Smoke ventilation
bill of quantities will clarify what will be supplied, it is particularly diffi cult for suppliers and end users to compare and contrast the different options available, and ultimately judge which would be best at implementing the fi re strategy, in the absence of detailed technical standards to refer to. In fact, the only clear benchmark on which
they can compare and make decisions is the price. Obviously, this is far from the best method of selecting an option, as it cannot ensure that the specifi ed system will meet the criteria as outlined in the fi re safety strategy. Specifi ers who lack the in depth knowledge of fi re safety systems have to rely on the supplier’s information and a promise of compliance with the regulations, the system’s past performance, and the reputation of their brand to make procurement decisions. The only situation where a supplier would
be required to provide additional detail on how the proposed system meets regulations would be when a report needs to be submitted to the local authority for building approval. Due to the fact that each development is treated as a bespoke design, project specific computational fluid dynamics (CFD) analysis is required. Unless the entire smoke extraction system is
supplied by FläktGroup – which is authorised by LABC (Local Authority Building Control) approval – the CFD analysis adds to the complexity of the process. Furthermore, the report does not need
to be submitted to the council until either prior to handover or at practical completion – by then, the system has already been installed.
System variables
The rate of extraction achieved by a mechanical system can be controlled and varied by pressure detection or door actuation systems during the life of a fi re. Different fan speeds may also be needed when extracting smoke from basement areas split into different fi re zones. Legislation and design guidance of products and systems related to the control of fans used in mechanical extraction systems have been updated, whereas ADB has not been revised since 2006. For example, BS EN12101 part 3 was updated
in 2015, which precludes the use of inverters in emergency mode unless they have been fi re tested with the fans or are equipped with additional fi lters and the fan motors derated by 20%. As the current Building Regulations are still
referring to old documents, they do not give the full picture when a mechanical smoke extraction system is used in conjunction with other measures that affect fan speeds and smoke extraction rates. Therefore, if the performance of a mechanical smoke extraction system is controlled or affected by other parts of the system design, clarifying the minimum technical
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www.frmjournal.com MARCH 2019
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