FIRE SAFETY

US Emergency Systems Cables Certification Withdrawn:CRISIS OR CROSSROAD?

For more than twodecades Professor ArnoldDix has developed aninternational reputationfor assisting clients withcomplex technical,scientific and legal issues.An accomplished lawyer,as well as a technical andscientific expert in hisown right, Dix hasextensive experience intunnel construction,operations, insurance,disasters andinvestigations, sits onstandards bodies NFPA130 and 502, PIARC, andITA committees in the USand Europe for road andrail tunnel fire safety. He

also advises clients on managing the special risksarising in tunnels, transportation, life, safety and theenvironment. Current projects include expertinvestigator for the coroner in the Burnley Tunneldisaster, the development of safe emergency interimoperational strategies for the New Doha InternationalAirport (Qatar) and the development of safe emergencyinterim operational strategies for the Perth Metro.

IT IS AN EXTREMELY serious turn of eventswhen one of the worlds leading certificationbodies (UL laboratories) withdraws its firerating for entire classes of safety critical high-temperature tunnel power systems[1]. Theseare the power delivery systems used for themission critical tunnel safety circuits, rangingfrom alarms to emergency ventilation fans.

Consider further, the facts that underlie thewithdrawal were brought to UL’s attentionproactively by a leading safety critical firecable manufacturer with a reputation forsound corporate citizenship, and there can beno doubt this matter must be taken seriously.

Importantly, once UL became aware ofissues with its fire rated tunnel powersystems in conduit it expanded its testingmore broadly. As a result of these broadenedtests UL lost confidence in the performance ofall its fire rated tunnel power cable systems –not just those tested in zinc dipped conduits.

Other confounding factors identified in theUL tests are understood to include the typesof mechanical lubricants used to pull cables,sample numbers for testing and the specificdetails of cable assemblies. The results of UL’sprivate tests have not been made public.

If UL is to be criticized for anything it wouldbe for withdrawing all its ratings for fireresistant power systems without disclosing tothe industry the nature and extent of theperformance failures beyond the disclosedhot dipped zinc rigid conduit failure mode.

UL’s withdrawal of the fire ratings hasimpacted at least five manufacturers of listedfire cables and all associated manufacturers of

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hot dipped zinc conduit. At stake is thereliability of fire rated equipment listings,standards, certification, prescriptive standards,performance standards and the relationshipbetween standards (such as NFPA), certifiedproduct manufacturers and their certifyingbodies. The fact that it was a reputable cablemanufacturer that brought its own adverseresults from its internal due diligence productsystems testing to the attention of itsindependent certifier (UL) is to be highlycommended. This act must have resulted in asubstantial adverse impact upon their firerated cable sales and created opportunities forother companies whom did not share itsviews on the seriousness of the issue.

But there is likely more here at stake thanmeets the eye. Industry observers in the USare quick to identify companies seeking toachieve a market advantage by changing theregulatory standards - such as via changes toNFPA standards. Legally the US has stronganti-trust laws but recognizes also theimportant role of standards in achieving publicsafety. In this case the cable manufacturerwhom identified the deficiency in the firerating of its own cables has also impacted theUL ratings on its principle US competitors andalerted the market to weaknesses in thestandards testing procedure. There arepotentially serious commercial consequencesfor both cable and conduit manufacturers andstandards bodies that flow from the UL firerating withdrawal.

The seriousness of the relationship betweenmarkets, standards and litigation in the US isgraphically revealed in the case of Allied Tubeand Conduit Corporation v. Indian Head, No.87-157 Supreme Court of the United States,1988, which involved NFPA[1]. It appears highlylikely that in this litigious US context the failuremodes for the fire rated UL listed cables aremore extensive than has been disclosed todate and that factors such as the sensitivity ofcorporations and individuals to allegations ofanti-trust activity and market manipulation arerestraining a more open debate.

The results of the latest UL testing squarelyraise the possibility that the levels of life safetyin our tunnels are lower than we thoughtbecause of a disconnection between productperformance, standards certification, fireratings and the inferences that can be drawnfrom them. This issue has the potential tobring tunnel safety into question because itreveals a gap between practice and reality. Italso exposes the gap in our knowledge aboutexactly what fire testing achieves and how toquantify the consequences of the fire

performance of cables and equipment. These findings do not mean that

construction projects should be halted, oroperational railroads and road tunnels closed– but they do demand informed considerationand a steady hand when making decisionsabout how we proceed with this knowledge.

To better understand the seriousness of thisissue it is informative to take a step back andlook at the context of UL’s fire ratingwithdrawals. Prior to the failure mode for thefire rated cable being identified, UL provideddetailed information on the use of its firerated cables as part of a complete ratedsystem. These UL ‘systems’ are granted fireratings – not individual components[1].

In UL’s publication FHIT Guide Info ElectricalCircuit Protective Systems (e.g. early 2012) ULnoted on its user guide: “Cable is tested as acomplete system. The system includes thecable and/or raceway support, couplings,boxes/ conduit bodies, optional splices, verticalsupports, grounds, pulling lubricants, cabletray, etc. ...metal conduit (IMC) or rigid metalconduit (RMC) are acceptable for use insystems where electrical metallic tubing (EMT)is specified.”[1]

Initially, UL amended this advice by insertinga paragraph that included reference to theunacceptability of using the cables inproximity to zinc: “Unless specifically stated inthe design, all electrical circuit protectivesystem components that come into contactwith fire-resistive cables shall have an interiorcoating free of zinc. This includes raceways,couplings, connectors, boxes, conduit bodies,and the like.”[1]

UL also altered the guidelines it hadpublished for its fire listed cables, for example:“2. Conduit** – 1/2in diameter min trade sizegalvanized steel electrical metallic tubing(EMT), intermediate metal conduit (IMT) orrigid metal conduit (RMC). May also use ULListed flexible metallic conduit not to exceed6ft in length. All conduit is to have an interiorcoating free of zinc.”[1]

Today all these documents are withdrawnfrom the UL web site. The fire ratings havebeen withdrawn and UL has advised that theissue is broader than merely relating to zinc.The terms of UL’s fire listing withdrawal arenoted on their web site as follows:

“UL has recently conducted research on awide array of current products and systemsoriginally certified under UL 2196, Tests forFire Resistive Cables and ULC-S139, StandardMethod of Fire Test for Evaluation of Integrityof Electrical Cables and determined that theyno longer consistently achieve a two-hour fire-

resistive rating when subjected to thestandard Fire Endurance Test of UL2196 orULC-S139. Consequently, UL and ULC will notbe able to offer certification to the currentprogram related to these standards.”[1]

So why is something so seemingly dull as afire listing and certification so important?

It is because using listed high-temperatureemergency cables is deemed by implication tobe “safe enough” and legally this will mostlysatisfy a client, a fire safety authority, courtand coroner that an engineer or project hassatisfied its professional responsibilities forsafety, under the requirements of NFPA 130,NFPA 502 and more generally even where nostandard is prescribed in a contract or localregulations. Using certified or fire listed cablesis how, practically, we deem the electricalcabling system robust enough to control andpower tunnel emergency systems in a fireemergency. For example, NFPA 502 (RoadTunnel Fire Safety, Chapter 12) provides anexample of how certification and the use ofsafety critical cables is regulated:

(1) A fire-resistive cable listed for 2 hours inaccordance with ANSI/UL 2196 or otherequivalent internationally recognizedstandards to 950°C (1742°F) when approvedby the AHJ.

(2) Circuits embedded in concrete orprotected by a 2-hour fire barrier system inaccordance with UL 1724. The cables orconductors shall be thermoset and shall besuitable to maintain functionality at thetemperature within the embedded conduit orfire barrier system.

These NFPA standards provide the crediblelink for consumers and designers toconfidently use fire rated emergency systemcables. Such cables provide the back bone offire alarms, emergency communicationssystems, control circuits and even the jet fans– all mission critical tunnel safety equipment.

For tunnels to operate safely in anemergency the performance of these cablesto control and power emergency equipmentis fundamental – this is why cables are firetested over arduous temperature andelectrical current conditions – and their timeto operational failure carefully recorded.

To understand how these issues emerged isfascinating in its own right. The detail is in thescience of the fire listing tests. Current ULtesting protocols (for these products) require acable to be tested in a furnace vertically ORhorizontally. There is no requirement fortesting of products in configurations and inconjunction with other materials they will beroutinely be installed in (e.g. cable trays,elbows and or dipped galvanized conduit).

Furthermore, it has become a practice that“assumed” minor changes to cable design donot result in a need for re-certification. Itappears that the combination of all theseholes in the listing practice “requirements”have incrementally led to a disconnectionbetween the installed performance of these

FIRE SAFETY

“The underlying issues raised by the withdrawalof the UL fire rating must be professionallyembraced and the responsibilities burdened uponus as public safety experts discharged.”

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FIRE SAFETY

safety critical cables and the performanceinferred from the fact that they are fire listed.

The straw to break the back of this firelisting practice is even more extraordinary – it’sthe story of how zinc and copper are mixed tocreate brass. When copper wire is housed inhot dipped zinc conduit the stage is set forcopper wires to be transformed into brass atcomparatively low temperatures. It is thisobscure chemical mechanism that makes thecircumstances of the UL certificationwithdrawal even more tantalizing as a matterof scientific fact. Adopting the Reason modelof systems failure, it appears our subsurfaceblock of Swiss cheese has zinc lined holes[2].

Urgent laboratory tests have now shownthat when hot dipped zinc conduit is heated,it liberates zinc (zinc melts at around 400°C),which runs to low points inside the galvanizedconduits. The liberated zinc contained withinthe conduit passes through insulationsurrounding the copper cable and reacts withthe copper to form brass (brass melts ataround 900°C compared with 1000°C forcopper). The tests commissioned by the cablemanufacturer revealed unexpectedly shortfailure times of some cables – far less than the2 hour requirement. Following confirmationof these concerns by the UL laboratories, ULwithdrew its fire listings.

Although the practice of using hot dippedgalvanized pipes for mechanically protectingemergency system copper cables has beenpracticed for over 100 years, it is understoodthat vulnerability to this mode of cable failurehas only occurred over the last decade or soas cable construction has changed. Thisproposition has, however, not been tested.

NFPA is currently grappling with theseissues: meetings of both the committees NFPA130 and 502 this month (October) in the USare proposing urgent revisions to emergencycable requirements, likely imposing moreprescriptive requirements for performance byformulating NFPA fire rating criteria. UL hasalso urgently convened meetings to rewrite itsfire listing procedure. However, in a countryoften crippled by fear of assuming corporateor personal responsibility (a reasonably heldfear of litigation) this issue may yet generateadministrative and regulative paralysis withneither corporations nor individuals preparedto step forward and exercise judgement andleadership or legal intervention from othersprecluding them from doing so.

The situation demands, at the very least:• Informed prescription of minimum cable

performance requirements• Urgent revision of what constitutes “Listed”

fire cable• The establishment of pragmatic testing

criteria – to better represent the conditionsof real cable installation and set reliable,functional, performance requirement

• Quantification of the expected performanceof existing installed cables in a fireemergency

• And, depending upon the results of theexpected cable performance, mitigation ofany unacceptable consequential safetyperformance deficiencies

For those of us tasked with making andadvising on immediate decision making onoperational and in construction subsurfaceinfrastructure matters a steady hand with aneye to documentation and detail must beapplied. Now is the time to exercise informedexpert judgement and to well document theprocess. In the event of failed tunnelemergency systems with implicated failedemergency wiring the importance of this stepwill be critical.

Exercising judgement in the absence of agenuinely fire rated cable or a proscriptivecode demands expert judgement. In priorcenturies judgement was often sought fromexperienced (‘grey haired’) practitioners asthey often had wisdom. Unpopular as it maybe in some circles, asking the opinion of elderexperienced practitioners about how toproceed has its place in situations like this. Thevalue of experience should not be dismissed:modern quantitative approaches to riskassessment has its limitations too, and thisissue is an example that tests its boundaries[1].

It is by no means clear the extent to whichthe vulnerabilities revealed in the US are alsomirrored in other markets where othercertification and standards are applied. Itwould be naive to presume there are no issueselsewhere.

In the short term UL is offering interimrevised testing of cables while there may beother listed Fire Resistive Cable Systems thatare not installed in conduit that can provide areliable solution for tunnel applications.

The wheels of tunnel standards fire safetysystem reform are moving in the US. Theindustry must rise to ensure certification is asound basis for the use of emergency cablesand other equipment in safety critical systems.Certification must provide a level ofconfidence for designers, owners, users andinsurers as to the performance of missioncritical tunnel safety systems.

Defining appropriate performancerequirements for cables and other safetycritical equipment, including appropriate testcriteria, is essential. A failure to professionallyrespond to the crisis at this time willfundamentally undermine our standing astunnel safety experts. If a failure of cabling (or

other certified safety critical systems) occurs inthe circumstances now revealed anddescribed – and it results in injury and death –we may well be held accountable for ourinaction - professionally and morally.

The challenge is to make informedconsidered decisions today and to documentthe decision making process. Legally andprofessionally we are not judged in retrospect,questions about the fire performance ofemergency cables are now squarely on ourprofessional decision making agenda.

There are ways to navigate the potentiallysevere short term economic implications forcable manufacturers, projects and certifyingbodies by the current certification withdrawal.A strong hand from standards bodies such asNFPA 130 and 502 coupled with aprofessional response from the industry canmake this issue a watershed in theprofessionalism, not only in the US, butaround the world. The issue does not stopdecisions being made – it means strongdecisions must be made.

I expect there are forces at work whom willwish to trivialize this matter withoutconducting appropriate enquiries into itssignificance. These forces must be resisted. Itis essential that projects under constructionare able to make informed fire resistant powersystem selections and proceed withconstruction on an informed basis. Existingsubsurface transport infrastructure must beable to continue to operate – it is as safe

today as it was yesterday. Our task, armedwith our new knowledge is to ensure it is safeenough. The underlying issues raised by thewithdrawal of the UL fire rating must beprofessionally embraced and theresponsibilities burdened upon us as publicsafety experts discharged.

The changes to the fire ratings of powersystems has not altered the level of safety inour tunnels – it has however altered ourunderstanding of the level of confidence wehave in the fire performance of our tunnelsafety systems. We are at an importantcrossroad – we need to act, and we need todo so professionally, using expert judgement.

Tunnels must continue to operate,construction projects need to proceed, andwe as professionals need to assumeleadership roles in navigating the decisionmaking required. I urge a professionalresponse to this issue as a matter of urgency.

1. http://www.arnolddix.com/usa-cable-fire-rating-withdrawal.html2. Reason, J. 2000. “Human error: models & management.” British Medical Journal 320 (7237): 768–770

REFERENCES

“We are at an important crossroad – weneed to act, and we need to do so professionally,using expert judgement.”

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