Electrical Circuit Integrity during Fire

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"Fireproofing" cables or cable trays or conduit can mean two different things. Cable Coating is generally considered a fire retardant, which lowers the spread of flame and generation of smoke along the combustible cable jacketing. "Circuit Integrity" measures typically mean and enclosure, which is meant to keep cables operational during a fire. In Canada, this means testing to ULC-S101, according to the building code. Unfortunately, S101 is ill equipped to deal realistically with circuit integrity, particularly for enclosures. There are two ways of achieving circuit integrity. One may either choose mineral insulated or otherwise fire-resistant (tested for that purpose) cables, or one may use an enclosure that was tested for that purpose. This is where we get into grandfathered systems in Canada. Our code indicates that 2" of concrete coverage over or around electrical circuits is sufficient to obtain an unquantified duration of circuit integrity. If this were evaluated to the state of the art, this would most definitely cause problems (failures). 2" of concrete, regardless of the conductor configuration, percentage fill, etc. is of course a gamble. I asked once what this was based on and did not so much as get a response. The other grandfathered approach of course is drywall shaftwall systems. Drywall shaftwalls were tested as a flat wall, no corners, no turns. This approach has pretty much been negated for use around ductwork (i.e. pressurisation and grease ducting, which are required to have a fire-resistance rating) since  the adoption of the more suitable ISO6944 test regime by ULC as well as ULI, whereby a duct is suspended from a full scale floor slab and the enclosure is built around the duct (or an inherently fire resistant duct is similarly tested without an enclosure, since it already contains a layer of insulation), for a more realistic configuration and exposure. Drywall shaftwall systems were entirely grandfathered for this application and are not representative of due diligence the instant a properly and purposely tested system with bona fide listings became available. The same thing applies to circuit integrity enclosures. The only difference is that we are lagging behind the US in this country again.  For the ductwork, a Canadian entrepreneur went ahead and got ISO6944 passed by the ULC standards council and then went and performed testing. This made all the old grandfathered stuff junk and essentially indefensible. No one has gone ahead and done the same thing in Canada with a similar product to address circuit integrity. However, this has happened in the US, through UL and other laboratories. Since UL is accredited by the SCC in Canada and its listings are on public record up here, one is ill advised to use grandfathered Mickey Mouse systems for circuit integrity. And make no mistake: 2" of concrete and drywall shaftwall, which was never tested with all those corners around a tray or a duct, is Mickey Mouse compared to anything that has passed the real McCoy: UL1724 Standard for Tests of Thermal Barrier Systems for Electrical System Components as well as its cousin, UL2196 Standard for Tests of Fire Resistive Cables. UL1724 had its origin with USNRC Generic Letter 86-10 Supplement 1. "Supplement 1" was to address lessons learned from the Thermo-lag 330-1 bamboozle. Supplement 1 is one tough and expensive test to pass. Nothing is done in anything less than a full scale fire test, running easily into 6 figure costs per burn MULTIPLIED BY all the applications one desires to test. You have to test the smallest as well as the largest application (12" and 36" cable tray). This is extremely pricey to do. Accordingly, the materials are extremely expensive. After all, manufacturers are not in the charity business and must recocover their costs. Novices might look at the highly simplistic materials used for this purpose and think there is nothing to this. And in fact, as far back as the 1970's, it was never a real secret, that if you wrap enough insulation around the conductors, you will get a rating. The only thing that really defeated this idea was Thermo-lag 330-1 (which is not a fibrous insulation). No matter what was done to this material (used for fireproofing purposes over electrical circuits in full scale fire testing) by various nuclear power plant owners (USNRC licensees) who sponsored extensive testing, where they piled more and more Thermo-lag onto the old stuff, in effect trying all they could, it just would not pass. Also, since the fore-runner of this testing was the USNRC, and the commercial version of it (UL1724) has undergone various revisions, the UL systems listed in the UL Building Materials directory are not necessarily qualified to the latest USNRC compliant or the latest UL version. But that does not mean that the older listings are simply discarded or that the manufacturer just went ahead and ran a new test. In fact, there have been a number of test failures, where contractors in the nuclear field applied UL listed systems to the latest Supplement 1, which is state-of-the-art. All materials qualified to the latest UL1724 or Supplement 1 are astronomically expensive. The only time they get used in Canada is if someone made a mistake and installed normal wiring instead of mineral insulated cables and had to fix it up afterwards. And with the dollars involved either way, such bamboozles typically get buried instead of remedied. For small runs of cabling, there is absolutely no point in even bidding such enclosures. Only for large and full trays is it worthwhile considering. Then you also have to consider the added weight of the wrap. By the same token, 2" of concrete and shaftwall are nonsense now. The technical justifications for this grandfathering have all but evaporated years ago. The best answer is mineral insulated cable, 99% of the time. But even there, you need some enclosures, namely at the point where the cables are terminated. You can run MI into a box in an electrical room. But just because that room is a service room and may be rated all around, this does not mean you no longer need a rated box or wrap around the electrical outlet box or junction box where the wiring is terminated because that box can fry from a fire within the room. The cable may thus be OK but the circuit is toast because the junction box was not protected. This is truly Cheech and Chong at work one might think, but it happens ALL THE TIME. Unprotected termination points in circuits that are required to have a fire-resistance rating are an extremely common deficiency in Canada, rarely policed, sometimes unnoticed. For a peek at a product data sheet on 3M's electrical circuit integrity enclosure product, please click below:

http://www.mmm.com/us/arch_construct/firestop/product/p_14.html

Germany has standardised this sort of testing via DIN4102 Part 12, dated January 1991, Fire behaviour of building materials and elements, Fire resistance of electrical cable systems, Requirements and testing. Part 12 encompasses both enclosures for cabling and bus ducts, as well as inherently fire-resistive cables, such as mineral insulated cables. Enclosures for ductwork as well as wiring are a regular part of passive fire protection work over there. It is also not nearly as expensive as North American qualified approaches. Typically, lightweight mineral boards are used, such as calcium silicate and bonded vermiculite. One product that was fully qualified for the US nuclear market was Promat. Unfortunately, they were taken advantage of in some dealings, which meant their considerable testing investment was all for naught. And also, the test facility used was not accredited by the SCC for testing or certification purposes, which makes it all fairly irrelevant for use in Canada, meaning we're stuck with our ultra-expensive solutions - and MI cables. All circuit integrity products must also be tested for ampacity derating where power cables are concerned. It is important to keep in mind that the configuration tested to the latest version of UL1724 be tested for ampacity derating, since there have been failures when older systems were tested to newer requirements. This means that thicker systems (more wrap, more money) may have to be used than you may originally think by just browsing through the UL listings. Thickness is a factor in ampacity derating. There have been assorted ill-conceived tests over the years where cable coatings have been used to obtain circuit integrity. But this has never resulted in the minimum hourly ratings we need in Canada, nor are there any bona fide listings complying with Supplement 1, UL1724 or DIN4102 Part 12.

Firestop Page

Main Page

Glossary

Contact

Main Site

Firestop Site

Code Evaluations AVAILABLE!

Glossary of Fire Protection Terms

3M Fire Barriers

Vectorising Drawings and Maps; Paper to CAD

Circuit Integrity Fireproofing

Bounding

Code Req's for Firestops

Essay on Performance Based Codes

Master Spec. Section 07840 Firestopping

Related Sections to 07840

Penetration Seal Drawings

Building Joint Drawings 1

Building Joint Drawings 2

Building Joint Drawings 3

History of Firestops in North America

Warnock Hersey Experience

Firestop Trade Jurisdiction

Achim Hering Bio

Man Made Mineral Fibres

Fire Protection Industry Links

Firestop Products and Equipment

Firestop Mortar

Firestop Silicone Foam

Intumescent Products

Endothermic Products

Insulation Products

Caulking & Paint Firestops

Firestop Pillows

Firestop Devices

Firestop Slide Show 1 of 10 Basics

Firestop Slide Show 2 of 10 Code

Firestop Slide Show 3 of 10 No Seal

Firestop Slide Show 4 of 10 Deemed-to-comply

Firestop Slide Show 5 of 10 Misinstalled

Firestop Slide Show 6 of 10 Re-entered

Firestop Slide Show 7 of 10 Faulty Spec.

Firestop Slide Show 8 of 10 Proper Firestops

Firestop Slide Show 9 of 10 Test

Firestop Slide Show 10 of 10 Smoke and Trays

Sample Firestop Listing

Kitchen Exhaust Cleaning; Boiling-Hot Pressure Washing

ULC           UL

T O S

(Theory of Survival)

DIBt

TU Braunschweig iBMB

CONTACT

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