Staircase Lobby Enquiry

[Messy]

Can anyone explain the significance of providing lobby protection to a staircase consisting of 2 x FD30s, compared with a single FD60 between the accommodation & the staircase?

I have a office building with multiple staircases. All are lobbied and need to be as the premises is almost fully occupied/utilised. (Think of sardines in a can and you will get the idea). It is necessary to maintain the lobbies as far as possible to avoid discounting a staircase when determining the premises occupancy figures

On one staircase, some accommodation - a couple of small sofas and a printer-  has 'spread' from the floor and is now located within a rather large staircase lobby. The vast majority of the floor remains separated by 2 x FD30s, but this reception area only has one FD30 between the room and stair.

I wish to replace the final FD30 (opening onto the staircase) with a FD60 and am relatively happy that the fire loading is minimal and ignition sources in that lobby space are restricted to a printer and overhead lighting.

[AnthonyB]

Most texts suggest it's for smoke control, both to protect the escape and to aid fire fighting. As mentioned in another thread I've a building that hasn't lobbied it's main stair opting for a single FD60S instead, with only a couple of floors retrospectively lobbied as part of BC requirements when refurbished.

The fire service are pushing for retrospective lobbying using Reg 38 and touting formal enforcement.

Discounting the stair isn't an issue as the floorspace is very small and almost within single travel distances to the lobbied, ventilated alternative stair, it's only really needed due to building height requiring the two escapes, plenty of other mitigation based on occupancy type and L1 AFD, they are digging their heels in though.

On one of the lobbied floors is using their lobby as a cloakroom which has also attracted the risk of formal enforcement too (adding up all the various things in this site scores enough points to look at getting the lawyers OK to go formal with court prospect)

[Golden]

Hi Messy, to be honest from my knowledge the lobby requirement is based in history but is basically to give an added level of confidence as in the early stages of the fire it is unlikely that the door between the firefighting lobby and the accommodation would be directly attacked by the fire, the Bickerdike Allen guidebook 'Design Principles of Fire Safety' goes on to say that lobbies "safeguard against the penetration of products of combustion into the vertical enclosure and to provide a higher level of confidence in the effective operation of the protection to the shaft" as my old mentor would say 'one for the fire and one for the smoke'.

I believe that the basics of the practice is that the overpressures generated in a fire will be dissipated by the first fire door therefore the second (staircase) door will be able to withstand the reduced pressures and preventing the combustion products from affecting the staircase particularly in the early stages of the fire. I don't know where the theory came from and whether or not there are studies to support the theory but I can vouch for its effectiveness in most fire situations that I've encountered where a lobby has been involved its done its job. I don't believe that a FD60 door will give the same confidence; large staircase lobbies (and large 'sterile' areas) designed into buildings are a pain in the rear as occupiers tend to regard this as usable space and don't understand the need to keep the areas clear of combustibles and/or ignition sources.

[Dinnertime Dave]

Bickerdike Allen guidebook 'Design Principles of Fire Safety' -


http://file.zums.ac.ir/ebook/203-Fire%20from%20First%20Principles%20-%20A%20Design%20Guide%20to%20Building%20Fire%20Safety,%203rd%20Edition-John%20Abraham.pdf

[Messy]

Many thanks for your replies. I am most grateful

I do intend in replacing the lobby in due course, but with a FD60S and measures to reduce the fire loading and sole ignition source from the lobby, I am happy to wait until the next financial year as requested.

DD: Many thanks for the book. I had heard of this and will print &  read it next week as I am working away and have some long evenings to fill!!

[Phoenix]

It's virtually all been said above, e.g. Golden, but here's my thoughts.  The increase in pressure in the upper part of the fire room can be quite high (several hundred Pascals have been recorded in some cases), and this is particularly significant if a ceiling jet is moving hot gases towards the door.  The over-pressures will tend to take advantage of any gaps around the top of the door.  (This is an important point - We know that doors do develop faults and gaps over time.)  The over-pressures will not generally fully transfer into the lobby so any gaps around the lobby-to-stairs door will not have smoke and hot gases forced through to the extent that the first door will.  A single door, whether 30mins or 60 mins, reduces significantly the additional protection to the stairs that is otherwise given by the lobby.

This has varying importance in different buildings.  It's a more important consideration in a single staircase hotel than it is in a multi-staired office block.  But remember that people with impaired mobility might take a considerable time to descend the stairs in a taller building, whatever its use, so the protection to the stairs should not be skimped on.

As for discounting whole staircases where lobbies aren't provided, I think that this can be over the top but, at the moment, I don't have an alternative to suggest.

[lyledunn]

Would several hundred pascals be sufficient to offset a door sufficiently to cause maloperation of the seal especially where the self-closer has been adjusted to allow disabled passage?

[Phoenix]

Fire pressures wont cause seals to fail but they will exploit seals that are already faulty.

[lyledunn]

Phoenix, I meant would fire pressure be sufficient to push say one leaf of a double door set even just a tad ajar such that the intumescent strip on meeting stiles would fail to seal?

[Fishy]

It's my understanding that lobbies a) reduce the probability that smoke will enter the staircase; and b) increase the probability that there will be effective fire separation between staircase and accommodation.

As regards a) - the sterile space between doorsets will (if both are closed) act to prevent smoke movement between accommodation and staircase (for all the reasons outlined above).  Regarding b) - in any fire protection installation there is a probability that it would fail to function 'on demand' - could be because it wasn't specified correctly; because it wasn't designed correctly; because it wasn't installed and commissioned correctly; because it hasn't been maintained correctly or because it isn't operated correctly.  By having two fire protection features in series between the risk and the area to be protected, you significantly reduce the probability of some of these failure modes manifesting themselves (but not necessarily all of them).  In short, two fire resisting doorsets in series will tend to provide a higher level of reliability than a single doorset (even if they are half the fire resistance).  That's why replacing 2 x 30 min doorsets with 1 x 60 minute doorset doesn't really offer the same level of fire risk reduction.

There are some arguments against the above - it might be viewed that with a lobby arrangement on a staircase that is used often it becomes foreseeable that users will find using the two doors a pain (and therefore will prop one of them open), but a decent level of fire safety management should help to avoid that form of 'misuse'.