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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: davincey on August 26, 2008, 04:17:49 PM
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At the risk of sounding like a complete idiot.....!
Can anyone offer me opinions/advice on requirements for AOV's specifically relating to a 5 storey building with 2 staircases? I seem to be getting conflicting opinions as to their necessity under regulations and/or good practice.
All opinions welcome!
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What is the building used for? Flats? Offices?
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It is a block of flats in use as sheltered housing. Elderly and disabled residents, not a care home.
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Is the evacuation strategy based on total evacuation or do occupiers other than the unit involved stay put in their flat?
Are all walls and floors compartment walls to a one hour standard?
Are all flat entrance doors FD30S?
Is the longest dead end situation no more than 7.5m?
Theres a few indicators. For a stay put policy, - if the answers to the other questions are all yes- a common solution is to provide 1.4sq m natural AOVs to the lobbies or corridors adjoining the staircse and a 1 sq m OV in the staircase. If all automatic the lobby AOV should open before or atthe same time as the stair OV.
There are other ways of doing it with mechanical powered smoke extract systems rather than relying on natural ventilation, the shaft size can then come down to about 600mm.
The whole idea is to protect the staircase against the ingress of smoke to ensure that it is safe to use even if later in the incident it is necessary to evacuate more people. The AOV in the lobby adjacent to the staircase creates a small negative pressure differential between lobby relative to the staircase and therfore protects the staircase against the ingress of smoke. Well thats the theory.
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We do operate a stay put policy (yes is the answer to all the other questions).
However, the area for which I am responsible suffered a serious (and tragic) fire a few years back in a tower block and the FS were of the opinion that the AOV had a negative effect. I am led to believe that there are now conflicting opinions within the FS as to the benefit of AOV's and that discussion/investigation is taking place.
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The whole approach to the use of AOVs in tower blocks was changed as a result of a BRE study and the new thinking was incorporated into the updated ADB in April 2007. Your tragic fire would not have been to the new approach that I have summarised in my earlier posting.
All these methodologies are very much prone to other influnences especially where relying on horizntal ventilation as a result of wind pressures, vertical smoke shafts being the more reliable- and some would say mechanical systems being more reliable still. Pressurisation of staircases is a more reliable but much more costly approach.
The BRE research document is available for free download via the planning portal website and the new approach has been discussed at length on this forum previously- a search on AOVs should find it easily.
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Many thanks kurnal. Once again you have proved yourself to be an invaluable source of information and assistance! Thank you
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May be of some help http://www.bre.co.uk/adb/page.jsp?id=555 ?
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Thank you twsutton