occupation capacity levels - which guide to use??

[Meady]

Hi - we're after a bit of advice please...

A room in a large college (built circa 1800's) is going to be used for large assemblies including those who may not be familiar with building layout.

Floor space is 320M2, and has 2 opposite means of escape each taking occupants to a protected stairway which both discharge directly to fresh air.  

But both doorways are only 870mm...so when discounting one of them, the numbers reduce dramatically so the width of the doorway is being used for the capacity calculations.

Now, the debate is whether we use BS9999 or DCLG guides?  If we use BS9999 the width per person (for a B2 category occupancy) is 4.1mm which gives us a figure of approximately 200.  But the DCLG guide would suggest that for a door width of 870mm would only be suitable for 100 occupants...??

We've asked the local Fire Service and they've said to use BS9999 (but have said they won't put this in writing). Another consultant we've approached has said that DCLG uses Building Regulations ADB as its guide and we shouldn't be using that either. 

Please can anyone help us by telling us what guide we should be using???  We will comply with whatever guide we need but just want to get things right and safe!!

[Tom Sutton]

Did the building use BS 9999 as a fire safety design document, if not then you should not cherry pick and use DCLG guide plus your expertise on risk assessment.

ADB, BS9999 and BS 7974 are fire safety design documents for new build and if you are conducting a FRA in one of those buildings you should make sure you are aware of the appropriate document to be able to access if the escape strategy is satisfactory. If you are not sure what guidance was used, use DCLG guidance.

The days of prescriptive guidance and finding black and white answers are gone it’s all about risk assessment.

[AnthonyB]

As Tom says - BS9999 is not a risk assessment guide but an architect/designers alternative to approved document B and the occupancy calculations only work if the premises meet all the other aspects of the document, such as management level, structural protection, fire fighting facilities, etc, etc.

[Meady]

Excellent - thank you both for your replies.  Much appreciated.