Sprinkler Head Penetrating Compartment Ceiling

[GB]

I have sprinklers fitted throughout 4 storey flats to BS 9251:2005 Domestic using concealed sprinkler heads within the ceiling.

The construction is Timber Frame with adequate FR ceilings using plaster boards with taped joints, timber joists then timber sheet floors with insulation within the void.

I have been asked the question 'what about the sprinkler head breaching the compartmentation' - which is a good question!

I have had a look for any technical notes or details from BAFSA as well as contacting a couple of sprinkler installers and can not find anything providing a definitive answer.

My own opinion, which is open to argument, is that the sprinkler head will activate before any significant temperature is reached to be able to cause fire spread within the ceiling void. The insulation should prevent smoke travel particularly given the very small diameters we are talking about around the edge of the head.

I am keen to hear the thoughts of others with this experience.

[nearlythere]

I have sprinklers fitted throughout 4 storey flats to BS 9251:2005 Domestic using concealed sprinkler heads within the ceiling.

The construction is Timber Frame with adequate FR ceilings using plaster boards with taped joints, timber joists then timber sheet floors with insulation within the void.

I have been asked the question 'what about the sprinkler head breaching the compartmentation' - which is a good question!

I have had a look for any technical notes or details from BAFSA as well as contacting a couple of sprinkler installers and can not find anything providing a definitive answer.

My own opinion, which is open to argument, is that the sprinkler head will activate before any significant temperature is reached to be able to cause fire spread within the ceiling void. The insulation should prevent smoke travel particularly given the very small diameters we are talking about around the edge of the head.

I am keen to hear the thoughts of others with this experience.

Not a hazardous as recessed lighting units which many sparks install nowadays. Don't they know the issues?

[kurnal]

I have not thought this fully through yet but my initial thought would be tha a  domestic sprinkler system from a tank supply would only have a duration of 10 mins and a residential system 20 min whereas the ceiling would nomally have a minimum requirement of 30 min or  1 hour FR .

[Phoenix]

This question has been floating around for years but, of course, it has been relatively unusual to come across such installations so the problem hasn't had a high profile.  Kurnal, you have the problem summarised very nicely (residential systems have a minimum duration of 30 minutes though).  In domestic systems this is a potential breach of compartmentation that has to be dealt with in some more passive way.  I believe there are proprietary covers available but it would be best to enquire with sprinkler manufacturers.  What you mustn't do is restrict the air flow from beneath the ceiling through the 'cup' that holds the sprinkler head.

Stu

 

[wee brian]

read this

http://webarchive.nationalarchives.gov.uk/20120919132719/http://www.communities.gov.uk/documents/planningandbuilding/pdf/bd2551.pdf

[Phoenix]

Thanks Brian, that's interesting.  I guess the risk of fire spread through sprinkler penetrations is offset by the small number of penetrations and by the fact that they will probably put the fire out.  And, even if fire does spread through the hole, it will be spreading to another sprinkler controlled area.  It seems a sensible balance of probable harm against cost and trouble of additional passive fire protection.

Stu

 

[wee brian]

I saw some of the testing - interestingly, where the holes are relatively small, hot gases don't rush into the floor space as quickly as you might expect. The feeling was that the cold air in the space had nowhere to go so the hot air couldn't get in.

You do need some movement past the sprinkler for it to respond quickly and boxing them in might do more harm than good.

However, dont forget sound insulation, smells etc. not so dangerous but still important.

[Fishy]

The thing to remember with horizontal fire resisting elements is that, at least 95% of the time the requirement applies to the entire floor, not to the ceiling (for the most part there’s no such thing as a “fire resisting ceiling” that provides fire separation on its own).  So, the fire resistance is a product of the ceiling, the capacity of the joists/beams and the floor construction itself.  Therefore the effect of holes in the ceiling membrane is greater if the floor condition and/or construction is poor than if the floor uses boards/panels well fitted and of a decent thickness and density.  You also have to remember that for floors you have to maintain the load-bearing capacity for the relevant period, not just the fire separation, so (for example) floors that use slim ‘engineered’ joists/beams rely more upon the contribution of the ceiling than floors that use traditional components.

So, if a floor is (say) 60 minutes fire-resisting, the ceiling part of it would probably only be required to last for a proportion of that.  Fire spread within the floor would occur as soon as the ceiling fails – likely to be well before 60 mins in this case.  Therefore if the floor and joists have relatively good fire resistance then small holes in the ceiling membrane don’t have as much of an effect on overall fire resistance performance as you might expect.

TRADA (the Timber Research & Development Association) did some testing on this – which they published in their document “Timber frame walls and floors: Fire resistance of service penetrations”.  I don’t have a copy but my recollection was that, provided that the floor construction itself was of a ‘traditional’ type and was up to scratch, that for 30 minutes F/R domestic floors the effect of small holes (e.g. down lighters) wasn’t significant, but that for 60 mins the effect was noticeable & protection was recommended.

The BRE report in the above link deals specifically with sprinklers & seems very sensible – especially given that sprinklers will only require a very few holes, compared with a typical down lighter installation.

[col10]

The guidance referred to "Guidance on ceiling penetrations in separating timber floor constructions" is for separating floors (as defined in Building Regs Doc E "Sound Insulation" . Basically the floors are relying on acoustic sealant to resist the passage of smoke in order to pass a fire test.  Fire is in the floor void in these tests.  In a real situation  there will be other penetrations of the floor, such as plastic soil pipe, water, gas, electric cables, fan ducts, which are not present  in the test.  Fire stopping and intumescent collars will be at ceiling level. If the sprinklers are off,  fire can spread, once in the void, due to the other penetrations, into the flat above.  Without doubt sprinklers are good.  Presumably the manufacturers paid for the test, but I would want to know:
Why are sprinklers provided?  What are they trading off? The layout? Inner bedrooms? The occupants? who may disable or not maintain the system?
What other penetrations in the compartment floor are there? and can fire spread along them?  It would be fairly inexpensive to protect other penetrations with minerable fibre eg "Rockwool."
Also, the flats will need to hold up to an air permeability, test under Part L Energy conservation.  The plasterboard is usually the line of the air permeability barrier.  Vented sprinkler heads will not help the permeability test at all. I would point this out to the person who has produced the design energy rating calculations.  Another also, is that there should be a continuous vapour barrier.  Vented heads will provide a route past the barrier and contribute to the risk of interstitial condensation of the external wall construction at the floor junction.  The plasterboard is normally the line of the vapour barrier.