An annular fire barrier structure (3, 3') which is mountable close to the pass-through point of a fire damper on a wall or ceiling structure, where it is adapted about the duct sleeve element (2) of the fire barrier to receive heat conducted along the duct element and further conduct the heat, e.g., to the wall structure (1) wherein or whereon it is mounted, and which fire barrier structure has placed thereon a tightening band structure. The invention is implemented by having the fire barrier structure (3, 3') comprised of two or a greater number of fire barrier flanges that are adjacently joined with each other in the longitudinal direction of the center axis of a ventilation duct (2).