BS 9999 - Fire Fighting Shafts

[AM]

In BS 5588 pt 5, it states that to ventilate a fire fighting lobby natural ventilation can be used, except for basements deeper than 10m. In 9999, this has been updated to say that natural ventilation can only be used up to 30m, above which a pressure differential system should be used.

Can anyone point me to the reasoning behind the inclusion of this upper limit.

Thanks

[Phoenix]

Good question!

Don't know.

Seems onerous and I'm not sure it's being applied generally.  The BRE report 79204 makes reference to testing their smoke shaft results up to 101 storeys (though they didn't allow for expected winds at that height so they recommend caution).  It could be the result of the BSI committee being over-exuberant in their acceptance of some theory or little tested research/modelling, or they might have just got it wrong.

Or maybe someone will explain....

[FSO]

Stack effect I would say.

[Phoenix]

The stack effect increases with the height of the building.  Therefore, if a smoke shaft is provided, this works more efficiently for taller buildings,  and if the staircase is ventilated by windows on an outside wall, these windows work more efficiently.  So, I'm sorry, but it's not due to any limiting factor of the stack effect.

I regularly deal with buildings over 30m in height and it is rare to find one with a pressurisation system that was installed for purposes of fire-fighting.  I have come across a number in London.  The recommendation for pressurising 10m deep basement shafts, I've always supported because of the difficulty in providing ventilation to the shaft but above ground I don't know where they are coming from with this recommendation.  I don't think this recommendation is frequently complied with - it is simple to get around because you just have to use ADB instead of 9999 for the recommendation to disappear as quickly as a puff of smoke in a pressurised staircase.

The BSs do have some shocking errors in them here and there and there are some jarring errors elsewhere in 9999.  Everyone should bear this in mind generally when reading BSs - they're not the be all and end all.

Here's hoping someone can provide an answer 

Stu

[CivvyFSO]

it is simple to get around because you just have to use ADB instead of 9999 for the recommendation to disappear as quickly as a puff of smoke in a pressurised staircase.

Not really, not if you want the benefits of increased travel distance and all that stuff.

(FWIW, I am not reallly saying that I would insist on the pressurised stair, more looking at the principle...

[Phoenix]

Not really, not if you want the benefits of increased travel distance and all that stuff.

That's true.  Most still use ADB for t.d.s and numbers but that is changing.  They certainly shouldn't mix and match these two standards.

But, like you, I'd be reticent about applying this recommendation even if I was going with 9999 over ADB for everything else.

Unless, it's explained why it's required.

Stu

[CivvyFSO]

I am presently trying to find out from someone who should know.

Some people involved with BS9999 were also linked with BDAG so it might be linked to BDAG research or NFPA codes formulated since the World Trade Centres Collapse.

[jokar]

If you read BS 9999 it alllows you to mix and match standrads so you can you both to get your minium package and additional bits and change back to ADB for the other stuff.

[Phoenix]

If you read BS 9999 it alllows you to mix and match standrads so you can you both to get your minium package and additional bits and change back to ADB for the other stuff.

You have to be careful though.  ADB only has no recommendation for pressurised stairs by virtue of the fact that it refers to BS5588-5 for the construction of fire fighting shafts.  This, of course, has gone and been replaced by BS9999.  But ADB does not say, "refer to BS9999."  So there is a sort of gap that is open to interpretation as befits an individual's needs.

It would be great, Civvy, if you can come up with something.

Stu

 

[Phoenix]

I wonder if 30m is the maximum height you can have openable windows at and it slipped the minds of the BSI committee that you could use smoke stacks above this height and so they concluded that pressurisation was the only option.

Stu

[jokar]

The 5588 series has not gone.  There seems to be somewhat of a difference between what 9999 states and what is actually occurring.  People are still using 5588 as a design guide and it is being accepted by AI's and BCO's.

[Phoenix]

Well, that's a bit naughty because at the beginning of BS9999 it says,

"Supersession
This British Standard supersedes the following publications, which will
be withdrawn on 6 April 2009:
• BS 5588-0:1996;
• BS 5588-5:2004;
• BS 5588-6:1991;
• BS 5588-7:1997;
• BS 5588-8:1999;
• BS 5588-9:1999;
• BS 5588-10:1991;
• BS 5588-11:1997;
• BS 5588-12:2004;
• DD 9999:2005.
BS 5588-1 is not being superseded by BS 9999 but is expected to be
revised in due course and issued with a new identifier."

Parts 2,3 and 4 had, of course, already gone.


Stu

[wee brian]

http://www.planningportal.gov.uk/england/professionals/en/4000000000240.html

Scroll down to the last FAQ

[Phoenix]

Thanks for that reference, Brian - a noteworthy point that tidies up that little side issue. 

We're still not getting near an answer to the question though.

Stu