"When pipes, ducts, conduits, wires or other objects penetrate fire resistive barriers such as walls, floors or ceilings, the openings create a path for heat and smoke to spread through a structure. The building codes require these 'penetrations' to be firestopped with materials that meet the requirements of ASTM [American Society for Testing and Materials] E 814, Standard Test Method for Through-Penetration Fire Stops or UL 1479, Standard for Safety for Through- Penetration Fire Stops."
Coffee Break Training - Fire Protection Series No. 2005-3
United States Fire Administration: http://www.usfa.fema.gov/