Compartment floors in basements

[Fishy]

Something we're working on at the moment where I thought I'd punt some details out to you guys for some feedback...

Industrial facility (can't be more specific, but it isn't a factory - more process plant with large water pumps and lots of air handling plant) - A2 risk profile under BS 9999 - a few A3-type risks but they're isolated and fire separated.  Extensive basement well over 10m deep (4 sub-floors).  Top floor over 18m above ground but less than 30m.  Roughly square in plan - 4000m2 footprint.  Two fire-fighting shafts provided serving all floors (but separated at ground level so the above-ground & below-ground parts of the shaft aren't directly connected).  F/f shafts mechanically ventilated & also form part of the means of escape, with all vertical escape stairs being within protected shafts. Building is un-sprinklered with an L2 BS 5839-1 alarm system and simultaneous evacuation. Concept design stage (RIBA 2-ish) so it isn't built yet!

Basis of design is BS 9999 with some 'tweaks'.  One big issue with the current concept is, though, that there is a massive piece of plant that sits on the lowest level in the basement within a void that extends all the way up through the basement & ground levels & reaches roughly to +10m AGL.  At the moment none of the floors are fire separated from the void.  Falls foul of 32.4.2 of BS 9999 in that none of the basement floors are currently compartment floors - neither is the ground floor.  For various reasons we can't practicably fire separate the void from the rest of the basement accommodation and the amount of plant and services transiting the basement floors would mean that making them fire-resisting would be a nightmare.  What we can do is to make the ground floor fire-resisting (with the exception of the large void) and provide a certain amount of vertical fire separation within the basement to break it up unto several multi-floor zones, with progressive horizontal evacuation being possible to the adjacent zone(s) and to the protected shafts.  Ground floor is the operating floor with infrequent personnel access being needed to the basement.

I'm reasonably comfortable with this concept being safe in terms of means of escape, and that it provides acceptable fire-fighting access, but what I'm struggling with a bit is coming up with a definitive explanation of what compartment floors in basements are actually for!  I'm thinking that it's primarily to reflect the difficulty of accessing basements for fire-fighting purposes, rather than for means of escape ('cos I can't see much difference between a basement floor and a floor above ground in terms of being able to reach a storey exit, if that exit leads directly into a protected shaft)? Would my learned colleagues agree, or am I missing the mark?

[kurnal]

Few observations from an outsiders point of view (all of which you are fully aware of but a reminder may be useful):

The building regulations do not require anything to be done that does not contribute to life safety.

ADB and BS 9999 give solutions for most typical buildings. This is not a typical building.

Whilst there is a large item of plant in the basement is there an open, large space above that might  reduce the level of risk of smoke logging or flashover and therefore the risk to occupants and firefighters?

I may be misinterpreting the risk, I am relating to my experience of a number of buildings of this nature and size in the water industry where the main risk was electrical and there was very little by way of other combustible materials. When analysing the number and nature of persons at risk, the protected escape routes, the rate of fire growth, the risk of smoke logging and flashover, access for firefighters, installation and maintenance of plant at basement level, we took the open aspect as a benefit and omitted the compartment floors. Always with access to protected routes though

But your situation may be very different.

[Fishy]

Thanks for your comments, Kurnal.  As you say this isn't by any stretch of the imagination a 'typical' building but we're happy applying BS 9999 to it rather than going down the BS 7974 route (though we might use the principles to agree our 'variations'). 

Anyone else with any thoughts on what basement compartment floors might be for?

[wee brian]

Basements are just in the "here be dragons" category of fire safety. So codes tend to impose more requirements on them. Also, you are much less likely to want to have open arrangements in basements as they tend not to be used for that kind of accomodation.

As I understand it, there are two real issues with basements

1 - they dont have windows so heat/smoke etc cant get out.

2 - evacuation and fire servive ops are more of an issue because smoke and heat go up.