Overview of NFPA 502 Standard for Road Tunnels ... - SCATnow

Overview of NFPA 502 Standard for Road Tunnels, Bridges andOther Limited Access Highways, 2008 EditionWilliam ConnellParsons Brinckerhoff, Inc., Boston, MassachusettsJason R. GamacheNational Fire Protection Agency, Quincy, MassachusettsABSTRACT: NFPA 502, Standard for Road Tunnels, Bridges and Other Limited Access Highways establishesminimum fire protection and fire life safety requirements for road tunnels, bridges and other roadwayswhere access by emergency responders is physically limited.The 2008 edition of NFPA 502 represents the Technical Committee’s consensus of current best practice forfire protection and life safety requirements for road tunnels, bridges and similarly limited access highways.Research of national and international test programs, design guidelines and regulating standards was performedand considered in an effort to establish a singular, comprehensive document representing a recognizedbase threshold of fire safety in these type facilities.This paper provides an overview of the more significant revisions including the application of fixed firesuppression systems, guidance on tenable environment, protection of structure and dangerous goods transport.INTRODUCTIONIn recent years road tunnel fires and subsequentinternational research projects suggest that vehiclefires within tunnels are likely to develop more rapidlythan expected, degrade the tenability of an environmentmore quickly than originally calculated,and have the potential to burn for longer periods oftime and at higher temperatures that may resist interventionof fire fighting operations.In light of this the NFPA Technical Committeeon Road Tunnel and Highway Fire Protection determinedit timely for NFPA 502 Standard for RoadTunnels, Bridges and Other Limited Access Highwaysto revisit a number of its provisions withrespect to fires in road tunnels. The 2008 editionincludes revisions that further clarify the categorizationof road tunnels, a revision of the discussion topicsin the Annex on fixed fire suppression systems,and revisions regarding tenable environment, protectionof structure and the transport of potentially dangerouscargoes.In particular there has been a broad reconsiderationof the requirements and recommendations for:• Application of fixed water-based fire suppressionsystems• Protection of structure and structural elements• Maintaining a tenable environment• Transport of regulated and unregulated cargoesSeveral other modifications have been madethroughout the Standard that are intended to capturethe latest thinking on the best practices for fire andlife safety provisions. Annex material has beenadded and expanded to share relevant informationand source material related to specific provisions.APPLICATION OF FIXED FIRESUPPRESSION SYSTEMSThe use and effectiveness of fixed water-based firesuppression systems in road tunnels is still not universallyaccepted. However, recent research throughfull-scale testing and real life operational experiencehas demonstrated that fixed fire fighting systems canbe effective in controlling vehicle fires in road tunnelsby limiting the spread of the fire, reducing thetemperature of surrounding air and surfaces, andreducing the fire heat release rate.One of the reasons why many countries havebeen reluctant to use fixed fire suppression systemsin road tunnels is that most vehicle fires start in themotor compartment,, and fixed fire suppression systemsare of limited use in suppressing the fire untilthe fire is out in the open. Fixed fire suppressionsystems can be used, however, to cool down vehicles,to stop the fire from spreading to other vehicles(i.e., to diminish the fire area and propertydamage), and to stop secondary fires in tunnel liningmaterials. Experiences in Japan and Australiashow that fixed fire suppression systems are effectivein cooling down the area around the fire site, sothat fire fighting can be performed more effectively.The 2008 Edition of NFPA 502 now includesguidance for the installation of fixed water-basedfire suppression systems and has revised annex languagewhich acknowledges the potential benefits offixed fire fighting systems in road tunnel application.189

Specifically, Annex E now suggests the considerationof fixed fire suppression systems when it canbe shown by engineering analysis that the level ofsafety can be equal or exceeded by their use as partof an integrated approach to the management of lifesafety. Annex E also addresses, as follows, the previouslylisted concerns which had been expressed bytunnel designers, engineers and worldwide (authorities)regarding the application of fixed fire fightingsystem in road tunnels:Concern (1) Typically fires in road tunnelsusually occur inside vehicles or inside passengeror engine compartments designed tobe waterproof from above; therefore, fixedfire fighting systems might not have an extinguishingeffect.It is now recognized that the purpose of afixed fire fighting fire suppression system is toprevent fire spread to other vehicles so thatthe fire does not grow to a size that cannot beattacked by the fire service.Concern (2) If any delay occurs betweenignition and fixed fire fighting system activation,a thin water spray on a very hot firecould produce large quantities of superheatedsteam without material suppressingthe fire.Fire tests have now shown this concern notto be valid. A properly design fixed fire fightingsystem suppresses the fire and cools thetunnel environment. Since a heavy goodsvehicle fire only needs 10 minutes to exceed100 MW and 1200°C, which are fatal conditions,it is important to operate the fire suppressionsystem as soon as possible.Concern (3) Tunnels are very long and narrow,often sloped laterally and longitudinally,vigorously ventilated, and neversubdivided, so heat normally will not belocalized over a fire.Nevertheless advances in fire detection technologyhave now made it possible to pinpointthe location of a fire in a tunnel with sufficientaccuracy to operate a zoned fixed firefighting system.Concern (4) Because of stratification of thehot gas plume along the tunnel ceiling, anumber of the activated sprinklers would not,in all probability, be located over the fire. Alarge number of the activated sprinklerswould be located away from the fire scene,producing a cooling effect that would tend todraw this stratified layer of smoke downtoward the roadway level, thus impeding therescue and fire fighting effort.Independent laboratories have commentedthat they do not observe smoke stratification.Any activated fixed fire fighting system, notover the fire, would cool the tunnel to helprescue services to intervene. Zoned systemsare released by a detection system that isaccurate even with forced ventilation.Concern (5) Water spraying from the ceilingof a subaqueous tunnel could suggest tunnelfailure and induce panic in motorists.This was a theoretical concern not borne outin practice. In the event of fire motorists arelikely to recognize water spraying from nozzlesas a fire safety measure. Behavioralstudies have shown that people do not panicin a fire, even when they are unable to see.Concern (6) The use of sprinklers couldcause the delamination of the smoke layerand induce turbulence and mixing of the airand smoke, thus further threatening thesafety of persons in the tunnel.This has been shown not to be a valid concern.Fire tests have demonstrated thatsmoke does not usually form a layer at thetop of the tunnel but quickly fills the crosssection.Normal air movement in the tunnelaccelerates this process. A fixed fire fightingfire suppression system reduces temperaturesand the risk of fire spread to other vehicles.Concern (7) Testing of a fixed fire fightingsystem on a periodic basis to determine itsstate of readiness could be impractical andcostly. Inspection can be performed whenother facilities are inspected.A full discharge test is normally only performedat system commissioning. Duringroutine testing the system can be configuredto discharge flow to the drainage system.PROTECTION OF STRUCTURE ANDSTRUCTURAL ELEMENTSIn the last edition (2004) NFPA 502 introduced newrequirements for the protection of structural elementswithin road tunnels. The 2008 edition has190

een significantly revised to provide specific guidancefor the evaluation structural fireproofingrequirements. The following requirements have beenincluded to further support road tunnel designrequirements as they pertain to both life safety andprotection of property:• Regardless of tunnel length, all primary structuralconcrete and steel elements shall be protectedin accordance with this standard inorder to:– Maintain life safety and provide a tenableenvironment.– Mitigate structural damage and prevent progressivestructural collapse.– Minimize economic impact.• The structure shall be capable of withstandingthe Rijkswaterstaat (RWS) (Netherlands) time /temperature curve, or other curve that is acceptableto the Authority Having Jurisdiction.The time/temperature development is shown inthe table below:Time(Minutes)Temp°C °F0 20 683 890 16345 1140 208410 1200 219230 1300 237260 1350 246290 1300 2372120 1200 2192• After 120-minute period of fire exposure, thefollowing failure criteria shall be satisfied:– Tunnels with cast in-situ concrete structuralelements shall be protected such that:i. The temperature of the concrete surfacedoes not exceed 380°C (716°F).ii. The temperature of the steel reinforcementwithin the concrete (assuming aminimum cover of 25mm (1 in.) does notexceed 250°C (482°F).– Tunnels with pre-cast, high-strength concreteelements shall be protected such that explosivespalling is prevented.– Steel or cast iron tunnel linings shall be protectedsuch that the lining temperature shallnot exceed 300°C (572°F).– Structural fire protection material shall benon-combustible in accordance with ASTME 136 or equal international standard.i. It shall have a minimum melting temperatureof 1350°C (2462°F).ii. It shall not produce toxic smoke or fumesunder fire exposure in accordance withASTM E 84 or equal international standard.iii. It shall meet the fire protection requirementswith

MAINTAINING A TENABLEENVIRONMENTThe 2008 Edition includes a complete revision to theannex material relating to tenable environment. Thisis intended to correlate with similar guidance materialin NFPA 130, Standard on Fixed GuidewayTransit and Passenger Rail Systems. The purpose ofthe annex is to provide guidelines for the evaluationof tenability within the tunnel evacuation paths. Currenttechnology is capable of analyzing and evaluatingall unique conditions of each path to provideproper ventilation for pre-identified emergency conditions.The same ventilating devices might or mightnot serve both normal operating conditions and preidentifiedemergency requirements. The goals of theventilation system, in addition to addressing fire andsmoke emergencies, are to assist in the containmentand purging of hazardous gases and aerosols such asthose that could result from a chemical/biologicalrelease.Environmental conditions, geometric considerations,and time considerations should be taken intoaccount. Following are some factors that should be consideredin maintaining a tenable environment for periodsof short duration.Heat EffectsExposure to heat can lead to life threat three basic ways:• Hyperthermia• Body surface burns• Respiratory tract burnsFor use in the modeling of life threat due to heat exposurein fires, it is necessary to consider only two criteria—thethreshold of burning of the skin and theexposure at which hyperthermia is sufficient to causemental deterioration and thereby threaten survival.Air Carbon Monoxide ContentAir carbon monoxide (CO) content should be as follows:• Maximum of 2000 ppm for a few seconds• Averaging 1150 ppm or less for the first 6 minutesof the exposure• Averaging 450 ppm or less for the first 15 minutesof the exposure• Averaging 225 ppm or less for the first 30 minutesof the exposure• Averaging 50 ppm or less for the remainder of theexposureThese values should be adjusted for altitudes above984 m (3000 ft).Smoke Obscuration LevelsSmoke obscuration levels should be continuouslymaintained below the point at which a sign internallyilluminated at 80 lx (7.5 ft-candles) is discernible at30 m (100 ft) and doors and walls are discernible at10 m (33 ft).Air VelocitiesAir velocities in the enclosed tramway should begreater than or equal to 0.76 m/s (150 fpm) and lessthan or equal to 11.0 m/s (2200 fpm).Noise LevelsNoise levels should be a maximum of 115 dBA for afew seconds and a maximum of 92 dBA for the remainderof the exposure.TRANSPORT OF REGULATED ANDUNREGULATED CARGOESRecent road tunnel fires suggest that goods traditionallynot characterized as ‘hazardous’; i.e. flour andmargarine (1999 Mont Blanc Tunnel), paint (1999Gothard Tunnel), and tires (2005 Frejus Tunnel),may constitute a greater risk to tunnel users and tunnelstructures than expected. As a result Chapter 13Control of Hazardous Materials has been re-titledRegulated and Unregulated Cargoes to provide guidanceto tunnel operators, first responders andenforcement officials on developing rules regardingany and all cargoes allowed passage through a particularroad tunnel facility.The authority having jurisdiction must adoptrules and regulations that apply to the transportationof regulated and unregulated cargoes. Design andplanning of the facility must address the potentialrisk presented by regulated and unregulated cargoes.When developing vehicle cargo regulations fora particular road tunnel facility, fire, accident, andresearch experience of the vehicles and cargo of thetype expected within the tunnel—and particularly ofgoods and vehicles not normally characterized ashazardous or otherwise regulated—should be considered.Some types of cargoes not normally consideredhazardous may in certain circumstances inconfined spaces within tunnels behave as, or equivalentto, hazardous materials in terms of the rate offire growth, the intensity of the fire, discharge ofnoxious materials, destruction to infrastructure, andthreat to users’ safety.In developing regulations, the following mustbe addressed:1. Population density2. Type of highway3. Types and quantities of hazardous materials192

4. Emergency response capabilities5. Results of consultation with affected persons6. Exposure and other risk factors7. Terrain considerations8. Continuity of routes9. Alternative routes10. Effects on commerce11. Delays in transportation12. Climatic conditions13. Congestion and accident historySUMMARYThe 2008 Edition of NFPA 502 is intended to correlatethe fire and life safety provisions that arebased on the latest research, technologies, and reallifelessons learned so that tunnel designers, engineers,first responders, and operating authoritieshave an immediate source recognized requirementsfor creating a fire safe road tunnel environment.The NFPA 502 Technical Committee fullyanticipates that ongoing research programs beingconducted both nationally and internationally suchas The International Road Tunnel Fire DetectionResearch Project sponsored by The Fire ProtectionResearch Foundation, the Large-Scale Fire HeatRelease Rate Tests conducted by a variety of consortiumsin collaboration with UPTUN and the SPSwedish National Testing and Research Institute,and sprinkler system testing such as that conductedby The Netherlands Organisation for Applied ScientificResearch, will continue to yield valuable information.As the Technical Committee looks forwardto the development of the 2011 Edition of NFPA 502it fully recognizes that diligent attention to theresults of these research programs is necessary sothat fair evaluation and consensus of results can beexpeditiously considered for incorporation.193