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FIRE SAFETY => Fire Risk Assessments => Topic started by: novascot on June 03, 2011, 06:06:23 PM
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Comments and thoughts please.
A Category B Listed Victorian Building (3 floors) with modern renovations used as an Hotel, plan to apply for a change of use to a Residential Care Home.
Problem we find is that Building Control want to apply Building Standards for Care Homes which means the retrospective fitting of sprinklers. The ceilings in parts of the building are 30+ feet and the effect of sprinklers from that height on a 2-3 Megawatt Fire would be negligible. That is the problem. What do you think is the solution?
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Are you talking a BSEN12845 or a BS9251 system? And although the sprinklers will be a long way above the fire do you have any particular reason to think they will have negligible effect?
What use are those diffficult parts of the building used for?
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Hello Kurnell,
the highest ceilings are in circulation areas. Reception and Lounges. The type of system will be open to discussion. I haven't done a modelling to ascertain the effect but experience tells me that by the time the sprinklers actuate the fire would have grown in size and the heat produced would possibly be outwith the capabilities of the available water droplets.
If you think differently, then please give me an indication of the effectiveness in these circumstances.
I am looking for guidance here.
Thanks.
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I dont believe the height of the ceiling to be a concern, I know of nothing to suggest that it might be in BSEN 12845 or BS9251.
It is discussed in BSEN12845 in that there has long been a clause relating to High Hazard Storage systems saying that the height of the head above the storage should not exceed 4m but every sprinklered warehouse and every insurance company that I have ever seen or worked with suggest that this is unworkable.
Clearly the higher the head above the fire the slower it will operate but it will operate at 68 degrees and this temperature will surely be reached fairly early on in the fire. All fire simulation programs will allow you to model the setup and predict how quickly the head will operate. You will no doubt be using fast response heads as per the BS. Is a fire likely to spread laterally faster than the convective fire plume rises ? I doubt it in a care home. In a warehouse full of hanging garments maybe.
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Very high ceilings can be a problem for sprinklers. The spray spreads a bit too far and they tend not to trigger at the right time.
You can resolve some of the problems with sidewall heads. Talk to somebody who knows what they are doing - John Stephens at FPA is about you best bet.
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Yes, 12845 doesn't make any recommendation in this respect except the one kurnal mentioned. Look up in any large sprinklered out-of-town retail outlet and you'll see sprinklers at around 10m above the goods that are no more than 2 to 2.5m above the floor. They will be slow to respond but once they go off they will do their job.
The droplets falling directly towards the fire may evaporate in mid air before they reach the fire but remember that the job of the sprinklers is to wet everything around the fire so that it won't catch fire. It is not to put the fire out (though that is often a beneficial side effect). The droplets that are wetting the ceiling and the walls and the doors and all the goods around the fire will get to their targets and will restrict the spread of fire.
As kurnal has discussed, the delay in actuation is not of critical important because during that time delay the fire is growing vertically within the very space that is causing your concerns and its lateral growth will be restricted because of the absence of a ceiling immediately above it.
Yes, high sprinklers can be an issue and you're right to have concerns but I guess you're talking about relatively small spaces (as compared to a warehouse, say) and, as such, you can be fairly confident that the temperature will build up at ceiling level fairly rapidly. Also, you shouldn't get the problem that some warehouses with high sprinklers might experience where sprinklers some distance away from the fire can actuate.
Regarding the sidewall sprinklers that were mentioned, these cannot offer you a feasible solution. I suppose the suggestion is to have them lower down the walls in the vicinity of the fire load but they are designed to be at high level (albeit on a side wall) just the same as other heads - they won't go off if they're at low level, not unless the fire is directly below them or until the smoke layer has descended right down to their level.
Stu
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Thank you all for your comments and suggestions. Clearer picture now. I remember seeing a video at MiM of an experiment carried out by Fire Reasearch of different height heads used on same fire size and there were delays and a lack of effectiveness the higher the heads were placed. But as you say, the lateral spread will be negligible. Again thank you.
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You still havent answered the question about wether its a proper sprinkler system or a resi one.
Flow rates etc are much lower for resi systems and this might make the issue more significant.
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Have just only picked this up following a couple of weeks away in Yorkshire.
It might be worth considering a misting system of the sort installed in the refurbished 'Grand Hotel' at St. Pancras - smaller pipework and water storage needs may be positive offsets against the expense of a retrofit in an older building.
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John , dont think water mist is a good idea for compliance with building regs in a care home.
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Maybe the building is simply not suited to residential care.
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John , dont think water mist is a good idea for compliance with building regs in a care home.
Colin - is this because water mist is not yet accepted under BRs? If it puts out fires I can't see any problem with it, and there is always the BR clause re fire-engineered alternatives. Having seen some examples of water mist I would have thought it well-suited to care homes - but I'll accept there may be factors I've overlooked!
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John, The jury is still out on some aspects of water mist. The issues are a little more sophisticated than it puts out fires.
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There are water mist systems out there already installed within residential housing ;)
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Yes, there are. And this proves what.........
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Worth while taking a look at BS DD 8489