FIRE SAFETY

48 TUNNELLING JOURNAL

Active orPassive?

THE RUNEHAMAR ROAD TUNNEL inÅndalsnes, Norway, has been the scene ofseveral major fires over the last 15 years. Whilesome have been controlled by fixed fire-fightingsystems (FFFS) others have burned on, reachingtemperatures of almost 1400°C.

These fires have been no accident, however.The Runehamar tunnel is disused and the firesare experimental ones, aimed to give insightinto how fires in road tunnels behave and howthey should be tackled.

Some of the latest tests have been carried outon behalf of the Swedish TransportAdministration which has been developing anew valve to fight fires on the StockholmBypass. Currently under construction, thebypass runs underground for 18km of its 21kmlength and with heavy traffic expected, an un-

Could the combination ofpassive and active fireprotection measures lead tobetter value solutions for roadtunnels? Kristina Smith reports.

Top right:PassiveTec fire

protection boardsinstalled by BAMNuttall and BBV

at HeathrowAirport’s main

road tunnel.

Middle right:Fogtec

installation at theDartford Tunnel

Below: PassiveTecinstalled at theTåsen Tunnel in

Norway

FIRE SAFETY

TUNNELLING JOURNAL 49

checked fire could spread fast from vehicle tovehicle.

Active systems, such as water spray and mistsystems are relative newcomers to the tunneldesigner’s arsenal of fire protection measures inmost parts of the world. They can control orsuppress a fire, allowing people time to escapeand allowing fire fighters safe access. They canalso allow the designer to downsize ventilationand passive requirements, although this is apoint of some contention.

“The big question at the moment is how canwe consider reducing fire sizes and proposals totrade off other critical systems,” says PaulSparrow, global support manager, tunnels, atPromat. “But active systems should be anaddition to passive ones, not as an opportunityto reduce passive protection. Designers shoulddesign for tomorrow not today, by usingcurrent worst case scenarios, not looking to tryto reduce the size of fires.”

The latest guidance on fire protection relatingto refurbishment of existing tunnels fromWorking Group 6 of the InternationalTunnelling and Underground Space Association(ITA) – covered on pages 43-47 – ducks thisquestions altogether. It is titled ‘Structural FireProtection for Road Tunnels’ and sticks firmly tothat brief, saying nothing about the interactionof active and passive systems.

“It was a lost opportunity to address theseissues: do we really need that much passive fireprotection or not,” asks Dr Fathi Tarada,managing director of specialist consultancyMosen. “The issue of cost versus being safe isalways there. That gives us engineers achallenge that means we cannot always godown the prescriptive route. We have todevelop new ways to optimise things, and lookat whether the investment in safety hasprovided the right benefit-to-cost ratio.”

Life and livelihoodFire in road tunnels are not a rare occurrence –they happen often and are dealt with safelyand effectively. Serious fires are rare, but whenthey do happen the impacts can be devastatingin terms of loss of life and connectivity.

Such events can act as a catalyst for tunnelowners and engineers to re-examine their

approaches to fire protection, control andmanagement systems. The infamous MontBlanc Tunnel fire in 1999, and another one laterthat year in the Tauern Tunnel in Austriatriggered a raft of testing – including tests inthe Runehamar tunnel – and work on variousguidance documents.

Tunnel owners and insurers are also lookingbeyond the initial capital cost to assess whatthe wider costs of closure would be. Forinstance, the Swedish Transport Agency hascalculated that every time they close the SouthLink in Stockholm it costs society €70M a day.

Passive measures, such as boards and spray-applied materials, are the most established andunderstood means of fire protection. Promathas been involved in tunnel fire protection sincethe 1960s, according to Sparrow, and has fittedits board systems in over 300 tunnels. Promatalso supplies sprayed protection, having joinedforces though acquisition with CafcoInternational ten years ago.

Promat’s biggest current project will see itsupply a massive 330,000 sq m of Promatect-Hboard to the immersed tube tunnel sections ofthe Zhuhai to Macau link which will link HongKong and China. “That’s equivalent to aroundthree years’ normal activity in one project,” saysSparrow.

Refurbishment projects account for animportant – and growing – proportion ofPromat’s workload. “We are seeing more andmore refurbishments coming on stream,” saysSparrow. “When tunnel owners are looking toreplace ventilation and lights and upgrade otherthings, they are beginning to incorporate fire

protection where they previously had not done.There is a growing global awareness that fireprotection in tunnels needs to be addressed,principally because of the high-profile disasterswe have seen.”

The growing awareness and market meansthat new passive protection suppliers areemerging, hoping to steal a slice of the piefrom Promat, which has somewhat dominatedthe market. One new brand is PassiveTec,owned jointly by SIG and PFP Group, whichcame to the market in 2014.

“We are providing better fire insulation witha thinner product,” says Iain Giffen, businessdevelopment director at PFP Fire Systems. “Wehad to take a different approach, we’re battlingagainst a 20 or 30-year legacy. We offer abetter value proposition with better fireprotection and a better margin for thecontractor. That’s our niche.”

Giffen says that PassiveTec boards are bettedsuited to damp tunnel environments. They are

made from fibre reinforced magnesium andallow water to pass through them, whereas themost widely-used calcium silicate boards absorbwater.

However, Tarada explains that for calciumsilicate boards, their absorption of water isintegral to how they work. “We havedeveloped a model for the movement of waterand steam within passive fire protection boardsthemselves in order to work out their level ofresistance,” he says. “It’s not the fact that thesefire protection bards don’t conduct heat verywell, that they are good insulators, it’s the factthat they have got a lot of water in them and

Road tunnel fires

Road tunnel Date of fire Brief description Of note

Mont Blanc, 1999 39 people died after a truck carrying There was no fire protection in the Italy/France flour and margarine caught fire, with tunnel and many of the deaths were

the driver failing to notice initially. due to people staying in their vehiclesThe fire burned for two days. rather than going to refuges. The tunnel

was closed for three years for repairs and upgrades.

Tauern, Austria 1999 12 people died and over 40 were The tunnel was closed for three months. injured when a truck ran into a Repairs included upgrades to the walls queue of stationary vehicles. and ventilation system.

Gotthard, 2001 11 people were killed when a The tunnel was closed for two months Switzerland collision between two trucks for repair and cleaning. The number of

created a fire. trucks in tunnel is now limited.

Fréjus, 2005 2 people were killed after a fire in a A safety tunnel and connection cross-France/Italy tyre truck spread to other vehicles. passages is currently being constructed

at a cost of €408m

Burnley, 2007 3 people died after multiple vehicles Deluge fixed fire fighting system limitedAustralia crashed into a stopped truck. fire to allow fire fighters in and safe

evacuation of other drivers

Brynglas 2011 A truck caught fire causing extensive Upgrade work, currently underway,Tunnel, UK damage to the tunnel, although includes tunnel lining and M&E repairs

there were no fatalities. costing £40m

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50 TUNNELLING JOURNAL

that’s how they resist the heat flow.“Magnesium oxide-based materials rely on

the fact that they are such a poor conductor ofheat,” he adds. “One of their downsides is thatthey are very difficult to drill and cut – they canblunt your blades.”

Working for Heathrow Airport, BAM Nuttall,BBV and Mott MacDonald are using 24mmPassiveTec tunnel liner boards on therefurbishment of the main road tunnel at theairport. The work, which is taking place withsome night-time tunnel closures, includesupgrades to the ventilation, FFFS, detection andalarm, electrical and fire mains as well as thefire protection element.

The modular sandwich panels, which BAM isinstalling in a framing system onthe walls of the road tunnel, haveundergone independent testing toRWS 120. RWS is one of a numberof time-temperature curves whichwas developed by the Netherlands’ministry of transport, theRijkswaterstaat, as a result of testscarried out in 1979.

The RWS curve, which is referredto in current guidance documents,is based on the heat that wouldcome from a fire in a petrol tankerin an enclosed space. Thetemperature of the fire rises quicklyto reach 1350°C after 60 minutes,falling to 1200°C at 120 minutes.

PassiveTec boards have also beeninstalled in the Tåsen Tunnel inNorway. The panels were cut to size andcoated off site.

“Norway is one of the countries where weare concentrating our efforts because there areover a thousand tunnels, all of which have tocome up to EN standards before the end of2025,” says Giffen. “They all have to beupgraded, not just for fire protection, forsignage and protection of services too.” PFPand SIG are also pursuing projects in Asia, theMiddle East, North America South America andAustralasia.

Sparrow, who was a primary contributor tothe ITA Working Group 6 document, highlightsthe fact that the group’s new guidance warnsagainst the use of magnesium oxide boards.The guidance states that ‘magnesium oxy-chloride materials’ which it says are also knownas ‘fibre reinforced magnesium’ and‘magnesium oxide, silicates and other additives’contain chlorides and that these can bedetrimental to durability and to life safety in theevent of a fire.

The rise of waterIt has taken a long time for the US, WesternEurope and elsewhere to reach the conclusionthat Japan did 40 years ago and Australia morerecently with respect to FFFS. That is that waterspray and mist systems limit the impact of a fireby lowering the temperature and/or preventingit spreading as far.

Water spray systems tend to work at lowerpressures, typically less than 12 bar, producinglarger water droplets. Mist systems operate atover 35 bar and produce smaller, highervolume drops.

Very broadly speaking, water spray systemstend to operate by cooling and wetting fuelsurfaces whereas mist works on the gases ofthe fire. The available space, water volume, sizeand use of tunnel all impact on what is the bestchoice of system.

PIARC, the world road association, hasmoved gradually from a position in 1995where it said that sprinkler systems should notbe used in tunnels – citing problems such asthe danger of steam and impacts of water on

smoke – to a position today where it recognisestheir use. In 2008 it published ‘Fixed firefighting systems in road tunnels: currentpractices and recommendations’, a documentit updated in 2016.

“PIARC have changed their view from arather negative one in the 1990s to being reallypositive in the latest edition,” says ArminFeltmann, business manager – tunnel systemsfor Fogtec.

As well as recognising the impact of FFFS onprotection of life, the 2016 update recognisesthat active systems can enable a reduction inpassive systems. In Section 3.5 on assetprotection, the PIARC document says: “FFFSmay be considered as a compensatory measurein fire-engineering design. It is recognised thatpassive measures are normally considered to bethe most reliable, nevertheless, in somecircumstances, it may be possible to reduce thelevel of passive fire protection.”

In the US, the National Fire ProtectionAssociation (NFPA) has also changed its stanceon FFFS. In the 2014 edition of its guidancedocument NFPA 502 ‘Standard for RoadTunnels, Bridges and Other Limited AccessHighways’ information on fixed systemsappeared in the appendix and in the latestedition, issued in May last year, there is a wholechapter devoted to the subject.

The latest NFPA 502 says that the effect offixed water-based fire-fighting systems should

be taken into account when sizing ventilation.And it says that such systems can be taken intoaccount with respect to structural protection, ifthere is appropriate evidence and if approvedby the relevant authority.

For Fogtec, refurbishment is a growingsector: “For tunnel refurbishment projects,there’s a tendency more and more to go toactive fire protection systems,” says Feltmann.“With FFFS, you can easily upgrade the firesafety standard of a tunnel with limitedinvestment and only very minor interruptions totraffic during installation. In some cases, theinsurance costs for tunnel operators can bereduced significantly.”

With more and more projects, FFFS keepdeveloping, says Feltmann. “Thetechnology is improving constantly,we learn from each and everyproject we are doing.”

For instance, Fogtec hasdeveloped a system which canremotely test the section valveswhich separate the various sectionsof the mist systems along thetunnel’s length. This remote testingcapability has been installed inseveral tunnels including theDartford Tunnels on the M25, Eastof London, which were upgradedin 2011-2012.

For the Dartford Tunnels, thewater mist system was integratedinto a SIL2 (safety integrity level 2)certified tunnel control system,

which made it the world’s first SIL2 FFFS, saysFeltmann.

Currently Fogtec is installing a water mistsystem into the Tunnel Wald in Austria. “Themain reason for its installation there is toprotect the infrastructure and to keep thehighway running,” says Feltmann. “It carriesone of the main North-South highways whichconnect Germany to Slovenia.”

The Swedish experienceThe construction of the Stockholm Bypass hastriggered an extensive research anddevelopment programme by the SwedishTransport Authority, Trafikverket.

The main goal of the programme was todevelop new nozzles for deluge systems, witha view to specifying them for the StockholmBypass and other planned projects such as theGöta Tunnel in Gothenberg. That goal hasbeen achieved, with a system that is effectiveand costs around one-third of the cost toinstall, when compared to standard deluge andmist systems.

The work, carried out jointly with researchbody Science Partner (SP) – now ResearchInstitute of Sweden (RISE)) - included twoseries of large-scale tests in the Runehamartunnel. The first tests in 2013 looked at TYCOTN-25 nozzles, designed by Johnson Controls(formerly Tyco Fire Protection Systems), basedon a design by consultants Brandyskyddslaget

NOZZLESAND FITTINGS

SHOWNENLARGED

TN-17/TN-25NOZZLE

VEHICLES SHOWNFOR REFERENCE ONLY

Tyco Nozzles designed by Johnson Controls

52 TUNNELLING JOURNAL

– which in turn were based on Tyco’s existingSW-24 open sprinklers.

The TN-25 is a horizontal spray nozzle with awide opening; it has a K-factor of 25.2 (K360).The K-factor describes the flow rate throughthe nozzle.

The 2013 tests mimicked the sort of fire youmight expect from a fuel tanker and the aimfor the water system was to keep the heatrelease rate below 50MW and to prevent thefire spreading to a target 5m away from themain fire. The nozzles were positioned back-to-back, suspended from the centre line of thetunnel ceiling at 5m intervals.

The 50MW value is the level below whichthe Swedish fire fighting teams can enter thetunnel to perform search and rescue andmanually fight fires. The TN-25 performed well,easily beating the target.

The 2016 tests were set up in the same wayas their predecessors but this time theresearchers were looking at the TN-25 withlower water pressure, a smaller version calledthe TN-17. Johnson Controls’ existing SW-24sprinkler was also put through its paces.

The SW-24 has been installed in Sweden’sNorthern Link, since the tunnel was designedbefore the findings from this research whichmeant that an existing product had to bespecified. Recently it was activated successfullyduring a car fire of around 5MW.

The second tests set a lower target of 30MWfor the heat release rate. All the nozzles metthe targets, the TN-25 being the most effectiveand the SW-24 the least. One interesting pointto note was that the TN-25 with lower waterpressure worked better than when higherpressure was used.

“The smaller pressure leads to bigger waterdroplets which means there is a better impacton fire,” explains Arjan Ten Broeke, JohnsonControls’ business development manager forwater-based systems, Benelux and UK. “Wewere able to meet the goals of the test andprove that with reducing the amount of waterand pressure on nozzle, we got better resultson the fire.”

The TN-17, says Henrik Johansson, JohnsonControls business development manager forNordic countries, will be useful in longertunnels or in situations where water supply islimited since it requires a lower flowrate thanits sister. “If you have wider tunnels, the TN-17will flow further than TN-25 and it can also beset to discharge less water per nozzle.”

For all types of FFFS, early detection andactivation is essential if the fire is to besuppressed or controlled. In the tests, theactivation of the systems was delayed. First, theresearchers waited until the temperature of thefire reached 141°C, which took around fourminutes, and then delayed a further fourminutes before activating the nozzles.

In a ‘live’ situation, the detection systemshould set the nozzles into play much sooner.Johnson Controls would recommend a lasercable detection system, such as its ZETTLER

MZX SensorLaser Plus, because the laser is veryaccurate and not affected by wind. Water flowand pressure to the nozzles is also important;Johnson Controls uses its deluge valve DV-5which can be reset remotely after beingactivated.

From an investment perspective, the newnozzles have advantages over existing systems,largely due to the fact that Johnson Controlshas designed them to operate from the samepipework that feeds the hydrant systems forfire fighters. “With TN-17 and TN-25, we havereduced the installation costs of the system bybetween 70 and 75 percent compared totraditional water-based systems by using lesspipes and different type of pipes,” saysJohansson.

According to Johansson, calculations fromTrafikverket put the capital cost for systemsusing the TN-25 nozzle at €500,000 per km,compared to €1.5m to €2m for high-pressurewater mist systems and €1m to €1.5 m fortraditional water spray systems.

The first tunnel to benefit from thedevelopment of the new nozzles is theRantatunneli tunnel in the city of Tampere inFinland. The 2.3km tunnel, Finland’s longesttoad tunnel, opened in late 2016 and hasJohnson Control systems which features theTN-25 nozzles.

StandardisationA lack of standards for fire protection, in termsof both requirements and testing, is seen asone of the biggest challenges in this market.Although PIARC’s guidance is well-respectedaround the world, it is only guidance – ratherthan a standard.

Sparrow hopes the new ITA document,which he says was peer-reviewed by PIARCbefore publication, will create some clarity,highlighting the link it makes betweentemperature curves and heat release rates:“Different engineers use different measures intheir specification. Some reference heat releaserates, some use time temperature curves, butthere has never been a connection betweenthe two before. If the specification asks for fireprotection to meet a 50MW fire, what timetemperature curve is that?”

We need more research and guidancerelated to FFFS, and how they interact with

other systems, says Johansson. “Test protocolsdiffer for each manufacturer and system asthere is no globally recognised standard,” headds. “This makes it difficult for tunnel ownersto compare systems, as well as the trade-offwith passive fire protection measures.”

Firms such as Mosen are using advanced 3Dcomputational fluid dynamics (CFD) modellingand computation to look at tunnel systems intheir entirety. “It’s a bit of a tall order but youhave to get the picture of the whole tunnel, allat the same time,” says Tarada. It used thisapproach, verified by full-scale testing, todevelop its MoJet ventilation system.

Sparrow cautions against a reliance onmodelling and calls for better full-scale testing.“Don’t try to be clever with CFD modelling tosay fires are not as hot as they used to bebecause we don’t know,” he says. “Mosttesting conducted on FFFS is with pool fires -fuel on a tray - or single vehicles. We need tobe more accurate in our full-scale testing, notrun the risk of becoming too heavily reliant ondesk top modelling.”

Giffen thinks that testing is vital, particularlywhere high-strength concrete is involved. “If Icould make one change it would be to requirefull-scale tests on concrete samples on everysingle project because of spalling in new typesof concrete – 55MPa and higher – which spallat lower temperatures,” he says.

Testing, of course, adds to the capital cost offire protection. So we come back to thequestion of cost versus benefit. This is adynamic subject, which can only become moreso with the advent of autonomous and semi-autonomous vehicles and connected cars;these can only reduce the risks due to erraticdriver behaviour during incidents.

If we want to see more roads goingunderground, reducing congestion and airpollution in urban areas, belt-and-bracessolutions do not help make the economic case.

“If you make tunnels unattractive becausethey are far too expensive to construct andmaintain, you will clog up the surface routes,potentially creating additional safety andenvironmental risks, and hinder economicprogress,” says Tarada. “We don’t have firesevery single year and those that affect thestructure are even rarer. We have to accountfor that.”

FIRE SAFETY

Photo show-ing full scalefire testcarried out byMosen usedto verify its3D computa-tional fluiddynamicsmodelling indevelopingthe MoJetvent system

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