Stair pressurisation systems will require the integrity and insulation criteria to be satisfied for the whole system, hence any hanging rods must also have the same FRL as the ductwork, or alternatively the hanging rods must be fire engineered.


Smoke Exhaust systems are designed to extract hot gases from compartments affected by fire. As the fire is restricted to travelling inside the duct, it is often assumed that the suspension rods to these HAVAC systems do not require FRL upgrading or consideration. Although the fire will be restricted inside the duct, AS 1668.1 requires that the ‘System’ works under any circumstance. So in the case that the duct travels through another fire compartment, it must satisfy both the integrity as well as insulation criteria. In line with stair pressurization ducts, any hanging rods must have equal FRL as the ductwork, or alternatively, the hanging rods must be fire engineered.


For Kitchen Exhaust ductwork, AS 1668.1 requires the sheet metal to be of 1.2 mm gauge. However, with the Vermiduct system, 1.0 mm sheet metal is all that is required for ductwork up to 4.8 m wide x 3 m deep. In some special cases ducting not exceeding 1200 mm x 1200 mm may be constructed from 0.8 mm sheet metal.


PVC softens below 90°C and this raises the issue of compliance with AS 1530.4, BS 476.24, AS 1668.1 and BS 5599.9 requirements whereby during the fire test, a smoke extraction duct cross-sectional area must not reduce by more than 25%. 

LAF has tested 78 mm of Vermiduct installed over a 750 x 750 PVC duct to successfully achieve a 3 hr fire resistance level to AS 1530 Part 4.

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