Playing catch up on cables

Code amendments to be voted on this month
March 10, 2009
Written by Marek Kapuscinski

March 11, 2009, Toronto - Fire protection features of Canadian buildings are based on the National Building Code, which is updated every three to five years. The current fire protection revision proposals will be voted on in Calgary March 23-25. One especially important proposal to improve the fire safety in commercial buildings in Canada concerns plenum spaces and the myriad computer wires and cables inside them.

Not every part of a building is visible: as every fire fighter knows, there are hidden spaces – and what accumulates in these hidden spaces can play a life-or-death role in a fire.

Some spaces are more hidden than others. We have all glimpsed cluttered fire escapes, closets and storage rooms. But how many of us have looked into the plenum spaces in the suspended ceilings of commercial buildings? If we did, we would see the massive cabling infrastructure that supports our modern computerized, internet-connected offices: we would see cable jungles. And all of these cables are made with plastics that will burn and emit smoke.  

Modern offices could not exist without this cabling infrastructure. However, the National Building Code of Canada provisions for controlling the fire safety of these cables were written before the computer revolution. Indeed, the code was well written in the early 1980s for the realities of the early 1980s. Plenum spaces must be of non-combustible construction. This is the strictest limit on fire spread and smoke emission and it is appropriate for an air plenum. It was true then and it’s true today. A building code must be practical, so a few combustible items were allowed into these plenum spaces, because their quantities were low. Cable was allowed, and because it was then present in small quantities a simple maximum flame spread control (FT-4) was considered appropriate. And it was – in 1980.

Photo 1 shows a typical Canadian installation today. Two things are obvious: the quantity of cabling has increased; and the cabling is intertwined and bundled, making the selective removal of abandoned cables a prohibitive challenge.  

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Photo 1
 
The responsibility for updating the fire safety provisions of our building code rests with the Standing Committee on Fire Protection, a pan-Canadian panel of experts.  One of the proposals the members will vote on is to bring the minimum fire safety requirements for these computer cables up to the same standards that are in force in Ontario, VancouverU.S. This standard is called FT-6 (or CMP), as opposed to the old standard called FT-4 (or CMR/CMG). and most of the

Let’s look at the difference in fire safety between FT-4 and the proposed FT-6. 

An FT-4 test is a vertical flame test and it places a limit on the maximum distance the cables burn when exposed to a standard flame. Smoke emissions are not measured – these cables can emit unlimited smoke and still pass. 

The FT-6 test is a horizontal test during which the cables are exposed to a standard flame, but a strong air draft is added, just like that present in an air plenum. In the FT-6 test, both flame damage and smoke emissions are measured against fixed limits.

The tests are quite different but the question that needs answering is how different are the actual FT-4 and FT-6 cables available in Canada when measured in one of these tests?

That is the question that the Cable Fire Research Association (Canada) took to CSA Canadian Standards Association?, asking where it would suggest such comparative testing should be carried out. It recommended the FT-6 test facility at the ETL Laboratories in Cortland, NY.

The FT-6 test protocol was followed with one modification: the gas burners were turned off after three minutes rather than 20. This allowed measures to be made on how the cables propagated flame and emitted smoke after the gas burners (ignition source) were shut down.

The differences found between the FT-4 and FT-6 rated cables follow:

 

Report No.3052423-001, CRFA, April 6, 2004

FT-4 Cable

FT-6 Cable

Flame/burn spread at 3 min – feet

5.75

0.75

Peak optimal smoke density

3.5

0.49

Average optical smoke density

1.02

0.025

Final air temperature

131

38

Char from end of flame exposure (feet)

19.5

5

Total smoke

20.4

0.495

Flame spread after burner shut off (feet)

>25

0.5

Total smoke after burner shut off

15.8

0.184

 The FT-6 rated cables are clearly superior to the FT-4 in all respects, the highlights being:

  • Combustibility: FT-6 cables propagated flame seven times less than the FT-4 cables.
  • Total smoke: the FT-6 cables gave of 40 times less smoke.
  • And, amazingly, the FT-4 cables smoldered significantly once the ignition source was closed down, giving off more than 80 times more “smoldering smoke” than the FT-6 rated cables.

So, we have at our disposal a simple way to update our national building code provisions on the fire safety of computer cables installed in air plenums. 

If the quantity of cabling is greater, then the fire safety rating of each cable must be correspondingly better. And, equally important, no material placed inside an air plenum in any significant quantity should have zero controls on smoke emissions.  As every firefighter knows, smoke is the prime killer in any fire, and having unlimited smoke generation potential from a large amount of cabling in air plenums is simply unacceptable. Air plenums should circulate breathable air, not smoke. This month, the Standing Committee on Fire Protection can vote to afford all of Canada this level of fire safety.

Marek Kapuscinski is an independent consultant with more than 30 years experience in communications cabling. He holds a doctorate in the physics of polymers. He is presently the chair of the Cable Fire Research Association and Partners (Canada). He can be reached at: This e-mail address is being protected from spambots. You need JavaScript enabled to view it