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Fire alarm systems in mixed used sites


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I am a fire risk assessor that has always been of the opinion that an interlinked fire alarm system (between flats and commercial units) is not necessary in a mixed use property that has been constructed to current or post 1991 building regs - if no escape routes are shared. However recently I have come across two new build blocks that have commercial units on the ground floor, and flats on upper floors  - sharing an escape route ( the commercial units are in a protected ground floor area, exiting via the protected stairwell at ground floor level. The route to the apartments (on the upper four floors) is protected from the stairwell by a 60 minute fire door in one block - and in the other block no separation is provided i.e the ground floor has a single 30 minute door to the commercial space and then the stairwell to the first floor flats is open.

Both blocks are armed to the teeth with fire detection and warning systems that are interlinked between both residential and commercial. My question is - how would another assessor advise in relation to stay put and detection within the residential areas in these circumstances? My gut feeling is retain the stay put and remove the audible alarm for the residential areas.  The amount of coverage necessary for the commercial units is subject to their own risk assessment...other views appreciated. Many thanks. Trinnie

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Have you tried to obtain the fire strategies for the blocks? Doesn't sound like Approved Document B was followed for the builds so the rationale used needs to be understood, perhaps single stage evacuation for the whole premises was used (it's rare a new bulid resi has full evacuation but it's not unprecedented).

If it wasn't mixed use or was mixed use to strict rules of ADB I'd be removing the resi call points and sounders and leaving the detection for the operation of the smoke control systems.

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Even if you can provide the sixty minute fire separation I think you have to consider the whole of the building, a fire in the commercial premises would affect the residents in the flats. The stay put policy relies on the FRS being turned out as soon as possible, to get the fire under control within the sixty minutes. Consider who is warned, which enables them to call the FRS, especially at 4 o'clock in the morning, a fire in the flats the category D system would, but what about the unoccupied flats or commercial premises or are you going to rely on passer by. 

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