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Author Topic: Detection, Structural Beams & BS 5839  (Read 992 times)
Tadees
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« on: May 19, 2017, 11:17:35 AM »

A beam is say 300mm in depth.   The depth of the beam is less than 10% of the ceiling height.  11.2 k) 1) suggests that the detector should be sited on the underside of the beam, because the depth of the beam is less than 600mm. 

However, the next paragraph suggests a different siting methodology, i.e. should not be sited ?closer to the beam than twice the depth of the beam or 500mm, whichever is less.?

Can someone explain the apparent contradiction.
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colin todd
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« Reply #1 on: May 23, 2017, 04:00:05 PM »

Yes, I can.
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Colin Todd, C S Todd & Associates
Tadees
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« Reply #2 on: May 24, 2017, 10:18:48 AM »

Hmmm.
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wee brian
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« Reply #3 on: May 24, 2017, 10:41:58 AM »

Its probably the difference between being fixed onto something rather than being next to it.

As I recall, you can get a buffer of cleaner air adjacent to obstructions (such as a downstand beam). so smoke might bypass a detector mounted close to a beam. this wont happen to a detector mounted on the underside of a beam. but you could get a delay if the beam is very deep (smoke filling down from the ceiling before it flows over the beam) so that probably why there's a restriction on the beam depth.

Of course, I wasn't on the committee so I don't know for sure.

This question has come up before - read this
https://www.crisis-response.com/forum/index.php?topic=4884.msg52092#msg52092



« Last Edit: May 24, 2017, 10:52:24 AM by wee brian » Logged
Tom Sutton
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« Reply #4 on: May 24, 2017, 03:33:37 PM »

What version of BS 5839 are you using I cannot find your reference?
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All my responses only apply to England and Wales and they are an overview of the subject, hopefully it will point you in the right direction and always treat with caution.
colin todd
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« Reply #5 on: May 25, 2017, 03:47:07 AM »

Old CivvyFSO did a nice job in 2010, so he knows too.  And now he works for me and knows even more than he did in 2010.
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Colin Todd, C S Todd & Associates
Tadees
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« Reply #6 on: May 25, 2017, 04:23:53 PM »

What version of BS 5839 are you using I cannot find your reference?

Hi Tom,

Page 30, 2013 version, although it won't surprise me if another version has come out since I last checked, which changes 3 lines and we all have to pay for the update.
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Tom Sutton
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« Reply #7 on: May 26, 2017, 08:48:19 AM »

Sorry Tadees I was looking at Part 1 not part 6, the way I read it you have to abide by both clauses. Clause 1) if the beam is vertically 10% greater depth than ceiling height, then you need the detectors each side of the beam if it is vertically less than 600mm the you can fix it to the underside of the beam  Clause 2) If you are fixing the detectors to each side of the beam they must be no closer than 500mm horizontal or twice the depth of the beam with ever the smaller. CivveyFSO did an excellent submission why.

In your case with the 300 mm beam fix it to the underside of the beam, job done.
« Last Edit: May 26, 2017, 08:52:39 AM by Tom Sutton » Logged

All my responses only apply to England and Wales and they are an overview of the subject, hopefully it will point you in the right direction and always treat with caution.
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