Network Cabling Specification and Installation Practices Impact Building Safety  

Thousands of fires occur in U.S. business facilities every year. According to the National Fire Protection Association (NFPA) reports, each day 323 non-residential structure fires will occur, injuring four people and causing $7.4 million in property damage. In a fire, cables can be a significant source of fire load and smoke. Smoke can obscure evacuation routes and is the leading cause of damage to electronic equipment found in local area networks and data centers. Smoke damage is possible even when the source of the fire is distant from the data center. In fact, in a typical data center cabling is often the largest single source of combustible material. Combustible cabling may quickly spread fire and smoke throughout a building, putting workers at risk. As the smoke spreads, it carries conductive microparticles and moisture throughout the building, which contaminates equipment by creating shorts and bridges in the microelectronics. The result can be immediate equipment failures, or failures that can take days or weeks to manifest as corrupted data and sudden system failures. It is smoke, rather than flames, that does the real damage. In fact, studies attribute 95 percent of the equipment damage in a typical data center to smoke. Data center fires are not uncommon-in the U.S. alone, an estimated 400 data center fires occur annually.

The concerns are legitimate and rising about the growing amount of combustible cables present in commercial buildings required to service the ever-increasing demands of IT networks. More workstations, each with expanding capabilities and increasing bandwidth requirements, are taxing our infrastructure. Communications cabling, which carries important data packets to and from computer rooms is as common in building ceiling cavities as duct work. While most users select communications cable on the basis of its electrical performance requirements, fire rating factors are often overlooked beyond what is minimally required by code. This fact places each building at a greater fire risk with each new installation of communications cable.

Courtesy of: DuPont Cabling Solutions

Communications cabling is governed by NFPA's set of model codes as adopted by most local jurisdictions in the U.S. in local building and fire codes, then enforced by the local authority having jurisdiction. The question of who is ultimately responsible for code compliance is an issue requiring legal counsel. In the event of a fire, both the building owner and tenants are likely to bear some responsibility. However, these codes represent minimum safety requirements, leaving meaningful improvements in the fire safety performance of network cable in the hands of a few key groups of people, architects among them. Not only is knowledge of specification options for best in class fire safety performance a competitive advantage, it is central to an architect's understanding of appropriate standards and regulatory requirements. In short, equipped with a comprehensive working knowledge of cabling fire safety issues, architects can design buildings which pose lower risks and provide more secure, sustainable environments.

Fire Evidence

The communications cable most often used in commercial buildings is called plenum cabling. It is designed for use specifically in hidden spaces within dropped ceilings that handle return airflow to HVAC equipment-the plenum space-and distributes the network from telecommunications rooms to the users' workstation. Since the 1970s, several significant fires occurred where cable running in plenum spaces greatly increased the severity of the fire damage. A fire that occurred in offices at the World Trade Center in 1975 brought the fire hazards associated with cables installed in plenum spaces to the fore. According to a report by NY Board of Fire Underwriters, "The worst and most hazardous condition is when wires and cables with combustible insulation are run through plenums to service the floor above. This provides a double hazard by introducing combustibles into the air conditioning. It should be noted that the mass of cables to supply communication equipment in many office occupancies is sufficient to sustain a substantial fire. While an individual cable is extremely difficult to ignite, a group of cables lying parallel will burn intensely, similar to the situation that exists with a group of logs in a fireplace."

In May 1988, a fire in the Bell Central Office in Hinsdale, Illinois caused $90 Million in damages and a 17-day outage; calls were disrupted for four weeks. An NFPA fire investigation recounts a chilling scenario: "Fueled by the insulation, the fire quickly spread into the groups of cables in the cable tray and eventually emerged at the top of the cables. The fire was able to travel horizontally both in the confined spaces between cables in the trays and in an open space between the top layer of cables and the ceiling."

Courtesy of: DuPont Cabling Solutions

In October 1996 a fire at Rockefeller Center in New York was described in The New York Times: "The fire, reported at 3:59AM, jumped helter-skelter from floor to floor following the snaking utility products, feeding on insulation and thick cable-housing and breaking out into office here and there, fire officials said."

A United States Fire Administration, National Fire Data Center report about a 1991 fire at One Meridian Plaza in Philadelphia found that "Within the telephone and electrical rooms, unprotected penetrations of the floor assemblies allow conduits and exposed wires to travel from floor to floor. Several breaches of fire-resistance rated construction were observed in the walls separating the electrical and telephone rooms from the ceiling plenums and occupied spaces on each floor."

From these and other fires, valuable lessons were learned. Prime among them are the fact that the ignition source is often electrical failure, and cables can add significant fuel load and spread fire rapidly along the cable pathways and spaces. Investigators further concluded that even small fires can cause extensive smoke damage, and combustible materials in concealed spaces are of great concern.

Cabling's Contribution to Fuel Load and Smoke

Electronic communications systems began to be installed on a large scale in the 1970s and 1980s. Seeking ways to cost-effectively run cable through a building, cables were run from floor to floor, through vertical air shafts or other openings. Within a floor, cable was installed above raised ceilings, below raised floors, or within horizontal air ducts, or plenums, obviating the need to break through walls, and enabling cable to be installed out of sight and out of the way. Unfortunately, and not realized at the time, was the fact that these vertical and horizontal runs maximize the spreading of smoke and fire in the building. Smoke and fire quickly rise to higher floors via unobstructed vertical risers. But because these vertical spaces have a higher fire rating and are not part of the building's HVAC system, fire safety requirements for vertical riser cable are less stringent than those for plenum cable. The horizontal plenums, often used to carry forced-air heat and air conditioning, can now carry smoke to all ventilation ducts. The pressurized air flow within a plenum served to force-feed and accelerate the fire with oxygen.

Compounding matters further, over the past two decades, the amount of electronics in a typical office building, hospital, school, or data center has increased dramatically. As a result, there has been a surge in the cabling that connects these systems. In fact, an estimated 60 billion cable feet of local area network cables has been installed in horizontal concealed spaces during the last 20 years in the United States alone. Granted wireless communications and networks are on the rise. Even so, physical cabling still represents the linchpin of a communications or computer network-wireless included. Stoked by ever increasing needs for IT systems, the use of cabling can only continue to soar.

Combustible Components of a Typical Plenum Cable

Plenum cables-whether copper or fiber optic-contain large quantities of plastics, and many plastics will burn and/or generate great amounts of smoke in a fire. A typical cable for data or voice transmission has two main components, a cable core made up of insulated copper wires twisted in pairs and a jacket. The industry standard cable is 4-pair UTP, with four twisted pairs of insulated wire, with "U" meaning "unshielded" and "TP" meaning "twisted pair." More than half of this cable is potentially flammable plastic. In an office with 100 workstations each with two cables run 100-feet (average) to each workstation can contain as much as 300 pounds of combustible cabling materials in the ceiling or floor plenum. Considering multiple floors and high-density areas like computer equipment rooms, it is easy to understand cabling's significant contribution to a building's fire load. Cable insulation and jacketing material are an undeniably significant fuel source, and, when they are heated, can generate a tremendous amount of smoke-a scenario with dangerous repercussions for building occupants and equipment.

Fuel Load of Commonly Used Cable Insulation and Jacketing Materials

The cabling industry has been challenged by developing materials that excel at three, often divergent, goals: electrical transmission properties; reasonable processing parameters for productive cable manufacture; and high performance ratings on flammability, smoke generation and fuel load.

The three most commonly used materials in cabling today are Polyethylene (PE), polyvinyl chloride (PVC), fluorinated ethylene propylene (FEP), all of which have a significant impact on the level of fire hazard. When comparing the performance of each, the first, PE, offers excellent electrical properties for insulating copper. However, in a fire, it is highly combustible, extremely high in fuel load, and readily generates dense smoke, which creates significant life and equipment fire safety hazards and risks. The second, PVC, has poor electrical properties but offers better fire performance than PE; yet, it alone is difficult to melt-process and has poor flexibility in cable applications.

To resolve these issues, other materials are added. The resultant PVC compound offers better electrical performance, greater flexibility, and are easier to melt when the cables are manufactured, compared with PVC alone. However, while PVC compounds represent an inexpensive material that creates a relatively safe jacket for most plenum cables, it remains combustible in nature.

Lastly, FEP has electrical insulation characteristics on copper equal to PE, and needs no additives to meet fire safety standards. Meeting the highest performance criteria for flame spread, fuel load, and smoke generation, FEP has inherently good fire and smoke characteristics that help cables meet code and insurance requirements by a comfortable margin. In fact, PE and PVC, which are combustible materials by the NFPA standards, can increase the combustibility of a cable, and contribute up to eight times as much fuel as FEP.

Smoke Generation and Flame Spread Properties of Commonly Used Cable Types

Not all communications cables are alike-and not all pose the same fire risk. There are several basic cable types: Limited Combustible Cable (LCC), which has its FEP insulation and jacketing, communications multipurpose plenum cable (CMP), which has an FEP insulation but a PVC jacket; and CMR riser cable and CM (general purpose communications cable), both of which have PE insulation and PVC jackets.

In a fire test replicating a real world office fire, in a very short period of time the CMR cable generates large quantities of smoke, with the fire spreading down the length of the cable. The burning CMR cable produces temperatures of 1000°C-at 800°C temperature the integrity of a building's steel structure starts to be compromised. Better performance is seen in the CMP cable, which generates less smoke and less fire. The LCC fares even better. After a prolonged exposure to the heat source, the LCC evidences almost no smoke and no sustained ignition or flame spread.

One of the most telling battery of tests comparing these cable types was performed by the Building Research Establishment (BRE) facility in Bedford, England. This BRE test is more severe than the Steiner Tunnel test, specified under UL 910. Here, a real-scale test set-up was constructed which matches the environment found in the air plenum of a typical building. During the test the CMP cable generated approximately 15 times the smoke of LCC. But the fact that by the time only 30 seconds have elapsed, the CMP cable has generated approximately 10 times the smoke of LCC means people in a burning building could be engulfed in smoke literally in a matter of seconds, making a safe evacuation and a chance to protect expensive equipment virtually impossible.

Courtesy of: DuPont Cabling Solutions

Further data from the test fire show that flame-retardant PVC-as used in CMP cabling-has approximately the same fire loading as wood. This is comparable to sticks of wood in a plenum, on fire at one end, and being bathed in a stream of air-a graphic image of the extent of fire hazard of CMP cabling in a plenum. The quick spread of such a fire is compounded by the fact that flame retardant PVC catches fire at a much lower temperature than FEP.

Due to its FEP insulation, the LCC generates much less smoke, the lowest possible fire load, and is much less likely to burn than existing CMP plenum. In fact, when compared to minimal CMP, LCC has up to 20 times lower smoke generation as well as eight times lower fuel load and lower flame spread. It also resists the effects of aging and corrosive environments, and has enhanced performance over a wide temperature range.

To be listed as LCC, the cable must pass strict tests. The NFPA has developed a smoke index rating and a flame spread index rating. Under this system, burning Red Oak is defined as having a smoke index and a flame spread index of 100. To carry the LCC designation, the cabling must have a smoke index of 50 or lower on this test, and a flame spread index of 25 or lower. LCC cabling must also possess a maximum fire load (potential heat) of 8.1 mega Joules per kilogram (3500 BTU/lb), and it must meet the standards described under the new UL listing UL2424 for "Limited Combustible FHC 25/50 CMP" cabling.

While listed 25/50 limited combustible CMP meets or exceeds all current and proposed cable fire safety standards worldwide, it is important to note that conventional CMP cable still meets many minimum standards and fire codes, and is clearly superior to CM and CMR cable, and it represents a major safety improvement over those cable types. However, the polyethylene used in CMX, CM, and CMR cable has a fuel load comparable to gasoline.

What Works: Best Practices to Reduce Cable Fire Risk

Based on experience, two key initiatives are considered best practices with regard to communications cables in today's rapidly advancing IT environment. Taken together, these two practices represent the optimum available safeguard against reducing fire risk and promoting sustainability within a building.

Use of Cables with Advanced Fire Resistance

To prevent or minimize the effects that a fire will have on their business, companies invest in safety measures. Using LCC cables with advanced fire resistance like UL listed FHC 25/50, is a passive fire protection measure, and an important element in a fire protection strategy. Passive protection measures, which seek to compartmentalize a fire through walls, doors, ceilings and their components, are often more reliable than active methods, which encompass systems that must be activated, such as sprinklers, or fire alarms. In fact, studies have shown that sprinklers fail to operate in one of six fires and when they do operate, they only extinguish the fire 25 percent of the time. In comparison, passive measures rarely fail. Yet both active and passive measures must be employed as an effective way to protect people, facilities, and equipment.

It's important to consider that advanced fire resistant cabling is not a major expenditure. While higher performance cable costs more than cable which meets only minimum requirements, the average increase in total installation costs (labor and materials) of a system that includes LCC is minimal, less than 10 percent, when compared to traditional combustible plenum cable. Fire retardant cable helps protect a cabling system against obsolescence as data rates increase, and avoids costly recabling. In terms of life cycle costing, enhanced cable performance along with electrical properties that remain stable and reliable over time can help maximize the long-term value of a network investment. Studies have shown that in the context of total network cost, the incremental cost of premium performance cable is less than one percent.

Removal of Abandoned Cable

A main cause to the rising amount of cable in a building is the continual upgrading of existing equipment. As equipment is upgraded, existing cable often becomes out of date. Removing this cable is considered an unnecessary expense, and it is often left where it is, although it is no longer used. In place, though unused, cable is so-called abandoned cable. Most at risk for an abandoned cable problem are older buildings and those with a high turnover or those that have undergone renovations within the past five years. In addition, buildings with one long-time large and/or multi-floor tenants or those serviced by multiple vendors and contractors may also have an abandoned cable problem.

Abandoned cable is problematic because it constitutes a hidden fire hazard, contributing unnecessary fuel and smoke load, creating structural problems, interfering with air flow and leaving no room for new cable. Insurance companies recommend its removal. Recognizing the serious potential hazard, the National Electrical Code (NEC) requires that abandoned cable be removed or tagged for future use. The NEC is the most widely recognized and adopted model from which most states and local jurisdictions develop their codes. Jurisdictions that have adopted the 2002 or 2005 NEC require the removal of abandoned cable. While most jurisdictions follow the NEC and require the removal of abandoned cable, specific requirements for the jurisdiction in which the building is located must be followed. Failure to comply with codes requiring the removal of abandoned cable can result in fines and the withholding of certificates of occupancy. Failure to comply may also result in liability in the event of a building fire. Left unmanaged, abandoned cables can also create problems in obtaining building permits and in negotiations with network users and/or tenants.

While the NEC calls for removal of abandoned cable, it does not address the issue of when to remove abandoned cable. Most end-users initiate removal projects when new cabling systems are added, or when a major renovation is being done. However, timing is up to local jurisdiction. Another issue not addressed by the NEC is how to dispose of abandoned cable once removed. Local code and statutory requirements may come into play here. Some states do not allow disposal of these cables in landfills. While the copper in cables is often recovered and recycled, the major problem is adequately disposing of the large amount of plastic material used for insulation and jacketing. In the past, this problem has not been adequately addressed through recycling. However, advanced cable recycling technology available in the marketplace converts end-of-life abandoned cables to reusable copper and separated plastic streams.

Proper management of abandoned cable will facilitate code compliance and building safety. First, an assessment of existing conditions and plans and budgets for abatement projects should be developed. Such an assessment can fulfill several objectives. Not only will it help building owners, property and network managers identify and evaluate the magnitude and nature of abandoned cable in their structure, an assessment is also a critical cost-effective tool for project planning as well as developing a budget and specifications for the removal project by fully understanding conditions up front. In addition, for installed cable in-use, an assessment can identify critical deficiencies that can affect the performance of the communications infrastructure. Subsequently, an experienced contractor must be identified to handle safe removal. A plan for proper disposal of the entire cable must be prepared and implemented, taking into account that plastics can be recycled in addition to copper. Completely recycling abandoned cable-widely recognized as the new Best Practice-may contribute to LEED Certification under the following categories:

• New Commercial Construction & Major Renovation Projects
• (LEED-NC)
• Existing Building Operations (LEED-EB)
• Commercial Interiors Projects (LEED-CI)
• Core & Shell Projects (LEED-CS)
• Homes (LEED-H)
• Neighborhood Development (LEED-ND)

Once the old combustible abandoned cable is removed, it is a wise management practice to minimize the future buildup of fuel load by installing cable with advanced fire safety performance.

Sustainability Issues

Product manufacturers and services providers are vital to advancing the U.S. Green Building Council (USGBC) mission of market transformation. Although USGBC does not certify, promote or endorse products and services of individual companies, products and services do play a role and can help projects with credit achievement. While there is work underway with the EPA and the USGBC to develop a category for recognizing the environmental improvements in electronics and recycling programs, cable is not officially considered today for Leadership in Energy and Environmental Design (LEED) credits. LEED is a voluntary, consensus-based program of developing high performance sustainable buildings. LEED emphasizes site development, water savings, energy efficiency, materials selection and indoor environmental quality. A framework for assessing building performance, LEED is based on a system of prerequisites and credits. LEED projects earn points during the certification process and then are awarded one of four certification levels: certified, silver, gold, or platinum.

Yet the choice of cable can enhance LEED submittals if reviewed under the following sections:

MR Credit 2.1-Construction Waste Management Divert 50 percent from landfill. In typical CMP cables, the challenge associated with PVC recycling makes this target difficult to reach. Many LCC is fully recyclable.

MR Credit 4.1-5 percent recycled content (post-consumer and 1/2 post-industrial). LCC may exceed this post-industrial recycled content in the future; some advanced LCC may currently exceed the post-industrial recycled content.

MR Credit 5.1-Regional materials, 20 percent manufactured regionally, within 500 miles of the building site.

As LCC is made in the U.S., companies can support local businesses, while providing a high quality product and best cable technology available. Recycling removed and waste communications cable can also contribute toward LEED credits.

Cable Made with Recyclable Materials

LCC is made with less total plastic. Because only one type of stable plastic, FEP, is used LCC generally have high re-use value and are more easily recycled. Other guiding purchasing principles recommend that cable:

• Does not contain any substance or component regulated under the RoHS and Waste Electrical and Electronic Equipment (WEEE) Directives. Enforceable on July 1, 2006, RoHS sets maximum concentration limits in hazardous materials used in electrical and electronic equipment. The substanaces are lead, mercury, cadmium, hexavalent, chromium, polybrominated bihphenyls (PBB) and polybrominated diphenyl ethers (PBDE).

Designed to tackle the fast increasing waste stream of electrical and electronic equipment, thereby reducing landfill and incineration of waste WEEE became European law in February 2003, setting collection, recycling and recovery targets for all types of electrical goods.

• Is free of heavy metals and phthalates
• Is free of hazardous substances
• Is compliant with California Proposition 66, which requires warning labels on products • Offers recyclability of both copper and plastics at the end of the cable life
• Contains post-industrial recycled content, with options for post-consumer content in the future

Codes and Standards

Organizations such as Underwriter's Laboratories (UL), Interek Testing Services (ITS/ETL), the NFPA and other institutions have been involved in the development and setting of fire safety standards for communications cabling. As mentioned previously, the NFPA publishes model codes that are adopted wholly or in part as local regulations by cities, states, and municipalities throughout the United States.

In 1975, the NFPA added a provision to its NEC for "conductors having inherent fire-resistant and low smoke producing characteristics, approved for…ducts and plenums." As a result of this provision, in the early 1980s, the NEC defined the three following categories for copper communications cable, with respect to the venue in which they would be deployed. The following designations are for certain copper (low voltage signal) communications cable. Other types of cables used in specific applications, including fiber optic, power limited Class 2 & 3, and community antenna (CATVP), and fire alarm have equivalent designations.

• CM-installations requiring the least stringent fire and smoke performance. This "general purpose" cabling could not be run through risers or plenums.
• CMR-to be used in risers, or other locations requiring high-level fire and smoke performance.
• CMP-to be used in air plenums. CMP designated cable must have the highest level of fire and smoke performance due to its deployment in areas with the greatest potential for spreading smoke and fire. Page: 9

These designations are for copper (multipurpose) communications cable. Other types of cables used in specific applications, fiber optic (OFNP), power limited Class 2 & 3 (FPLP), community antenna (CATVP) etc. have equivalent designations.

Key to the NEC was the directive that these cable types be routinely tested and audited by an independent lab. UL is the primary test lab for these purposes in the U.S., Canada and Mexico. UL uses a variety of testing protocols for the most common communications cable types.

Generally speaking, the following codes govern communications cables:

NFPA 90A-Standard for Air Conditioning and Ventilation Equipment

NFPA 90A is responsible for plenum spaces in buildings. In the 2002 Edition, this standard sets requirements for flame, smoke and fuel load in the following section: 4.3.10.2.6-"All materials exposed to the airflow shall be non-combustible or limited combustible and have a maximum smoke developed index of 50..." (From the 2002 edition). This refers to NFPA's smoke index rating and a flame spread index rating.

Under this code, combustible cables are allowed as an exception.

When designing network infrastructure to a standard of protection as opposed to minimal code compliance, it is advisable to design to the NFPA 90A primary requirement that all materials installed and exposed to environmental airflow be noncombustible or limited combustible as opposed to compliance with wire and cable exception. LCC cabling meeting the requirements of NFPA 5000 model building code, and NFPA 13 model sprinkler code for limited combustible materials allows it to be installed in virtually any noncombustible building construction without the need for additional fire protection (sprinklers or noncombustible conduit).

The NFPA 70-National Electrical Code (NEC) is responsible for cable products and applications

This code recognizes need for higher fire safety performance for cables installed in plenums. NEC 2002 requires removal of abandoned cable from plenums. NEC 2005 acknowledges that plenum (CMP, CATVP, OFNP) cables are combustible with reference to NFPA 13 requirements for protection of concealed spaces

NPFA 13 sets the requirements for sprinklered buildings

Plenum-sprinklers are required in sprinklered buildings if there is a loading of unprotected ‘combustible' materials such as like traditional CMP, OFNP, CATVP, etc. plenum cables. In sprinklered buildings, use of combustible cables in concealed spaces, including plenums, requires installation of sprinklers in these spaces. However, use of limited combustible cable does not require sprinklers in these spaces. The options are clear: either install sprinklers in concealed spaces, or use the more cost-effective LCC cable.

NEC 2005 now refers users to NFPA 13 (2002) for guidance on fire protection needs for traditional ‘combustible' plenum cables.

Because existing fire codes were established as a result of the testing and analysis of many organizations and knowledgeable engineers, many consider that merely meeting existing fire codes is sufficient. However, many of the standards regarding the flammability of communications cables were developed over two decades ago, when building cabling referred to a few telephone service cables. With a phone on each office desk, and a centrally-located PBX-type switch, the amount of cabling was extremely limited by today's standards. Computer networks continue to increase, as does the amount of electronics and the size of buildings-all of which point to a much greater fire risk. With the spread of sensitive electronics comes greater dependence on these systems, so that fire and smoke damage will almost certainly exact a greater financial toll today, than when these standards were first developed in a markedly different business and technological environment. In fact, a case can be made that many of the existing safety standards were developed to correspond to circumstances that are non-existent today-and that have evolved over time to pose far more hazards with the potential to generate a host of negative consequences.

An Effective Program for the Future

With the enormous amount of cable present in commercial buildings required to service the ever-increasing demands of IT networks, fire safety is a growing concern. Many leading cable system suppliers offer LCC with advanced fire resistant capabilities that exceed code and contribute to sustainability. As pending codes are adopted, LCC may allow building owners to do without plenum sprinklers. In jurisdictions requiring that CMP cabling be installed inside metal conduit, LCC may replace both. In such cases, LCC may be more desirable than CMP-rated cable in terms of cost and convenience. A UL-listed LCC system combined with a program to remove abandoned cables represents a proven, effective way to reduce the risk of personal injury or death, property damage or business loss, addressing contemporary needs and contemporary circumstances.