120 Minute Insulated Durasteel Fire Rated Ductwork (EI120)

The 4-sided SMT duct system is constructed with a single layer of 9.5mm thick Durasteel boards supported by a welded framework of steel angles, 50 x 50 x 3mm thick, at the corners of the duct and at duct joints. The boards are fastened to the steel framework with M5.5 steel self drill and tap Tek screws at 200mm nominal centres. The flanges of adjacent duct sections are fastened together with M8 steel bolts at each corner and at 250mm maximum centres. FSi Pyrocoustic acrylic sealant is applied to the meeting faces of the flanges. The duct is clad in 90mm Rockwool DuctRock Slab on all sides using 3mm diameter stud-welded pins and 3mm diameter steel washers. The maximum length of duct section is 1500mm. The maximum size of the duct is 6.0m wide x 2.0m high.

The hangers consist of threaded steel drop rods and steel angle or channel bearers. The maximum tensile and shear stresses that unprotected steel hangers can bear in the standard fire test are 10N/mm² for fire exposures of up to 120 minutes and 6N/mm² for fire exposures of up to 240 minutes. The maximum spacing of the hangers is 1500mm. Where the width of the duct exceeds 1.5m an additional steel drop rod is fitted at each hanger at mid width of the duct. The rod passes through the duct and supports the bearer under the duct. The rod is also fitted with a steel nut and large steel washer so that it supports the upper wall of the duct. In the same way, where the internal width of the duct exceeds 3000mm, two or more additional threaded rods are fitted at each hanger position at centres not exceeding 1500mm across the duct. The penetrations of the rods through the duct are sealed with FSi Pyrolastic silicone sealant or FSi Pyrocoustic acrylic sealant.

The drop rods are connected to the floor soffit either directly with an all-steel expanding anchor at least the same size as the rod or via steel channel brackets. Each bracket is 75mm long, made from 127mm x 64mm x 6mm-thick hot-rolled channel and is fastened to the concrete floor with an all-steel expanding anchor. The anchor bolts must penetrate the concrete by at least 50mm for fire ratings up to 120 minutes and at least 65mm for fire ratings up to 240 minutes. The anchors must be of sufficient strength to support the weight of the duct and be fitted in accordance with the manufacturer’s instructions. The maximum tensile stress values for the anchor bolts are 14.1N/mm² for fire exposures of up to 120 minutes and 7.8N/mm² for fire exposures of up to 240 minutes.

At a penetration, where the duct passes through a fire compartment wall, a duct joint is positioned in the line of the wall. The gaps between the duct and the reveals of the opening are filled with Durastop 150mm thick.