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Number of fire exits required - single stair office block


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Scenario is a new office block - ground plus 4 storey above (no basement). All office / administration use.  All standard construction and each floor has lobby approach to staircase.  No alternative means of escape from the upper floor levels.

Under ADB Vol 2 (3.3 - Single escape stairs) from what I can read, a maximum of 60 occupants is permitted at each floor level subject to travel distance criteria being met and if any floor is above 11m, a second means of escape is made available...

But, then looking at 2.9 in ADB Vol 2 (Number of occupants and exits) if the total occupancy for the building is >60 then 2 or more final exits are required...

In my example, each floor has 50 people & therefore total being 250.  

Question is should there be at least two final exits provided at ground level at base of stairs, separated by fire resistant structure from one another as total occupancy will be >60?

Or is a single final exit adequate at the base of stairway leading directly to fresh air be acceptable, as long as stairway width is suitable and final exit width considers total numbers of occupants in building who will need to use it, i.e. 200? 

Ground floor occupants will have several other final exits they could use, but people on upper floors (approximately 200) will all have to use the main entrance / exit doorway which is at base of stairway.

Any guidance much appreciated!!

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14 hours ago, AnthonyB said:

If it's new build the designers may have used BS9999 instead of ADB as it can reduce the number of exits and stairs needed - it may also be fire engineered.

The design fire strategy will give you the answers you seek.

Hi Anthony...thank you for your reply.  It is definitely ADB they have used, but as with many cases I am seeing, a fire strategy document is a mythical item which architects and main contractors ignore to produce...

Thanks anyway for your reply.

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