Cable that is run in the plenum spaces of buildings. In building construction, the plenum (pronounced PLEH-nuhm) is the space that is used for air circulation in heating and air conditioning systems, typically between the structural ceiling and the suspended ceiling or under a raised floor. The plenum space is typically used to house the communication cables for the buildings computer and telephone network(s). However, use of plenum areas for cable storage poses a serious hazard in the event of a fire as once the fire reaches the plenum space there are few barriers to contain the smoke and flames. Plenum cable is coated with a fire-retardant coating (usually Teflon) so that in case of a fire it does not give off toxic gasses and smoke as it burns. Twisted-pair
versions of cable are made in plenum versions.