A cylindrical tube of extendable length, the tube having open ends. A first, second and third transverse flanges fastened at one or both of the opposing ends of the tube. The first flange is integral with the tube and sandwiched between the second and the third flanges. A ring is coextensive with the first flange and covers part of the open end of the tube. A heat expansive material is placed within the tube for expansion during fire to cover spaces between utility conduits and the inside wall of the tube.