In building construction the space used for air circulation is called the plenum. This space is also often used to route communication cables. This poses a serious hazard in the event of fire due to lack of barriers to contain the smoke and flames. Because of this, various fire codes and the National Electrical Code (NEC) require the use of fire resistant and low smoke producing cable in these spaces.
This type of cable is called plenum cable and is coated with a fire retardant coating to produce a cable that is fire resistant and has low smoke producing characteristics.