Can test results for rectangular ductwork be used for circular or flat oval ducts; circular or flat oval ‘spiral wound’ ducts; and flexible ducting systems?
ANSWER – The answers are different for those ducts tested to BS 476 Part 24 or tested to BS EN 1366 test methods. In the case of BS 476 Part 24 test data, circular and flat oval straight seamed and spirally wound steel ducts may be assessed on the basis of the tests on rectangular ducts. Details of the construction of circular and flat oval, straight seamed and spirally wound steel ducts must be provided by the duct manufacturer. Further details are provided in ASFP ‘Blue Book’ publication ‘Fire resisting ductwork – 2nd Edition Section 6.2.1.10’ In the case of BS EN 1366 test data, no equivalence is permitted and all ductwork systems must be individually tested. The published European DIAP and EXAP rules apply. As the vast majority of fire tests on ducts are conducted with rigid ducts it is not appropriate to extrapolate this data for flexible ducts. Therefore, unless the flexible duct system has been fire tested, the guidance cannot be assumed to apply.
