vent shaft in the forward and reverse fan direction. The total pressure loss also provides input to the calculation of the fan sound power generated. The sound generated by the ventilation fan is required to meet the environmental impact statement (EIS) and specific project sound criteria at each designated “receptor” location (where a person might typically be standing). NLLREP ventilation system receptors are located at the tunnel platform, station atri-um, and outside ambient, each of which needs to meet the regulatory compliance of the EIS and project criteria. The sound attenuation by each component in the duct system reduces the total sound emitted to the receptor.

Method of Integrating Pressure and Sound CalculationsThe ventilation system is a series of duct components that provide pressure resistance losses and sound gen-eration and mitigation. These components contribute to the overall pressure loss and sound at the receptor.

The methodology integrates the calculation of pressure loss and sound generation and attenuation of each component in the system using the computer software Mathcad for documentation and validation of engineer-ing calculations. This software is particularly helpful be-cause it provides a fully documented calculation that can be easily reviewed and altered for different projects. The program is structured by common variables, common geometry, component pressure, component sound, total pressure, and total sound.

Common variables and geometry are defined at the front end of the software program to allow for simplifying input and reducing errors. The same reasoning applies to de-fining common geometric parameters for plenums, damp-ers, and silencers at the front end of the program.

PressureEach air pathway in the fan forward and reverse direction is considered when calculating pressure loss as shown in Figure 2. Often only one pathway needs to be deter-mined if it can be shown to be the highest resistance path. If there is no clear distinction of the highest resis-tance pathway, all air pathways should be evaluated.

I.E. Idlechik’s Handbook of Hydraulic Resistance provides resistance coefficients for various components within an airstream such as elbows, tees, structural interferences, and dampers, as well as sudden expansions, sudden con-tractions, and diverging and converging transition losses. Figure 3 is a sample calculation from a Mathcad file de-scribing the pressure loss for a seven foot silencer. In this example, the face velocity (Vs) is calculated to obtain the pressure loss in the forward direction.

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Figure 2 - South Roosevelt Station elevation layout

Figure 3 - Silencer pressure loss from Mathcad®

EXHAUST / INTAKE

PUSH / PULL

EFAN

EFAN

Length of Silencer

Face Velocity

Pressure Loss (SMACNA pg 9.10)

Lz : = 7. ft.

Counter z := z + 1z = 10

Pressure Loss/SilencerPressure loss through the silencer may be given by manufacturers’ data (IAC Type L Sound Attenuator), however, the pressure loss is taken by SMACNA pg 9.10. The fl ow rate for this type of system is considered a medium attenuator.

= 1875: = .Q

f

As

ft.min

Vs

–0.3 in:=Pfz

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Sheet Metal and Air Conditioning Contractors' National As-sociation (SMACNA) has published that pressure loss is a function of velocity. Similarly, a pressure loss is to be calculated for every ductwork component along the highest resistance pathway.

SoundIn conjunction with the pressure term, a sound power component is considered for all segments in which sound is either regenerated or attenuated. The sound reduction or absorption is defined as the insertion loss (IL). When sound travels through a duct component such as a silencer an insertion loss occurs.

Equation 1 describes the sound power after a compo-nent loss where Lw1 is the sound power level before the component loss and Lw2 is sound power level after the component loss (Reference 2). The insertion loss reduc-tion is calculated over each of eight frequency bands which range from 63Hz to 8000Hz. The human ear is only sensitive to this range of frequencies.

Equation 1

The regeneration gain by the silencer is used to calculate the total sound power (Lw3) as shown in Equation 2. The total sound power after the silencer insertion loss (Lw2) is then added logarithmically to the regeneration (LwR) val-ues (Reference 2). The decibel (dB) scale is logarithmic and as such a doubling or halving of energy changes the sound level by 3dB; it does not double or half the sound level as might be expected.

Equation 2

A silencer insertion loss and regeneration values for a si-lencer are available from manufacturers' data for each of the eight frequency band levels in both the forward and reverse fan direction. Insertion loss can be determined for any component in the system. Sheet Metal and Air Conditioning Contractors' National Association (SMACNA) provides methods to calculate insertion and regeneration values for various types of ductwork components.

Total Pressure/SoundThe total pressure loss of the ventilation system is deter-mined by a summation of losses for components along

the flow path. After each component has been evalu-ated for pressure loss, the total summation is used to evaluate the fan brake horsepower. The fan sound power is evaluated from the total pressure loss as shown by Equation 3 (Reference 2).

Equation 3

When calculating the total sound power at the recep-tor, each component is evaluated from the fan to each receptor location. In other words, the fan sound power calculated from Equation 3 is taken to be reduced from the insertion component by Equation 1. For com-ponents with regeneration, the total sound is com-bined using Equation 2. Sound power, which is a mea-sure of the sound intensity, must then be converted to sound pressure or the power component that directly affects the ear drum. The sound pressure levels are evaluated for the receptors, typically in a tunnel, sta-tion, or ambient locations.

ExampleDuring the design of the ventilation system at U-District station, the use of tunnel fans to exhaust the atrium pre-sented a challenging sound control problem. The fans were in close proximity to the atrium receptor. This al-lowed very little attenuation to occur. Early in the design, it was determined that the sound levels did not meet project criteria with the configuration of the atrium damp-er in-line with the fan.

Three options were investigated to attenuate the sound. The first option was to add a matrix of silencers at the atrium wall opening. This was a viable solution but not considered to be the best choice due to the cost and aesthetics. The second and third options were to offset the damper to provide additional elbow attenuation. The second option utilized an unlined elbow, whereas the third option used an acoustically lined elbow.

Figure 4 shows the final configuration of the ventilation system. The acoustically lined elbow option provided the necessary attenuation to meet project criteria with minimal impacts to the fan horsepower. The program allowed exploration of different options to reach a fea-sible, cost effective, and architecturally appealing solu-tion by understanding the parameters that controlled the sound.DE

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ConclusionTraditionally, pressure loss analysis has received more at-tention in the design of tunnel ventilation systems than sound analysis. In recent years, environmental policy, reg-ulatory requirements, and space constraints are making it more important to understand sound mitigation. This methodology of combining sound and pressure simulta-neously in the design of ventilation systems provides an efficient tool for understanding how both sound and pres-sure are influenced by each system component. In addition to demonstrating compliance with the regulatory require-ments, the method provides a means to explore other op-tions more efficiently than before. It allows for an optimum design that minimizes motor power requirements, meets sound requirements, and minimizes space requirements.

References1. Idelchick, I.E., Handbook of Hydraulic Resistance. 4th

Edition.2. HVAC Sound and Vibration Manual. s.l. : Sheet Metal

and Air Conditioning Contractors' National Associa-tion, First Edition Dec. 2004.

3. HVAC Systems Duct Design. s.l. : Sheet Metal and Air Conditioning Contractors' National Association, Third Edition 1990.

Michael MacNiven is a Senior Mechanical Engineer with a tech-

nical background in HVAC, piping, and fire life/safety systems

along with large scale tunnel emergency ventilation systems. DECE

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ADD ACOUSITCAL MATERIAL TO

WALLS

SOUND PATHWAY

STAIR-6

SOUND POWER FOR SINGLE

ATRIUM DAMPER

SOUND POWER PROVIDED AT

AMBIENT AT TOP OF SHAFT

SOUND POWER PROVIDED AT

TUNNEL DAMPER AT CEILING

OF PLATFORM LEVEL (TYP)

Figure 4 - Sound attenuation material at U-District Station

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Cost-Effective Power Supply Scheme for Tunnel Booster Fans in Long Tunnelsby CC Cheung, Hong Kong/Singapore, +852-2579-7066/+65-6589-3674, cheung.chuncheong@pbworld.com; andSteven Lai, Hong Kong/Singapore, +852-2963-7625/+65-6589-3661, lai.steven@pbworld.com

Background – The Technical ChallengeFor long vehicular tunnels or tunnels with slip roads (ramps), tunnel booster fans may assist the ventilation of the tunnel. For metro systems, tunnel booster fans may be installed near the crossover to direct the air flow in the desired direction.

In general, tunnel booster fans are powered from a mo-tor control center (MCC) and operated at a low voltage of about 400V. However, if the fans are not located near the power supply, it becomes necessary to run long cables to the tunnel booster fans, which leads to:

• An excessive voltage drop in the cable due to the long cables from the power supply to the fans;

• Increased cable sizes and possibly additional cable sets to reduce the expected voltage drop (which is expensive);

• Reinforcing the feeder cable mounting system due to the additional weight of the upgraded cables;

• Space congestion along the entire tunnel services mounting system, in particular due to the upgraded ca-bling systems;

• Provision of a large cable termination box to connect the upgraded cables to the tunnel booster fans; and

• Risk of fan operational problems due to substandard voltage regulation, especially when starting “across the line” with electro-mechanical contractors.

Since it can be shown that an increase in a feeder nomi-nal voltage results in a significantly higher power capac-ity (proportional to the square of the percentage volt-age increase for the same voltage drop), boosting the system nominal voltage was considered in order not to increase feeder sizes in long fan booster feeder applica-tions; these solutions can be economical, especially if the low voltage equipment insulation classification does

not have to be upgraded. Therefore, an increase in the nominal voltage of the serving power distribution system for big motors and fans, such as tunnel ventilation fans or smoke exhaust fans, has been adopted as a feasible solution for some tunnel projects, including a road tunnel project in Hong Kong (forty 660V tunnel ventilation fans, rated at 200 to 600kW).

For smaller fans (e.g., tunnel booster fans), increased voltage is also becoming popular as the cost savings for the feeder cabling system is very attractive, espe-cially when tunnel space is at a premium. For example, there are more than 70 tunnel booster fans (1250mm diameter, 60kW for each fan) in another road tunnel in Hong Kong.

Examples of SolutionsSome projects in Hong Kong, India, and Singapore have considered or adopted this approach of using tunnel booster fans of increased voltages of 660V (i.e., √3 x 380V), or 690V (i.e., √3 x 400V) as appropriate1 (using step-up transformers inside the MCC rooms). This nomi-nal voltage boost approach will reduce the nominal oper-ating currents of the tunnel booster fans proportionally; however, the percentage voltage drop along the feeder will be reduced with the square of the nominal voltage boost, which in turn results in significantly reduced feed-er cable sizes for the same voltage drop requirements, and therefore results in significant savings for the overall feeder cabling costs.

To illustrate this approach/solution, it is assumed a tun-nel project in Singapore has tunnel booster fans (45kW each) with an average cabling distance2 of over 200 me-tres (656 feet) from the MCC room. For this situation, two schemes were considered:

1Note: In the US – the “nominal” voltage of a fan motor is relatively standardized (3-phase 208V, 480V, 575V, 2400V, etc.) and normally cannot be customized as stated in this paper.

2Average cabling distance = Total cable length / Number of tunnel booster fans.

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Scheme 1 – Low Voltage Supply for Tunnel Booster FansThe tunnel booster fans’ power supply is connected from the MCC which is operating at 400V. The MCC is dual-fed from two low-voltage service switchboards (see Figure 1).

Scheme 2 – Higher Voltage Supply for Tunnel Booster FansTransformers for step-up of the voltage from 400V to 690V are proposed to be connected to the MCC for the power supply of the tunnel booster fans. With the in-creased operating voltage, the tunnel booster fans’ op-eration current would be reduced by 1/√3 proportionally. This would also reduce the cable size required and lower the cable costs.

However, the size of the MCC room would have to be enlarged to accommodate the two step-up transformers and the additional switchboard that supplies the tunnel booster fans (see Figure 2).

Cost ConsiderationsAn example of a cost comparison is shown in Figure 3: twenty (20) 45kW tunnel booster fans spaced along three parallel tunnels at an average cabling distance of 255 metres (836 feet) from the MCC.

It shall be noted that the cost of a MCC (690V) may be sufficiently high in some countries, as additional effort is required to design and construct the upgraded equip-ment, especially if the local low voltage classifications and certifications cannot be met by off-the-shelf units. Also, additional tests may be required to obtain the au-thorization and required equipment certifications, espe-cially when a variable voltage variable frequency (VVVF) drive system is used.

Other Considerations• Cabling System

The cost saving as illustrated in Figure 3 is 7.6 percent, based on the adoption of low smoke zero

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Figure 1 - Schematic of Scheme 1

MCC 3(400V)

Tunnel Booster Fans, Tunnel Ventilation Fans,and Other Environmental Control System Loads

MCC 1(400V)

MCC 2(400V)

Tunnel Booster Fans

Tunnel Ventilation Fans and Other Environmental Control System Loads

MCC 4(690V)

MCC 3(400V)

MCC 1(400V)

MCC 2(400V)

Figure 2 - Schematic of Scheme 2 Figure 3 - Cost comparison between Scheme 1 and Scheme 2

DescriptionScheme 1Cost (US$)

Scheme 2Cost (US$

Power cables totunnel booster fans

$736,000 $427,000

Two (2) step-up transformers (300kVA) and the additional cost for ventilation/cooling necessary

for the booster transformer

- $54,000

MCC (400V) $266,000 $199,000

MCC (690V) - $210,000

Twenty (20) tunnel booster fans $480,000 $480,000

Total: $1,482,000 $1,370,000

Overall Savings(by using Scheme 2):

$112,000(Cost Saving of 7.6% using Scheme 2)

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halogen (LSOH3) type fire resistant cables. This is generally a cabling requirement for emergency/life safety systems of all underground tunnel installations in Singapore. In Singapore and Hong Kong, where the low voltage (LV) power distribution system is rated at 230V/400V and 220V/380V respectively, the standard LV cable (Uo/U) is rated at 600V/1000V.

• Energy Savings/Efficiency From a viewpoint of energy savings, VVVF drives can

be considered for many fan/motor installations. VVVF drives can achieve a very steady current ramping for dif-ferent fan speeds to suit different air flow requirements. As the energy consumption for a fan with VVVF drive is in direct proportion to the speed, the energy savings will be generally as shown in Figure 4.

• Location of VVVF Drive For this project, the VVVF drive for each fan will be

located inside the MCC room so maintenance does not have to be performed in a tunnel environment.

RecommendationTechnically, the use of a step-up boost transformer or autotransformer for tunnel booster fans requires more distribution equipment and more space to accommo-date the plant. If the tunnel booster fans are too close to the MCC (e.g., within 200 metres) and the fan quan-tity is small (e.g., four fans), it will not be worthwhile to consider the use of a higher supply voltage cable distribution system.

Parsons Brinckerhoff successfully has applied the above-mentioned cost saving scheme to various road tunnels and metro projects.

CC Cheung is an Electrical Engineer at Parsons Brinckerhoff.

He has been involved in a number of road tunnel and metro

projects in Hong Kong and Singapore which have required long

distant LV power distribution. He is now working in Singapore as

an Electrical Discipline Leader for a metro project.

Steven Lai is a Mechanical Engineer and a Senior Professional As-

sociate at Parsons Brinckerhoff. He is an M&E Project Manager for

a road tunnel project in Hong Kong which has used tunnel booster

fans and semi-transverse ventilation system. He is now working in

Singapore as an M&E Project Manager for a metro project which

has tunnel booster fans along some of the tunnel area.

3In the US, the acronym for low smoke zero halogen is LSZH.

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Speed 100% 90% 80% 70% 60% 50%

Energy Consumed

100% 73% 51% 34% 22% 13%

Figure 4 - Energy consumption for a fan with VVVF drive is in direct proportion to the speed

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Air Purification Systems (APS) have been applied to many road tunnel projects around the world in order to maintain tunnel air quality and/or reduce tunnel emissions. However, less than ten projects use APS to remove both dust and nitrogen dioxide (NO2) or mono-nitrogen oxides (NOx).

A new road tunnel is being constructed in an urban district of Hong Kong. Eight APS plants will be installed in three ventilation buildings of the tunnel. To satisfy the environ-mental requirements, an electrostatic precipitator (ESP) to remove dust has been installed. To further improve vis-ibility and air quality, equipment for removing NO2 is also provided in the project. In case of fire, the APS is bypassed and the tunnel ventilation system will control and effective-ly discharge smoke to ensure the safety of tunnel users. The purification system provides added benefit to the sur-rounding environment as well; the APS produces cleaner outdoor air for local residents around the tunnel portals and ventilation buildings.

The proposed APS is one of the largest in the world. Par-sons Brinckerhoff is the designer for all the mechanical and electrical (M&E) systems of the project, including the APS. This tunnel project employs Building Information Mod-eling (BIM).

In designing an APS for a road tunnel, the major challenges and technical requirements are:

• Ensuring the Efficiency of the APS The APS consists of an electrostatic precipitator (ESP)

and a de-nitrification system (De-NO2) for the removal of dust particulates and NO2 in the tunnel exhaust air stream. With consideration of the current technology and the long term operation of the APS, the APS shall achieve at least 80 percent efficiency for removing the dust par-ticulates and NO2 from the airflow stream.

• Selection of De-NO2 Filter To avoid excessive replacement work, the lifetime of the

De-NO2 filter shall be longer than 3 years under a tunnel operation environment. To achieve a comparative tender price, the filter shall be available on the open market.

• Fire and Life Safety Features in APS Safety interlocks of the APS with personal access doors

and motorized fire dampers connected to the smoke ex-traction system shall be provided.

• Control and Monitoring of the APS Adequate heat detection, particle detection, and NO2 de-

tection will be provided to monitor the performance of the ESP and De-NO2 systems.

• Civil, Mechanical, and Electrical Provisions for APS Sufficient provisions shall be reserved for the APS, espe-

cially for the regeneration plant. Civil provisions include space for the plant and the associated delivery route, sump pit for the regeneration plant, lifting provision for the equipment. Mechanical and electrical provisions in-clude water supply for the cleaning of the ESP, drainage system for the wastewater produced by the APS, high volt-age power supply system for the ESP, control and monitor-ing system, etc.

• Avoid Converting Air Pollution to Water Pollution Wastewater is mainly generated from the ESP cleaning

system. Reducing the amount of wastewater from the ESP is one of the key considerations in the design (refer to Network Issue 77, February 2014, “Wastewater Reduc-tion in Road Tunnel Air Purification System”).

It is essential that the major parameters of the APS are speci-fied in the tender document and that a sufficient number of market players can join the competition. Parsons Brinckerhoff has considered all features and spatial constraints and devel-oped a design that is feasible for various suppliers to bid for the project, thereby providing fair market opportunities while meeting local environmental requirements.

Cathy Kam is a Mechanical Engineer who participates in road tunnel and metro projects and has experience in using Primavera P6 on projects.

Chris Ma is a Mechanical Engineer who participates in road tunnel and metro projects and has experience with building information modeling (BIM), Subway Environment Simulation (SES), and Primavera P6 on projects. He is an engineer for a road tunnel project which will use an Air Purification System (APS) for the first time in Hong Kong.

Steven Lai is a Mechanical Engineer and Senior Professional Associate at Parsons Brinckerhoff. With 25 years of experi-ence, he has served as lead engineer on many tunnel ventila-tion system and environmental control system related proj-ects. He is MEP Project Manager for a road tunnel project in Hong Kong which will use an Air Purification System (APS) for the first time in Hong Kong. DE

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Air Purification System for a Road Tunnel Project by Cathy Kam, Hong Kong, +852-2579-7465, kam.cathy@pbworld.com; Chris Ma, Hong Kong, +852-2579-8533, ma.chris@pbworld.com; and Steven Lai, Hong Kong / Singapore, +852-2963-7625 / +65-6589-3661, lai.steven@pbworld.com

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Elimination of Portal Flaresby Kenneth J. Harris, Sacramento, CA, US, +1- 916-567-2503, harris@pbworld.com;

Bobby J. Melvin, Sacramento, CA, US, +1-916-567-2508, Melvin@pbworld.com; and

Steve Gleaton, Sound Transit, Seattle, WA, US, +1-206-398-5335

The expertise of Parsons Brinckerhoff in tunnel aero-dynamics was utilized in eliminating an expensive and complicating feature—flared tunnel portals—indicated by preliminary engineering for Sound Transit's Northgate Link Extension tunnel in the state of Washington. The analysis performed also provided an additional benefit, eliminating some station ventilation shafts that were ini-tially perceived to be required.

Portal FlaresModification of tunnel portals by using a flared portal design serves to reduce the train’s nose pressure as the nose enters the tunnel portal, and also to reduce the sharp change that occurs as the train’s tail crosses that portal. The interior nose pressure on portal en-try is usually the highest pressure that occurs on train passage. This pressure also initiates acoustic wave pressure that is eventually reflected back onto the train. By increasing the local annular area of the portal structure, this initial nose pressure can be reduced. A transition flare can accomplish this objective and then allow the main bore annular area to be maintained for the remainder of the tunnel.

BackgroundPressure transient calculations were performed for the entire extension tunnel. The calculations were divided into three parts: North Portal to Roosevelt Station, Roos-evelt Station to Brooklyn Station, and Brooklyn Station to the University of Washington. The purpose of the calcu-lations was to determine the wayside and interior pres-sures that exist on the proposed subway design and de-termine if these pressures were within the design criteria limits. The system was analyzed in segments between stations. The southern direction was used because the North Portal entry is expected to create the most severe condition, both as the train enters the portal and as the train tail crosses the portal face. In addition to the pres-

sure changes that occur, the air flow through the station elements is estimated and compared to the design cri-teria requirements.

The Subway Environmental Design Handbook1 (SEDH) is the reference source. The equations and expressions in the calculation describe the effects of pressure transients caused by train movement into and within enclosed spac-es. These transients can place large loadings on trains and wayside facilities and can cause passenger discom-fort, particularly ear discomfort due to pressure.

The SEDH criteria for changes of pressure inside a train are: if the pressure change exceeds 2.78 inches water column (0.69 kPa), then the rate of pressure change should be less than 1.67 inches (0.42 kPa) per sec-ond. These are the same as the project design crite-ria. These requirements reflect passenger comfort for subway operations involving frequent pressure changes due to portals, vent shafts, and other discontinuities in metropolitan underground transit operations.

There are no standard criteria for exterior pressure changes; however, they do represent cyclical loads that must be accounted for on tunnel surfaces, particularly doors, ductwork, and other large metal surfaces. Special construction, reinforcing, or other treatment is usually necessary to handle these cyclical loading conditions.

In addition to the pressure changes from train passage described above, acoustic waves are generated at discon-tinuities such as portals, vent shafts, and tunnel shape changes. These waves are generated at the discontinuity location, travel at the speed of sound along the tunnel, and are then reflected back and continued forward. The reflected wave passes over the train providing a pressure spike. These are all evaluated with respect to the project/SEDH criteria.

1Subway Environmental Design Handbook (Vol. 1 & 2), prepared by Parsons Brinckerhoff as part of a joint venture for the U.S. Department of Transportation, publication date 1975.

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Calculation ResultsCalculation results can be classified into the following:• Train Interior Pressures; • Train Exterior Pressures;• Pressure Waves; and• Station Air Flows.

For this article, the calculations presented are from one part of the study—the North Portal to Roosevelt Station. The x-axis shown in figures 1-4 (“Distance in the Subway”) refers to the North Portal (0 feet) and Roosevelt Station (6,336 feet). Calculations of pres-sure and air flow assume no pressure relief shafts at stations and no portal flares. The maximum train speed is 59 miles per hour (95 kilometers).

Train Interior PressuresCalculations were performed for both interior nose and interior tail pressure and are summarized in Table 1. For the nose, as the train enters the North Portal of the tun-nel, a pressure rise occurs at the nose until the train tail crosses the portal. Then there is a sharp drop followed by a gradual decline where the train is in transit through the tunnel as shown in Figure 1.

Figure 2 shows the interior tail pressure from the tail crossing the North Portal until tunnel portal exit at Roosevelt Station. Following a gradual rise and a gradual fall while the train travels through the tunnel, there is a sharp rise as the nose enters the Roosevelt Station, until the train tail leaves the tunnel. The pres-sure change criterion is exceeded at the nose entry into the North Portal and tunnel transit; however, the rate of change is not. Therefore the pressure change criterion is met.

Train Exterior PressuresThe exterior pressure represents loading conditions on wayside facilities such as ductwork, doors, etc. There are no criteria for wayside facilities, but the loads are neces-sary for design purposes. The maximum exterior pressure is +7.7 inches water column (1.92 kPa) and minimum exterior pressure is -2.5 inches water column (-0.62 kPa).

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Figure 1 - Interior Nose Pressure

Figure 2 - Interior Tail PressureTable 1 - Summary of Pressure Transient Conditions (Southbound Train)

0Distance in subway (feet)

Interior Nose Pressure

Pres

sure

(inc

hes

wat

er)

2000

-1.967

3.909

1.441

∆ = 3.408

∆ = 2.468

4000 6000 8000

4

2

0

-2

Roosevelt StationNorth Portal

0Distance in subway (feet)

Interior Tail Pressure

Pres

sure

(inc

hes

wat

er)

2000

-1.81

-2.54

-3.67

∆ = 1.86

∆ = 0.11-3.78

∆ = -1.24

4000 6000 8000

-1.5

-2

-3

-4

-3.5

-2.5

Roosevelt StationNorth Portal

In. wc 3.909 2.468 1.441 3.408 1.967 2 4

kPa 0.97 0.61 0.36 0.85 0.49 0.50 1.00

In. wc 2.54 1.24 3.78 1.86 3.67 1.81 1.5 2 2.5 3 3.5 4

kPa 0.63 0.31 0.94 0.94 0.46 0.91 0.45 0.50 0.63 0.75 0.83 1.00

LocationPressure Change

(inches water column) (kPa)

Rate of Change(inches water column)

(kPa) per second

Noseat portal entry

3.91* (0.97) 0.94 (0.23)

Noseat tail crossing

portal entry-2.47 (-0.62) n/a

Nosetransiting tunnel

-3.41* (-0.85) -0.05 (-0.01)

Tailat portal entry

-2.54 (-0.63) n/a

Tailtransiting tunnel

-1.24 (-0.31) n/a

Tailat nose exit into station

0.11 (0.03) n/a

Tailat exit into station

1.86 (0.46) n/a

* Exceeds pressure change criterion of 2.78 inches water column, however rate of change is below 1.67 inches water column per second threshold.

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Figure 3 shows the nose pressure and Figure 4 the tail pressure. The design values may be considered as be-tween the maximum and minimum, although the loca-tions are different and the actual cyclic differentials will be less. Pressure wavesThere is a pressure wave generated at the North Portal entry that is reflected back from the station. This pressure is 1.38 inches water column (0.34 kPa) and occurs 887 feet (270 meters) from the portal. This pressure wave is less than the criteria value, so no mitigation is necessary.

Station Air FlowsThe airflow from train operations should not signifi-cantly impact the station environment. Based on the station cross section area, the longitudinal velocity through Roosevelt Station would be a maximum of 359 feet per minute (1.82 meters per second). The narrow-est egress opening is 1230 square feet (114 square meters) resulting in a flow of 328 feet per minute (1.66 meters per second). These are less than the project de-sign criteria averaged maximum of 600 feet per minute (3.05 meters per second). Both of these represent all piston effect2 air traveling through the entrances and no air going down the tunnels which is a very conserva-tive configuration.

Conclusion• The Northgate Link system train speed of 59 miles (95

km) per hour precludes the need for portal flares.• Air pressure criteria for the vehicle interior can be met

without portal flares or vent shafts in the Roosevelt Station.

• Air flow criteria for Roosevelt Station can be met with-out portal flares or vent shafts in that station.

• Air pressure criteria for the vehicle interior can be met without flares at the North Portal or pressure relief vent shafts in Roosevelt Station.

• Air flow criteria for the Roosevelt Station can be met without flares at the North Portal or pressure relief vent shafts at Roosevelt Station.

Kenneth Harris, PE is a Tunnel Mechanical and Fire Protection

Specialist and Principal Professional Associate with 40 years of

experience in design, construction, and inspection of large civil

and industrial projects.

Bobby Melvin is a Supervising Mechanical Engineer in the

Sacramento office of Parsons Brinckerhoff where he has

worked for 15 years in the field of tunnel mechanical sys-

tems design3.

Steve Gleaton, Structural Engineering Manager at Sound Tran-

sit, has 25 years of diverse experience in structural design and

construction support engineering for bridges, underground struc-

tures, and buildings, including fifteen years with large projects for

rail transit systems.

2Piston effect refers to the forced air flow inside a tunnel caused by moving vehicles.3For other previous Network articles by Bob Melvin, see “Mitigating Pressure Effects in High Speed Rail Tunnels,” Network #60, June 2005, pp 90-91, 95; and “Geometric Enhancement of Fire Size in Road Tunnels,” with Joe Gonzalez, Network #70, November 2009, pp 15-17.

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Figure 3 - Exterior Nose Pressure

Figure 4 - Exterior tail pressure

0Distance in Subway (feet)

Exterior Nose PressurePr

essu

re (i

nche

s w

ater

)

2000

7.72

5.26

-0.02

4000 6000 8000

8

6

2

-2

0

4

Roosevelt StationNorth Portal

0Distance in subway (feet)

Exterior Tail Pressure

Pres

sure

(inc

hes

wat

er)

2000

0.80

-2.49

-0.01

-1.12

4000 6000 8000

1

-1

-3

-2

0

Roosevelt StationNorth Portal

In. wc 7.72 5.26 0.02 2 4 6 8

kPa 1.92 1.31 0.00 0.50 1.00 1.50 2.00

In. 0.01 2.49 1.12 0.80 1 2 3 4

kPa 0.00 0.62 0.28 0.20 0.25 0.50 0.75 1.00

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Comparison of 3-D and 1-D CFD Simulation Approach for Aerodynamic Effects in a High Speed Railway Tunnel Systemby Dicken KH Wu, Hong Kong, +852-2963-7631, wu.dicken@pbworld.com; and Rambo RB Ye, Hong Kong

IntroductionUsually, the aerodynamic analysis of a high-speed rail-way tunnel system can be done by using a highly ef-ficient one-dimensional (1-D) computational fluid dy-namics (CFD) simulation program such as ThermoTun. However, the pressure wave propagation and airflow speed inside some complicated geometries, such as an underground station, plenum, and vent shaft, may no longer be 1-D in nature, and so we investigated the possibility of three-dimensional (3-D) CFD as a suitable method to be adopted.

To ensure that this method is applicable for a high-speed railway aerodynamic analysis, it is necessary to verify the approach and estimate the computational resources re-quired. To accomplish this, full-scale experimental data was used to compare 3-D CFD simulations with the 1-D ThermoTun results.

Geometry Model and Train SpeedsBased on the full-scale experimental data1 tabulated and further details from the ThermoTun website2 regarding a full-scale experiment, a 3-D CFD model was constructed. Figure 1 illustrates the general configuration of the tun-nel, portals, vent shaft, and train based on this informa-tion. ThermoTun software provides pre-defined configura-tions that are representative of real tunnels.

The detailed geometrical data for the tunnel, vent shaft, and train are as follows:

Based on the information provided, two train speeds were analyzed: 177.5 kilometres per hour (110.2 miles per hour) and 204 kilometres per hour (126.7 miles per hour) respectively. And the 3-D CFD and 1-D ThermoTun approach results would be compared with the full-scale test measurement.

3-D CFD ApproachTo model the train entering the tunnel at the given speed, special CFD techniques had been adopted, namely slid-ing mesh and dynamic layering3. In this model, the com-putation domain is divided into two parts, stationary (the tunnel and portals) and moving (the train and the column of air in both ends and around it). The CFD code used, ANSYS FLUENT Version 14, calculates the flux between the interfaces of two domains sliding relative to each other. On both ends, layers of meshes are created and destroyed according to the domain movement. With this

1Full-scale flow measurements in a tunnel airshaft”, A. Vardy, 12th International Symposium on the Aerodynamics and Ventilation of Vehicle Tunnels, Organized by BHRA Fluid Engineering, Portoroz, Slovenia, 2006, p. 343

2http://www.thermotun.com/airshaft3FLUENT Version 14 User Guide, Chapter 11, Modelling Flows Using Sliding and Deforming Meshes

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Figure 1 - General configuration of tunnel, vent shaft, and measurement location

SouthPortal

NorthPortalSouth

Shaft

Monitoring Point

Tunnel and Vent Shaft Section

75.9m

9m462m

1633m542m

3m

8m

12.25m

Emmequerung Tunnel: Area: 75.9m2 Length: 1633m

Vent Shaft: Area: 12m2 Length: 12m

Train (Cisalpino ETR 470): Area: 10m2 Length: 236m

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approach, the mesh quality and quantity, and also the required computer resource, could be controlled. Figure 2 illustrates the general concept of this CFD technique.

Figures 3 and 4 illustrate the surface mesh arrangement of the 3-D CFD model, covering the tunnel portal, train nose, and the vent shaft. The portal areas are extended and inclined to model the portal geometry, which should be critical in the portal entry and exit stages. The tunnel section is also assumed constant from portal to portal. The train is modelled with a wedge shaped nose. With a nominal length scale of 0.45 metres, the total mesh num-ber for the model is approximate 2.8 million.

One very important issue on the mesh arrangement is the interface mesh topology. The interface surface meshes were arranged so that they aligned perfectly during the simulation. This arrangement turns the 2-D surface flux interpolation on the interface to 1-D. Based on our project experience, this arrangement is neces-sary; otherwise, divergence would occur.

For the high-speed air flow and pressure wave analysis of the train/tunnel aerodynamic interaction, the viscous effect was considered negligible and could be ignored. Many successful numerical schemes developed for the same purpose also adopted the same assump-tion4 5. Therefore, inviscid flow was assumed for all the CFD analysis.

4“Prediction and validation on the sonic boom by a high-speed train entering a tunnel’, Yoon, T.S., Institute of Advanced Aerospace Technology, School of Mechanical and Aerospace Engineering, College of Engineering, Seoul National University, Journal of Sound and Vibration (2001) 247(2), pp. 195-211

5“Numerical and Experimental Investigation of Wave Dynamics Processes in High-Speed Train / Tunnels”, Jiang Zonglin, ACTA MECHANICA SINICA (English Series), Vol. 18, No. 3, June 2002.

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Figure 3 - General train nose and portal CFD model arrangement

Figure 2 - Concept of sliding mesh and dynamic layering to model the moving train

Figure 4 - General vent shaft CFD model arrangement

Apart from the numerical methods adopted, the boundary conditions used are as follows:• The ideal gas law to account for the air compressibility, i.e., the relationship between

absolute pressure, temperature, and density;• Ambient condition: absolute pressure at 95802.79 Pa (13.89 psi) and at 287.15K

(also as initial condition for the whole domain);• Density-based, spatial, and temporal implicit solver;• Green-Gauss Node-based for gradient interpolation;• Second order discretization for � ow;• Flux type: Roe � ux-difference-splitting (FDS) scheme;• Implicit time stepping with time step around 0.0013 second;• Initial air speed = 0 meters per second (m/s) for the whole domain;• Initial train location = 50 metres from south portal; and• Train speeds: north bound 177.5 kph (110.29 mph) and 204 kph (126.76 mph).

Stationary Domain

Moving Domain

Mesh Interface

Layers of meshes created Layers of meshes removed

TRAIN

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The 3-D CFD simulations were conducted on a high per-formance workstation supporting 24-CPU parallel pro-cessing. The nominal time required for each time step of 0.0013 seconds is around 20 seconds. For the train to run from the starting position to the other end of the tunnel, the total travelling time required for speeds of 177.5kph and 204kph is 40 seconds and 35 seconds respectively. And the computer time required is 171 hours and 150 hours respectively. Unfortunately, due to the limited computer resources available, the com-plete train entry and exit could not be simulated. Only 12 seconds and 17.5 seconds of simulations were conducted for 177.5kph and 204kph train speeds re-spectively. The total simulation time required for these two cases using the same workstation is approximately one week.

3-D CFD Results and Comparison with Experimental DataTwo pressure measurement points (A and B) are defined in the 3-D CFD model. The first point (A) is identical to the on-site measurement point of the experiment mentioned above. The second point is in the same chainage but lo-cated on the other side of the tunnel for comparison pur-pose. Figure 5 illustrates these two CFD model measure-ment positions.

With reference to the data sets provided in the Thermo-Tun website and the CFD simulation results recorded for Point A and Point B, Figure 6 and Figure 7 are the com-parisons of the pressure measurement for 177.5kph and 204kph respectively. The time axis is adjusted so that the pressure values and pattern could be compared in detail. Table 1 summarizes the key pressure parameters for detailed comparison.

Apart from the numerical values, it is clear from the fig-ures that the 3-D CFD simulation approach could predict the major pressure wave peaks and troughs correctly at their time of occurrence. However, the 3-D CFD simulation approach appears to underpredict the positive pressuriza-tion before the train nears the measurement point but

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Figure 5 - Pressure measurement locations inside tunnel

Figure 6 - Comparison of pressure measurement and CFD results for train speed 177.5kph

Table 1 - Comparison of pressure parameters from experiment and ThermoTun results

Figure 7 - Comparison of pressure measurement and CFD results for train speed 204kph

Train Speed 177.5kph 204kph

Exp. 3-D CFD Results Exp. 3-D CFD Results

Entry Pressure Gradient (Pa/s) 2050Point A: 2708 (>32%)Point B: 2600 (>27%)

3280Point A: 3748 (>14%)Point B: 3632 (>11%)

1st Peak (Pa) 492Point A: 571 (>16%)Point B: 557 (>13%)

667Point A: 719 (>8%)Point B: 700 (>5%)

2nd Peak (Pa) 554Point A: 470 (<15%)Point B: 457 (<18%)

769Point A: 601 (<22%)Point B: 583 (<24%)

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overpredicts the negative pressurization after the initial stage of the train passed through the measurement point (Figure 7). After that the variations in magnitude appear to be less regular. It is clear from Table 1 that the pressure gradients (im-portant for sonic boom generation) and first peak values are overpredicted by CFD and the second peak values are underpredicted.

1-D ThermoTun APPROACHThermoTun software is for studying pressure waves within high speed train tun-nels. Since Ther-moTun is a 1-D approach, some natural disad-vantages that may affect the accuracy are raised below:

• The train is modelled to have the same section from the nose to tail. However, in the full-scale experiment, the train (Cisalpino ETR 470) has a wedge-shaped nose as shown in Figure 8. Therefore, it would be nec-essary to adjust certain parameters to represent the train nose configuration.

• The vent shaft is modelled as a branch of the tunnel. While all elements are 1-D, the connection point of the vent shaft and tunnel is a point in a line, but in fact it has some position character (left, right, or top side of the tunnel) that will affect the flow and pressure propagation in the shaft.

• The tunnel section is far more complex than the Thermo-Tun model. So if the study is focussed on a non-typical position, the variation may increase.

1-D CFD Results and Comparison with Experimental DataDue to the nature of the 1-D approach, only one point is needed for recording the pressure history in ThermoTun. The chainage of the measurement point (D) is the same as points A and B in the 3-D CFD model, for comparison purpose.

With reference to the data sets provided on its website and the ThermoTun simulation results recorded for Point D, Figure 9 and Figure 10 are the comparisons for the pressure measurement for train speeds of 177.5kph and 204kph respectively. As discussed previously, in this ThermoTun test the train nose is modelled by aerodynam-ic parameters but it is not perfectly modelled; thus, the pressure gradient when entering is more close to a verti-cal line than shown in the experiment.

Similar to 3-D CFD results, it is clear from the figures that the ThermoTun simulation approach could predict the many major pressure wave peaks and troughs correctly at their time of occurrence. However, the ThermoTun simula-tion approach appears to overpredict the pressure peak.

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Train Speed 177.5kph 204kph

Exp. CFD Results Exp. CFD Results

1st Peak (Pa) 492 Point A: 585 (>19%) 667 Point A: 779 (>17%)

2nd Peak (Pa) 554 Point A: 576 (>4%) 769 Point A: 805 (>5%)

Table 2 - Comparison of pressure parameters from experiment and ThermoTun results

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Figure 9 - Comparison of pressure measurement and ThermoTun results for train speed 177.5kph

Figure 10 - Comparison of pressure measurement and ThermoTun results for train speed 204kph

Figure 8 - Cisalpino ETR 470

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The time axis is so adjusted that the pressure values and pattern could be compared in detail. Table 2 summarizes the key pressure parameters for detailed comparison.

The time required to complete the analysis was several hours from modelling to result analysis. With the balance between result accuracy and time requirement, Thermo-Tun has its own advantage over the 3-D CFD approach.

Discussions and ConclusionsWe conducted and compared 3-D CFD simulations against the full-scale experimental results. With the two train speeds analyzed (177.5kph and 204kph), the comparison of the pressure values at a specific measurement point inside the tunnel indicate that 3-D CFD simulations could generally model the pressure wave variation with a proper prediction of the wave pat-tern. However, the exception is the peak values of the first maximum positive pressure. The 3-D CFD simu-lations appear to provide an improper pressure mag-nitude. The findings in fact are similar to the axisym-metrical model used in a previous study6. To enhance the accuracy of CFD approach, further investigation of the numerical methods used is necessary. Due to the long turn-around time for the 3-D CFD simulation, it is recommended that such further investigation first be conducted on the axisymmetrical model before being extended to 3-D.

Even with the use of the latest high performance paral-lel processing technique, the overall progress of 3-D CFD simulation is very slow. The computational resources and time span required also prohibit the use of the 3-D CFD method as a design tool for high-speed railway aerody-namics analysis. The 1-D ThermoTun approach cost less to run the same scenario compared to 3-D. Although the ThermoTun simulation amplifies the pressure peak, for design applications this can be treated as a safety factor.

In short, with more numerical method refinement and en-hancement of computer speed and capacity, 3-D CFD is expected to perform more accurately and provide more detail when simulating tunnel pressure waves. However, with the current computational resources and the time span required, the 3-D CFD approach cannot achieve more accuracy within reasonable time and cost. It is con-cluded that 1-D ThermoTun is the best choice for engi-neering design purposes under current technology.

Dr. Dicken K.H. Wu specializes in computational fluid dynam-

ics (CFD) simulations and various types of computer simula-

tion analysis. He has designed pressure comfort control sys-

tems for high-speed subway systems in Hong Kong, Mainland

China, and Taiwan.7

Rambo RB Ye was formerly a specialist in simulation methods at

Parsons Brinckerhoff.

6“Aerodynamic design of underground station with high-speed train passing”, D.K.H. WU, 13th International Symposium on the Aerodynamics and Ventilation of Vehicle Tunnels, Organized by BHRA Fluid Engineering, 2009. An abstract of the same paper is in Network #70, November 2009, p 26.

7For a previous Network article by Dicken Wu and YF Pin about FLUENT, see “New and Efficient Techniques for Modeling and Meshing with FLU-ENT and FDS,” in “The Engineer’s Crystal Ball,” Network #70, November 2009, pp 4-6.

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Railway Cooling Challengesby Mark Gilbey, Godalming, UK, +44 (0)148 352 8506, Gilbey@pbworld.com

Parsons Brinckerhoff has been providing engineering sup-port to London Underground, the Buenos Aires Metro (Subterráneo de Buenos Aires), and the proposed UK High Speed 2 project in identifying, understanding, and overcom-ing the challenges associated with warming railways.

The ChallengesMost of the heat in a rail tunnel emanates from the trains and train operations. London Underground and the Bue-nos Aires Metro are examples of metros currently ac-commodating passenger demand well above what was originally envisaged. With improvements in train signaling and control technology, higher train frequency can often be realized, creating the potential for warmer tunnels and reduced thermal comfort and safety. The higher train frequency can also be coupled with higher train speeds to meet passenger demands for reduced journey time. This means more braking kinetic energy to dissipate, and thus more heat. Another issue common to both of these metros is the desire to meet passenger expectations for rolling stock air conditioning. Failure to manage tempera-tures can increase discomfort for passengers, making the railway a less attractive transport mode. However, retrofit-ting air conditioning adds further heat into the tunnels.

High Speed 2 (HS2), a planned UK high-speed rail net-work from London to Birmingham and to Manchester and Leeds, presents similar challenges, but the key factor in this railway has proven to be the very high train speeds, meaning that a very large quantity of kinetic energy is gen-erated when the trains brake. A good proportion of this energy can be regenerated, but the remainder still pres-ents a great thermal stress on the tunnel environment.

An external challenge to railways relates to the changing climate. Railway infrastructure has a life of over 100 years and over this period reasonably foreseeable climate

change could cause warming of 1½ to 2 degrees C in the UK. Over time, the inside tunnel environment would experience change similar to the outside environment. Compounding the challenge, passengers entering a railway from a warmer temperature would be less willing and able to accept a warm condition on the trains.

Failure to manage increasing temperatures in tunnels can also drive up operating costs by increasing the amount of energy required to cool the trains and sta-tions. It could also cause safety concerns for passengers and staff if tunnel temperatures became so hot that the air conditioning of trains in tunnels cut out because their condensers could not reject their heat. Other in-tunnel equipment, such as electronic wayside communications and signalling equipment, can become less reliable and have a shorter life when operated in higher tempera-tures. For example, an average temperature increase of 10 degrees C (18 degrees F) may more than halve the useful life of an electronic component when calculated using the techniques given in MIL-HDBK-217F (Reliability Prediction of Electronic Equipment).

Mitigating HeatEnergy efficiency is first and foremost a measure that can be employed to take on the challenges; this tackles the heat release at its source. Optimizing rolling stock and traction power specifications, train speed operating profiles, and maximizing regenerative braking1 receptivity all play a major role in reducing temperatures, as well as reducing energy usage. For example, it might be prefer-able to provide more motored axles on the train to allow more regenerative braking (the number of motored axles might otherwise be rated on acceleration requirements alone). Such energy efficiency was an important part of the scope of work for London Underground where Par-sons Brinckerhoff played a key role in the optimisation of

1Regenerative braking is when the train motors are used to slow the train down. When they work in this way the motors act as generators, providing energy back to the traction power system for use by other trains. Without this technology the braking energy would be released as heat.

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the cooling and traction energy demands for the recent Victoria Line upgrade. This was part of a suite of three London Underground projects that recently won the In-stitute of Civil Engineers 2014, Greatest Contribution to London Award.

When practicable traction energy optimisation methods have been adopted, the next logical step is the provision of cooling. For new systems, measures such as plat-form edge doors, air-tempering of platforms, and night time cooling may be used. For existing systems it can be significantly more challenging. Sustainable methods can be evaluated as a first alternative. For example, under-platform or over-track exhaust provides air extraction points near the heat sources, allowing the heat to be taken away in the ventilation ducts before it influences conditions in the station or tunnel. For the Victoria Line upgrade it was possible to upgrade 13 existing mid-tun-nel ventilation shafts. This, however, generated challeng-es in mitigating the noise from the larger fan shafts that are now surrounded by dwellings and offices. In hotter climates, ventilation might be inadvisable on hot days and mechanical cooling may be preferred.

Where mechanical cooling is required, natural water sources may offer significant energy savings. The use of groundwater in tunnel cooling systems can be traced back to New York City’s Brooklyn Bridge subway station in 1906, and it is still viable today. The technology has recently been successfully delivered by London Under-ground at Green Park station where Parsons Brincker-hoff provided engineering support across a range of disciplines. The Green Park system uses a submersible pump located approximately 60 metres (197 feet) below ground to extract 25 litres (6.6 US gallons) per second of water from an aquifer below London. The water is naturally at 13 degrees C (55 degrees F) and is pumped through a heat exchanger belonging to the main station cooling system. The borehole water is warmed by about 8 degrees C (14.4 degrees F) before being re-injected back into the aquifer via re-injection wells (see Figures 1 and 2). Note that Figure 2 shows only the wellhead chamber, the borehole is about 450mm diameter and starts at the base of the wellhead chamber.

The main cooling system uses a secondary water cir-cuit with air handling units (a cooling coil and fan) lo-cated at the platform level of the Green Park station (see Figure 3). The system successfully cools the sta-tion and tunnels and was awarded the first prize in the Environmental and Sustainability category for the 2013

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Figure 2 - Borehole wellhead near Green Park station.

Figure 1 - Borehole locations and pipe routes near Green Park station

Figure 3 - Air handling unit delivering 100 kW of cooling to the platform of Green Park station

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UK Rail Industry Awards. Parsons Brinckerhoff is reviewing the potential application of this technique to one of the High Speed 2 railway stations. Note that borehole cooling is just one of the techniques being used by London Under-ground; numerous other mitigations, including ventilation shaft upgrades and the use of mechanical cooling via air cooled chillers have recently been implemented.

Re-using HeatSustainability may be further improved by heat recov-ery. For example, a heat exchanger in the tunnel may capture the heat from the tunnel, and a water circuit transfers the heat to the heat-sink side of a heat pump. The heat-source side of the heat pump may be con-nected to a third party’s building or small-scale district heating system, again by a water circuit, and provided with monitoring systems to record the amount of heat captured and utilised. Capturing the heat from the tun-nel in a cost-effective manner remains a key challenge. Parsons Brinckerhoff has been involved in the investi-gation of several technologies including tunnel cooling pipes2, pipework embedded within the tunnel liner (see Figure 4), and the location of air source heat pumps in exhaust air plenums. For High Speed 2 we have devel-oped a finite difference model of tunnel wall heat trans-fer and airflow within the tunnel (called Dynamo, see article in this issue on Dynamo by Jolyon Thompson) and are looking at the most cost effective way to re-use the heat from these tunnels.

Building the CaseOne of Parsons Brinckerhoff’s key roles on railway proj-ects is the modelling and financial appraisals of cooling demands and cooling schemes. Typical methods include multi-train simulation to understand and optimize train energy usage, often done in conjunction with tunnel ven-tilation modelling. We have industry-leading tools for the evaluation of transient thermal comfort, and have devel-oped methods in which changes in thermal conditions can be mapped to customers’ willingness to pay.

A Sustainable OutcomeSustainability is a key factor in railway cooling, and in the broadest possible sense. Social sustainability can be enhanced by providing the temperature control to sup-port railway capacity upgrades that improve the quality of life for transit users and city dwellers. Environmental sustainability can be enhanced by reducing heat release in the railway through increased energy efficiency and low energy cooling methods such as groundwater cooling systems. Economic sustainability can be enhanced by optimising the cooling provisions and customer benefits to minimize whole-life costs with a demonstrable benefit to cost ratio. Parsons Brinckerhoff has an enviable track record in balancing these sustainability needs.

Mark Gilbey is EAME Head of Discipline for Tunnel Ventilation. He

is a Mechanical Engineer and has worked for Parsons Brinckerhoff

since 1998 in Hong Kong, US, and the UK.

2For the abstract of a previous article by Ting, Drake, and Gilbey on “CFD Estimation of Heat Transfer Enhancement on a Cooling Pipe in Under-ground Railway Tunnels,” see Network #70, November 2009, p 42.

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Figure 4 - Thermal analysis of the heat recovery potential for pipework embedded into a 300mm tunnel liner with a soil depth of 20m

25mm diameter pipe200mm below the surfaceof a 300mm thick liner and spaced at 350mm centres

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Dynamo – Enhancing Tunnel Ventilation Modellingby Jolyon Thompson, Godalming, UK, +44 (0)1483 528666, thompsonj@pbworld.com

IntroductionThe Subway Environment Simulation (SES) software pro-gram was co-developed by Parsons Brinckerhoff for the US Department of Transportation in the 1970s. It allows engineers to mathematically model aspects of the subway environment on a second-by-second basis and continues to be regarded as an industry standard tool in the field of tunnel ventilation. SES is used worldwide for a variety of underground construction and tunnel applications, including high speed rail, commuter rail, metros, freight tunnels, road tunnels, and cable tunnels. A supplement to the SES has been developed by Parsons Brinckerhoff to enhance the ca-pabilities of SES and to meet specific requirements of other tunnel system projects. This supplement is called Dynamo.

Dynamo is a one-dimensional (1-D) model of a single length of tunnel which can simulate the effects of a ven-tilation shaft connected at any point along the length of the tunnel. Dynamo predicts the thermofluid interactions

using a variety of boundary and initial conditions which can be specified at each tunnel portal. Dynamo has been developed for use in tunnel ventilation and, as such, all relevant properties of air are encoded into the analysis engine. However, the Dynamo approach would work for any Newtonian fluid1 providing the relevant fluid param-eters were input to the model.

Dynamo has been used by Parsons Brinckerhoff on proj-ects, two of which are described below.

Cable Tunnel DesignA recent project consisted of an 18 kilometre (11-mile) long cable tunnel carrying 132kV cables beneath a natural bay. The cable circuits emitted a considerable amount of heat (over 800 watts per metre of tunnel length). The tunnels must be kept cool enough to limit the conductor temperatures in the cable and provide a safe environment for maintenance workers.

1A Newtonian fluid is any fluid that exhibits a viscosity that remains constant regardless of any external stress that is placed upon it. This could include mixing or a sudden application of force. A Newtonian fluid can change viscosity if the temperature or pressure changes. The fluid would still be regarded as Newtonian providing the viscosity remained constant at these new temperatures or pressures.

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DYNAMO Parsons Brinckerhoff created a calculation tool to estimate the annual temperatures of long tunnels and with the ability to calculate the heat transfer from heat recovery mechanisms such as embedded liners and tunnel cooling pipes. The tool is named Dynamo.

Dynamo uses a similar set of modelling assumptions to SES and therefore a single Dynamo � le can and may need to take input from several SES simulations to account for variations in fan, train operations, or other signi� cant variations in the system. The most signi� cant difference is in the treatment of the deep heat sink effect through the surrounding soil. Dynamo uses a fully transient � nite difference approach to allow thermal evolutions to be calculated in response to the tunnel environment, allowing complete year pro� les to be developed.

Dynamo uses an energy balance approach to determine the thermo� uid interactions. The energy balance is at the core of the � exible Dynamo methodology. Any technology or system which can be formulated into an energy effect upon the system (input, output, or storage) can be included.

Dynamo is a modular program which enables additional functions to be easily added and tested. All that the function requires is to be formulated to add to the energy balance in the correct manner. Examples of technology systems that have been added in this manner include cooling pipes and embedded tunnel liners.

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Due to the length of the tunnel, considerable airflow would be needed to prevent the air from becoming too hot. It was initially proposed to divide the tunnel into short sections and construct artificial islands within the bay which would provide ventilation inlets and outlets. However, this design would be expensive and could negatively impact the ma-rine environment. An analysis of a cooling pipe system was therefore considered necessary.

Previously a two-stage approach using an initial SES sim-ulation supplemented with an Excel calculation sheet would be used. This required iteration between the two models to get the final result. If the cooling pipes loop and return to the portal-based cooling plants, this would result in a circular formula within the Excel analysis. The calculation therefore required a macro to control the process. The system was then iterated to ensure the accuracy of the calculation. The calculation process was thus bespoke to the situation and would need adjusting before it could be used with another tunnel layout option and it also took several days to complete.

Dynamo, in contrast, can be set up to evaluate the sys-tem in an integrated way. Since the only source of air flow is that generated by the fan against a constant re-sistance, the ventilation rate is also constant. The Dyna-mo analysis took less than four hours to set up, check, and simulate.

The SES/Excel calculation outputs would have provided a temperature prediction along the length of the tun-

nel for summertime peak hours only. Dynamo provided an hourly temperature prediction along the length of the tunnel for the whole-year. The temperatures predicted by Dynamo for both a ventilation only situation and the ventilation cooling pipe solution can be seen in Figure 1 and Figure 2. The x-axis (horizontal) shows the length along the tunnel and the y-axis (vertical) shows the time of year (summer being in the middle of the y-axis). The summer peak hours predicted by Dynamo compared very well with those predicted by the combination of SES and the Excel spreadsheets. The reduced time to set up the Dynamo simulations allowed for more options to be considered to optimise the cooling pipe design by comparing different water flow temperatures and pipe arrangements. This resulted in improved economic and environmental sustainability for the final design. The use of Dynamo also allowed for whole-year temperature pre-dictions to be made, allowing annual system energy us-age to be evaluated for each of the options and providing more accurate whole-life costing to be used in the de-sign. This is an increasingly important facet of delivering sustainable design and represents a significant improve-ment in Parsons Brinckerhoff’s predictive capability.

Dynamo for Waste Heat Recovery Dynamo can also be used to enhance the capabilities of SES in the analysis of recovery of waste heat from railway tunnels. This is an area which has received in-creased attention in recent years but is one which SES alone is not able to directly analyse.

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Figure 1 - Dynamo predictions for no cooling case

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In a recent project, a 13.5 kilometre (8-mile) long high-speed rail tunnel was analysed using SES and predicted to be at a significantly elevated temperature over a sub-stantial length of the tunnel during summer. To allow the tunnel to meet the design criteria, a cooling system was proposed and designed with a total peak cooling capac-ity of approximately 4MW.

Whilst the cooling was expected to be mostly needed in summer, it was considered desirable to recover low-grade waste heat from the tunnel all-year round and use this heat in conjunction with heat pumps to offset heating

energy usage for nearby properties and developments. Dynamo was used to analyse the impact of using cooling pipes and embedded liners as the means of cooling the tunnel and for waste heat recovery.

The heat and flow rate predictions from SES were used in the Dynamo analysis and similar temperatures for the summer peak hours were predicted. The cooling systems were then added into the Dynamo file and an assessment was made of the tunnel temperature reduction and the available temperature for heat recovery. The results of the tunnel temperature predictions can be seen in Figure 3.

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Figure 2- Dynamo predictions for cooling pipe case

Figure 3 - Annual tunnel temperature predictions before heat recovery

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The heat recovery system used a cooling pipe system that operates with a water flow rate of 70 kilograms per second (kg/s) supplied at 15°C (59°F) in 200 millimetre nominal diameter pipes. These cooling pipes are in the form of two loops which originate from chainage 10.7km and operate in opposite directions. Heat recovery may not always be considered as a method of reducing tunnel air temperatures appreciably despite producing significant benefits to other systems. The chart shows that heat re-covery provided a minor tunnel temperature reduction of approximately 1.5°C (approximately 3°F), but an impres-sive 1500kW of heat from the tunnel environment as an annual average. The heat recovery from the tunnel can then be matched to the demands of a local area. In this case, illustrative demand profiles are shown in Figure 4.

Dynamo enables the load profile variations to be accu-rately established and therefore matched to the demand profiles. Where the variations are in keeping with the available heat it is a relatively simple linkage between the heat source (the tunnel) and the heat sink (the heat load profile). Where there is significant variation, which is usual, the base level loading can be established and

any supplementary load requirements can be included in the design of the heat network.

ConclusionTwo examples of Dynamo usage have been provided in this article. Dynamo has been shown to be capable of supplementing SES predictions in some areas which en-hances the analysis capabilities of Parsons Brinckerhoff.

References • Subway Environmental Simulation User Manual, 2003,

prepared for the U.S. Dept. of Transportation

• Thompson J.A., Missenden J.F., Gilbey M.J. and Maid-ment G.G., Response of wall heat transfer to steady and transient flows along a cylindrical cavity, Int. Symp. Aero. & Vent. Vehicle Tunnels, New Brunswick 2009

Jolyon Thompson is a Senior Tunnel Engineer in the UK office

with a PhD in sustainable cooling of underground railways. He

has a keen interest in heat recovery and improving the sustain-

ability of tunnels through holistic design and was the lead devel-

oper of the DYNAMO analysis tool.

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Asset Management Database for the Brooklyn Battery Tunnelby Ferdinand Portuguez, New York, NY, US, +1- 212-631-3891, Portuguez@pbworld.com; and Debra Moolin, New York, NY, US, +1- 212-465-5443, moolin@pbworld.com

The database for the Brooklyn Battery Tunnel (BBT), now officially known as the Hugh L. Carey Tunnel, is the key tool in the management of the various facility assets – the tunnel and four major building systems. The data-base was developed by Parsons Brinckerhoff in collabo-ration with the client, MTA Bridges and Tunnels, in 2012 with the objective of maintaining the facility in a “state of good repair”. Assets included in the database are:

• Tunnel tubes, crossover passages, and construction shafts;

• Manhattan Blower Building;• Manhattan Underground Exhaust Building;• Governors Island Ventilation Building, pedestrian

bridge, fender structure, and riprap;• Brooklyn Ventilation Building; • Brooklyn Service Building and parking structure;• Manhattan Plaza, portal, and cellular structure;• Manhattan Plaza Emergency Garage;• Brooklyn Plaza and portal; and• Streets ancillary to the Brooklyn and Manhattan plazas.

Facility DescriptionThe Brooklyn Battery Tunnel (see Figure 1) crosses New York Harbor, connecting Brooklyn and lower Manhattan. The tunnel consists of two adjacent tubes, the east and west tubes, each approximately 9,000 feet long making it the longest continuous underwater vehicular tunnel in North America. Construction of the tunnel began in the 1940s but was suspended during the Second World War. The tunnel was opened to traffic on May 25, 1950 and now carries over 50,000 vehicles per day.

The database includes structural, architectural, mechan-ical, and electrical components – this article is focused on the tunnel systems which include:

The database was populated with inventory information for each facility asset. Existing documents, reports, and construction plans were reviewed by Parsons Brincker-hoff before the start of the inventory inspection. Informa-tion on deficiencies and functionality of the mechanical and electrical systems were collected during interviews with maintenance staff, conducted by Parsons Brincker-hoff, and incorporated into the database. An overall con-dition rating of the electrical and mechanical systems was assigned based on this information.

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Figure 1 - Brooklyn Battery Tunnel

Security Water and Fireline/Standpipe

Elevators Electrical Distribution

Compressed Air Tunnel and Plaza Lighting

Communications Carbon-Monoxide (CO) Monitoring

Tunnel Drainage Vehicle Fueling Station

Tunnel Ventilation Plumbing- Drainage, Sanitation

Power- UPS/ Standby Central Vacuum Cleaning

Building Lighting Traffi c Signals and Controls

SCADA/PLC Heating, Ventilation,and Air ConditioningHoisting-Mechanical

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Database ArchitectureThe database of tunnel tubes and plazas includes an in-ventory of 65 different structural, mechanical, and electri-cal element types. These element types were inventoried by location with over 23,000 uniquely identified database elements or “entries” resulting. The database identifies over 150 element types housed in the buildings.

These elements are defined by:• Asset – Identifies tube, plaza, building, or pedestrian

bridge;• Discipline – Structural, Mechanical, Electrical, or

Architectural;• System – Various tunnel and building systems; and• Location

- Tubes - subdivided by wall marker stationing; then Construction Type - cut and cover steel bent, cut and cover concrete, light cast iron ring, heavy cast iron ring; and then Level - exhaust duct, roadway, fresh air duct;

- Plazas - subdivided by expansion joints;- Buildings - subdivided by floor/(sub) levels; and- Pedestrian Bridge - subdivided by bents.

See Figure 2 for a sample listing of element types.

The comprehensive database also provides the following:• Identification of element-level electrical and mechanical

deficiency types for use in future inspections;• Identification of element level deficiencies observed dur-

ing the 2012 inspection with links to photographs of conditions;

• The ability to sort and search the data within the data-base to facilitate condition management and reporting;

• The ability to summarize condition ratings, deficiency types, and quantities of deficiencies;

• Installation year, age, and expected service life – Parsons Brinckerhoff worked with the TBTA, to identify the estimated service life. Data from Federal Transit Administration (FTA) ‘assumptions regarding useful life for effective cost comparisons’ was considered as well

as data being used for the Queens Midtown Tunnel inventory; and

• System Element Condition Rating – Each system ele-ment includes a condition rating from 1: Continue in-ser-vice (Satisfactory Condition) to 4: Remove from service (Unsatisfactory – High Priority).

Database Worksheets The database was developed in coordination with the client using Microsoft Office Excel 2007. This format was chosen in order to create an asset management tool that is commonly understood by the engineering staff that would be working with the system. The Excel spreadsheets provide ease in the creation and manipu-lation of the large amount of data through simple func-tions such as sorting and filtering, and provide the ability to produce reports summarizing filtered and sorted data through pivot tables.

Different groups of worksheets make up the Brooklyn Battery Tunnel’s database:• Support/Reference worksheets;• Master-Administrator Only worksheet;• End-User Database worksheets;• Database Expansion worksheets; and• Summary worksheet(s).

Support/Reference worksheets These worksheets are the source of defined and known information contained in the Master-Administrator Only worksheets. These include: a summary of the repair/rehabilitation projects and the coding used to define the element level that is inventoried and rated, along with the deficiency types applicable to each element.

The Support/Reference worksheets standardize the terminology throughout the databases and minimize manual work during database updates by simplifying the steps for modifying or expanding the current range of data in the databases. The vast majority of the current

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Figure 2 - Sample listing of element types

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information included in the Master-Administrator Only worksheet comes from the support worksheets through equations and links.

The identified elements for the Tunnel Ventilation Sys-tem within the tunnel worksheets are shown in Figure 3.

Master-Administrator Only worksheet The Master-Administrator worksheet contains all the original data from the inventory and condition inspec-tion. This worksheet is locked and can only be manipu-lated by users with necessary rights and passwords.

End-User Database worksheetsThe End-User Database worksheets include a Filter worksheet and a Pivot Table worksheet and are in-tended to be used for queries, data access, sorting,

filtering, and reporting without working directly in the database spreadsheet. The data is therefore protected from inadvertent changes while sorting and filtering are being performed.

The Filter worksheet is set-up with Microsoft Excel tools to filter specific data by area, regions, stations, element(s), and element ratings and/or deficiencies. This worksheet includes a sum of the quantity column and average of the rating column. This is also a dynamic calculation and provides the values for the elements that are visible during the filtering process. As an example, to manage the elements associated with the tunnel fireline, such as the fire hose valves and gate valves, the worksheet can be filtered as shown in Figure 4.

The Pivot Table worksheet allows users to extract spe-cific data from the databases by turning on specific col-umns from the master database and then filtering them to specific values. In contrast to the Filter worksheet, the Pivot Table allows for more specific extractions of data and allows users to display and print only the col-umns and rows that are needed (see Figure 5). On the right hand side, the “Pivot Table Field List” lists all the columns that are referenced from the Master-Adminis-trator Only worksheet.

As part of the tunnel drainage system, pumps are lo-cated in the Brooklyn Portal Pump Station, the Manhat-tan Blower Building, and the Governors Island Ventilation Building. A query of the tunnel drainage system housed on the Brooklyn side would result as shown in Figure 5.

Database Expansion worksheetsThe ‘New Element’ tabs within the tunnel and buildings da-tabase workbooks are intended for use only when adding

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Discipline System Element

Structural Tunnel Ventilation Acoustic Baffl e

Structural Tunnel Ventilation Damper Door Motor Support

Structural Tunnel Ventilation Duct - Horiz. & Vert.

Structural Tunnel Ventilation Fan Motor Pad

Structural Tunnel Ventilation Fan Housing/Shaft Pad

Structural Tunnel Ventilation Damper Door

Mechanical Tunnel Ventilation Damper Door Motor

Mechanical Tunnel Ventilation Fan

Mechanical Tunnel Ventilation Fan Housing

Mechanical Tunnel Ventilation Fan Shaft

Mechanical Tunnel Ventilation Fan Motor

Mechanical Tunnel Ventilation Fan Motor Belt Guard

Electrical Tunnel Ventilation Fan Motor Control PMP

Electrical Tunnel Ventilation PLC - I/O Rack Panel

Electrical Tunnel Ventilation Power Capacitor

Figure 3 - Identified elements for the tunnel ventilation system

Figure 4 - Filter worksheet with elements associated with the tunnel fireline

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new elements to the Master-Administrator Only worksheet. This allows the database to be expanded to include new items that are added as part of the facility’s updates.

Summary worksheetsThese worksheets are provided for the tunnel systems and sum each element’s total quantity and the element’s quantity per rating value, and quantity per deficiency type. The east and west tubes of the Brooklyn Battery Tunnel are tallied separately. Therefore the condition rating of various tunnel elements can be reviewed per query.

ConclusionThe asset management database is an essential tool that can be used on a day-to-day basis or when scheduling and budgeting projects that will maintain the facility in a “state of good repair”. Within the database there are several work-sheets that can be used to manage the various assets. Some are better suited for reports while other worksheets are better suited for obtaining data for monitoring the asset condition. Each worksheet aids in obtaining the necessary data, in the desired format, to make an informed decision.

During the aftermath of Superstorm Sandy, the data-base was used to determine replacement quantities for items damaged in submerged sections of the tubes (water filled approximately 6,000 feet of the 9,000 foot-long tunnel) and in the flooded sublevels of the buildings, and to obtain pertinent sump pump informa-tion. Its use during the operational response to that storm in 2012 contributed to the east tube reopening to limited bus service after 13 days and the west tube soon afterwards.

Ferdinand Portuguez is a Supervising Engineer with 22 years of

experience in structural design, construction management, con-

dition inspections, and cost estimating and assessment. He has

a structural background and is a registered PE in New York State.

Debra Moolin is a Structural Engineer (PE) with over 30 years

of experience and a focus on bridge and tunnel repair and

rehabilitation. She has worked on all project phases, from in-

spection, evaluation, and testing through design and construc-

tion support services.

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Figure 5 - Pivot Table worksheet showing query of the tunnel drainage system

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Parsons Brinckerhoff is providing technical support to our client in specifying and procuring a new SCADA (supervi-sory control and data acquisition) system and associated equipment to replace seven obsolete control systems in use at two UK road tunnels. One tunnel was opened in the 1930s the other in the 1970s.

The project seeks to unify currently isolated tunnel control functions into a single SCADA interface, thereby reducing the number of separate control systems the tunnel opera-tors have to access. Modern SCADA is no longer separated from other systems and only used by those who supervise the process under control. It is a system that collects an increasing array of data from increasingly ‘smart’ equipment and provides greater levels of analysis or access to this data by users whose principle roles are business-related, such as forecasting, billing, asset management, or planning.

The method of project delivery presents the challenge here. In order to avoid disruption to tunnel users and at the same time align the SCADA works to a wider programme of tunnel maintenance and upgrade work, a four-year SCADA programme was developed by Parsons Brinckerhoff in col-laboration with the client. This programme will:

• Introduce a new SCADA platform and new programma-ble logic controllers (PLCs) which will communicate via the client’s converged Ethernet network;

• Initially connect SCADA to existing mechanical and elec-trical equipment in both tunnels for tunnel environmen-tal control (ventilation, lighting, dewatering, etc.);

• Expand the system at a later date to connect to new traffic management equipment (signage, barriers, etc.) that is planned;

• Latterly expand to take control of the emergency refuge areas installed in the 1930s tunnel, a four-lane single bore tunnel;

• Interface with other tunnel management systems, such as the automatic incident detection system, in order to deliver improved connectivity to the opera-tion of the tunnels;

• Progressively expand and upgrade what is monitored in order to deliver improved visibility of the tunnels’ opera-tional status; and

• Move toward a decision support environment where incidents are detected and responses identified to the operator, simplifying the resultant control actions.

Having defined this approach with the client and procured the services of a SCADA system integrator, we are now at the beginning of the journey to realize this vision, and to face and meet the challenges of delivering the programme and achieving the client’s objectives.

ChallengesThe client’s primary objective is to ensure the safe and se-cure operation of the tunnels. Whilst a multitude of factors play a part in this, the security of the new control system is an important element and the requirement that the new SCADA and PLCs migrate onto the client’s converged Ether-net network becomes relevant. This network has both op-erational uses (the management of road tunnels and bus, rail, and ferry terminals) and business uses (office and en-terprise IT for staff). Therefore a traditional separation and isolation of the control system is not straightforward.

The challenge is specifying security requirements at the outset. This needs to happen ahead of the design work that will identify how the control system is integrated on the converged network, and these requirements will need to remain relevant as the control system is upgraded over the next four years. Equally, whilst the SCADA system inte-grator will hold overall responsibility for the SCADA system design, the client - through its IT department – will be in-volved in the design and delivery of the communications, server, and workstation environment. Here there is a need to ensure that a secure system can be implemented and to identify which party will be responsible for delivering the various elements of this.

Our solution to this challenge has been to specify, with-in the SCADA system technical specification, adher-

SCADA System Security for Two UK Road Tunnelsby Peter Massheder, Manchester, UK, +44 (0) 161 2005 015, masshederp@pbworld.com

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ence to two international standards, ISO/IEC 27000 and IEC 62443.

Application of Cybersecurity StandardsCybersecurity standards have been created because sensitive information is now often stored on networked computers. This holds the potential for unauthorised ac-cess from within an organisation’s network or even via the Internet. With the greater integration of SCADA with other computer systems there is also a heightened risk that unauthorised access and manipulation of the pro-cess under control could occur; therefore, there is a need for information assurance and security.

ISO/IEC 27000: Information Technology – Security Tech-niques was published some time ago and is generally ap-plied by organisations to help define a security manage-ment system for their enterprise information systems. However, this standard does not consider the specific requirements of a time-critical control system and, whilst relevant to the wider security context in which the SCADA system will reside, we need something more to shape the design. This is where IEC 62443 comes in.

IEC 62443: Industrial Communication Networks – Net-work and System Security is an emerging series of stan-dards with parts still under development. The scope of the standards is specific to defining procedures for im-plementing electronically secure ‘industrial automation and control systems’. This guidance applies to end-users (i.e., asset owners), system integrators, security practi-tioners, and control systems manufacturers responsible for manufacturing, designing, implementing, or managing industrial automation and control systems. Whilst some parts are yet to be completed, what is published defines enough of a relevant approach to control system security to make its adoption beneficial.

This recognises that during the four-year programme of SCADA work, the IEC 624443 series of standards will mature and its adoption at the outset, a strategic move, will ensure future SCADA system upgrades are able to build upon sound foundations. Further, the series is de-signed to build upon the guidance of ISO/IEC 27000 se-ries and expands on ISA-99: Industrial Automation and Control Systems Security, a standard published by the International Society for Automation that has been in use and evolving for a number of years now. In summary we have judged that, whilst not yet complete, the IEC 62443 standard is mature enough to adopt.

Conclusion Work on implementing the SCADA programme is now underway. It is at the initial concept design stage and the high-level design necessary for the full SCADA system as envisioned is being explored. To this end the application of the IEC 62443 standard is coming into play. Although experience applying the standard across all parties is still in its infancy, we are learn-ing valuable lessons as we go. For example, one such lesson is what we are calling our ‘levelling layers into zones lesson’.

This lesson, put simply, is to ensure that there is a mu-tual understanding and use of terminology among all stakeholders. This is a common lesson in collaborative work and in this case is not one that reflects negatively on the standard itself, which is well constructed and clear. Rather the distinct uses of relatively interchange-able words such as ‘level’, ‘layer’, and ‘zone’ within the specification are recognised and highlighted for the stakeholders. Whilst seemingly a minor point, the current design work needs to ‘correctly’ define a logi-cal segmentation of the control system in order to build defence in depth1 (in this instance, segmenting the sys-tem into zones within the operational level, a level that corresponds to layers 0 to 4 of the standard’s reference model – you see the potential for confusion if words are interchanged when communicating).

To conclude, where other security guidance gives equally valuable insight into good practice, the IEC 62443 series of standards also helps in the develop-ment of a security management system that meets the needs of a SCADA control system. Further, as the standards build on guidance of ISO/IEC 27000 the resulting security approach may integrate better with an organisation’s information security management system, helping an organisation’s IT and automation control functions to more effectively collaborate on se-curing a SCADA control system. Whilst the full suite of the IEC 62443 series of standards is not yet complete and its application is in its infancy, we are seeing that this standard does form a valuable point of reference on security when specifying, developing, and ultimately maintaining a tunnel SCADA control system.

Peter Massheder is a Principal Engineer with 26 years of expe-

rience in delivering automation, computing, and ecommerce so-

lutions to clients across the utilities, transport, environment, and

banking sectors.

1Defence in depth is a concept in which multiple layers of security controls are built into an information technology system rather than relying on a single layer of security control. Its purpose is to provide more than one line of defence in case any one layer fails.

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CCTV Design for a US Road Tunnelby Ryan Williams, New York, NY, US, +1-212-631-3875, williamsry@pbworld.com

Parsons Brinckerhoff was engaged by a client to under-take remedial and resilience design work on a tunnel in the US that serves as an important thoroughfare for motor vehicles and was flooded in a storm.

Safety is always the main factor for tunnel operation and control systems. Roadway tunnels are closed environ-ments that must be monitored and controlled for the safety of vehicle occupants and tunnel personnel. The restrictive nature of tunnels, compared to open routes, makes it extremely hard to remove disabled vehicles and to evacuate or rescue accident victims. Congestion and incidents such as breakdowns, fire, or above-limit carbon monoxide (CO) levels must be detected and dealt with in a timely manner and the most effective way for operators within the control room to monitor the safe operation of the tunnel is via the tunnel’s closed-circuit television (CCTV) system.

In addition to verifying roadway incidents, monitoring current traffic conditions, and fire and smoke detection, CCTV systems can be used for security surveillance of the tunnel facility and fire control zones. CCTV cameras are the main traffic monitoring devices for highway and transportation systems.

The tunnel’s existing CCTV system is an analog sys-tem, with fixed cameras providing continuous views of the tunnel to tunnel operators in the control room. In other words, each camera provides a separate feed on a screen (four cameras per screen) in the control room.

Parsons Brinckerhoff was engaged to design a new digi-tal IP CCTV (internet protocol closed circuit television) system, replacing the existing analog system whilst maintaining the existing operation.

The tunnel environment presents several challenges for proper design and implementation of CCTV, including hu-midity, dust, salt, and frequent vibration of equipment

caused by the passing of heavy vehicles. Since vibra-tion can negatively affect devices and their connections, hardened enclosures should be considered. Prior to commencing detailed design of the new CCTV system, the following design criteria needed to be addressed:

• Coverage (including sensor type, lenses, aspect ratio, and camera angles);

• Mounting; and• Communication System.

CoverageIt is extremely important to identify the right locations for CCTV cameras and associated equipment panels. Cam-eras should be located to provide a clear line of sight with minimal obstructions. Tunnel cameras used in low light conditions should be located such that the main view is with the camera looking away from bright light. This is because video images in bright light taken from low light vantage points tend to appear washed out. Where changeable message signs (CMS) are installed, cameras should be located so that the message of an adjacent CMS can be read. This allows for visual verifica-tion of CMS status.

Large trucks and buses are moving obstructions to CCTV camera views. To overcome this obstruction issue, the design provided additional cameras with overlapping coverage to increase CCTV coverage. Overlapping cam-eras were also provided for curved tunnel sections and any other location with slower traffic movement. An op-tion of using pan-tilt-zoom (PTZ) cameras was reviewed, which would give the operators additional functionality. This option was rejected, however, as it would introduce a risk of misaligning the cameras, and it would change the existing operational procedures in the control room.

In a CCTV system, the camera visualization options or functions for different types of applications or surveil-lance are measured by “pixels per foot”. A higher num-

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ber of pixels gives a higher resolution (e.g., in order to read license plates and recognize faces) and a lower number of pixels gives a lower resolution (e.g., to get a general idea of what is happening). The camera func-tions can be classified as:

• Monitoring (a minimum requirement of 10 pixels per foot-vertical);

• Object Detection (a minimum requirement of 20 pix-els per foot);

• Observation (a minimum requirement of 30 pixels per foot);

• Recognition (a minimum requirement of 40-60 pixels per foot);

• Identification (a minimum requirement of 60-80 pixels per foot); and

• Strong Identification (a minimum requirement of 80-100 pixels per foot).

To fulfill the application requirements for the tunnel proj-ect, the Object Detection and Observation functions (a minimum of 20-30 pixels per foot) were designed to be maintained throughout the whole tunnel. Recognition and Identification functions were provided for some stra-tegic locations.

To verify full CCTV coverage, a CCTV simulation tool with three-dimensional (3D) view capability was used to as-sess coverage and provide simulated views at each of the proposed camera locations (see Figure 1). MountingThree camera mounting hardware mechanisms were analyzed for the tunnel installation:• wall-mounted hardware with short arm; • ceiling-mounted hardware; and• surface-mounted camera enclosure.

Most camera manufactures have wall and ceiling hard-ware accessories but a surface camera enclosure would require a special order.

During the conceptual design, the possibility of mini camera integration to the lane-use sign (LUS) was also studied. This option would be an alternative to ceiling mounting and could provide better view angles as the lane-use signs are installed on the ceilings, above the road lanes. However, there are limited mini cameras available for such integration. This camera assembly also requires full integration of LUS and mini camera in NEMA 4X (IP 66/67) rated housing, which has limited space constraints.

Three mounting options are described and depicted below:

Wall-MountedFigure 2 shows the arm and wall-mounted option for the CCTV camera. The height of the camera may lead to obstructed views when large trucks and buses are in the tunnel. This lo-cation also poses a problem for mainte-nance, requiring the wash trucks to be particularly careful around the fixtures. Despite the disadvantages, fixtures at this height would be easily installed and maintained. This mounting option also provides more selection of cameras.

Ceiling-Mounted Figure 3 shows the ceiling-mounted dome camera option. This option provides ad-equate height for the camera to minimize the obstruction of views by large trucks or buses. The height also moves the cam-era out of the way of the maintenance trucks, but this type of mounting could still be knocked loose and installation may be more difficult due to the height.

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Figure 1 - Simulated view of camera coverage.

Figure 2 - Typical Wall-Mount

Figure 3 - Typical Ceiling-Mount

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Surface-Mounted EnclosureFigure 4 shows the wall-mounted dome camera option. The camera inside the dome enclosure is ad-justable to the angle with an optimum view. This option provides enough height to minimize view obstruction by large trucks and buses. The height also allows for easy instal-lation. Finally, this type of mounting will result in minimal damage from maintenance and wash trucks, but limits camera selection options as few fixed cameras are manu-factured with this mount.

Communication SystemMigrating from an analog CCTV system to a digital IP-based system enables the tunnel controllers to gain a level of efficiency and control not previously available in overall operations. However, doing so requires a commu-nication network to transmit the CCTV camera footage to the tunnel control center. On this project, various network types (star and ring topology) were considered based on ease of maintenance, redundancy, and resilience.

A star topology is when each edge switch (switches in the field equipment panels) is connected to a central switch, typically in a control room. A ring topology is where each edge switch is connected to next and previous edge switch, forming a large ring. This option provides redun-dancy in that, if one of the switches were damaged, com-munication to downstream switches can be established through the other side of the ring.

For the maintenance department, a star topology was preferred because it meant that all of the back-end equip-ment would be located in one central location. This means

that if something goes wrong, the maintenance personnel would only need to go to one place. It also means that if one part of the network goes down, it would not affect the resilience of the rest of the network. In an environment where it can be difficult to access and maintain network equipment, the operators can choose to leave a malfunc-tioning field switch out of service and not worry about a larger part of the network becoming inoperable if another fault occurs. It also means that there is a single point of failure at the core, control room switch (in the control room). That is, if the center of the star in the network went down, the whole network would be inoperable.

To overcome the issues of a star network, a modified ver-sion of the star network was designed, with backbone switches installed in physically diverse locations (vent buildings and the control center) in a ring configuration and the edge switches (field switches) connected to each backbone switch in a star configuration. This provided the capability to operate the network from the vent buildings, in case the control center went down.

Cybersecurity measures were implemented in Parsons Brinckerhoff’s design. Cybersecurity is an important com-ponent of all digital networks and requires diligent atten-tion. It is not addressed in this article as it calls for much further discussion.

In ClosingCCTV systems are integral to the safe operation and control of roadway tunnels. While CCTV technology can be fairly simple, the tunnel environment, maintenance, project requirements, and number of cameras can make the CCTV system design complex. This approach to CCTV system design is recommended for other projects to facil-itate maintenance, whilst providing a robust system that can be verified through simulation prior to construction.

Ryan Williams is a Senior Systems Engineer in our New York City

office, having spent the last 8 years with Parsons Brinckerhoff in

Australia. He is a registered professional engineer with chartered

status and has substantial experience in transport and commu-

nication projects.

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Figure 4 - Typical Surface-Mount

Camera

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BackgroundThe Shatin to Central Link (SCL) is one of the ten largest infrastructure projects being constructed in Hong Kong. It is a 17 kilometre territory-wide strategic railway corri-dor with ten stations. The project is linked with a number of existing railways, forming two strategic railway corri-dors: the “East West Corridor” and the “North South Corridor” as shown in Figure 1.

The “East West Corridor” is formed by the Ma On Shan Line (the proposed Tai Wai to Hung Hom Section of the SCL) and the existing West Rail Line. Upon completion, passengers will be able to travel between Tuen Mun in the west and Wu Kai Sha in the east without interchang-ing (transferring) trains.

The “North South Corridor” extends the existing East Rail Line across the harbor via Hung Hom. Upon completion, it will link the immigration control points at Lo Wu and Lok Ma Chau to Hong Kong’s central business district.

Along the SCL, there are three (3) underground stations where the SCL interchanges with the existing Urban Rail Lines (URL). They are: Diamond Hill Station (DIH), Ho Man Tin Station (HOM), and Admiralty Station (ADM). As the SCL will be electrified at 25kV alternating current (AC) while the existing URL is electrified at 1.5kV direct current (DC), AC and DC traction systems will coexist in these un-derground interchange stations (also referred to as “AC/DC interchange stations” in this paper).

All interchange railway lines at Ho Man Tin Station and Admiralty Station are accom-modated within the same station structure, whereas the existing Diamond Hill Station (DIH) station and the future DIH station of SCL (hereinafter referred to as “SCL-DIH”) are separate structures connected by an adit. With a common station structure, the earthing (grounding) systems at Ho Man Tin Station and Admiralty Station will essential-ly be bonded together. For DIH, there was an option in the design of bonding the earthing system of the existing and the future DIH station or introducing an isolation zone be-tween the two station structures.

Parsons Brinckerhoff was appointed by the MTR Corporation Limited to carry out the de-tailed design of the trackside auxiliaries of the SCL. As part of the design, Parsons Brincker-hoff carried out a detailed study on the risks associated with the coexistence of AC and DC traction systems in the interchange stations and established the earthing and bonding strategy to mitigate the risks.

How Alternating Current Interacts with Direct Current in the Shatin to Central Link Traction Systems in Hong Kong – A Quantitative Approachby Sam Pang, Hong Kong, +852-2963-7777, pang.sam@pbworld.com

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Figure 1 - Alignment of the Shatin to Central Link

Lok Ma Chau

Tuen Mun

Tai Wai

Diamond Hill

Wu Kai Sha

East West Corridor

North South Corridor

Lo Wu

Hung Horn

Admiralty

West Rail Line

East Rail Line

Ma On Shan Line

Shatin to Central Link(Tai Wai to Hung Horn Section)

Shatin to Central Link(Hung Horn to Admiralty Section)

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ChallengesAt the time of carrying out the study, apart from a handful of papers on the subject of AC and DC railway interfaces and the European Standard EN50122-3:2010, there were very limited references on the subject of mutual in-teraction of AC and DC traction systems, in particular on its quantitative analysis. The Parsons Brinckerhoff proj-ect team approached the challenges from fundamental theories and developed quantitative analysis methods in order to establish the earthing and bonding strategy for the SCL to mitigate potential problems.

Problems of Mutual Interaction of AC and DC Traction SystemsThis section gives an overview of the potential issues associated with the mutual interaction of AC and DC traction systems. The AC traction system can affect the nearby DC traction system or vice versa by cou-pling, which is the physical process of transmission of energy. The effects of coupling can be galvanic and non-galvanic.

The galvanic couplings refer to conductive voltages and currents. These occur when the AC traction system is connected or bonded to the DC traction system, in par-ticular at the interchange stations. The major problem is that the DC currents in the DC traction system can flow into the AC traction system and return to the DC trac-tion system through galvanic couplings. The DC currents when flowing through the AC train-borne transformers and AC traction transformers may cause saturation of the core of these transformers. Related studies indicate that a small DC bias can have the following consequenc-es: complete saturation of the core with the generation of harmonics (distortion of signals); a very considerable reduction in the magnetising impedance of the trans-former; internal electrical resonance in the transformer winding; increased noise level; increased no-load cur-rent and losses. Moreover, when the DC current flowing into the AC traction system returns through the metallic parts of the station structure, stray current corrosion will occur.

The non-galvanic couplings are inductive and capacitive in nature. The effects of inductive coupling are induced voltages and currents. These voltages and currents de-pend on the distance, length, inducing current conductor arrangement, and frequency. The effects of capacitive coupling are induced voltages into a conductor. The in-duced voltages depend on the voltage of the influenced system, the distance, and the frequency.

Apart from the galvanic and non-galvanic couplings, the following operational issues associated with the design of power supply systems require particular attention in the dual electrified interchange stations:

• Electric shock caused by 25kV flashover to common sta-tion metallic infrastructure and extraneous metal parts;

• Voltages induced by the 25kV traction currents causing interferences to the signalling, communications, and low voltage circuits, or electric shock in the DC electri-fied railway;

• Earth faults in the high tension side of the 25kV AC trac-tion substation may lead to rise of earth potential and rail potential in the AC and DC traction systems; and

• Increased AC traction current causing increased mu-tual couplings, and increased DC traction current caus-ing higher stray current corrosion due to more frequent train service.

This article focuses on the quantitative approach taken to analyse the effects of DC stray current corrosion at the underground interchange stations and DC traction currents flowing into the AC traction system.

DC Stray Current Corrosion at the Interchange StationsFigure 2 illustrates the flow paths of the DC traction cur-rents and the voltage thus created at the station struc-ture of an interchange station where AC and DC traction systems coexists.

To review the degree of stray current corrosion at the interchange station, it can be reasonably assumed that adverse corrosion will occur at the point where the maxi-mum DC stray current passes through. That should be the point within the interchange station that interfaces with the DC return. At this point of maximum stray cur-rent, the voltage with respect to earth is calculated and benchmarked with the reference value of +0.2V as speci-fied in European Standard EN 50122-2:2010. Accord-ing to clause 5.3 of EN50122-2:2010, experience has shown that there is no cause for concern if the average value of potential shift between the structure and earth in the peak traffic hour does not exceed +200mV for steel in concrete structure.

To estimate the maximum voltage or the potential shift of the station structure and metallic parts in the inter-change station, a DC equivalent circuit as illustrated in Figure 3 was constructed for the typical rail section as shown in Figure 4 with the circuit parameters given by

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the client and the train modelled as a current source of 4,000A. For a conservative analysis, the train positions that would give rise to higher stray current at the inter-change stations were taken in the voltage calculations.

With the equivalent circuit, calculations were then per-formed to estimate the maximum potential shift at the sta-tion structure of the three interchange stations for several

different train positions and rail-to-earth resistance (RTE).

As as shown in Table 1, for DIH, ADM, and HOM, the re-sults of the estimated maximum potential shift of the sta-tion structure are all below the +200mV criterion listed in clause 5.3 of the European Standard, suggesting that there would not be an adverse effect of stray current cor-rosion at the interchange stations. However, for better DE

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DC OHL Network

AC/DCINTERCHANGESTATION

DC RAIL NETWORK

DC STRAY CURRENTRETURN PATHS

MAXIMUM VOLTAGE FOR STRAY CURRENT AT AC/DC INTERCHANGED STATION

STRAY CURRENT

DIODEEARTH

DC FEEDERSUBSTATION

STRAY CURRENT

CONNECT TO STATION STRUCTURE AND OTHER METALLIC PARTS

Figure 2 - Potential Created by Stray Current at the Interchange Station

Figure 3 - DC Equivalent Circuit for Calculation of Potential Shift at Station Structure

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protection of assets, good practice, and consistency of design, it was recommended to the client that mitigation measures be implemented and such measures are sum-marized in Table 1.

DC Traction Current Flowing into AC Traction SystemThe flow path of DC traction current through the AC -borne transformer and AC traction transformer is illustrated in Fig-ure 5. This represents an adverse condition in that the DC traction current reaches its maximum when one motoring train is leaving a station and another train under regenera-tion is approaching a station. When the overvoltage protec-tion device (OVPD) at the interchange station operates, the maximum DC traction current will flow from the motoring train through the DC return rail to the regeneration train, and concurrently will also flow through the OVPD and then through a series of paths to the regeneration train.

To estimate the magnitude of DC traction current flow-ing through the train-borne transformer and AC traction

transformer, the traction power systems and earthing networks of the related railway lines were modelled by a 3-layer network for current flow simulations with the circuit parameters given by the client. The motoring train and regeneration train were modelled as DC cur-rent injection and DC current source respectively in the network. To estimate the maximum DC current under different operating conditions of the railways, a total of 168 current flow simulation cases were established in consultation with the railway operator.

The results of the various modelling simulations showed that short-circuit or resistance-bonding of DIH can reduce the maximum DC current flowing through the AC train-borne transformer and AC traction transformer. Therefore, it was recommended that an isolation zone not be pro-vided at DIH. Besides, it was also recommended that the possible DC current flows in the AC train- borne transform-ers and AC traction transformers are monitored at the commissioning of each network extension or new line to confirm integrity of the railway systems.

ConclusionThis article addresses the impacts of coexistence of AC and DC traction systems at the underground inter-change stations of the Shatin to Central Link in Hong Kong and describes the approach taken to quantify the impacts. It was noted that at the time of conducting the study, there were very limited references on this subject, in particular on its quantitative analysis. Con-servative assumptions on the train positions and injec-tion currents were made in the analysis in consultation with the railway operator for a more realistic estimate of the worst case.

Results of the analysis indicated that DC stray current corrosion was less of a concern at the interchange sta-tions. However, for asset protection and good practice,

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Circuit ATrain positioned at middle of rail section

Circuit BTrain positioned at 250m from interchange station

0

-3.89E-15

0.05

0.1

0.15

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2.161.92 2.4

Distance (km)

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Figure 4 - Potential Shift vs. Train Positions with Rail-to-Earth Resistance Decayed to 15 ohm/km per track

Table 1 - Effects of DC Stray Current at the Interchange Stations and the Recommended Mitigation Measures

Interchange station

Estimated Maximum Potential Shift at Station Structure(all at R

TE1 = 15

ohm/km per track)

Recommended Mitigation Measures against

Stray Current Corrosion

Platform Screen Door (PSD)

Other Metallic Equipment

DIH 0.12 V (< 0.2V) Provide insulation or isolation between PSD and civil structure

Provide insulation or isolation for other metallic equipment from structure

ADM 0.1 V (< 0.2V)

HOM 9.4 mV (<< 0.2V) Although stray current corrosion will unlikely be a concern in HOM, for consistency of design it is recommended that the same earthing and bonding strategy as DIH and ADM be also adopted for HOM.

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it was recommended to the client that mitigation mea-sures be implemented. With regard to the DC current flowing through the AC train-borne transformer and AC traction transformer, results of the quantitative analysis indicated that this requires careful attention and moni-toring of the DC current flows in the AC traction equip-ment, as saturation of the transformer core by the DC current will bring adverse impacts to the transformers. Moving forward, in future application of the analysis

methods described in this article, consideration will be given to improving the model with statistical running of those parameters with key assumptions and modelling the earthing diodes in the DC traction system which were not taken into account in the analysis.

Sam Pang is a Professional Electrical Engineer with 30 years of ex-

perience in design and project management of infrastructure proj-

ects. He is based in the Hong Kong office of Parsons Brinckerhoff.

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NORMAL PATH FOR DC TRAIN CURRENT

AC/DCINTERCHANGESTATION

AC/DCINTERCHANGESTATION

REGENERATION

DC OHL NETWORK

DC RAIL NETWORK

STATIONEARTH

STATIONEARTH

AC FEEDER SUBTATION

DC FEEDER SUBTATION

OVPDOPERATED

DC EARTHING NETWORK(CABLE ARMOUR/FCRW)

STATIONEARTH

MOTORING

DC TRACTIONSYSTEM

AC TRACTIONSYSTEM

AC OHL NETWORK

AC RAIL NETWORK

AC EARTHING NETWORK(AEW/EARTH STRAP/

FIRE HYDRANT)

STATIONEARTH

DIODEEARTH

Figure 5 - DC Traction Currents Flowing Through AC Traction Equipment

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IntroductionThere are currently over 366 highway tunnels in the United States over 300-feet long. Most of these tunnels range in age from 50 to 100-years old.

All tunnels need periodic in-depth inspections of their structural integrity. However, many highway tunnels have electrical, lighting, communication, fire protection/sup-pression, and mechanical systems that require periodic inspection as well. This article presents some of the basic elements involved in preparing for, performing, and reporting on mechanical and electrical inspections of roadway tunnels in the United States.

The United States Federal Highway Administration (FHWA) is in the process of developing National Tunnel Inspection Standards that will become part of a federal law.

The Inspection ProcessThe FHWA “Highway and Rail Transit Tunnel Inspection Manual” forms the current basis for inspector qualifi-cations, tools, preparation, methods for access, safety, inspection procedures, and documentation of tunnel in-spections in the United States1.

Here is presented a broader, general overview of steps required to perform in-depth inspections of roadway tun-nel mechanical and electrical systems.

Preparation and PlanningProbably the most essential part of performing a safe and comprehensive inspection of any portion of a tunnel is proper preparation and planning. Preparation includes investigations of any revisions to applicable codes, de-sign standards, and inspection manuals. Preparation also involves reviewing the tunnel plans and specifica-tions, as well as past inspection reports.

Planning involves coordinating scheduling with own-er’s personnel, maintenance of traffic (MOT), testing

vendors, and the inspection staff. This is also the time to identify potential hazards associated with the inspection and to start developing the Inspection Safety Plan.

A vital step in the planning process is a site visit to acquire first-hand information of the tunnel layout and equipment access as it is not always possible to envi-sion all potential access and safety issues from the tun-nel design drawings.

As-Built DocumentsTunnel drawings and plans used for an inspection need to be complete, accurate, and up-to-date. Plans and drawings are often changed during construction and revisions made to effect repairs or improve the safety and reliability of the tunnel systems. The National Fire Protection Association’s (NFPA) Standard No. 25: “Stan-dards for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems” requires owners to retain as-built system installation drawings, hydraulic calculations, original acceptance test records, and de-vice manufacturer’s data sheets for the life of the sys-tem. This includes as-built documents for any system modifications made after the original installation.

As-built documents are key components for effective troubleshooting of system failures or planning for sys-tem upgrades or modifications.

Inspection and Testing ReportsPast inspection reports can provide insight to degrad-ing or failed systems, special access needs, or envi-ronmental conditions that can affect, or even prevent inspection work.

Part of the inspection of the mechanical and electrical sys-tems in roadway tunnels is verification of compliance with testing requirements required by the local authority having jurisdiction (AHJ). If the requirements indicate testing to

Tunnel Inspection Basics for Mechanical and Electrical Systemsby James Stevens, Tampa, FL, US, +1-813-520-4430, stevensja@pbworld.com; and Mark VanDeRee, Tampa, FL, US, +1-813-520-4433, vanderee@pbworld.com

1This document is available at http://www.fhwa.dot.gov/bridge/tunnel/inspectman00.cfm.

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be done per NFPA 25, the inspector has a responsibility to verify compliance with required standards. In cases where inspectors are not present for required periodic testing, reviewing the test report records is the only means to determine the owner’s compliance with appli-cable regulations.

Site and Area ScoutingSite scouting visits serve an important role – that of see-ing the current general condition of a tunnel. Structural damage, improperly supported or damaged equipment, and inoperable life safety systems can be reasons for an inspection to be postponed or canceled until repairs are made.

There may also be environmental issues that impede in-spection efforts. Dead animals, animal waste, excessive dirt or debris, and standing water are only a few issues that pose hazards to personnel and should be corrected before inspections are performed.

Staffing and Safety TrainingStaffing for an inspection of a tunnel mechanical and electrical system can sometimes be very challenging. In-spection staff needs to stay abreast of changing codes and standards in order to gauge how the installed sys-tems measure up to the present requirements.

Safety training is the most critical type of training an inspector receives. There are many hazards associated with mechanical and electrical inspections in tunnels, and knowing how to recognize, remove, reduce, or pro-tect against these hazard cannot be overemphasized. Each inspector must also review, understand, and sign the safety plan before beginning on-site inspection ac-tivities where they are exposed to hazards.

Tunnel inspections should be performed by teams com-prised of at least two people and large tunnels may re-quire several teams working simultaneously. Team lead-ers coordinate the teams’ efforts.

The inspections of tunnel mechanical and electrical sys-tems require specialized equipment and training. Special-ized vendors or subcontractors are usually employed for the special testing. Coordination and safety planning is needed for specialized testing vendors or subcontractors, equipment leasing, MOT, and the owner’s personnel.

Project Safety Plan and Maintenance of TrafficIn order to keep inspectors as safe as possible when performing roadway tunnel inspections, detailed safety plans are developed which list potential hazards and ways to control, remove, or reduce them. It is always preferable to have the entire tunnel roadway closed to traffic when inspecting inside the tunnel, as some mechanical and electrical components and systems cannot be fully inspected with a partial roadway closure.

To minimize the inconvenience of tunnel or lane closures to the traveling public, it is important to provide timely and accurate information of the upcoming closures in several forms of media. Detour plans should be developed and notifications should start early, and be widespread.

Mechanical Systems and ElementsMany tunnels are equipped with large and complex mechanical systems which include: ventilation fans and ducts, dewatering pumps and piping, fire protec-tion standpipes, water or foam deluge systems, carbon monoxide sensing and alarming systems, emergency or standby generators, and motorized gates and doors. Each of these systems requires periodic inspection and maintenance to keep them reliably operable. Fire DetectionSeveral of the longer and more heavily traveled roadway tunnels have fire detection systems which may include heat and smoke detectors, a monitoring station, and au-tomatically activated fire suppression systems.

Inspections of fire detection systems require special training and a thorough understanding of the systems’ equipment specifications and are usually performed by fire protection system specialists.

Fire SuppressionFire suppression systems in tunnels may include wa-ter or foam deluge systems, pumps, valves, stand-pipes, and hydrants. NFPA 25 is very specific about how often and in what manner these systems shall be inspected and tested and, while the inspections are fairly straightforward, testing requirements of NFPA 25 call for specialized training and equipment. Fire sup-pression system specialists are usually contracted to perform this testing.

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VentilationTunnel ventilation was originally designed to remove nox-ious vehicle fumes, however, it was discovered that a ventilation system, if properly designed, could also re-move smoke from an in-tunnel fire. The most common types of powered tunnel ventilation systems are longitu-dinal, transverse, and semi-transverse. The distinct dif-ferences of these systems require special access and experience in order to be evaluated properly. Ventilation systems inspections may include airflow rate measure-ments, fan and fan drive system conditional evaluations, duct inspections, and damper operational testing.

FansDifferent ventilation systems employ different types of fans. Longitudinal systems use high velocity, low volume jet fans mounted inside the tunnel (see Figure 1). Trans-verse and semi-transverse systems use high volume fans connected to ducts that distribute exhaust, and sometimes supply, air flows to strategic locations (see Figure 2). The equipment for transverse tunnel ventila-tions systems can be quite large. Fan operation may be initiated manually, or automati-cally if sensing systems are installed. Fans may be axial or centrifugal, direct drive, gearbox driven, or belt driven. Fans that are not directly coupled to the motors also have shafts and bearings. All these components need to be inspected. Often, special vibration analysis vendors are used to quantify potentially damaging vibrations from out-of-balance fans. Ventilation fans can produce wind velocities that exceed 90 miles per hour (MPH), and move volumes of air that exceed 350,000 cubic feet per minute (CFM).

Carbon Monoxide Sensing SystemsSome tunnels have sensing systems to detect high lev-els of carbon monoxide (CO). These sensing systems may provide alarms and initiate operation of the venti-lation systems. Inspections of CO monitoring systems require specialized training, equipment, and span gases and are normally performed by the owner’s maintenance staff or an outside vendor.

DampersDampers can alter the exhaust and supply of air rela-tive to zones in the tunnel, improving the effectiveness of removing smoke and providing a safe egress route. There are several different types of damper operating systems and inspectors need to be familiar with gears, chains and sprockets, hydraulics and pneumatics, and

linkages. Access inside the ducting is usually required to visually inspect the damper vanes.

Dewatering SystemsPumping systems are needed to remove the water that enters the tunnels, either from the entrances or at joints between tunnel segments. The pumps may be centrifu-gal, turbine, or submersible and usually have automatic

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Figure 1 - Tunnel Longitudinal Ventilation System Jet Fans

Figure 2 - Tunnel Transverse Ventilation System Supply Fan

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level sensors for turning the pumps on and off. Most de-watering systems have hydrocarbon-sensing equipment.

Inspections of these systems involve running pumps (pumping water if possible), gauging pump flow rates, and visually scrutinizing the condition of pumps, valves, piping, sumps, and water collection grates and gutters. Flamma-ble gases may also be used to test hydrocarbon sensors.

Electrical Systems and ElementsMost roadway tunnels require electrical power and of-ten have extensive electrical power and control systems going to every tunnel location. Electricity is needed to power lighting; operate fans, pumps, and valves; manip-ulate cameras; detect heat; control signs and signals; and power emergency phones and fire alarms.

Inspecting and testing tunnel electrical systems are im-portant to verify the systems are functioning properly.

Electrical Power ServiceThe electrical power service to a tunnel is the primary link for the electrical current that powers all the electri-cal components. Line service technicians from the elec-tric power company typically perform the inspection of the electrical service system. The tunnel owner’s electri-cal system usually begins on the load side of the meter-ing equipment. Since electricity is important to many of the life safety systems in tunnels, power is often also provided by emergency or standby generators and auto-matic transfer switches. In case of the loss of primary electrical power, tunnel electrical loads are automatically transferred to the emergency source.

Power DistributionElectrical power distribution for tunnel systems is gener-ally 3-phase medium voltage (5kV to 15kV) or low volt-age (208V to 480V). Damage from traffic incidents and environmental effects are common deficiencies noted. These systems are inspected to verify compliance with the requirements of NFPA-70 (National Electric Code) and include operation and testing of circuit breakers and safety disconnects. The condition of conductors, trans-formers, buses, and switches are also checked using insulation resistance testing. Circuit breaker trip testing is usually performed by specialized testing vendors.

Electric MotorsTunnel equipment with electric motors includes: fans, pumps, compressors, damper and valve actuators, and operating machinery for gates.

The inspection of electric motors involves performing visual assessments, measuring and graphing operating current draws, and testing the insulation resistances of the motor windings. All testing measurements are tabulated or graphed, and all pertinent photographs are logged and captioned.

LightingTunnel lighting is inspected by taking different types of light measurements in specific locations of the tunnel and its portal entrances, thresholds, transition zones, and exits. The light measurements are recorded and compared with those recommended by ANSI/IES RP-22, a standard for tunnel lighting – developed by the Ameri-can National Standards Institute and the Illuminating En-gineering Society – that minimizes the visibility problems associated with roadway tunnels.

Emergency lighting mandated by NFPA 502 requires in-spection for proper operation and serviceable condition.Facility spaces and maintenance access routes should have adequate lighting to permit inspection and servic-ing of the tunnel systems. These areas should also have emergency egress lighting.

Control SystemsControl systems for tunnels are primarily used to moni-tor tunnel conditions and manipulate equipment in a way to keep people and vehicles safe. Tunnel controls can be monitored and operated from a local control room, or a remote location many miles away. In some cases, controls are located both locally and remotely.

Systems that may be monitored or controlled include: fire detection, heat and smoke detectors, carbon mon-oxide monitoring systems, cameras, traffic loop detec-tors, ventilation, lighting, pump systems, public ad-dress systems, and access/flood gate positions. In most cases, operations of all equipment can be per-formed from the control room. Many systems allow for local control at the equipment.

Inspection of tunnel control systems includes evalu-ating the installed systems for adequacy based on applicable codes, and testing every function the sys-tems are designed to perform. Evaluations are made based on: the accuracy of sensing systems, verifi-cation that interlocks and permissives are fail-safe, proper response of systems to automated and manu-al commands, and the physical condition of all control system elements.

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Experienced tunnel inspectors should be capable of in-specting and evaluating a tunnel control system, only requiring assistance from the owner’s control systems operations personnel.

ConclusionSome basics for inspecting tunnel mechanical and electrical systems are presented. The main purpose of inspecting tunnels is to note deficiencies and com-municate findings to the owner. The owner can then use this information to budget and schedule needed repairs or modifications to correct the deficiencies.

Figure 3 presents a sample of some electrical and mechanical findings and recommendations from tun-nel inspections.

James Stevens is a Mechanical and Electrical Engineer who has

worked at Parsons Brinckerhoff for 12 years on movable bridge

and tunnel system designs and inspections.

Mark VanDeRee is the Senior Supervising Engineer for the

Mechanical and Electrical Technical Excellence Center in the

Tampa office and he has led the mechanical and electrical work

on several movable bridge and tunnel designs and inspections.

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Figure 3 - Sample findings and recommendations for a tunnel inspection

Findings Recommendations

The Simplex control system did not keep each foam pump running to the low level sensor on the tank, nor did the system start the lag pump if the lead pump failed to start.

Troubleshoot and correct the problems with the Simplex control system program not properly controlling the foam pumps.

The arc fl ash hazard warning labels on the low voltage distribution systems were non-compliant with the requirements of the NEC, NFPA-79, and NFPA-70E: Standard for Electrical Safety in the Workplace.

It is recommended that arc fl ash warning labels be installed on the electrical enclosures to comply with NEC Article 110.16.

The trip mechanism of the US2B-TF2B medium voltage feeder breaker was diffi cult to operate. The mechanism was lubricated and exercised during the inspection, but the condition could not be corrected.

It is recommended that the trip mechanism be investigated and corrected, or the breaker replaced.

Five of the ventilation fan motors were found to have elevated bearing vibrations, and one ventilation fan motor was found with a slightly elevated bearing temperature. The motors with elevated bearing vibrations were SF-23 (drive end bearing), SF-27 (both bearings), SF-28 (both bearings), SF-29 (both bearings), and SF-30 (both bearings).

It is recommended that elevated bearing vibrations and temperatures be monitored to determine if the conditions are worsening.

MSD-118 Balancing Damper Starter Panel: the panel heater has burned wires.

It is recommended that the wiring to the MSD-118 Balancing Damper Starter Panel heater be replaced with high temperature insulated wires and away from the heater.

Balancing damper D-120 did not actuate the fully open position limit switch when it was fully open.

Adjust the fully open limit switch for balancing damper D-120 so the damper position indicates correctly in the control room.

The radio signal override system was noted as not being functional.

Repair the failed radio signal over-ride system that alerts vehicles inside the tunnel of emergencies through broadcasts on AM and FM stations.

The tunnel ceiling mounted axial type jet fan motor inspection cover had two broken fasteners.

The owner dispatched an on-call repair crew to repair the broken fasteners for the motor inspection cover on the tunnel ceiling mounted axial jet fan.

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Tunnel Sump Construction Savings Through Drainage System Design Modificationby Kevin Stewart, Brisbane, Australia, +61 7 3854 6339, stewartk@pbworld.com

IntroductionThe Waterview Connection is the largest road project ever undertaken in New Zealand. At a cost of NZ$1.4 billion (approximately US$1.2 billion), it involves building a 4.8 ki-lometre (3.0 miles) long six-lane motorway to link two high-ways and complete Auckland’s Western Ring Route. The highway includes a 2.5 kilometre (1.6 miles) long twin-tube tunnel, with three-lanes in each tunnel, bored by a 14.4 metre (47.2 feet) diameter tunnel boring machine (TBM). The twin-tube design includes cross-passages which con-nect the tubes, house mechanical and electrical (M&E) systems, and provide escape paths in emergencies.

Parsons Brinckerhoff is a member of the Well-Connect-ed Alliance, which is both delivering the project, and operating and maintaining the facility for 10 years after opening. This project structure gave all parties an inter-est in cost-effective design for both construction and maintenance.

The tunnel's vertical alignment has a low-point, requir-ing a sump and mechanical drainage system to remove

water. Sources of water include groundwater seepage through the tunnel lining, runoff from the road surface, vehicle spills, and the tunnel deluge sprinkler system. Road surface runoff and seepage above road level is gravity piped to the sump. Seepage below road level, however, is directed to the tunnel invert (Figure 1), where it collects at the low-point. The tunnel invert also includes a service tunnel to reticulate electrical power cables. A means was therefore required to remove seepage water from the tunnel invert and deliver it to the low-point sump for pumping to the surface. Tendered concept designThe tendered concept design used gravity drainage to convey water to the sump. Pavement runoff would be directed to a pipe in the services tunnel, and at the low-point a DN500 (20-inch) pipe would penetrate the tunnel lining and pass through a horizontal bore to the sump. The small amount of seepage water would flow down the tunnel invert to the low-point where it would be directed through a smaller parallel pipe to the sump (Figures 2 and 3).

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Figure 1 - Tunnel Cross Section

TUNNEL INVERT

SERVICES TUNNEL

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The sump was designed as a 5.7 metre (18.7 feet) di-ameter vertical shaft located under the floor of the cross-passage at the low-point. To avoid backflow through the invert drainage pipes into the service tunnel, the sump high water level was set below the level of the tunnel invert. This high water level, combined with the required sump storage, resulted in a sump shaft design depth of approximately 12 metres (39.4 feet) under the cross-passage floor.

Proposed redesignReasons for redesignThe concept design provided several construction challenges:

• Time and cost in constructing a deep shaft;• Technical difficulty in penetrating the tunnel lining for

the large drainage pipe; and

• Difficulty in boring pipe connections from the tunnel invert to the sump.

Details of proposed redesign and benefitsA revised scheme was proposed based on enlarging the cross-passage and using the volume under the passage floor for water collection. This proposal required signifi-cantly less excavation with corresponding reductions in construction time and cost. The pavement runoff drain could be raised to pass through the cross-passage open-ing, removing the need to penetrate the tunnel lining and bore horizontally.

Functional challengesThe revised sump shape reduced the active storage vol-ume, which in turn influenced the run time of the dewa-tering pumps: a small volume would result in frequent starting and stopping of the pump. DE

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Figure 2 - Sump Concept (Elevation)

Figure 3 - Sump Concept (Plan)

(FLOOR DRAIN PIPE TOTERMINATE 200 BELOW

MINIMUM WATER LEVEL)

DRAIN FROMRISING MAIN

(DRAIN FROM RISING MAIN)

MINIMUM WATER LEVEL

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PAVEMENT RUN-OFF DRAINCONNECTION TO LOW POINT SUMP

MINIMUM SLOPE 1:100

PAVEMENTCONNECTIONMINIMUM SL

PAYMENT RUN-OFF DRAINCONNECTION TO LOW POINT SUMP

PLAN VIEW – SERVICES TUNNEL DRAIN

LOW POINT SUMP

DN100 SOUTHBOUNDTUNNEL INVERTCULVERT FLOOR DRAIN

D450 PAVEMENTDRAIN

D250 PAVEMENTDRAIN

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The new sump shape also raised the top water level well above the tunnel invert, meaning the invert drain could no longer connect directly to the sump. Some form of pumping was therefore needed for the seepage flows in the invert. The revised proposal therefore included a small pump in the services tunnel, operated by float switches, to automatically pump collected water to the main sump.

Operation and maintenance considerationsThe service tunnel is a 2.5 kilometre (1.6 mile) “tun-nel within a tunnel”, running below the road surface with entry points only at the ends. As a result, access to the service tunnel requires procedures similar to a confined space, including a dedicated ventilation system, a mini-mum of two people, and radio contact with the surface at all times.

Due to these restrictions, the operations and mainte-nance (O&M) strategy was to minimise equipment that required servicing in the service tunnel. This challenged the proposed sump redesign, as any pumping equipment in the service tunnel would conflict with the O&M strategy.

Final designTunnel invert drainageA solution was developed to meet the functional require-ments for removing water from the service tunnel drain-age while satisfying the O&M strategy of limiting equip-ment in the services tunnel.

From an O&M perspective, the best place to position the pumps was in the cross-passage M&E equipment area. This meant the pumps would be installed about 4.6 metres (15.1 feet) above the tunnel invert and re-quire a positive displacement pump to lift the water. To further satisfy the O&M strategy of limiting equipment in the services tunnel, inclusion of a foot valve to keep the pump primed was avoided, and instead a self-priming pump was used. The solution was to use a progressive cavity pump, which is able to self-prime and can tolerate short periods of running dry if the suction line drains and priming is lost. The inlets and outlets can be arranged so that even if

the suction line loses prime, a nominal amount of water is left in the pump stator to provide initial lubrication to the rotor on start-up.

A drainage pump would normally rely on float switches for control, starting the pump when sufficient water had collected and stopping it again once the water is pumped away. To minimise equipment in the service tun-nel, we required an alternative to float switches. As the groundwater seepage into the service tunnel will be at a near-constant rate, water will collect at the low-point in a predictable fashion. This will allow the pump con-trol to be based on a combination of a timer and flow sensor. The plant management and control system will activate the pump on a predetermined schedule, allow-ing seepage water to collect to a sufficient volume, and will cut the pump once the sensor indicates flow has stopped. The flow sensors also act as a safety check, deactivating the pumps if no flow is detected on start-up. Redundant pumps and suction lines are also provided in a duty-standby arrangement, maintaining dewatering while a pump is being serviced or if a suction line be-comes blocked.

The tunnels' construction program allows monitoring of the seepage rate, with the timer setting to be determined during project commissioning. The plant monitoring sys-tem can be used to review pump run times over a period and determine if the groundwater seepage rate is chang-ing and the timer requires adjustment. The new mechanical drainage design met all the func-tional requirements and the redesigned sump struc-ture enabled a reduction in construction time and cost compared to the initial concept. The O&M strategy to minimise difficult maintenance was preserved by finding alternatives to standard drainage system designs and taking advantage of specialist pumping equipment.

Kevin Stewart is a Mechanical Engineer who specialises in

hydraulics and mechanical services, and he has experience in

the design, construction, and commissioning of tunnel fire sup-

pression and dewatering systems and has worked on projects in

Australia and New Zealand, including Brisbane’s Clem7 tunnel,

Auckland’s Waterview Connection, and Victoria Park Tunnel.

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The Modernization of Tunnel Lighting and Controls: Technology, Challenges, and Cost of Implementing a Tunnel LED Lighting Systemby Christopher J. Leone, Boston, MA, US, +1-617-960-4944, LeoneC@pbworld.com ;

Jonathan T. Weaver, Boston, MA, US, +1-617-960-4880, WeaverJT@pbworld.com; and

Kimberly Molloy, Boston, MA, US, +1-617-960-5520, MolloyKM@pbworld.com

Tunnel lighting systems provide proper visibility for the safe passage of motorists entering and navigating a tun-nel. As a result, the components of the system have to be reliable, durable, corrosion resistant, and able to be maintained during traffic flow. When entering a tunnel during the daytime, the human eye has to adapt very quickly to lower light levels. To accommodate this, tun-nel lighting is designed to be significantly brighter at the entry of the tunnel and gradually decreases in intensity inside the tunnel.

Until recently, lighting equipment was limited to fully en-closed luminaires utilizing fluorescent, metal halide, and high pressure sodium lamps. These sources are bright, have a long life, and are robust enough to withstand the harsh environment of a tunnel. Light emitting diode (LED) technology provides an alternative that has significantly improved in longevity and adaptability. Traditional high in-tensity discharge (HID) systems utilizing high pressure sodium or metal halide lamps require the least number of luminaires as the light output available from each lu-minaire is high. Fluorescent systems require more lumi-naires, and are often supplemented with the higher watt-age HID sources. LED fixtures have a steadily increased light output and control and are now comparable in inten-sity to the HID. Tunnel luminaires are expensive, and LED luminaires have the highest initial cost.

When developing a tunnel lighting strategy, a life cycle approach needs to be used and consideration given to initial cost, maintenance costs, and operating costs over the life of the system. Initial costs include the number of luminaires required to achieve a specific light level, the controlling equipment, the supporting structural and electrical infrastructure, and the installation costs asso-

ciated with each. Maintenance costs include removing and replacing burned out and damaged equipment, and the periodic cleaning of the lighting system. Operating cost is the cost of the energy consumed by the light-ing system. By comparing these factors, the choices, trade-offs, and challenges of a tunnel lighting system become readily apparent. The method of identifying the cost of the light produced, dollars per thousand lumens ($/klm), is a more inclusive metric than the individual cost of the luminaires.

Controlling a tunnel lighting system is necessary to en-sure that the amount of artificial illumination is in tune with the outside daylight conditions. If it is sunny or cloudy throughout the day, or from dawn to dusk, the lighting control system will switch luminaires off and on as needed or dim the supplemental lighting in the thresh-old and transition zones of the tunnel. Both switching and dimming control systems utilize either an intelligent photocell or a special camera that records luminance levels outside of each portal. Another reason for lighting control is simply for energy savings.

LED Lighting Systems - Benefits and ChallengesLED lighting systems offer unique challenges that the lighting designer needs to consider when recommending and finally specifying for a client. With the advent of the LED as one of today’s most rapidly-developing lighting technologies, many startup lighting manufacturers have been formed, some producing subpar products using in-expensive LED packages.

The way the industry has tested and measured the elec-trical, photometric, and life of luminaires has changed to

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adapt to LEDs. As a solid state source, the very defini-tion of lamp life has been modified to correctly model sources that may well run for 11 years. Also a challenge is the rapidly evolving LED chips that make it increasingly difficult for manufacturers to test their fixtures life ex-pectancy. The Illuminating Engineering Society of North America (IESNA) has developed several technical manu-als for LED luminaire manufacturers to follow which in-clude a procedure for the manufacturers to interpolate an expected life of their products.

Traditionally the evaluation of lighting products is based on a separate test for the lamps and luminaires, but with LED luminaires the test has to be completed on the whole package because the LEDs rely on the luminaire for heat dissipation which affects the lumen output and life. The lu-men maintenance of a LED luminaire must also be tested; this is the method for measuring the lumen depreciation from the LED’s original light output. LEDs do not typically burnout; a degradation of their light output occurs continu-ously to a point where they are beyond their useful light output. Methods have been developed by the IESNA to measure the lumen maintenance and to estimate the life of the project based on the measured results.

Parsons Brinckerhoff Project Experience Recently Parsons Brinckerhoff has had the opportunity to develop tunnel lighting systems for Colorado Depart-ment of Transportation (CDOT) and Virginia Department of Transportation (VDOT)/Elizabeth River Crossing (ERC).

I-70 Twin Tunnels - Idaho Springs, CO Parsons Brinckerhoff was responsible for the design of the lighting system for the I-70 Twin Tunnels in 2012. The focus of the project was the widening of the westbound and eastbound bores of the tunnel on I-70, east of Idaho Springs. This is the first tunnel project by Colorado Depart-ment of Transportation (CDOT) and Parsons Brinckerhoff that fully utilized light emitting diode (LED) technology for both the day and night time tunnel illumination. The origi-nal design concept for the tunnels was a traditional high pressure sodium (HPS) light source, however CDOT offi-cials inquired about the benefits associated with using the emerging LED lighting technology. A cost comparison was performed on the eastbound tunnel only. The conclusion was that although purchasing and installing LED tunnel lighting over HPS would result in an additional $1 million ($97/klm), that would be offset by a payback of approxi-mately 10 years of maintenance and energy savings.

While lighting manufacturers have been developing and perfecting LED luminaires across all interior and exterior applications for the last 8 to 10 years, tunnel lighting had been slow in development. Mostly due to the market not supporting the need, it came down to tunnel owners and operators recognizing the long-term benefits of LEDs in their tunnels even with the upfront added expense; know-ing that this newer lighting technology offers more flex-ibility and control as well as energy savings and reduced maintenance. Parsons Brinckerhoff had to work closely with the lighting manufacturer to be sure the same qual-ity and testing requirements were enforced as specified with a more traditional tunnel lighting fixture.

The biggest challenge when using LED lighting in a tun-nel is the ability of the fixture to dissipate the heat that is generated by the LED light engines as well as from their driver(s). An LED light engine is a combination of one or more LED modules together with the associated electronic control gear, also known as an LED driver. LED light engines must have a way to dissipate all the back heat they produce as the exponent of creating light as heat affects the light output of the system. The best way to accomplish this is similar to how a computer takes heat away from the central processing unit - a heat sink is applied to the back of the diodes and this moves the heat out and away from the LED. All manufacturers apply the same principle in different ways and each must be carefully reviewed for each tunnel application.

Fixture placement within the tunnel can also affect heat dissipation. Placing a LED lighting fixture in an open rack for the Twin Tunnels design provided optimal airflow around the fixture so that heat dissipated appropriately around and away from the fixture. However, an open, suspended rack may not always be a possible solution in other tunnel projects, especially when retrofitting. So special consideration and close working relationships with manufacturers must be in place when specifying LED fixtures to make sure the fixture is not being in-stalled in a way that would shorten the life expectancy of the LEDs or void manufacturer warranties.

The overall construction of the luminaire must also be scrutinized, including the housing, gasketing, ingress protection, dissimilar materials (galvanic reactions be-tween dissimilar metals can cause corrosion of materi-als in a tunnel environment), and of course the quality of the light.

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Midtown and Downtown Tunnels – Norfolk and Portsmouth, VA In December 2011, the Virginia Department of Transpor-tation (VDOT) entered into a $2.1 billion comprehensive agreement with the developer, Elizabeth River Crossing (ERC), to build a new Midtown Tunnel, rehabilitate the existing Midtown Tunnel and two Downtown Tunnels, and extend the Martin Luther King (MLK) Freeway. Under this agreement, VDOT will maintain ownership of the facili-ties and will oversee ERC’s activities. ERC will finance, build, operate, and maintain the facilities for a 58-year concession period and assume the risk of delivering the project on a performance-based, fixed-price, fixed-date contract. The project, scheduled for completion in late 2017, is the largest design-build project in the history of Hampton Roads, and Virginia’s first full-scale all-elec-tronic toll collection system.

Parsons Brinckerhoff is serving as lead designer to the design-build team responsible for doubling the capacity of the Midtown Tunnel by building an additional two-lane tunnel near the existing one under the Elizabeth River; rehabilitating the existing Midtown Tunnel and both of the Downtown Tunnels to provide enhanced fire and life safety features to the tunnels; extending the MLK Freeway from London Boulevard to I-264, with an inter-change at High Street; and modifying the interchange at Brambleton Avenue/Hampton Boulevard in Norfolk.

The 3,760 linear foot (1,146 meter) immersed tube tun-nel will include two 12-foot (3.6-meter) travel lanes, two 2-foot (0.6-meter) shoulders, an escape corridor, high walkway, and utility corridor.

During the initial development phase, the cost of the lighting for the new Midtown Tunnel was based on a combination of high pressure sodium (HPS) point source lighting and linear fluorescent luminaires. As the design process evolved, lighting manufacturers

were developing LED luminaires that could finally with-stand the environment of a vehicular tunnel. Parsons Brinckerhoff carried out a cost and performance com-parison of the HPS and LED luminaires. The conclusion was that the LED system would have a substantially lower life cycle cost.

ConclusionLED luminaires are suitable for the tunnel environment and will be more widely used in the future. There is a de-mand for LED as a lighting solution from tunnel owners and operators as a way of reducing operating and main-tenance costs for a project, while embracing a leading edge technology. This demand will put pressure on the engineer to fully understand the challenges of LEDs while pushing manufacturers to produce durable, reliable, and consistent products. A rigorous testing procedure should be an integral part of the tunnel luminaire specification. In addition, a warranty that covers the luminaires needs to be in place for a significant portion of the anticipated life of the light engine in the luminaire, considered by Parsons Brinckerhoff to be 10 years.

Christopher Leone is a Lighting Engineer in the Boston office of

Parsons Brinckerhoff with 14 years of experience in tunnel and

roadway lighting. He is a current member of the IES Roadway

Lighting Committee.1

Jonathan Weaver, an Architect and Lighting Engineer, works as

an internal consultant for Parsons Brinckerhoff teams across the

country. He is a current member of the IES Roadway Lighting

Committee, and contributing author to IES RP-22-2011 Recom-

mended Practice for Tunnel Roadway Lighting.

Kim Molloy is an Electrical and Lighting Engineer in the Boston

office of Parsons Brinckerhoff with more than 15 years of ex-

perience in tunnel lighting. She is the current secretary of the

Tunnels and Underpasses Subcommittee of the IES Roadway

Lighting Committee.

1For a previous Network article on lighting by Chris Leone, see “Lighting a 3D World: Design and Analysis,” Network #70, November 2009, pp 64-65,69.

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Evaluating Freeze Protection Needs with CFDby Raylene C. Moreno, Sacramento, CA, US, +1-916-567-2525, morenorc@pbworld.com

Introduction Freeze protection of wet pipe fire protection systems can be a costly requirement for tunnel systems. It is needed for water-filled piping systems which are installed in environ-ments subject to freezing conditions. Typical installations consist of electrical heat tape attached to the pipe and fit-tings underneath a layer of pipe insulation. The heat tape and insulation must span the entire length of piping that will be subject to freezing. In many situations, it is difficult to determine whether freezing conditions will occur within proposed structures, particularly tunnel systems. Parsons Brinckerhoff provided engineering design services for a new tunnel. By developing a computational fluid dynamics (CFD) model to simulate heat flow within the new tunnel, Parsons Brinckerhoff was able to determine that freeze protection would not be required on the fire suppression mains in the tunnel utility corridor. This resulted in first-cost savings, as well as elimination of all future operation and maintenance costs, for the client.

Analysis Approximately 1158 meters (3800 feet) of the tunnel consisted of segments immersed and buried below a river with the elevation varying by as much as 18 meters (60 feet). The two 6-inch piping systems of concern, a

fire protection standpipe and a sprinkler main, were to be located within a utility corridor which connected to tunnel support buildings at the ends of the tunnel near each portal. A typical tunnel section is shown in Figure 1. A thermal analysis was performed using a CFD tool to evaluate tem-perature distribution within the tunnel spaces. Rather than model the entire 3800 feet of tun-nel, a small segment of the tunnel length was modeled near the tunnel portal where incoming air would be coldest. Figure 2 provides a partial sec-tion view of the modeled tunnel segment. The thickness of this mod-eled segment was 1.2 meters (3.92 feet) along the x-axis (not shown). The cor-ridor is located on the left and the roadway is on the right. Note—dimensions indicated are in meters.

To assess freezing potential, transient calculations were carried out for unusu-ally cold weather conditions until a steady-state solution was reached. Initial tem-perature boundary conditions for backfill at the side and the bottom of the tunnel were set to 12.8°C (55°F) while all other regions began at 6°C (43°F). These temperatures were deemed appropriately conservative and justification for this is provided in the ‘Discussion’ section below. Air at -10°C (14°F) and 5 meters per second (11 miles per hour) flowed through the roadway area in the direction of traffic. The air temperature

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Figure 1 – Typical tunnel cross section

Figure 2 – Cross Section of Model Geometry and Dimensions (shown in meters)

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is based on the two and three-day averages for a period with the lowest recorded temperature for this region (see Table 1). The lowest air temperatures for this region gener-ally occur in January with a monthly average ranging from 1.7 - 8.3°C (35 - 47°F). The top surface of the backfill, the water interface, was set to a constant temperature of 0°C (32°F) while outer backfill boundaries were set to 12.8°C (55°F). An adiabatic, or thermally insulated, boundary con-dition was applied to the outer boundaries of the model, with the exception of the roadway area where domain boundaries remained open.

The following simplifying assumptions were applied to the analysis:

• Highest heat transfer rates would occur near tunnel por-tals where incoming air is coldest.

• Material properties were assumed constant with tem-perature and direction.

• Effective properties of backfill material assumed a fully saturated state with 30 percent water.

• Tunnel walls, ceiling, and floor were assumed to be the same concrete material.

• Tunnel section geometry and dimension were slightly modified to minimize computational processing time.

This was assumed to have negligible effect on overall heat transfer as modeled heat transfer surface areas were nearly equal to actual section geometries.

• Thermal energy input from conduit co-located within the corridor was neglected.

Material properties for concrete and soil are provided in Table 2. The simulation was carried out to final time of 13.9 days. A steady-state condition was assumed when the temperature at a fixed location varied by less than one-tenth of a degree (°C) per hour. Figure 3 indicates locations where temperatures were measured.

DiscussionGenerally, boundary temperatures assumed in the analysis were conservative. For example, available wa-ter temperature measurements for 2011, a year which experienced average air temperatures in the lower range, indicate a minimum hourly water temperature of 2.8°C (37.1°F) and a monthly water temperature av-erage of 4.4°C (40°F) for the month of January. While the depth at which these measurements were taken is unknown, it can be certain that the temperature of 0°C (32°F) at the top of the fill surface was lower than would be expected.

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DateDaily Minimum,

°C (°F)Daily Average,

°C (°F)2-Day Average,

°C (°F)3-Day Average,

°C (°F) 7-Day Average,

°C (°F)

18-Jan 1.11 (34) 2.63 (36.73) 3.97 (39.14) 0.80 (33.44) -2.64 (27.25)

19-Jan 2.22 (36) 5.31 (41.55) -0.11 (31.80) -4.97 (23.05) -

20-Jan -15.61 (3.9) -5.52 (22.06) -10.11 (13.80) -8.77 (16.21) -

21-Jan -19.39 (-2.9) -14.70 (5.55) -10.40 (13.28) -7.65 (18.23) -

22-Jan -10.61 (12.9) -6.10 (21.02) -4.12 (24.58) -2.06 (28.29) -

23-Jan -8.89 (16) -2.14 (28.14) -0.04 (31.92) - -

24-Jan -3.89 (25) 2.06 (35.70) - - -Source: Weather Underground, http://www.wunderground.com

Table 1 – Summary of Historical Temperature Data for the Region of Analysis

Figure 3 – Locations of Temperature MeasurementTable 2 – Material Properties

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0°C(32°F)

B5

B5A

B5B

B6

T3T2

12.8°C(55°F)

12.8

°C(5

5°F

)

-10°

C(1

4°F

)

Z

Y

Soil

Thermal conductivity, k 0.6 W/mK

Density, р 1700 kg/m3

Specifi c heat, Cp 2.5 kJ/kgK

Concrete

Thermal conductivity, k 1.4 W/mK

Density, р 2100 kg/m3

Specifi c heat, Cp 0.88 kJ/kgK

Source: The SFPE Handbook of Fire Protection Engineering, Fourth Edition, National Fire Protection Association, June 1995; andIncropera F., Dewitt, D., Bergman, T., Lavine, A., Fundamentals of Heat and Mass Transfer. Wiley. 6th Ed. 2007

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Similarly, the initial ambient temperature of 6°C (43°F) within the tunnel is lower than would be expected. While extensive ground and groundwater measure-ments for this area are not readily available, studies by Kusuda et al. report groundwater temperatures at 9 to 18 meters (30 to 60 feet) below surface to be approxi-mately equivalent to the average annual air tempera-ture for the region. In this depth range, a groundwater temperature of 13.9 - 16.7°C (57 - 62°F) is expected. Temperature profiles for depths less than 9 meters (30 feet) will generally experience cyclic fluctuations with the largest change occurring at the surface for annual timescales.

Figure 4 shows the evolution of inner wall temperatures for the corridor. All walls began at 6°C (43°F) and slowly approached a steady-state condition with the wall sepa-rating the corridor from the roadway tunnel being the coolest (T4). As expected, the cooling due to the air flow at -10°C (14°F) has a significant thermal influence on the corridor. Figure 5 shows three air temperatures measured within the corridor for the same case. Similar to the walls, the air temperatures began at the ambient temperature and decreased over the period of the simu-lation. This indicates that under steady conditions for the boundary conditions assumed, the air temperature within the corridor is about 0°C (32°F). Note that the one-week and one-month average air temperature for this historic low temperature event were -2.6°C (27.3°F) and 1.7°C (35°F), respectively.

To further investigate the influence of ambient air tempera-tures on temperature within the corridor, a simulation was run with the influent air flow temperature of -19.4°C (-3°F). This temperature corresponds to the lowest recorded tem-perature since 1946 and is considered to be quite conser-vative. Figures 6 and 7 show the resulting interior corridor walls and air temperatures, respectively. Similar to the case with a -10°C (14°F) air flow, both the corridor walls and the air began at ambient temperature and decreased over time. For this case, the corridor air temperature reach-es 0°C (32°F) after 2.3 days. Note that the one-day and two-day average temperatures for this historic low were -14.7°C (5.6°F) and -10.4°C (13.3°F), respectively.

For both cases considered, the corridor air tempera-ture reaches freezing conditions after some length of time. However, the length of time required for the air temperature to reach 0°C (32°F) was longer than the expected duration of the low temperatures assumed in this calculation.

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Figure 4 – Evolution of inner wall temperatures for the corridor

Figure 5 – Three air temperatures measured within the corridor12

0,00

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Figure 6 – Interior corridor wall temperature

Figure 7 – Corridor air temperature

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ConclusionThe analysis concluded that the buried tunnel structure provided significant thermal mass such that the effects of surface level temperature fluctuations were minimized within the tunnel utility corridor. Significant cost savings were realized for the client as it was conservatively de-termined that a provision for freeze protection of the wet pipe fire protection systems within the tunnel utility cor-ridor would not be necessary. CFD software continues to be a valuable analysis tool for various applications within mechanical engineering design for tunnel systems. Future work will continue to utilize this tool for tunnel systems.

References • Calvache, M.L., Duque, C., Gomez Fontalva, J.M., Cre-

spo, F., Processes Affecting Groundwater Temperature Patterns in a Coastal Aquifer. International Journal of En-vironmental Science and Technology. 8, 223-236, 2011

• Incropera F., Dewitt, D., Bergman, T., Lavine, A., Funda-mentals of Heat and Mass Transfer. Wiley. 6th Ed. 2007

• Kusuda, T., Earth Temperature and Thermal Diffusivity at Selected Stations in the United States. U.S. Depart-ment of the Army. 1965

• Lapham, W.W., Use of Temperature Profiles Beneath Streams to Determine Rates of Vertical Ground-Water Flow and Vertical Hydraulic Conductivity, United States Geological Survey Water-Supply Paper 2337, 1989

• The SFPE Handbook of Fire Protection Engineering, Fourth Edition, National Fire Protection Association, June 1995

Raylene Moreno is a Registered Professional Mechanical Engi-

neer with experience in plumbing, fire protection, and heat trans-

fer. She provides engineering design, analysis, and construction

support services on various rail and tunnel projects.

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Computational Modeling as an Alternative to Full-Scale Testing for Tunnel Fixed Fire Fighting Systemsby Kenneth J. Harris, Sacramento, CA, US, +1- 916-567-2503, harris@pbworld.com

IntroductionRequirements for implementation of fixed fire fighting sys-tems (FFFS) in road tunnels often include a full-scale test or series of tests to be performed.

Tunnel FFFS have been a relatively recent development, particularly in Europe. Therefore full-scale testing became the reasonable requirement to understanding the perfor-mance of fixed fire fighting systems in the very different conditions of their application from buildings to road tun-nels. Recent road tunnel fire events have shown tunnel FFFS to provide a significant benefit in reducing fire dam-age and many new tunnels are being required to have them on this basis alone. However the requirement for full-scale testing still exists, particularly in Europe and sometimes in the US, and this expense may be creating an unnecessary obstacle to their effective implementation.

Computer modeling is an alternative to full-scale testing. Its use has been well-accepted in fluid mechanics and heat transfer, but combustion and the interaction of wa-ter introduces a complexity in energy exchanges that has made the acceptance of computer modeling for this use problematic. A series of fire tests were carried out by the Land Transport Authority (LTA) of Singapore that provides a means to calibrate a computer model that can be used for design purposes. Physics of Water/Fire InteractionFire point theory relates the effectiveness of the suppres-sion agent, water, to fundamental fire properties. This mod-el is based on the interaction between the heat required to vaporize a solid or liquid fuel and the effect that water has on the prevention of this vaporization. This interaction is illustrated in Figure 1. It is important to note that a solid or liquid fuel itself will not burn. A fuel will burn only after it is converted to a gaseous state by vaporization, which requires energy, often expressed in terms of heat flux.

Computational modeling can be used to compare the ef-fectiveness of water application rates for solid-fuel types of fires, provided an accurate representation is made of the items affecting heat flux (convection, radiation, sur-face cooling, water evaporation, etc.). Fuel can be de-fined in terms of a heat of combustion, reactions, prod-ucts, and reaction rates. Selected material properties can be determined from literature or testing. The primary objective is to generate sufficient power from the fire to simulate the design scenario. For most tests, wood and plastic have been used as common sample fuels.

Computer CalibrationFire TestsIn March 2012, LTA of Singapore conducted a series of tests in the A86 Tunnel in Spain. These tests were per-formed with various standard drop nozzle configurations and water application rates. Three in particular were of interest for calibration purposes described in Table 1.

H20

Fuel (∆HT)

Flame

∆HW

∆Hg

m”w, ex

m”

q”

Legendq” - heat source or net fl uxm” - mass loss rate of the fuel∆H

g - magnitude of the heat required to vaporize the fuel

∆HT

- the fuel souce∆H

W - heat of gasifi cation

m”w, ex

- critical water application rate

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Figure 1 - Dynamics of Fire and Extinguishment

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Computer ModelsComputer models were developed in fire dynamics simu-lator (FDS) by the author for these three tests. The model quantities and reported test values are tabulated and summarized in Table 2. The grid size was chosen as a cube with lengths of 0.125 meters, a value that has been shown to give reasonable results in other simula-tions performed by the author.

ResultsThe results of the free-burning test show reasonable cor-relation between the model and the test for the heat re-lease rate and gauge heat flux as indicated in Figure 2. The modeled peak heat release rate is slightly higher than the test. The growth rate is slightly faster than the test. The extreme decay period is not considered significant because the major effects of the fire have passed. The modeled gauge heat flux is considerably more aggressive

than that measured. Gauge heat flux is measured with respect to some reference temperature in the gauge, of-ten determined by a cooling water feed. While there are peaks that are higher and lower than that measured, the overall magnitude reasonably tracks that of the fire and can be used for design purposes. Heat release rate can be used as an indicator of the fire power. The net heat flux was not measured. Net heat flux is the parameter used to determine if fuel vaporization can occur and with it result-ing target ignition. In both cases, the target ignited. Gas temperatures were compared in Figure 3. For the un-suppressed fire, the model shows reasonable correlation with the test. For the suppressed fire, the model gas tem-peratures are lower than tested. However, both model and test showed temperatures too high for tenable conditions and low enough not to be a concern to the structural in-tegrity. This is reasonable correlation for design purposes.

Figure 2 – Comparison of model and test results for unsuppressed fire

Heat Release Rate

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x (k

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2)

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Free burning (Test 7)

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Table 1 - Description of LTA Fire Tests

Table 2 - Tabulation and comparison of fuel quantities

LTA Test No.Water Application Rate

(mm/min)Activation Time

after 60° CPeak Fire Heat Release Rate

(FHRR) (MW)Target Ignited?

Max Target Heat Flux (kw/m2)

1 12 4 minutes 37.7 No 2

2 8 4 minutes 44.1 Unknown Unknown

7 0 none 150 Yes 225

Model Values Wood Plastic Total Test Values

Volume (m3)/% 7.6/82 1.7/18 9.3 80/20

Mass (kg)/% 3,410/67 1,711/33 5,121 5,000

Energy (GJ)/% 58.0/61 37.6/39 95.6 99.2

Total inc. Target (GJ) 117

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Figure 3 – Comparison of model and test results for unsuppressed and 12 millimeter/minute suppressed fire

Gas temperature (10m downstream of fi re) Gas temperature (10m downstream of fi re)

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Figure 4 – Comparison of model and test results for 12 millimeter/minute suppressed fire

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The fire heat release rate (FHRR) and heat flux test re-sults for the 12 millimeter/minute (mm/min) suppressed fire, as shown in Figure 4, did not compare well at all. The model heat release rate was calculated as considerably higher than that tested. This is acceptable for design pur-poses, as the calculation indicates a higher value than measured. The reverse would be problematic.

The model gauge heat flux was also calculated as higher than the measured target gauge flux. The net heat flux was much closer to the gauge flux. In the model, like the test, insufficient target fuel vaporization occurred, resulting in no target ignition.

It should be remembered that the purpose of this work is to develop a spray system that meets a particular ob-jective. Fire point theory shows that net heat flux is the key parameter for predicting water effectiveness and understanding this allows for better predicting of spray performance. In the case of comparison with the LTA tests, this modeling exercise showed reasonably good correlation with the unsuppressed test for heat flux, and FHRR profile, as well as gas temperatures. In the case

of the suppressed test, the model showed higher val-ues than the test, but still showed that spread to the target fuel pile was prevented.

ConclusionFull-scale testing of fire suppression systems is expen-sive. Computer modeling provides a cost-effective means of demonstrating proposed system performance. The fuel vaporization process is well-defined in fire science and the computer models can be structured to utilize this approach.

Comparison with a test is beneficial to calibrate the model. For this reason, the LTA tests are a significant milestone in providing a benchmark to compare model results and their contribution to the knowledge of the industry is extremely important.

Kenneth Harris, PE is a Tunnel Mechanical and Fire Protection

Specialist and Principal Professional Associate with 40 years of

experience in design, construction and inspection of large civil

and industrial projects.1

1Kenneth Harris has written a number of articles for Network including “Hydraulic Modeling of Fire Protection Pipelines for the Westside Rail Tunnel” Network #34, Spring 1996, pp 24, 25.

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Latest Enhancements to the Subway Environment Simulation (SES) Programby Andrew Louie, New York, NY, US, +1-212-631-3767, louiea@pbworld.com; Tom O’Dwyer, New York, NY, US, +1-212-613-8821, odwyer@pbworld.com; and Silas Li, New York, NY, US, +1-212-465-5217, lisilas@pbworld.com

The Subway Environment Simulation (SES) computer program is a designer-oriented tool which provides es-timates of airflows, temperatures, humidity, and air con-ditioning requirements for both operating and proposed multiple-track subway systems.

The capabilities of the SES program are comprehensive, permitting the user to simulate a variety of train pro-pulsion and braking systems; various systems of envi-ronmental control (including forced air ventilation, sta-tion air conditioning, and trackway exhaust); airflows in any given network of interconnected tunnels, stations, and underground walkways; any desired sequence of train operation (including the mixing of trains with dif-ferent operating characteristics and schedules); various steady-state and non-steady-state heat sources; emer-gency situations with trains stopped in tunnels and air movement solely by mechanical ventilation and buoyant forces; and a special feature to simulate the long-range thermal impact of a possible reduction in the heat ab-sorption capacity of tunnel walls after many years of sys-tem operation.

The SES program was originally developed by Parsons Brinckerhoff in 1975 under the aegis of the National Transportation Systems Center of the United States Department of Transportation. The last publicly avail-able version of SES was version 4.1 distributed by the Department of Transportation and was released in IP (inch-pound) units in 1997. The first SES program in SI (international system) units, SES2000, was released in 2003, based on SES version 4.1, and added many new features such as: jet fan de-rating, air curtains, section pressure changes, nighttime cooling, platform screen doors, and many other components that enhanced the normal analysis features of SES. The SES2000 was the first version that was developed entirely by Parsons Brinckerhoff and released to selected clients with a

hardware security lock to prevent the unauthorized dis-tribution of the program.

SES Version 6 is an update to SES2000 that incorpo-rates many new features as well as software bug fixes and an updated security lock system that no longer re-lies on unreliable hardware dongles. All of the new com-ponents, bug fixes, and new software-based security sys-tem were developed in-house by Parsons Brinckerhoff’s tunnel ventilation team in the New York office. SES Ver-sion 6 is in internal testing right now, due to be released in December 2014. The new features of SES Version 6 are described below:

AC (alternating current) MotorsModern subway and passenger rail vehicles are using more advanced train propulsion technologies that are not analogous to the original DC (direct current) pow-ered train propulsion systems that were state-of-the-art when SES was originally developed. A new motor con-troller model was developed to complement the existing DC controlled motors modeled in SES. The new motor controller allows the SES user to input the manufactur-er's provided motor efficiency versus train speed curve to compute the energy losses for this new motor. This model simplifies the computation of heat generation due to accelerating trains and no longer requires the user to input line current or voltage data.

Cooling PipesCooling pipe networks are a novel and effective method for cooling subway environments. In these systems, rela-tively cool ground water is pumped through pipes that run along the trainway in subway systems. The circulat-ing water acts as a heat sink and cools the subway sys-tem environment. The Channel Tunnel between France and England is the first major transit system to utilize cooling pipes to cool the tunnel environment as shown

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1Ting, Y S, et al., "CFD estimation of heat transfer enhancements on a cooling pipe in underground railway tunnels", 13th Annual Symposium on Aerodynamics and Ventilation of Vehicle Tunnels, p. 629, BHR Group, 2009.

in Figure 1. The SES cooling pipe model was developed based on published research presented at the 13th An-nual Symposium on Aerodynamics and Ventilation of Ve-hicle Tunnels1. SES allows the system designer to set up a number of cooling pipe networks and will compute the heat transferred to the pipe network and its correspond-ing effect on subway system temperature.

Location Specific Train Energy RecoveryThe desire for greater energy efficiency in subway sys-tems has led to the development of wayside energy recovery systems (WERS) that consist of an electrical energy storage system such as a flywheel or battery. As a train reduces speed in the vicinity of the WERS, the train's traction motors convert the train's kinetic energy to electrical energy and feed it back to the traction power system where the WERS stores this braking energy and then supplies it back to the traction power system when a train in the vicinity starts to accelerate. The effect of this system on the tunnel environment is a reduction in heat generation by the train's braking system. SES can now account for this reduction in heat from the train's braking system at specific locations in the tunnel sys-tem as designated by the system designer.

Variable Junction Losses for Type 2 Dividing WallsTypically subway stations with center island plat-forms have trackway dividing walls at the platform ends. The SES airflow junction losses for this type of geometry was developed assuming a certain width of the dividing wall. For stations with very wide or nar-

row dividing walls, the junction losses may be different than the built in losses in SES. SES now allows the designer to adjust the turning losses based on the actual geometry of the dividing wall termination.

Coefficient of Drag for the Back of the TrainBy default, SES computes a rear train drag coef-ficient assuming a rectangular profile. New high speed trains may have more aerodynamically shaped rear train profiles and therefore this would affect the airflow resistance of a train in the sub-way system. SES now allows the designer to spec-ify the rear train drag coefficient exactly as it al-lows the designer to specify the front of train drag

coefficient. This feature also allows road tunnel designers to more precisely capture the airflow resistance due to vehicle profiles, which are modeled in SES in the same way as trains. Typical passenger cars have more aerody-namically shaped rear profiles than typical subway trains.

Software-Based Security SystemThe security system gives Parsons Brinckerhoff con-trol over the distribution and use of the software which would allow Parsons Brinckerhoff to license the software so that it remains the industry standard. Licensing fees could be used to continually develop SES and provide great value to our customers and clients.

Andrew Louie is a Professional Associate in Tunnel Ventilation.

He has worked on tunnel ventilation projects for Parsons Brinck-

erhoff for the past 9 years across the United States and England.

He is currently one of the main developers of the SES program.

Tom O’Dwyer is a Professional Associate in Tunnel Ventilation.

He has worked in this field for over 22 years and had designed

the ventilation systems for many road, rail, and transit tunnels

throughout the world. He has been involved in the development

of the SES program beginning at version 4.0, and is currently

one of the main developers of the SES program.

Silas Li is Manager of the Parsons Brinckerhoff Tunnel Ventila-

tion Analysis Group and chairman of the NFPA 130 ventilation

task group. He has 29 years of experience in the design and

simulation modeling of fire/smoke management and ventilation

systems for numerous projects involving transit, rail and road

tunnels in seven countries.

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Figure 1 - Cooling Pipe Cross Section Schematic (left), Actual Cooling Pipe Installation in the Channel Tunnel (right)

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Use of Building Information Modelling (BIM) on Road Tunnels and Metro Projectsby YF Pin, Hong Kong, +852-2579-8899, pin.yf@pbworld.com; R. Ashok Kumar, Singapore, +65-6290-7834, rajamani.a@pbworld.com; and Steven Lai, Hong Kong/Singapore, +852-2963-7625/+65-6589-3661, lai.steven@pbworld.com

BackgroundOne method to shorten the construction period, reduce uncertainty factors, and lower overall cost of infrastructure projects is to reinforce the coordination between systems by using Building Information Modelling (BIM) to virtually imitate the construction sequence. Parsons Brinckerhoff has completed the first large-scale mechanical and electri-cal (M&E) BIM model for a road tunnel in Hong Kong. The project is in the construction stage and the contractor has taken the responsibility to further develop the BIM model to a higher Level of Development (LOD)1. Parsons Brinckerhoff is also currently working on the first large-scale metro BIM model with M&E services in Singapore. Some of the systems in the BIM model are shown in Figure 1.

At present, building information modelling (BIM) soft-ware is replacing two-dimensional (2-D) drafting software in the design stage as computer technology advances. BIM can greatly help MEP engineers in their analyses through integration with third-party software for heat load calculations, lighting analysis, etc. BIM software can assist engineers in identifying potential problems or clashes among different disciplines (including inter-discipline and intra-discipline clashes). Based on the three-dimensional (3-D) model, a four-dimensional (4-D) timeline and a five-dimensional (5-D) cost analysis can also be developed.

By using BIM, the project team can identify uncertain-ties, potential impacts, and safety concerns before con-struction even begins. As a result, the project schedule is potentially shortened, and resources and budget are more accurately defined.

Key Challenges and Samples of Recommended SolutionsThe following lists the key challenges faced in develop-ing BIM models for infrastructure projects with many M&E systems and sub-systems:

• Many resources are required to develop a standard li-brary for M&E equipment and BIM standards for infra-structure projects. Information from suppliers of BIM services and software for infrastructure projects is lim-ited. Parsons Brinckerhoff is using BIM experience from other projects in different regions to help develop and recommend standards across various disciplines.

1 The Level of Development (LOD) is a reference to help the designer and owner specify BIM deliverables and get a clear picture of what will be included in a BIM deliverable. It is defined and developed by the American Institute of Architects (AIA) for the AIA G202-2013 Building Informa-tion Modeling Protocol. At present there are six LOD levels (LOD 100, 200, 300, 350, 400, 500). LOD 100 – 300 are suitable for the design stage, LOD 350 and 400 are suitable for construction stage, and LOD 500 is specific to the as-built model for owner.

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Figure 1 - Systems in the BIM models for the Singapore and Hong Kong projects include, but are not limited to, the above.

Singapore Metro Project

Hong Kong Road Tunnel Project

Environmental Control System

Waterside System • •

Airside System • •

Mechanical Ventilation System • •

Electrical System

Power Supply System • •

Lighting System • •

Earthing System • •

Lightning Protection System • •

Road Lighting System Not Applicable •

Fire Services System

Fire Detection System • •

Sprinkler System • •

FH/HR System • Not Applicable

Clean Gas System • •

Smoke Control System • •

Plumbing & Sanitary System

Hot Water System • Not Applicable

Cold Water System • •

Sanitary System • •

Drainage System • •

Tunnel Ventilation System • •

Air Purifi cation System Not Applicable •

ELV System • •

TCSS System Not Applicable •

Control & Monitoring System • •

High Voltage System • •

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• As BIM is relatively new in the M&E discipline, there are limited skillful BIM modellers in the market. To develop the BIM model in a cost effective way, it is preferred to have BIM modellers with an M&E engineering back-ground. Furthermore, when resolving clashes concern-ing an M&E model, input from multi-disciplines is re-quired. A collaboration process is recommended, and it is effective to conduct coordination workshops so that experienced engineers and architects can resolve con-flicts together. All members of the project team should be encouraged to attend these workshops to ensure the model is kept up to date.

• The 2-D output generated from the BIM model will be different from the traditional 2-D layout, and the client as well as the engineer will need guidance and instruction on the expected drawing output from BIM.

• There are two major software options (Revit and AECO-sim) being used for infrastructure projects. Usually, the architect and the structural engineer will create an indi-vidual BIM model for buildings and another model for tunnels. For some projects, Revit software is used for developing the station or ventilation building BIM model and AECOsim software is used for the tunnel model. When integrating the building model and the tunnel mod-el, it is difficult but important to ensure continuity of the M&E services at the boundary between the two models, as compatibility issues and information loss has been experienced. Partnerships with Bentley and Autodesk will help to overcome the above issues and help to drive the software changes needed.

• Some engineering calculation programs and numeri-cal analyses are available as add-ons to BIM software. Input parameters for design can be gotten directly from the BIM model and the engineering calculation or analysis can be performed automatically. However, the results of these engineering calculation programs may deviate from other commonly used commercial engi-neering calculation programs. As a result, further de-velopment of these add-on programs is expected from the suppliers.

• The computer hardware requirement for creating a BIM model for MEP (mechanical/electrical/plumbing) design exceeds that for other disciplines. The normal worksta-tion cannot handle a BIM model for a large-scale infra-structure project and generally needs to be upgraded. M&E BIM models contain many systems and sub-sys-

tems, and the software tracks each of these components inside the model. Due to the constraint of hardware and software when working on a normal workstation, it is not always possible to include all M&E features (e.g., cable hangers, cable, cable brackets, etc.) in the BIM model for a large-scale project, as the software performance would degrade noticeably. Exporting the 2-D DGN format and the 2-D DWG format from the BIM model may not result in a 100 percent match of the exported layers. Although extra time and effort could be spent to modify the 2-D drawings to suit the traditional 2-D CAD stan-dards, this approach may result in human error.

• There is equipment designed by the M&E sector that will be installed by other disciplines (e.g., the civil sector) such as earthing mats, an underground trench for cable, and concealed conduit. Currently there is not always a recognized guideline on which discipline shall develop the BIM model, which services shall be shown on which BIM model, or how the services in the 2-D drawings gen-erated from the BIM model shall be shown. Communica-tion and managing coordination are important factors in the solution, and the above-mentioned issues can be discussed and resolved at BIM coordination workshops for a better collaboration among different disciplines.

Using BIM technology to create data-rich models in three or more dimensions to facilitate better design, improve construction efficiency, foster better collaboration, provide shorter construction periods, reduce conflicts and rework, improve productivity, and create higher project profits is the upcoming trend. Parsons Brinckerhoff has successfully used BIM technology in various road tunnels and metro projects and will continue to enhance the skills and re-sources on the use of BIM in projects.

YF Pin is a BIM Coordinator for a road tunnel project in Hong

Kong. His responsibilities include BIM E&M Coordinator, interface

coordinator, model management, and technical support. He is

also the BIM E&M Coordinator for other building projects, such

as hotels, hospitals, and high-rise commercial buildings.

R. Ashok Kumar is a BIM Manager for a M&E metro project in

Singapore. He is responsible for model management, production

documentation, inter-discipline and intra-discipline coordination.

Steven Lai is a Mechanical Engineer and a Senior Professional As-

sociate at Parsons Brinckerhoff. He is M&E Project Manager for a

road tunnel project in Hong Kong which has used BIM for the first

time. He is now working in Singapore as a M&E Project Manager

for a metro project which has used BIM for the first time. DECE

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Network ©December 2014.

Parsons Brinckerhoff Inc., One Penn Plaza, New York, NY 10119, 1-212-465-5000. All rights reserved. Articles may be reprinted only with permission from the executive editor. This journal is intended to foster the free flow of ideas and information among Parsons Brinckerhoff staff. The opinions expressed by the writers are their own and are not necessarily those of Parsons Brinckerhoff.

Past issues of Network are available electronically on Parsons Brinckerhoff’s web site, (http://www.pbworld.com) or go directly to: http://www.pbworld.com/news/publications.aspx. Past issues are available to employees via the Parsons Brinckerhoff intranet.

Employees may request printed copies to use for conferences, seminars, and proposals. Send your request to pbnetwork@pbworld.com.

Executive Editor: John Chow, New York, NY, chow@pbworld.comEditor: Susan Lysaght, Lancaster, PA, lysaght@pbworld.comGraphic Designer: Suzanne Daloisio, Lancaster, PA, daloisiosl@pbworld.comAdvisor: Judy Cooper, New York, NYGuest Reviewers for this issue: Guest reviewers for this issue: Doug Graham, Sydney, AUS; Kenneth Harris, Sacramento, CA; Kate Hunt, Godalming, UK; Steven Kam-Hung Lai, Hong Kong; John Munro, New York, NY; Norman Rhodes, New York, NY

NETWORK

Call for ArticlesWe invite all employees to participate in technology transfer and submit articles to Network. We look forward to hearing from you.

Network 79, ResiliencyParsons Brinckerhoff is helping communities to build or improve their ability to "bounce back" after hazardous events, extreme weather, or climate change. We will explore topics such as risk reduction through policy and engineering, flood mitigation, habitat restoration, climate change adapta-tion, green infrastructure, carbon reduction, layers of protection, and connections with sustainability, health, and livability.

Contact editors John Chow (chow@pbworld.com) and Susan Lysaght (lysaght@pbworld.com).

Our Goal The goal of Network is to promote technology transfer by featuring articles that:• Tell readers about innovative developments.• Appeal to a broad range of readers.• Include only essential information in a readable format. • Encourage readers to contact authors for more information.

Guidelines for Articles• Articles should conform to Network format (defined below).• Keep your article as short as you can—include only relevant

details and descriptions.• Papers written for other publications must be modified to conform

to Network format.

Network Format• Length: Articles should be 1,200 words or less.• Byline: Include the name, location, phone number, and e-mail

address of each author. • Introduction/Overview: Provide a brief paragraph stating your topic

and how it is significant.• Body of text:

– Clearly describe the challenge you faced and how you or your team solved it.

– Provide exact name of client and state your firm’s role and responsibilities.

– Tell what innovative technologies or approaches you developed or used.

– Provide all units of measures in metrics followed by US

Customary in parentheses. For assistance in converting measures, see http://www.onlineconversion.com/

• Conclusion: – What lessons did you learn?– What was the impact of your solution on your project? – What does your new technology or technique mean to our firm

and the state-of-the-art of the industry?– What is the current status of your project, technique,

or technology?• Biographical Information: Please provide your title and a brief

description of your work in 1–2 sentences at the end of your article.• Related Web Sites: Provide any web addresses that readers can go

to for related information.

File Formats (provide electronic files)• Text: must be an MS Word file without graphics embedded.• Graphics:

– Format should be bitmap, tiff, eps, jpeg, or psd. – Resolution should be at least 240 dpi.– Screen captures are only 72 ppi and not acceptable.

Submit Your Article E-mail article and graphics files to: John Chow, New York, chow@pbworld.com, 1-212-465-5249 and Susan Lysaght, Lancaster, PA, lysaght@pbworld.com, 1-717-859-7427.All graphics files and a clear hard copy at least 165mm (7 inches) wide must also go to Suzanne Daloisio, Parsons Brinckerhoff Corporate Graphics Services, 4139 Oregon Pike, Ephrata, PA 17522,1-717-859-7449, daloisiosl@pbworld.com

Netw

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104 Cover photo: Eurasia Road Tunnel (Istanbul Strait Road Tube Crossing), © Tolga Togan

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