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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Technical Advice => Topic started by: Benzerari on November 20, 2008, 09:12:59 PM
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Why a fire detection is required out side each lift and in each floor, we have a case where a lift lobby with five lifts, 2 in one side and 3 in the opposite side, the distance between them is about 3 to 4 meters the lobby has 6 smoke detectors..., 5 detectors to cover 5 lift lobbies and one extra detector in the middle of the lobby.
The question is; is that really required by BS 5839? Apparently the designer has applied the standard with no common sense! Why not one smoke detector covers all five lifts including the lobby itself?
Thank you
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There needs to be a detector within 1.5m of the lift opening if I recall correctly, so 1 would not do 5 lifts, but I've seen 1 between 2 lifts, 2 between 3, etc
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There needs to be a detector within 1.5m of the lift opening if I recall correctly, so 1 would not do 5 lifts, but I've seen 1 between 2 lifts, 2 between 3, etc
According to what you said, 6 SDs in lift lobby in our case is right then?
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Benz its all about the path that the smoke may take in the event of a fire.
Lift shafts are like a chimney- the stack effect can cause powerful suction effects drawing smoke into the shaft. As all lift doors are sliding doors you can never achieve a seal to prevent smoke smoke being drawn into the shaft. In the early stages of fire the limited heat and smoke plume may be shallow and fast moving as a result of the stack effect and may not acculumate at a sufficient depth across the ceiling to operate a smoke detector at conventional spacing. So the additional detectors are sited where this travelling plume is likely to pass over them in order to give the earliest warning of fire. The more lift shafts there are, the greater the problem.
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The previous confirmations of recommendation in BS are spot on.
However the 1.5m distance is definitely one of those that is not 'written in stone'.
If you have one lift then 1.5 m should be easily achievable.
If you have 6 lifts and it appears it would take 6 detectors for each to be within the recommended 1.5m of every door, then a bit of commonsense needs to be applied. For example; if, Just 2 detectors might be sufficient even though a couple of the lift doors would be, say, 3m away from a detector, then this would surely be acceptable to anyone apart from the most boneheaded codehugger.
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Benz its all about the path that the smoke may take in the event of a fire.
Lift shafts are like a chimney- the stack effect can cause powerful suction effects drawing smoke into the shaft. As all lift doors are sliding doors you can never achieve a seal to prevent smoke smoke being drawn into the shaft. In the early stages of fire the limited heat and smoke plume may be shallow and fast moving as a result of the stack effect and may not acculumate at a sufficient depth across the ceiling to operate a smoke detector at conventional spacing. So the additional detectors are sited where this travelling plume is likely to pass over them in order to give the earliest warning of fire. The more lift shafts there are, the greater the problem.
Prof., I would suggest another view converse to your argument, that in fact because lift shafts can be so tall, any smoke in the shaft could lose it's bouyancy, as it cooled, and not reach the detection at the top. In these circumstances the smoke is likely to leak out at a floor level through the lift doors and therefore a detector on the 'accommodation' side close to any opening into a vertical shaft between floors is a good idea. Whatyafink Prof.?
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Well its got to be a factor Dr Wiz. Its like the double glazing. Is it to keep the warmth in or the cold out?
Or Matrons girdle come to that?
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Benz its all about the path that the smoke may take in the event of a fire.
Lift shafts are like a chimney- the stack effect can cause powerful suction effects drawing smoke into the shaft. As all lift doors are sliding doors you can never achieve a seal to prevent smoke smoke being drawn into the shaft. In the early stages of fire the limited heat and smoke plume may be shallow and fast moving as a result of the stack effect and may not acculumate at a sufficient depth across the ceiling to operate a smoke detector at conventional spacing. So the additional detectors are sited where this travelling plume is likely to pass over them in order to give the earliest warning of fire. The more lift shafts there are, the greater the problem.
Thanks Kurnal for this technical info;
The lift shafts in our case is only one lift shut in each side, 3 lifts have got the same lift shaft and the opposite side 2 lift shafts having the same lift shut... etc, there are no walls between the lift shafts which makes the situation a bit different, I may think each side needs only one SD... etc isn't?
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I would consider the total length of the combined opening on each side and also the location and layout of the shaft and any combustible materials. Cant really be more specific without seeing it.
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I would consider the total length of the combined opening on each side and also the location and layout of the shaft and any combustible materials. Cant really be more specific without seeing it.
I mean 3 lifts share the same lift shaft, and in the opposite side, 2 lifts share the same lift shaft, in total there are in fact 2 big lift shafts, and the distance between them is about 3 to 4 meters. (Lobby’s distance)
I will try to make a layout and display it here soon
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Benzo; Spare yourself the agony. One detector is fine. The ideas about needing multiple detectors is rubbish.
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Benzo; Spare yourself the agony. One detector is fine. The ideas about needing multiple detectors is rubbish.
Ohh thanks a lot Colin, thanks for confirming the common sense :)
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Just taking this to another level..... the BS indicates a detector outside a lift, does this also apply to risers within buildings? As this is then a similar scenario and is a flue like structure?
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Just taking this to another level..... the BS indicates a detector outside a lift, does this also apply to risers within buildings? As this is then a similar scenario and is a flue like structure?
Yes!
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Benz its all about the path that the smoke may take in the event of a fire.
Lift shafts are like a chimney- the stack effect can cause powerful suction effects drawing smoke into the shaft. As all lift doors are sliding doors you can never achieve a seal to prevent smoke smoke being drawn into the shaft. In the early stages of fire the limited heat and smoke plume may be shallow and fast moving as a result of the stack effect and may not acculumate at a sufficient depth across the ceiling to operate a smoke detector at conventional spacing. So the additional detectors are sited where this travelling plume is likely to pass over them in order to give the earliest warning of fire. The more lift shafts there are, the greater the problem.
Can that be applied to risers as Fella mentioned?
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We must remember that most service risers are protected shafts with fire resisting doors provided with smoke seals.
Lift shafts are a little different as these are the only fire doors in Approved Document B not required to have smoke seals- this is always imossible to achieve in a sliding door.
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Also most risers I have seen have detectors inside in each floor, while in lift shaft has only one in the top...
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What if you have an open riser going through several floors. A detector would be mounted at the top. Would it be required to have a detector also outside the riser as you would a lift? Or am I missing the point?
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What if you have an open riser going through several floors. A detector would be mounted at the top. Would it be required to have a detector also outside the riser as you would a lift? Or am I missing the point?
As I previously advised, yes it would. Any flue-like structure penetrating through floors requires it - smoke sealed doors or not! (just in case the door was left open or the seals didn't work?). BS 5839 part 1 2002 22.2.C) refers.
Please note that the detector needs to be on the 'accommodation' side and not in the flue-like structure (apart from the one at the top of the flue-like structure, of course) and you only need it IF the accommodation side of the flue-like structure is an area that would require detection anyway by virtue of the system category designation.