BB100 Schools

[jayjay]

Final draft is now published copy available on the BAFSA site

See link

http://www.bafsa.org.uk/pdfs/publications/00000050.pdf

Not had a chance to look at it yet.

look forward to members comments.

[AM]

Date for full publication is apparently the 9th November, and should be downloadable from:

www.teachernet.gov.uk/fire

[Pete M]

Downloaded the final draft today and had a quick scan through.

Big improvement over the previous version but still a few bits need improvement - one example, open spatial planning (i.e. escape past a void) could do with further clarification as the illustration could be misread; travel C-D not to exceed 18m, but the remaining alternative directions of travel (both apparently within 4.5m) not described.

Will be intersting to see the 'final', 'ratified' publication!

[Ken Taylor]

As I've said on the BB100 thread below, JayJay, the BAFSA version isn't quite complete and contains editorial notes.

[AM]

The up-to-date version is now  up on the teachernet site

[jokar]

Has anyone looked at or even better understood the Risk Assessment tool and CBA tool on the teachernet site.  Why do we need to reproduce ADB in another document but change some of the figures presented in the original document?  For example the occupancy factor for adining room is 0.9 and an assembly hall 0.45.

[Pete M]

And another thing,

Can anyone explain the rationale behind the redistribution of occupants on the fire floor (assuming one exit is unusaable) when calculating stair capacities?  I thought the formula used in ADB took this into account; the text following each of the examples in ADB state that that the capacity will be adequate when a storey exit is discounted.

Is BB100 now saying that ADB is wrong?

Oh yes, whilst on the subject of ADB stair calcs - why do we have (n-1)? even discounting a storey exit, the standing capacity of the stair would not change. - Anyone shed any light here?

[kurnal]

The n in the stair formula is relating to the number of floors served. So the standing capacity of the stair will be related to the number of flights but the bottom storey doesnt have a flight so has no standing capacity?

[nearlythere]

And another thing,

Can anyone explain the rationale behind the redistribution of occupants on the fire floor (assuming one exit is unusaable) when calculating stair capacities?  I thought the formula used in ADB took this into account; the text following each of the examples in ADB state that that the capacity will be adequate when a storey exit is discounted.

Is BB100 now saying that ADB is wrong?

Oh yes, whilst on the subject of ADB stair calcs - why do we have (n-1)? even discounting a storey exit, the standing capacity of the stair would not change. - Anyone shed any light here?

Remember Animal Premises and Stables?
Probably came from the same office.

[Pete M]

Hmmmmm..  Might be right about the guidance coming from the same office!

Kurnal - are we saying that the 'floors served' are in fact the floor count of the building including the ground floor?  I didn't think stairs 'served' a ground floor.

I am still confuddled over the calculation change introduced in BB100 though - does anyone know the background to this?  Seems as if BB100 is saying that ADB stair sizing gives insufficient capacity based on the fact that one storey exit could be compromised; whereas ADB states that the formula and calculations will provide sufficient capacity without modifying the occupancy spread/split.

Does anyone have anything which documents the evolution of the stair sizing currently in ADB from the original 1950's PWBS?

[slubberdegullion]

For example the occupancy factor for a dining room is 0.9 and an assembly hall 0.45.

I hate to state the obvious, but the people are smaller!!

Now, regarding the (n-1) in the stair calcs, the figures in the table start with an assumption that 40 people will fit in each storey of an 1100mm stair.

They also have a starting assumption that with only one floor served for an 1100mm stair a width of 5mm per person will be sufficient to clear the floor through that stair in 2 and a half minutes (the desired outcome).

They then build on this by assuming that for every 100mm the stair gets wider an extra 5 people will fit per storey.

These three assumptions are the heart of the table and the formula, but they are based on more fundamental assumptions, such as that the height from one storey to the next is 3m (or 10 feet originally).  Just look up PWBS for the rest.

This is where the formula comes from:

If

w = width of stairs in metres
p = number of people served by the stair
n = number of floors served by the stair

p is going to be made up of three things:

1. the starting figure given by 5mm per person (e.g. 1100/5 = 220) for one floor served
2. an additional 40 persons for every additional floor served (i.e. add 40 per (n-1))
3. an additional 5 persons for every 100mm extra width on each of the additional floors.

Did you notice the (n-1) up there?  It's (n-1) because you add on the additional figures for every floor greater than the original one you started with.  For example, three floors served (n=3) you add on (n-1) two lots of 40 for an 1100mm stair.

Mathematically:

(remember w is in metres)

p = 1000w/5 + (n-1)40 + 5(n-1)(w-1.1)/0.1

(that's 5mm per person + 40 per additional floor + 5 per additional 0.1m per additional floor)

This, of course, transposes to:

p = 200w + (n-1)(40 + 50(w-1-1))

which in turn gives:

p = 200w + 50(n-1)(w-0.3)     The formula in the book!

Stay awake at the back there!!

Anyway, thats what the n-1 is all about.

It's all very theoretical and hypothetical of course and you can pick it to pieces but it's what we've all been using for 50 years.

Pete, as for your search for the evolution of this since PWBS, good luck!!

Stu

[kurnal]

I hate to state the obvious, but the people are smaller!!

Some of them may be stu. But take a look at the young folk coming out of the everage high school. Bet you wontt be picking any fights!!

I carried out an analysis of a school a few years ago that had been built to ADB by a firm of housebuilders on a PFI scheme in conjunction with  an approved inspector. Neither had heard of BB7 or the additional rules for schools that accompanied the ADB 2000 edition. Every lesson change the place just logjammed.  Staircases and corridors did not have sufficient capacity.  I concluded the reason for this was that every student was also carrying a bag so taking up additional space. Fixed it for fire with a couple of externals for fire (post opening, paid for by the approved inspector) and a one way system for lesson changes.

[wee brian]

That's the problem with designers. They just apply the minimum standards without thinking about day to day use. I suppose in a fire they would (mostly) leave their bags behind.

I had a similar issue with a TA centre. Designed like an office building - not very practical for blokes humping machine guns and mortars about - place got knocked to bits in no time.

[slubberdegullion]

That's the problem with designers. They just apply the minimum standards without thinking about day to day use. I suppose in a fire they would (mostly) leave their bags behind.

They'd probably chuck them on the fire!

[John Webb]

... For example the occupancy factor for adining room is 0.9 and an assembly hall 0.45.

I presume that for an assembly hall, the pupils are standing in their ranks (well, that's what I used to do) and only take up 0.45 of a sq m each.
In a dining hall they are sitting at tables and therefore not so many pupils can be in that room, at least during the lunch break, and some bright spark probably thought they'd just double the number they'd first thought of to allow for the reduced area.

I haven't looked at this document, and wonder if it actually gives advice on the layout of chairs and tables (or seating units combining both) for dining rooms to allow for easy escape in an emergency.