Void Detection

[BCO]

Am I reading this correctly? BS 5839 Pt 1 does not require detection to be provided in any void (greater or less than 800mm) unless the system is either an L1 or P1 system??  I am currently looking at multi storey office with phased evacuation. ADB requires an L3 system for phased evacuation. L3 is being provided, however it is not proposed in the voids. Voids are 940mm in most places with some 1200mm on occasion.  There are no combustibles in the voids. Construction is plaster board ceilings, metal stud work and concrete structural floors above. I don’t think the risk warrants detectors in the voids, but my question is, does the BS require it?

[CivvyFSO]

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d) If the system Category is such that automatic fire detection should be provided in any area that
contains a horizontal void of 800 mm or more in height, automatic fire detection should also be provided
in the void.
 
BS 5839-1:2002
--

I would interpret that as saying "If a detector is required in any room that has a void > 800m over it, then the void needs to be detected."

Then see:-

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NOTE 4 If the fire risk within a void of 800 mm or more is considered to be low, consideration might be given to omission of fire
detection from the void, subject to the agreement of the interested parties (see Clause 6), but this should be recorded as a variation
on the relevant system certificate. This might arise, for example, if the probability of ignition and development of fire in the void
were very low, or if the void were limited in extent so that spread of fire beyond the room of origin, via the void, were unlikely.
BS 5839-1:2002
---

So, if the risk is as you say it would seem reasonable.

(When you say there are no combustibles in the voids, are there false floors for all the data cables? Data cables can soon add to the fire loading in voids and they don't tend to appear until the building is occupied.)

[BCO]

Most data cables are in the floor (raised floor small void) other electrical cables are limited to lighting etc.

d) If the system Category is such that automatic fire detection should be provided in any area that
contains a horizontal void of 800 mm or more in height, automatic fire detection should also be provided
in the void.

BS 5839-1:2002


I see this, but to get this far it has to be system that is a ‘category that automatic fire detection should be provided in any area that contains a horizontal void of 800 mm or more in height’ To answer this I was looking at section 8.2 and paragraph f. It is only in paragraph f that voids get a mention. This paragraph relates to P1 and L1 only
 

It appears that if L2 or less then voids may not need to be protected because the requirements for those areas do not contain the words ‘all rooms and areas’

Yes no??

[Graeme]

voids over 800mm or with a fire risk relevant to the category.

i.e L4 would not need void detection above a room that opened onto an escape route etc.

[Tradeoff]

Its my understanding that only L1 or P1 require detection throughout. L2/P2 and so on would not require you to protect voids unless a specific risk existed.

[Wiz]

Its my understanding that only L1 or P1 require detection throughout. L2/P2 and so on would not require you to protect voids unless a specific risk existed.

My interpretation is that wherever and in any area a detector is required by the system category recommendations, and there is a horizontal void, above or below that detector(s), greater than 800mm in depth, then detection is also required in that void unless a fire risk assessment, agreed by relevant parties, suggests the fire risk is low. Omission, in these circumstances, must be recorded as a variation.

Furthermore voids less than 800mm may also require on the basis of the findings of a fire risk assessment

[David Rooney]

"22.2 d ......If the system Category is such that automatic fire detection should be provided in any area that contains a horizontal void of 800 mm or more ..... etc"

I'm with Wiz... whether its L1 - L5, P1-P2, all these categories require AFD therefore any voids (meeting the criteria) within the areas specified to be protected, should also be protected.

[Tradeoff]

L2,3,4,5 and P2,3,4,5 etc  standards do not specifically require you to provided detection throughout a building - for instance you may just provide detection within escape routes. As an end user i might decide to extend this protection into open offices / retail areas. By doing this i have improved upon the standard. It does not then require me to install in the void when i had no legal/insurance obligations to protect the area in the first place.

If one is required to protection the void where detection is located on the ceiling, then as an end user i would not provide any detection. - Dangerous, but cost reality!!

Fire engineering / risk analysis would argue that a non-combustible void does not need protecting - same for sprinkler systems using TB11 / 230.

Therefore, the reality is that many buildings do not provide void protection due to cost and maintenance practicalities.

[kurnal]

I think L3  and L4 are actually very specific on the provision of detectors as are P1 and P2.

L2 and L5 leave it up to the designer to specify.
Mu understanding is that a void is just an extension of the space it adjoins. If an L3 system requires escape routes and rooms off escape routes to be covered then any voids greater than 800mm in those escape routes or rooms also need to be covered, unless there is at least 30min separation between the room and the void.

[Graeme]

Agree with you Kurnal and also L2 is specific as it' an L3 with coverage in other rooms of risk which would also require void detection if applicable.

[Chris Houston]

L2,3,4,5 and P2,3,4,5 etc  standards do not specifically require you to provided detection throughout a building - for instance you may just provide detection within escape routes.

There is no P3, P4 or P5.

Only L4 would allow escape route only, L3 upwards includes the rooms that open into the escape route.

[David Rooney]

L2,3,4,5 and P2,3,4,5 etc  standards do not specifically require you to provided detection throughout a building - for instance you may just provide detection within escape routes. As an end user i might decide to extend this protection into open offices / retail areas. By doing this i have improved upon the standard. It does not then require me to install in the void when i had no legal/insurance obligations to protect the area in the first place.

Your quite right (apart from P3, 4 and 5 !!) you can specify a particular category within specific areas of a building, but if you elect to protect escape routes and call it L4 then you must protect any voids in those escape routes that meet the criteria. Otherwise it doesn't meet L4.

Surely if you don't protect the voids this would have to be agreed by all parties and listed as a variation?

[Graeme]

If one is required to protection the void where detection is located on the ceiling, then as an end user i would not provide any detection. - Dangerous, but cost reality!!

.

does not make any sense... Do you mean where you are asked to provide void detection above an area which already has detection below the void,then you would not provide any detection at all?...

[Wiz]

I think the point Tradeoff is making is that where there are voids in areas where detection is provided, but where detection wasn't actually required under the recommendations of the category of the system, then he wouldn't necessarily fit additional detection in any voids in these areas.

For example, an L4 system recommends automatic detection in the escape routes. This is achieved and the system is described as an L4 system on all documentation. However, it is decided to also install an automatic detector in a room (that's not part of the escape route) which has a 1000mm ceiling void. It is decided to not automatically install a detector in the void because the detection in the room wasn't an implied requirement of the L4 category and is therefore not subject to the BS recommendations.

Since the BS recommendations for detectors in voids, specifically only mentions they are required in areas where the category recommends automatic detection in the areas below/above the void, then I reckon tradeoff has fair argument not to fit them in the voids (this is obviously with the proviso that the risk assessment highlighted these areas of high risk etc. etc.)

However, I can't see the point in installing detectors over and above the minimum requirements of a particular category. Surely, it would be just wasting money?

[AnthonyB]

Unless for property protection of course - your building may only need and have had installed an L4 system to ensure life safety, but the tenant in one area wants some installation in a room provided with 24/7 early fire warning so bungs a detector in there on the lowered ceiling, connects it to the central system, but doesn't cover the void or other parts of their area.

Trying to determine the coverage in multi occupancies by category can be difficult as you have very randomised cover influenced by different tenants and refits over the years, many are a mix that could be classed as M/L5/P2!