Road Tunnel Fire-Life Safety and CFD Modeling

Matthew Bilson, PhD

Road Tunnel Fire-Life Safety and CFD Modeling

© A Purchase

March 2016

OUTLINE2

Road tunnel fire-life safetyNFPA 502Design topics:

Fixed fire fighting systemsVentilation

Design analysis:CFDOther design tools

Future challenges

ROAD TUNNEL FIRE-LIFE SAFETYWhy and What?

ROAD TUNNEL FIRE SAFETY INCIDENTS4

Mont Blanc, France, 1999:Truck carrying margarine39 fatalities, tunnel closed for several years

St Gotthard Tunnel, Switzerland, 2001:HGV collision11 fatalities, 23 vehicles destroyed, 250 m damage to tunnel

Caldecott, USA, 1982:Petrol tanker collision with stopped car7 fatalities

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ROAD TUNNEL FIRE SAFETY INCIDENTS 5

16 March 2016, Hiroshima, Japan:

Truck crashed into stopped vehicles2 fatalities, 70 injured

1 March 2016, Sydney Australia:

Bus fire in Lane Cove TunnelNo injuries, major traffic distruption

October 27 2015, South Korea:

Truck carrying paint thinner crashes in tunnel11 vehicles involved in fire21 people injured Source: YouTube

TYPICAL FIRE SAFETY FEATURES 6

Fire prevention:Height controlHazardous vehicle restrictions

Detection:CamerasAutomatic incident detectionLinear heat detectionAlarms on doors and cabinets

Egress:ExitsLighting (normal, emergency)Low level lightsExit sounders

Communication:Emergency phonesPublic address systemMobile phone transmissionRadio rebroadcastingVariable messaging signs

Smoke management:Jet fans and smoke exhaust

Fire protection:HydrantsHose reelsExtinguishersReliable water supply (tanks)Fixed fire fighting system

Structural fire rating

Controls and electrical:Dual power supplyUPS (lights and computers)Redundant control

Management and response:Response crewControl centerIncident response

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DESIGN STANDARDSHow?

NBFU 502 – 19569

NFPA 502NBFU was a precursor to NFPA 502Total pages = 8

NBFU – 1956 10


NFPA 502 – 201411

56 pages, 14 sections:Ventilation, traffic control, egressSuppression systems allowed, not requiredStandpipe requiredStructural protectionEmergency response planAnnex material (fire science, full scale tests, recommended practice, previous incidents)Performance-based

NFPA 502 – 2014 PRIMARY REQUIREMENTS:TRAFFIC CONTROL

Entry: Stop vehicles enteringExit: Means to expedite vehicles to exit

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© Richard Pearse Photography

NFPA 502 – 2014 PRIMARY REQUIREMENTS:EGRESS

Maximum spacing 1000 ftTenable environment for egress


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NFPA 502 – 2014 PRIMARY REQUIREMENTS:VENTILATION

Mechanical ventilation not explicitly required if L < 3280 ftL < 3280 ft requires analysis In all cases, must provide means for smoke control


NFPA 502 – 2014 PRIMARY REQUIREMENTS:FIXED FIRE FIGHTING SYSTEMS (FFFS)

Permitted but not requiredSometimes required if heavy congestion is likely and no other means for reliable egress/vent givenA standpipe is required

© Richard Pearse Photography © WSP | Parsons Brinckerhoff

HISTORY OF FFFS IN NFPA 50216

1956

2001

2014

DESIGN STANDARDS – SUMMARY 17

NFPA 502:Main standard applied in the USANot mandatory in all jurisdictionsPrimary goal is life safetyPrimary features: - Ventilation, FFFS, egress, traffic- Also covers structure, standpipe,

signage, electrical, incident responseOther standards:- EU 54 (Europe)- AS 1428- Norway, Sweden, UK- And others…

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DESIGN IN DETAILFixed Fire Fighting Systems

FFFS – KEY COMPONENTSValvesHeatingZonesActivationDesign fireFire fightingIntegrationWater supplyDrainageNozzle designVentilationFire fightingActivation policy




- Zones on the image shown are N178 and N179.

- Zone N178 is the foreground.

- Zone N179 is the background.

Plan view of roadway:

Fixed camera

Deluge zone / ventilation zone

Tunnel wall

Traffic and airflow

Linear heat detector

Roadway

Legend:

CCTV vision example:


FFFS ZONING

water application rate = nozzle flow / area covered


TRAFFIC CONSIDERATIONS


FFFS BENEFITS24

Reduced temperaturesPotential to suppress fireReduced damageImproved life safety

0

50

100

150

200

250

300

0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0

Tem

pera

ture

(deg

C)

Time (s)

CFD (WBP-06-04) vs exp't (z=1.8 m, 12 m downstream)

CFD

Exp't

FFFS activation

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FFFS RECAP26

Potential benefits:Reduced temperaturesReduced damage to structureImproved life safety

Cautions:Essential to correctly design, install, integrate, commission, maintain, test and operateNot appropriate in every situation


DESIGN IN DETAILVentilation

WHY IS VENTILATION IMPORTANT?28

Natural ventilation:

Mechanical (longitudinal) ventilation:

29

Source: Twitter post from Hiroshima Tunnel Fire 16 March 2016

VENTILATION SCHEMES30

Longitudinal with jet fans (Port of Miami Tunnel, Florida)

Longitudinal with mid-point exhaust and supply (Liberty Tunnel, Pittsburgh)

Full transverse (Queens Midtown Tunnel)

Single point exhaust (Clem 7, Brisbane, Australia)

Source: NFPA 502 – 2014 Edition

VENTILATION FEATURES31

© WSP | Parsons Brinckerhoff© Richard Pearse Photography



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VENTILATION RECAP33

Why?Essential life safety featureSmoke control

Features:A wide variety of schemesNot a one size fits all approachAnalysis necessary for design



DESIGN ANALYSISCFD and Other Tools

EXAMPLE DESIGN CASE

Direct smoke downstreamDetermine jet fan diameter, thrust, power, layoutScenario parameters:

100 MW fire (large truck)Fire location (3 or 4 locations is typical)Fan parameters (3 or 4 different fans is typical)Traffic mixWindFan out of serviceDesign development (different cross sections, fan layout, design iterations, coordination with electrical, civil and tunnel)

CFD or one-dimensional or testing?


METHODS OF ANALYSISExperiment:

Full scale is expensive and often impossibleSmall scale is simplified, measurement error, extrapolation

Theoretical calculation:Feasible for certain situationsCan be complex

Numerical (CFD):If the model exists it can handle almost any problemOnly as good as the model and skill of the modelerIt is a tool, nothing more and nothing lessNot reality and not a solution to every other problem

COMPUTATIONAL FLUID DYNAMICS (CFD)

Physics (develop governing equations):Turbulent fluid flow (momentum conservation)Heat transfer (energy conservation)Mass transfer (mass conservation)Combustion (chemistry)Develop governing equations

Numerical aspects:Divide the domain into small cellsApply a numerical solution (e.g. finite difference)

© M Bilson

TURBULENCE MODELSIn a direct numerical simulation (DNS) the length and time scales are fully resolved by the gridKolmogorov derived expressions for the smallest eddyNumber of cells ~ Re37/14 (Choi and Moin)For a tunnel, 500 meters long:

Need around 125,000 billion cellsIn the order of 100 billion years of computation time

We cannot, at this time, resolve the smallest scales of motionSmallest scales of motion should be more universal, able to model?Turbulence models are needed (time or spatial based)

LES DNS MEAN

CFD APPROACH?How many cells, how long to run?

Typical cell size = 0.25 m850 m by 60 m2 = 3 million cellsCould take “a few days” per run

Also need to model jet fans, vehicles, fire, windNot an advisable analysis methodology for this problemUse the 1D approachMight use CFD to check the critical velocity

1D APPROACH – CRITICAL VELOCITY

Source: NFPA 502 – 2014 Edition

1D APPROACHPressure/force balance computation:

Nf Pj = pveh + pf + pm + pb+ pfire

Nf Number of jet fans

Pj Pressure rise due to a jet fan

pveh Pressure loss due to vehicles

pf Pressure loss due to wall friction, entry, exit

pm Pressure loss due to meteorological effects

pb Pressure loss/gain due to buoyancy

pfire Pressure loss due to the fire

pf ( fL / D ) v2/2)


1D APPROACHOther elements / physics:

Discretize the tunnel into small elementsWall heat transferConvective heat transferFire heat release rateIterative solutionSystems and Equipment for Fire and Smoke Control in Road Tunnels, PIARC, 2007

Models (all can be easily modified and quickly run):

Subway Environment SimulationIDA TunnelExcel

0.0

20.0

40.0

60.0

80.0

100.0

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140.0

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180.0

0 500 1000 1500 2000 2500

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pera

ture

(C)

Chainage

Tun1

Tun2

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-5-4

-3-2-10

1234

5

0 500 1000 1500 2000 2500Ve

locit

y (m

/s)

Chainage

Tun1

Tun2

Fire

FFFS AND CFDNow?

Predict cooling of the environmentDroplet / ventilation interaction

Emerging?Fire spread prevention

Future?Fire suppression predictionFire heat release rate

fire

exhaust

exhaust

airflow airflow

airflow

fire

fire

exhaust

THE FUTUREChallenges

FUTUREMore safety features in old and new tunnels:

Pressure to do more with less?Emphasis at the design phase to SHOW safety:

100% safety is not achievableMust take care – the last 1% shouldn’t distract from the other 99%

Cyber security, computers and software, terrorismAgeing infrastructureDirty infrastructureData © WSP | Parsons Brinckerhoff

CONCLUSION

CONCLUSION48

Road tunnel fire safety:Relevant concernPast incidents

NFPA 502:Governing standardMajor requirements are egress, traffic, ventilation, FFFSAlso structures, standpipe, incident response

Fixed fire fighting systems:Integration is essentialNot always required

© Andrew Purchase

CONCLUSION49

Ventilation:Fundamental life safety

Design analysisCFD – not always1D can work well

Future challengesCyber securityAgeing tunnels

© Andrew Purchase

FURTHER READINGTunnel fire-life safety:NFPA 502 – Standard for Road Tunnels, Bridges and Other LimitedAccess Highways, 2014 EditionThe Handbook of Tunnel Fire Safety, Beard and Carvel, Thomas Telford,Second Edition, 2012Tunnel Fire Dynamics, Ingason, Li and Lönnermark, Springer, 2015.Computational fluid dynamics/fluid mechanics:Computational Methods for Fluid Dynamics, Ferziger and Peric, Springer,1996A First Course in Turbulence, Tennekes and Lumley, The MIT Press,1972Grid-point requirements for large eddy simulation: Chapman's estimatesrevisited, Choi and Moin, Center for Turbulence Research, AnnualResearch Briefs, 2011

FURTHER READING1D model:Systems and Equipment for Fire and Smoke Control in Road Tunnels,PIARC Committee on Road Tunnels Operation (C3.3), 2007FFFS:Fixed Fire Fighting Systems in Road Tunnels – System Integration, MBilson and S Marsico, PB Network, Issue 78, 2014Road Tunnels – An Assessment of Fixed Fire Fighting Systems, PIARCCommittee on Road Tunnels Operation (C3.3), 2008Fixed Fire Fighting Systems in Road Tunnels: Current Practices andRecommendations, PIARC Committee on Road Tunnels Operation(C3.3), to be published 2016

FURTHER READINGOther topics:Emergency Exit Signs and Marking Systems for Highway Tunnels,NHCRP Document 216, 2015Fires in Transport Tunnels – Report on Full Scale Tests, Eureka ProjectEU 499, 1995Runehamar Fire Tests, Ingason, Lönnermark, Li, SP Report 2011:55,2011Memorial Tunnel Fire Ventilation Test Program – Test Report,Massachusetts Highway Department, 1995CFD software:

Fire Dynamics SimulatorANSYS CFX and FluentSOLVENT

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Questions / Discussion

Matt Bilson

[email protected] 465 5510

Engineering

Road Tunnel Fire-Life Safety and CFD Modeling