| CPC F16L 57/04 (2013.01) [F16L 5/04 (2013.01); F16L 9/003 (2013.01); F16L 9/17 (2013.01); F16L 59/04 (2013.01); F16L 59/121 (2013.01); F16L 59/143 (2013.01); F16L 59/145 (2013.01); F24F 11/33 (2018.01); F24F 13/0245 (2013.01); F24F 13/0263 (2013.01); F24F 2221/30 (2013.01)] | 31 Claims | 

| 
               1. A ventilation duct for a fire rated ventilation duct wall penetration, said ventilation duct comprising: 
            one or more metal sheets forming said duct, wherein said metal sheet duct is covered on an outside by a heat insulating material, and said duct includes elongated stiffening members located on the outside of the duct and attached to said metal sheets; 
                wherein the stiffening members each comprise a metal profile and at least one non-combustible bar of inorganic material; and 
                wherein the metal profile is fixed to the metal sheet of the duct and retains the at least one non-combustible bar by at least partly encircling the bar. 
               |