Occupancy based on stair width

[Fireman1987]

In a local school hall there is a gallery overlooking the hall with a single, timber, dog-legged staircase leading into a lobby, protected from the hall and a tea point by FD30S doors and with an exit from the lobby.  The building is 140 years old with only a manual fire alarm system (I'm dealing with that).

The gallery has seating for 60 to 80 people, but the stair width is 630mm at its narrowest point (at the top) but doesn't get any bigger than 670mm, so I need to limit the number of people who can use it - but I can only find required standards occupancy calculations, not calculations for an existing stair width.  Where should I look, please?

My gut feeling is there shouldn't be more than about 20 people up there (and it's too high to drop over the side!)

Thanks

[Tom Sutton]

On 01/11/2019 at 08:02, Fireman1987 said:

 I can only find required standards occupancy calculations, not calculations for an existing stair width. 

No I do not think you will they all appear to be based on standard width staircases even if you go back to POST-WAR BUILDING STUDIES NO. 29 FIRE GRADING OF BUILDINGS 
PART 3 PERSONAL SAFETY and the narrowest is 2' 6" (750mm).

Check out http://www.highrisefire.co.uk/docs/HMSO 52_Fire grading of buildings Parts 2 to 4.pdf page 81.

[AnthonyB]

Without digging out old guidance I do recall being in a similar scenario with premises and from memory the approach from those was similar to existing wicket gates, fixed ladder and window accessed escapes, namely only suitable for areas with no greater than 5 able bodied employees.

Consider both escape time - you will only get slow single filing - and bunching as people pile up whilst queuing and as a result the risks of not having the required safe evacuation time and from trips and crushing (The Station Nightclub footage graphically illustrates the effects of too many people trying to use too narrow an exit too quickly)

[Fireman1987]

Thanks, guys.

I'm impressed with your recall about where to even look, too!  The Station Nightclub footage was one of my go to videos when teaching new fire safety inspectors about the subject.  It certainly helps focus the mind.

Thanks again,

Peter

[Tom Sutton]

No prob. ?