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Playing catch up on cables


March 10, 2009
By Marek Kapuscinski

WEB EXCLUSIVE

Playing catch up on cables
Amendments to fire protection measures in the National Building Code of Canada will be voted on this month. The chair of the Cable Fire Research Association explains why the amendment dealing with plenum spaces in commercial buildings is important.

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.  

c81530 
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: alimar@videotron.ca

         


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