Patent ID: 7195290

Claim:
A duct assembly suitable for fire-rated applications, said duct assembly comprising: a liner section having an inner surface and an outer surface and a first end and a second end, and said liner section being formed from a thin steel material; a non-combustible layer, said non-combustible layer being attached to and surrounding the outer surface of said liner section; a flange assembly for the first end of said liner section, said flange assembly being removably coupled to said first end; another flange assembly for the second end of said liner section, said flange assembly being removably coupled to said second end; at least one longitudinal member having a first end for connecting to said flange assembly and a second end for connecting to said other flange assembly, and having a surface for securing a portion of said non-combustible layer and said liner section; a fire-resistant sealant applied to joints between said liner section and said flange assemblies to prevent the flow of air from the inner surface of said liner section to exterior of said duct assembly; and wherein one or both of said flange assemblies are coupled to said liner section during fabrication at a factory.