Nailor Model 0722 Ceiling Dampers are for use in spherical apps, in lieu of hinged doorway form dampers in almost any UL/ULC ground/ceiling or roof/ceiling assembly with as many as a 3 hour fire resistance score the place air ducts are allowed. Industrial dampers use a heavy-duty flanged body damper with many blade variations https://heavy-duty-stainless-stee24456.targetblogs.com/37462292/how-much-you-need-to-expect-you-ll-pay-for-a-good-dampers-for-industrial-sector