CLG V ADB Corridor subdivision

[steveborack]

Gents (and ladies of course;(don't want to fall foul of the PQA's etc etc etc))

ADB states subdivision of corridors is required if longer than 12m serving 2 or more storey exits

CLG guide states under the same as above that the corridor should be separated but no length of corridor is given. Yet CLG also says that if the corridor is generally over 30m it should be subdivided...

Why is the CLG specific about general corridors but not about subdivision of corridors serving storey exits?

But more importanty, regardless of general or storey exit subdivision, 12m and 30m are slightly differing distances.

All I need is the knod of what is staring me in the face but can't yet see...

As ever, thanks in advance 

[kurnal]

The length of the corridor is not really a significant issue - its simply a matter that the door across the corridor  prevents both storey exits being made inaccessible to all rooms that open onto the corridor at the same time. But none of it is set in stone, I have just had a scheme approved in a sprinklered building with L1 to omit the door completely, effectively treating the corridor as an access room so no sub division.

The logic is that if it were a large room with inner rooms leading off there would be no need to subdivide the storey exits as the large room would take a lot longer to fill with smoke than a narrow corridor would. So put measures in place to detect the fire early and / or to suppress it and the main problem goes away. 

[Davo]

Tend to use 30m rule myself, but we have no high fire risks.
BC don't seem to bother as long as they can see some division


davo

[steveborack]

Ok all fair enough. What if you have an extended corridors. Would 2 subdivision doors be reasonable to reduce the number of rooms affected by the fire 

[Davo]

steveborack

yes, I have been known to do this, all three corridors reasonably similar lengths depending on whether you are looking for full compy (where convenient) or smoke door.
Consider stair positions and door locations too

davo

[Tom Sutton]

But more importantly, regardless of general or storey exit subdivision, 12m and 30m are slightly differing distances.

I do not know where the ADB 12m comes from but GLC guides simple recycled the old prescriptive guides with slight modification and this one, on subdivision of corridors, is almost a direct lift.

[wee brian]

The difference is probably historic.

Arguably it is reasonable to impose higher standards when a building is being built than in retrospect. Although both numbers are abitrary.

[John Webb]

I have a vague recollection that the ADB's 12m is derived from the smoke level required to operate a smoke detector - eg when the smoke is dense enough to operate the detector visibility through the smoke is around the 12m mark. But I stand to be corrected on this one. (And in corridor tests I've seen cool smoke form a plug in the corridor cutting out a view of the escape door and too far from a smoke detector to operate it.....!)

[Tom Sutton]

John I would have some doubts on the detector theory, the blue guide required smoke stop doors every 60ft in corridors and smoke detection was very rare, if at all. On reflection the 60ft was reduced to 12m in later guides and maybe smoke travel was a reason.

[wee brian]

ADB Para 0.21. Doesnt entriely answer the question but does give some context

Guidance documents intended specifically for
assessing fire safety in existing buildings will
often include provisions which are less onerous
than those set out on this Approved Document
or other standards applicable to new buildings.
As such, these documents are unlikely to be
appropriate for use where building work, controlled
by the Regulations, is proposed.

[AnthonyB]

Well it proves they are aware of the difference and reinforces the point that you should be using the right guidance in the right building in the right circumstances - you see them being jiggled about willy-nilly at times and that isn't always correct!