The information era has filled nearly every crack and crevice of office buildings with miles and miles of low-voltage communication cable, whether for phones, fax machines, IT networks, or high-speed Internet. As building owners try to keep up with tenant demands for the latest technology, new cable often gets piled right on top of existing cable.
Since much of this cable resides in return air plenums that feed fresh air to work spaces — either above ceiling tiles or below access flooring — excess cable has become one of the most dangerous but largely ignored fire hazards in today's office environment.
"Back in the late '70s nobody anticipated the amount of computers and networking we would have in our buildings," says Frank Peri, president of Communications Design Corp., a Kennedyville, Md.-based structured cabling consultant. "All this abandoned cable places a large fuel load up there that is potentially hazardous."
Low-voltage cable itself does not carry enough electricity to become an ignition source, says Peri, but older cable is combustible and can feed a flame ignited by another source, such as a power cable in an electrical closet. The smoke produced from burning cable will be discharged into office space by the return air.
Randy Thompson, senior director of program and project management with the Dallas office of real estate giant Cushman & Wakefield, says he's seen cases where plenum areas in office buildings, hospitals, and university buildings were so packed with generations of cable that the ceiling grids drooped from the weight.
"Many buildings have hundreds and hundreds of miles of flammable, poisonous, gas-producing cable hanging in air-plenum spaces," he says. "In the event of a fire, not only will these poisonous gases be thrown back down into spaces where people are working, but that return air in the plenum will draw across the cabling, causing it to flame longer."
Another concern is that most cable is concealed behind ceilings and walls, or under floors, oftentimes out of the reach of sprinklers and detection systems, says Rick Glenn, principal engineer of the Chicago office of Chantilly, Va.-based Gage-Babcock & Associates.
Cable is also often out of sight from building occupants, facility managers, and even firemen, says Peri. "There's a number of documented cases where the firemen could not even find the fire because it followed the cable run in the ceiling plenum space," he says.
So how did so much potentially combustible cable to make its way into one of the most critical areas of any building?
The problem is essentially two-fold: First, only recently have the two major related codes — the National Electrical Code and NFPA 90A, the Standard for the Installation of Air-Conditioning and Ventilating Systems — mandated the removal of abandoned cable from plenum spaces. Second, in 1975, the NFPA passed an exception for the NEC that allowed for a "limited" amount of low-voltage cable and wire that was tested to have "adequate fire resistance and low smoke-producing characteristics" to be installed in plenum spaces without conduit. Before then, any material installed in a plenum space had to be either noncombustible or installed in metal conduit.
"What started out to be an exception was completely bypassed when we hit the electronic age," John L. Lebduska, an architect and professor of technology in the School of Architecture at the New Jersey Institute of Technology, Newark. "Suddenly, an enormous amount of cable and wire had to be distributed throughout buildings. First it was a few telephone wires up there, then it was 50 telephone wires, then it was computer cable, which began to get bigger and bigger."
Combine the technology boom with the frequent tenant turnover that occurs in many office buildings, and suddenly there's a hazardous amount of cable in the plenum space, adds Lebduska.
As a result, says consultant Peri, nearly 60 billion feet of plenum cable has been installed in buildings throughout the U.S.
The most prevalent application for plenum cable is computer rooms, says Mark Earley, assistant vice president and chief electrical engineer with the NFPA, and secretary of the NEC. "Most companies in the '60s and '70s had quite a bit of real estate devoted to computer centers. This equipment requires lots of cooling, and raised floors and suspended ceilings accommodate that. This plenum space also became a natural place to run the cabling."
Recognizing the fire hazard association with castaway cable in plenum spaces, NFPA code officials stiffened the 2002 versions of NEC and NFPA 90A to require the removal of unused cable.
Owners and tenants have not necessarily embraced the code change with open arms, as the task of removing old cable can be expensive and laborious.
Cushman & Wakefield's Thompson says owners and tenants can expect a 15-30% increase in the cost of labor for a typical tenant build-out, depending of building type, size, and location.
"Tenants agree that it is a life-safety issue and cabling has to come out," he says. "But they become a bit disgruntled when they learn that in order to upgrade their network, they have to remove not only the cabling they put up there, but in some cases cabling four tenants ago put up."
Thompson says his firm is placing the burden of paying for this removal on the owners: "In all of our RFPs to landlords, we have a very clear statement that says the landlord is responsible for removing the abandoned cabling out of the air plenum space, so that if it does become an issue, our tenant is not paying that cost.
"It becomes a negotiating point, like any other cost," says Thompson. He says most owners simply recognize it as an additional tenant improvement allowance, which is typically given to tenants to build out the space. "Owners have to realize that this is another cost they have to bear, just like the costs of removing asbestos years ago."
Gage-Babcock's Glenn recognizes the threat of abandoned cable, but says the vast majority of buildings he's surveyed do not have a problem with abandoned communication cable, "at least not in enough of quantity that would really cause great concern," he says.
"If it's plenum-rated cable that has low burning and smoke characteristics, I'm not that concerned about it," says Glenn. "If it is not rated for plenums and there's a lot up there, then it's a problem."
While the code change is a step in the right direction, there are loopholes in the NEC code language that can leave the door open for building owners, tenants, and even building inspectors to interpret a specific situation virtually any way, says Peri.
"The code requires that all abandoned cable be removed from service, unless it's 'not accessible'— meaning you can't get at it to pull it out — or unless it's tagged for 'future use,'" says Peri. "Inspectors, for instance, may look into a ceiling area and see that the cable has tags and figure that it's tagged for future use. It's really not a well-enforced situation at this time." He adds that not all jurisdictions follow the 2002 NEC code.
Thompson expresses alarm that, despite the good intentions of the code revision, building occupants may not be safe from cable fire for years to come.
"The way the code is written, this thing is going to be with us for a long, long time," says Thompson. "We are not going to be fully through a removal cycle for at least 15-20 years, because the trigger that causes the requirement to remove old cable is when a business replaces its existing infrastructure."
Thompson points to one case where a tenant signed a 15-year lease for 40,000 sq. ft. of office space in 2001, before the new code was passed. "There were five generations of cable already there, and then the tenants installed their new cable infrastructure," he says. "It may be 10 years before they replace that new infrastructure."
Fire- and life-safety comparison of cable and wire distribution systems
|System||Required fire test||Protection against cable/wire smoke exposure||Electrical grounding provided||Comments|
|EMT conduit within the ceiling for both power and telecom||None. Assumed adequate||Very good. Cable smoke generated by a fire is kept within conduit.||Very good. Continuous ground to power panel.||A safe system for plenum use. No fire, smoke, or electrical shock threat. Restricted wire space and poor flexibility.|
|Cable trays supporting combustible plastic cable||None for cables, except for flame spread limit of 5 ft. in 20 minutes||Smoke developed limit of 850 for plastic-covered cables (essentially, unlimited smoke).||Good. Bolt connection of adjacent sections. Separate ground wires for power side.||Cost-effective and flexible method for telecom distribution. If a fire occurs, plastic cable insulation and jacketing can burn and release toxic smoke. Cable insulation has high fuel load. Abandoned cable must be removed.|
|Access floor for air and electrical delivery||None, except for flame spread limit of 5 ft. in 20 min. Plenum-rated cable required. Power wire must be in steel conduit.||None. Unlimited smoke permitted. Smoke will enter the breathing zone.||Poor. Care required to remove paint from pedestals to connect ground wire.||Very good system for air and electrical delivery. However, can be dangerous if fire occurs. Burning cable will introduce toxic smoke into work zone.|
|Access floor for wire and cable delivery only||None. Non-plenum-rated cable is permitted. Power wires must be in steel conduit.||Power wires are protected in steel conduit, but non-plenum-rated cable is allowed.||Poor. Care required to remove paint from pedestals to connect ground wire.||High-capacity wire distribution system that does not require plenum-rated cable. Extremely dangerous in a fire if large amounts of non-plenum-rated cable are installed.|
|Non-metallic surface raceway (plastic)||Non-plenum-rated cable and unprotected power wires are allowed. 50 second test of duct: 5 sec. burn, 5 sec. no burn for five sequences.||Protection for a 25-sec. fire exposure, then no protection.||Fair. Ground with separate grounding wires.||Plastic raceway is very popular as a retrofit system. Fire test does not adequately protect non-plenum-rated cable or PVC insulated power wires inside. Electric shock hazard exists if wire insulation melts.|
|Poke-through outlets||1- to 4-hour burn test to achieve UL fire rating. No smoke penetration criteria through outlet||Systems are heat-activated, so cold smoke can penetrate the outlet||Good. Steel conduit for power grounds each outlet.||Least expensive system on a first-cost basis. Some systems, however, need to be redesigned to eliminate cold smoke penetration. Sealant required to prevent "smoke thru."|
|Cellular floor systems||2-hr. minimum fire exposure at temperatures reaching 1850 F||No smoke exposure possible. All wire and cable is enclosed in steel compartments encased within concrete slab.||Good. All cellular units are welded to steel frame.||Good system for both power and telecom distribution. Provides permanent protection for cable and wire.|
|Note: These systems are evaluated with respect to the testing required by code, the expected risk to occupants in a fire, and the electrical grounding provided.|
|Source: John Michlovic, P.E., national technical manager with H.H. Robertson Floor Systems (now Centria)|