What do these risers do?

[Wiz]

I have recently visited a large 1960's-built building that have a number of risers built within it, which no-one knows for what purpose they were included in the original construction design. Can anyone help with guidance or opinions?

The facts are:

The building has approximately 5 storeys and contains multi-story style car parking on the lower levels. The highest levels contain office accomodation.

There are three concrete constructed risers running through the upper floors. Two of them are in the central core of staircases situated at each end of the building. The third runs adjacent to the lift shafts in the middle of the building.

At each floor level there is a large access point (approx. 1200 x 1200mm) into the riser from lift lobby or stairwell. This access point is constructed of Crittal window style openings glazed with opaque georgian-wired glass. The upper portion of the access point is a window (hinged across it's bottom edge) that can be opened inwards into the riser shaft but kept lock by a sprung latch that can be operated by a hook on a pole. The bottom part consists of two leaves (hinged on the sides) that presumably also open into the shaft. these are kept closed by a lock that would require a square-shaped key to open them.

The riser next to the lift contains a gas-main pipe running up the riser. The stairwell risers are empty.

At the top of the stairwell risers are electrically-powered louvred ventilation grilles that open directly in the ceiling of the shaft to the open air. These louvres do not seem to be controlled by the fire alarm system but we suspect they might be controlled by a 'fireman's switch' from somewhere.

The top of the central riser appears to have an open louvre into the side of the riser wall at the, or near, the  very top. We have no evidence that this louvre is anything but open to the air at all times.

At first it was assumed that these risers might be used to vent any smoke from the car park areas through the building out to the open air at the top of the building. However there is no evidence of any inlets at car park levels.

My specific questions are:

1) Does anybody know what the purpose of these risers might be?

2) What is the purpose of the glazed 'access' points at each storey level?

3) Although BS 5839 requires automatic detection at the top of such risers, they would be difficult to install for the staircase risers, and also because of the openings to open-air might be useless in providing any detection of smoke. Are they necessary in these sort of risers?

Any guidance or opinions gratefully accepted.

[wee brian]

Sounds like smoke venting for firefighting stairs . Are there rising mains in the stair?

[jokar]

I agree with Wee Brian and would guess it is a ventilation shaft for a firefighting staircase.

[Wiz]

Thank you for your reply Wee Brian.

Being a fire alarm engineer, I do not normally pay much attention to firefighting facilities. I assume that a 'rising main' would be pretty obvious (I have previously seen various pipe outlets etc. in other buildings in the past) but I can say I saw nothing similar to this in the staircases.

I agree that these risers seem to be provided for venting purposes, because of the grilles at the top. Can you explain how such a venting system would work? For example, would it work in such a way that if one floor was smoke-logged then the vents on that floor could be  opened to clear the smoke? If so, how can you be sure that the air flow would be suffcient to actually clear the smoke?

I'm only guessing here, but could it work in a manner that if you opened all three vents, the middle one created some sort of positive pressure that pushed the smoke down the  corridors to the vents in the staircases at either end?

As I say, I know nothing about the construction requirements of large buildings from the 60's, or how any such venting could work, or how firemen fight fires in large multistorey buildings.

Any further opinions or advice gratefully accepted.

[Wiz]

I agree with Wee Brian and would guess it is a ventilation shaft for a firefighting staircase.

Thanks Jokar.

What exactly defines a 'firefighting staircase' and are you saying the shaft is used to keep the staircase clear of smoke?

What would be the purpose of the middle shaft ?(it's basically in the middle of the building, has the same access facilities as the staircase ones, but I noticed that a large (150mm ? ) pipe marked GAS runs up it).

[John Webb]

Wiz, do we have two separate functions here? The outer risers are for venting smoke, the inner one is for the gas main and is vented to prevent gas build-up if there is a leak?
Just a thought.

[kurnal]

H Dr Wiz
Sounds like you have discovered the secret escape shafts created by Lucky and inspired by watching my other hero Clint Eastwood in the film Papillon.

Firefighting shafts are a requirement in some buildings, depending on size, height and what the building is used for. The rules have changed over the years but they are intended for tall buildings or deep basements where firefighters could not gain access by pitching ladders or breaking down doors and windows. In addition in very deep basements or high buildings there is a fire fighting lift installed so they dont have to carry their equipment too far.

There are two parts to the fire fighting shaft, a staircase and a firefighting lobby at each level. The lobby acts as an airlock and prevents too much smoke entering the staircase, where the firefighters would set up their brifdgehead on the floor below the fire (or the one below that). The lobby will contain the outlet from the rising main from which they charge their hose before entering the fire compartment.
 Clearly as they enter the fire floor with their hose the door will be held slightly open and some smoke will enter both lobby and stair during firefighting so these have to be ventilated to maintain safe conditions for the firefighters, to change their air cylinders etc.
This is what the shafts will be, and there will be seperate vents for the stair and for the lobbies, often manually opened vents are provided into and out of the shaft, in some cases the vents are automatic.

The requirement for shafts carrying gas mains in high rise buildings requires these shafts to be permanently ventilated in case of gas leaks.

Hope this helps.

[Wiz]

Wiz, do we have two separate functions here? The outer risers are for venting smoke, the inner one is for the gas main and is vented to prevent gas build-up if there is a leak?
Just a thought.

Thank you John for your help. I think you must be absolutely spot on with your thoughts. Professor Kurnal, in his reply, also mentions the middle shaft being for venting of gas.  I'm presuming that the gas must therefore be lighter than air to allow it to vent, although I always thought it was heavier! However I still don't understand why this shaft has the same 'access' windows as the firefighting staircase vents.

[Wiz]

Hi professor Kurnal

I was banking that my hero would come to my assistance!

I am a bit worried that you think that Clint was in Papillion. However I understand that you might now be suffering from 'tunnel' vision (and thinking) since I detailed you and Lucky to create the escape shafts from the home for the slightly bewildered we all now inhabit. Also, bad news, I think Lucky must be a goner. I haven't heard from him in months.

Thank you for your, as usual, excellent answer. Your description of the type of building is spot on. This building has an increasingly smaller 'footprint' size as you go up the floors. I would imagine trying to use ladders from ground level would be very difficult.

Just a few more questions, if I may ask.

Am I right in thinking that the shaft that contains the gas pipe, could also be used for smoke venting as well as acting for a vent in case of gas leaks? It appears to be similar to the ones on the staircases, but just also has a gas pipe running through it.

If these shafts are for the purpose described, can you think of any reason why installing a smoke detector at the top of them could be omitted from a category L3 design?

[kurnal]

My film knowledge is unsurpassed but on this occasion I was of course thinking of Steve Mcqueen in escape from alcatraz.  I enjoyed the bit where marylyn munro struck a match on her chin. I would have gone to see it again if I had a few dollars more.

What on earth have you got there?
Are there any openings or vents to the sides of the car parks? How is the car park ventilated?

It sounds like the openable windows are of fire resisting glazing probably intended to  be opened by firefighters.


The design of the shafts as you describe them does not conform to the normal design of firefighting shafts- there are no fire mains or lobbies. Without knowledge of the building history it is very difficult to understand what its all about.
Have the fire  mains been removed over the years?
It may make some sense if the shell of the building had been originally intended to be flats designed to CP3 but was then converted to offices.

I dont have any design guides dating from the 1960s and have tried googling without success- my earliest are the CP3 documents from 1971

Shafts containing gas mains should be ventilated at top and bottom, if we go by the book, though any vent would help to prevent a build up of positive pressure .
 From the point of view of an alarm system, I  think your analysis is right. I think there is little doubt that this arrangement as you currently have it could represent a flue like structure and so strictly speaking under 5839 should have detection at the top.

However it is more important to identify the true purpose of the shaft and most important to find out how the louvre at the head of the stair is opened, they can be manual or automatic- depending on number of stairs and whether they need to operate in conjunction with other systems. In an older building I guess they are likely to be manually operated but there should be a clearly marked control or switch for firefighters at the entrance.

So if speccing an alarm you really need to know whether its intended to be automatic or manual, if automatic whether it will be smoke detector controlled and whether you need to interface to it - probably doubtful.

I think thats the first step.  The responsible person has a duty to maintain facilities for firefighters and it may be worth asking the local fire safety officer for advice to find out exactly what you have got there.

 It could be a redundant arrangement or something entirely provided for environmental ventilation? If it were permanently open at the top and had no louvre vent then there may be no point in installing detection as you say, instead treating it like a light well.

Theres no point putting detection in a normal vent shaft provided as part of a fire fighting shaft as I see it,  if there is no fire risk within it, if these is good management control to make sure that the glazing remains in good order and that litter cannot build up in the shaft. But if litter could build up and a fire started in their without the top vent being open, the stair copuld be smokelogged and then detection becomes a necessity.

Its very difficult to know how to advise further without seeing the building, becuase it does not match what would be normally expected. You may wish to look at BS5588 part 5 for more information on the construction of firefighting shafts.  Sorry not to be much help.

[Wiz]

Thanks once again Prof. K

The good, the bad and the ugly of the problem is that my vision is going misty reading information about this. I'm turning every which way for a soution and if I fail I will be unforgiven and maybe considered a silly clint for raising it.

From all the comments and advice given, I am coming to the conclusion that these are definitely firefighting  ventilation shafts. Whilst the middle one is not strictly in a satircase, it is close to a staircase and in an adjacent lift lobby.

I believe the motor-driven vents at the top of the shaft to be manually controlled and I presume that the firefighters might operate these when they decide that doing so won't fuel any fire. They can then open the access windows to the shaft(s) at any level for use in clearing smoke if they decide it is necessary.

The problem with installing automatic detection is the whole top, of at least the staircase shafts, contains an opening louvre. When I was there they were open. If this was just because someone has forgotten to close them I don't know (could this fuel a fire?). Obviously installing a detector brings all the problems of it being affected by water, dust etc. coming through the louvre. If we provide some arrangement to protect it from the elements this will partially block the shaft (reduce the venting effect?).

The good news is, that whatever the decision is regarding the top of these shafts, we will be providing automatic smoke detection within 1.5 metres of each of the shaft access facilities at every level.

I don't know any more about the original intended design or use of the building and I suspect the local authority owners do not know either. The problem is that I get so much conflicting information from people who I think should know about even the most simple things on a site, that I lose confidence in what they are telling me! I will try to find out more information and have a better look at the things you have highlighted on my next site visit.

The fire risk assessment carried out on this building does not mention these shafts in any way. It does seem to be advising that disabled refugees should be provided at or near the vent shaft access facilities (I don't know if this is good or bad! Will the firefighters trample on the disabled?).

Advice from the local fire officer, so far, has not proven to be helpful. We have concluded that he might not really know and therefore won't commit himself.

Thanks for all your advice. I will let you know if we find out anything more.

[kurnal]

It sounds like you have to make a decision for them Wiz.

Is there any floor level in the building higher than 18m? If not I would suggest that the shaft that seves the lift lobby is probably more to do with venting the lift rather than firefighting access. Lift doors are pretty well impossible to seal against smoke and if the lifts penetrate car park and office levels a ventilation shaft would relieve any pressure trying to push smoke into the office accommodation.

I think I would re-iterate what I said earlier - we assume it is a ventilation shaft serving  a firefighting stair (even though without a firefighting lobby or riser), and - this is key-  if it is still maintained as such so that litter cannot accumulate in the shaft and all vents and glazing are secure and in good order I would not provide detection within it. After all  if its sole purpose is for the controlled removal of  smoke from the stair then thats where the detection should be. Same goes for the vent from the lift lobby. The fire risk assessment  should refer to the shafts assuming they do form part of the fire plan for the building and its the fire risk assessment that should make reference to how the shaft shall be maintained. I am not aware of any other smoke ventilation duct from a firefighting shaft that has had detection installed within it as part of a life safety system.

Lift shaft should contain detection as it will contain a significant risk but the vent shaft should not require it.

The building management should have made arrangements to assist people away from the refuges before the arrival of the service. Leastways thats how its supposed to work.

 If you did create a shoud to protect the detector how do we design it to ensure that the shroud does not divert the smoke plume away from the detector within the confines of a shaft, when as you say we must not detract from its efficiency.
I would be very happy to hear other peoples views on this one.

[wee brian]

If you have AFD elsewhere then I dont see any significant benefit from sticking it in the shaft.

Just put it down on the cert as a non-conformity and explain why (rain etc).

Perhaps a letter to the client suggesting that they find out what the shafts are for - maybe get a smoke control bod to have a look. This will, at least, ensure that you have covered youre own derriere.