Canadian Consulting Engineer

Cable Pile-Up

August 1, 2000
By Canadian Consulting Engineer

The "new economy" of data transfer depends on the cable that links its computers and central systems. Banks, stock exchanges, health care, national security and transportation organizations whisk data...

The “new economy” of data transfer depends on the cable that links its computers and central systems. Banks, stock exchanges, health care, national security and transportation organizations whisk data around the globe 24 hours a day through plenum cable conduits in office towers.

Yet the fire safety of this cable snaking through miles of ventilation ducts (plenum) in ceilings is a major concern for fire protection specialists. Fire reaching the circulation wind tunnels can be catastrophic. At best, fighting fires in skyscrapers is a major challenge, so high standards of flame and smoke retardancy for anything in these cable plenums has been the norm.

Even before the computer revolution, the plenum with millions of miles of staid old voice telephone cable was recognized as a hot spot requiring special regulations. Many major high-rise fires in North America over the past 30 years showed the deadly role of plenum. Consequently, anything in there had to be enclosed in metal conduit.

When manufacturers produced a cable that itself was equal in safety to cable in metal conduit, NFPA recognized a flame and smoke test called the Steiner Tunnel, and gave it a designation, UL910. If a cable passes UL910, it is as safe as cable in metal conduit. The Underwriters Laboratory standard for this test is UL444. In Canada, the equivalent is the CSA FT-6 standard.

Except in Canada

Before flame and smoke retardant cable was developed, Canada’s codes also required cable to be enclosed in metal conduit in plenum. The code people in Ottawa’s National Research Council (NRC) producing the National Building Code (NBC) had agreed plenum needed tough regulations. But then in ’84, an obscure computer program at NRC indicated the hazard was minimal in plenum. A massive deregulation was put on the books of the NBC. Despite the concerns of many in the industry, those deregulated standards are still in place today. The code went from the most stringent of fire safety standards to a moder- ate Ontario Hydro flame test developed in the 1970s for a PVC power tray cable. And there is no smoke test. Cable passing the NBC code emits copious billows of smoke. Chemicals put into the PVC/PE polymer compounds to retard flame produce lots of smoke in fires.

Ontario and British Columbia representing 65 per cent of the market for data cable in Canada rejected this deregulation. Backed up by extensive study and public hearings, the people responsible for building codes in these provinces stayed with the safe standard for plenum, UL-910, and maintained harmonization with the U.S. and NFPA codes and regulations.

Hence, in Canada, it became necessary to have a hierarchy of cable fire test standards. Canadian Standards Association’s (CSA) Committee 214 in conjunction with Underwriters Laboratories Canada established FT-1, FT-4, and FT-6 as test standards. FT-1 is the base, low hazard test. FT-4 is the Ontario Hydro vertical tray cable flame test, no smoke criteria. Finally there is FT-6, a flame and smoke test which is equivalent to the UL-910 test and considered as safe as cable in metal conduit.

The table on page 50 shows the major differences between a stringent FT-6 flame and smoke test, and the FT-4 vertical flame test.

Skyrocketing fuel load

The situation is reaching a crisis point. With each leap forward in computer technology, new voice and data cable is installed over old in plenum. Seldom does the installer bother to remove the old cable. Thus, if there were a fire, the cable fuel load has exploded commensurate to the growth in the use of computers and transmission of data. Fire scientists at the National Fire Protection Agency (NFPA) are wrestling with new standards to defuse the potential crisis.

If we need evidence of the plenum hazard, the Alexis Nihon Plaza fire of ’86 in Montreal provided ample proof. A fire occurred on the tenth floor of the 15-storey office tower, and the blaze lasted for 13 hours, causing a portion of one floor to collapse and major fire damage to three other floors. The fire also spread to the entire top floor of the building and completely gutted it. The plenum space where the communication wiring was installed provided a path for the fire up to the top floors.

Cable manufacturers are also uneasy with a lurking liability issue that is rooted in a court judgement of the early 1980s concerning another major fire that occurred in Canada. The court judged that cable manufacturers were liable for not adequately advertising that a safer cable existed than the infe- rior cable involved in that suit for damages.

Not surprisingly, cable manufacturers are clamouring for an emergency amendment to the National Building Code of Canada to harmonize its cable tests with the U.S., Ontario and Vancouver on the safety issue.

As Bob Kostash, director of sales and marketing at Lucent Technologies, said recently: “It is well past time that the National Building Code, Canadian Electrical Code, Canadian Standards Association and other provincial and municipal code authorities rectify what could become a serious life-safety issue. Canadians cannot and should not be treated differently in areas of safety. They certainly should not be subjected to an inferior standard than that in place in the U.S. “

Forced to adopt

lower standard

This dysfunctional code matrix and inequity across Canada for safety in plenum cable puts the spotlight on the process of code change. And there is a need for change. The NBC is a model code and a product of the NRC’s Institute for Research in Construction. Provinces are empowered to enact their own building codes, but traditionally, and for good economic reasons, they have adopted portions of the NBC, or adopted it in total. Traditionally as well, when major portions of the country deviated from the NBC on important issues of safety, NBC, the model code, would adopt the change, or at least quickly put it on the table for aggressive debate and resolution.

The industry expected similar action with the plenum issue after 65 per cent of the market deviated from the NBC, rejected deregulation, and maintained stringent safety standards for plenum. It didn’t happen.

Deviating from the NBC doesn’t come cheap. Human resources are required in the provinces to maintain these differences from NBC in their codes. The situation in British Columbia shows how this can lead to problems. In ’98, during a major cost cutting exercise, the province reduced its building codes staff from 12 to two. The NBC was quickly adopted by Victoria with few major exceptions. Hence, the cable industry was faced with deregulation from FT-6 to FT-4. Vancouver with a strong history of high professional content in electrical and building codes, and a separate charter, stood firm with FT-6. However, the fast-growing municipalities snuggled around Vancouver had no alternative but to adopt the lower standard, FT-4. This stressful dichotomy puts the issue of code change and the need for plenum safety back on the front burner. Electrical inspectors and the electrical cable industry know what is needed. And they cringe with the inequities.

Why didn’t the NBC take the proactive, traditional role of addressing major provincial deviations? The response to this question is muted. The provinces should have formally requested a review. Meanwhile a major percentage of high rise structures is protected with a safe standard while the rest exist with a standard a mere fraction of the norm for North America.

Ironically, the whole process of code change at NBC has been on hold for a couple of years in the efforts to change to performance standards. Yet a performance standard for plenum has been in place in North America for some time.

One issue delaying a timely emergency amendment to FT-6, allegedly, is cost. A high standard of safety often comes at a price, just as deregulation often means a windfall. The cost of FT-6 cable is about twice that of FT-4 affirms Gary Mistak, marketing director of Anixter, the world’s largest cable distributor. Yet cost was an incentive initially in the move to FT-6 from cable in metal conduit. In a
total cost analysis, including labour savings in installation, FT-6 is less costly than cable in metal conduit. In the scheme of total building costs, the price of safety with FT-6 is hardly a blip.

Fire marshals bristle at the idea that costs could take priority over safety; that cost savings can spur a deregulation, or increased cost can block adoption of codes that would save lives.

Yet cost savings in materials often bilk taxpayers at the end of the day since they eventually lead to higher costs in fire fighting equipment. They could also lead to a higher cost in lives. Hence, stringent safety standards must rule in plenum, the deadly air wind tunnels in high-rise office buildings.

How can you help? Write, telephone, e-mail your local building code branch or your local Member of Parliament.CCE

Dave Dykeman is president of Connec DJ & Associates in Oakville, Ontario and has been active for 15 years on Canadian Standards Association and Safety Council of Canada national and international committees.


Test conditions FT-4 FT-6
Ignition heat flux BTU/h 70,000 300,000
Cable length 7.5 ft. (2.3m) 24 ft. (7.3m)
Cable tray width 12 in. (300 mm) 12 in. (300mm)
Cable tray loading Single layer spaced Single layer touching
in centre 250mm full width of tray
of tray
Draught NO 240 ft/ min
Smoke measurement NO YES
Maximum damage allowed 1.5 m 1.5 m


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