Introduction:

The volume of cable used for data transmission and electronic communications in commercial buildings is increasing dramatically. More than 60 billion lineal feet lies in U.S. buildings today. In addition, advances in communications technology or building tenant changes can require that cabling be replaced as often as every 18 months. Roughly 30% of all cable systems are subject to a move, add, change or upgrade every year.

Conventional exception plenum cable (CMP, OFNP and CATVP, etc.) has been accumulating in hidden plenum spaces for more than 20 years; most of the cable in service is combustible and unprotected, which negatively impacts the fire safety of buildings and structures. This problem is exacerbated by the fact that as new cabling was added, old cable was left behind. This has further increased the total fuel load of the building and the risk of fire spread through concealed spaces.

Fire load fire hazards are measured by three criteria - flame spread, smoke development and potential heat (heat of combustion). Conventional exception cable generates a great deal of smoke; as much as twenty times more than other building materials. Heat generation from traditional combustible cable materials is also significant; up to eight times more than other building materials and enough to melt structural steel and fasteners.

Cable is typically located in the HVAC plenums in concealed ceiling spaces and in raised floors. Existing codes require that the concealed spaces in the ceilings of tall buildings be adequately fire protected if they contain extensive combustible cabling materials.

Therefore, there are three options in terms of installing new cable in Type 1 & 2 sprinklered commercial buildings:

• If conventional exception cable is installed in a building that is sprinklered, sprinklers or fire suppression systems must be also installed in the concealed ceiling plenum spaces or floor spaces (an expensive option)
• Install the conventional exception cable (combustible cable) in metal conduits (an option that limits the building's flexibility in terms of future layout configurations)
• Use Limited Combustible (LC) Cable

The new class of cable known as Limited Combustible Cable is identified by the UL marking "Limited Combustible FHC 25/50" or "FHC 25/50/8" on the surface of the jacket or on a marker tape under the jacket. This marking also includes the Type designations for plenum cable, such as CMP or CL2P.

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