Alternate approach to Protected Lobby

[SRJ]

Is there any alternate approach to Protected Lobby, Buidling is more than 18m.

Allowance for sub division above 11m.

It is office building, five storey. I understand that providing automatic fire detection probably L2 / L3 / smoke control in accordance with BS 12101 PART 6.

Any suggestions welcomed

[CivvyFSO]

A pressurised stair would be an alternative to lobbies.

It is unusual for a 5 storey building to be over 18m.

[SRJ]

Is there any alternate approach for sub division above 11m

[CivvyFSO]

So basically above 11m you have split the building and have ended up with single staircase conditions?

[SRJ]

Yes,

     Travel distance exceeds 18m so ABI has advised

1. To provide a lobby

2. No sub division above 11 meters as the property will be let to two different tenants

[CivvyFSO]

What you need to think about with the lobby is it's actual purpose. It is there to keep smoke out of the stair to ensure that the stair is always passable, so if you can acheive that by other means then you have cracked it. AFD does nothing to keep smoke out of the stair, the only choices you have are a positive pressure stair, or if you can have negative pressure in the accomodation area adjoining the stair. (This second option if very rarely used, and the positive pressure system is quite expensive) The only real benefit for you of using a positive pressure system is more useable/lettable floorpsace. Over a buildings lifetime the extra rental on the space may pay for the system. An engineered solution utilising a pressurised stair may be there to warrant the removal of other staircases, and as such would be a great saving on floorspace.

[SRJ]

Thanks for the response. The issue here is travel distance, which exceeds 18m in one direction for offices. I went through 9999 and the travel distances provided for A2 profile which is office, with additional fire protection measures (Automatic Fire Detection & Alarm) is 20m in one direction also it allows 5% increase in travel distance if the ceiling height is between 3 - 4m for A2 profile. If 9999 is to be followed as an alternate approach does this negate the requirement for the lobby

Thanks in Advance

[CivvyFSO]

You should wait a bit and see what the new BS9999 says when it comes out. It shouldn't be long now, but I would look at it in its entirety, not just pick out the parts that suit you.

If you have single direction travel you essentially must be looking at a single staircase condition for the same people. I suspect this is why the lobbies are required. Look at 4.3.4 of ADB.

This is also from the draft for public comment BS9999:

18.2.4 Added protection to stairs
An escape stair should have a protected lobby or protected corridor or a pressure differential system under the following circumstances:
a) where the stair is the only one serving a building (or part of a building) that has more than one storey above or below the ground storey;

[SRJ]

The building itself has two escape stairs well separated but as the client is planning to let the building to two tenants, ABI has advised that occupants of one wing won't be able to use the escape stairs of other wing. Eventhough the wings are only separated by a fire door. ABI's assumption is that the fire door which provides access into different wings might be unusable in fire. Does not agreement between two tenants to use eachother's escape stair and proper management procedures eliminate that possibility and ofcourse requirement for a lobby in one wing where the travel distance exceeds.

[CivvyFSO]

The only way this would be suitable under ADB is by ensuring either occupant does not have to travel through the other occupancy since they have no control over it. This would normally mean a fire seperated corridor leading from each occupancy towards their 'alternative' stair. (Which would be the main stair for the opposite occupancy) This would be a larger loss of space than the lobbies.

In my opinion the AI is quite right in his request, it is essentially a single stair for each occupancy and travel through a seperate occupancy should not be allowed. If the plans for such a premises landed on my desk I would be making the same recommendations.

If the premises was only split at the lower floors (Ground or first) then this would probably be ok.

[SRJ]

ABI is ok with splitting the floor upto 11m, in which case it is three floor but is adamant above that height & the client desperately needs a solution

[CivvyFSO]

I think it is quite clear in this instance, the solution is lobbies.

Someone else may have an opinion on this, but I can't see you getting away from it.