Grease duct joints are held collectively by the use of fashioned V clamps and sealed with 3M Fire Barrier 2000+. Reduction in cross-area: The internal dimensions (width and top for rectangular ducts, diameter for circular ducts) with the smoke extracting ductwork shall not minimize by over 10% during the check. https://fireresistingductworkinsu90122.activosblog.com/35647181/fire-resisting-ductwork-insulation-an-overview