240 Minute Durasteel Fire Rated Ductwork (E240)

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 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 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 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 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.

A longitudinal corner steel angle is fitted to the duct where it butts up to the soffit of the concrete floor or the concrete/masonry wall. The angles are minimum 50mm x 50mm x 3mm thick and are fastened to the duct with minimum M5.5 steel self drill and tap Tek screws at 200mm nominal centres. The angles are fastened to the floor or wall with minimum M8 all-steel expanding anchors at 500mm maximum centres. The size and spacing of the screws and anchors is adjusted depending on the weight of the duct assembly. The maximum tensile and shear stresses for the steel screws are 10N/mm² for fire exposures of up to 240 minutes. The maximum tensile and shear stress values for the anchor bolts are 7.8N/mm² for fire exposures of up to 240 minutes.

FSi Pyrocoustic acrylic sealant is fitted between the angles and the wall or floor. The penetration seal system is the same as for the 4-sided duct. Where the width of the 3, 2 and 1-sided Durasteel ducts exceeds 1.5m, a threaded drop rod is fitted at mid-width at 1.5m maximum centres along the duct, in the same manner as the additional threaded drop rods for the 4-sided ducts greater than 1.5m wide. The additional rods support the soffit of the duct with a steel nut and washer under the duct. The drop rods are M20 steel studding and where possible should coincide with the flanged cross-joints. Where the drop rods do not coincide with the cross-joints, the size of the steel washer under the Durasteel is at least 100mm square x 3mm thick. In the same way, where the internal width of the duct exceeds 3.0m, two or more additional threaded rods are fitted at centres not exceeding 1.5m across the duct. The penetrations of the rods through the duct are sealed with FSi Pyrolastic silicone sealant or FSi Pyrocoustic acrylic sealant.