Lift Shafts

[Sherpa]

BS 5839 states that a smoke detector should be sited approx. 1.5m to the opening of any flue like structure, ie lift shafts.

What is the common accepted tolerance on the word approximatley, is 1.6 m ok?

[Tom Sutton]

Check out http://www.fire.org.uk/punbb/upload/viewtopic.php?id=1519 its on the same subject but does not answer your specific question.

[Wiz]

BS 5839 states that a smoke detector should be sited approx. 1.5m to the opening of any flue like structure, ie lift shafts.

What is the common accepted tolerance on the word approximatley, is 1.6 m ok?

BS 5839 Part 1 is a set of recommendations.

Variation from the recommendations is recognised and allowed.

The maximum area of coverage of an automatic fire detector is specifically mentioned as an example where the recommended values are considered to be arbitrary

However any Variation from the recommendations should be clearly identified at every stage; Design, Installation, Commissioning and Documentation.

All of the above can be found at BS5839 Part 1 2002 Clause 7

Also all Variations should be agreed by all Interested Parties (Clause 6)

If you can prove, or get someone to agree, that siting your detector within 1.6m instead of 1.5m from the opening of the flue-like structure, does not detrimentally affect the performance of the system then you have no problem. If not, move it and enjoy the 'peace of mind' afforded by the 'protection' of the recommendations of BS5839 Part 1!!!!!

[kurnal]

I expect that the reason for the recommendation in the BS is that any flue like structure will cause air movement towards it due to the stack effect ( act like a chimney) and in the early stages of a fire these air movements may be stronger than the convection currents caused by the fire thus drawing smoke towards the flue rather than towards the conventionally sited detectors.

By placing a detector in the vicinity of the flue like structure we can ensure that if this occurs the fire will still be detected early.  If the detector is too close to the flue, or not in the line of the air flow between the area at risk and the flue, it may not be effective.

Similarly we could predict that the effect of beams and downstands across or in line with the air flow would have a major effect on the flow of air and smoke - probably of greater significance than the  proximity of the detector to the flue.

My gut feeling- and that is all it is- is that moving it a little further away is less likely to be a problem than moving it closer but other factors should also be considered in siting the detector.

[nearlythere]

BS 5839 states that a smoke detector should be sited approx. 1.5m to the opening of any flue like structure, ie lift shafts.

What is the common accepted tolerance on the word approximatley, is 1.6 m ok?

Is 1.6m not approximately 1.5m?

[Martin Burford]

Nearlythere
There isn't one..... you or the installer decides!
Conqueror

[Sherpa]

First off, thanks everyone for your opinions.

I'm sure there is plenty of designers faced with this problem every day, I have a lift lobby of 4 lifts, two on each side. As luck should have it, the opposing lifts are 3.2m apart.

As is usual, the client has specified he requires a BS5839 certificate with NO variations.

Its seems it would be good practice to abide by BS 5839, install the detector at 1.6m, record it as a variation on the certificate, and ask the client to agree to this rational variation.

[Wiz]

BS 5839 states that a smoke detector should be sited approx. 1.5m to the opening of any flue like structure, ie lift shafts.

What is the common accepted tolerance on the word approximatley, is 1.6 m ok?

Is 1.6m not approximately 1.5m?

Nearlythere has the best answer. The BS does use the word 'approximately' in these circumstances and I think the argument that 1.6m is 'approximately' 1.5m is a very very strong one.

[Sherpa]

Ah Ha, but does it then go on the certificate as a variation?

[kurnal]

Yes to cover yourself, but agree it first before commissioning with the building inspector  and fire authorities. and record that agreement to protect the client in the future.

[Wiz]

Yes to cover yourself, but agree it first before commissioning with the building inspector  and fire authorities. and record that agreement to protect the client in the future.

But Sherpa's custmer wants a certificate without Variations.

Since the recommendation includes the word 'approximately' I think Sherpa would have a strong argument for not having to record a 1.6m distance as a variation where the recommendation is 'approximately 1.5m' if the customer is so pedantic regarding Variations. Does any one else agree or disagree?

[kurnal]

If the customer is being pedantic about variations then I agree Dr Wiz.
To the chap on a clapham omnibus 1.6metres is approximately 1.5 metres. No doubt theres some case law somewhere to define the term "approximately", to me I dont make a fuss about 10% be it smoke detectors or travel distances.

But I am struggling with a building inspector at the moment who wants all sorts of compensating features for a 10m dead end hotel bedroom corridor  (guidance says 9m maximum) and have had similar difficulties with the siting of smoke detectors recently ( in this case proximity to a light fitting)

When pedantic Officer  visits in a couple of years when the dust has settled, he may well ask pedantic responsible person  to justify the siting of the detectors. If it is agreed and recorded at this stage it could save somehassle later. Thats all. As an alternative, post April 6 under the new Approved document B the decision could be recorded in the fire safety file.

Without such evidence we may have a rerun of little big horn. Recorded decisions of this type take no time at all and leave more time for smoking um peace pipe.

[Wiz]

I never disagree with Big Chief Kurnal. Him heap big wise man who survived battle of little big fire horn many posts ago.

Obviously when you have skirmishes with paleface who talks with forked tongue, it is always better to have copy of Variation to prove previous agreement over non-compliance with precise recommendation of BS.

However brave Sherpa have problem with this particular wigwam all caused by client not accepting ANY variation. I still think Sherpa has complied with recommendation so no variation needed anyway. Variation needed only when recommendation not achieved.

Last night, after drinking much fire-water, I had a dream where the client was being forced, by thousands of angry buffelo,  to move the walls of the wigwam to suit the detector position!

[kurnal]

Kurnal no longer drink fire water late at night. He find it make him wake up in night teepee.

[Thebeardedyorkshireman]

The figure of 1.5M is a very scientific and precise measurement derived from ( I THINK) ..........FOC rules 11th edition circa 1974 when it used to say 5 Foot. At one time I would have bet money on it, but that damned red wine has killed a few cells. My view is that your client is having a system designed by somebody who has the common sence  to question arbitrary numbers. Stick the thing at 1.6M and don't put it on the certificate because it is near enough for practical purposes. The smoke density will be (near enough) the same 100mm away. If you are using an annalogue system with the facility you could increase sensitivity on the head to compensate if somebody got picky.
Dave