sprinkler activation

[Ashley Wood]

Can anyone advise me what the fire size would be to activate a 57 degC standard sprinkler bulb and a fast responce sprinkler bulb at a height of between 2.4m and 3m in an office setting?

Thanks

[John Webb]

Dear Ashley,
I did some mock 'Office' fires with a 4m high ceiling some years ago. I don't have a copy of the results, but I recall that the fire size was around 200-300kW to activate FR1 solder-link sprinklers - the fire being central to four sprinklers on a 3.4m square grid. Standard response (glass bulb) sprinklers operated at around 500kw.
Hope this is of help.

[wee brian]

Ashley -thats a bit of a dodgy question. Like John-S I have seen a few test fires. Heat release on its own doesnt give you all the answers.

Why do you need to know?

[Ashley Wood]

John and Wee Brian, Thanks for your responses.

I am looking at a building that has an open floor office area with an atria in the centre (in effect cutting the floor area in half). Along each side of the atria are deluge nozzles to produce a water curtain. These nozzles sit on the edge of the office ceiling. The building and atria are 3 storeys high. The fire load in the atria area is low as it is predominantly an access and transit route from one part of the office area to the other, but there are some meeting tables in the atria (3.42m wide), that's the atria not the tables!

The office areas are sprinklerd as well. The reason for my question is this. They are looking to remove the deluge nozzles and replace them with fast acting sprinklers to produce the wall of water. My concerns are the speed of response due to the fact that the heat will rise straight to the top of the atria, and if they are lucky 10% of the heat will reach the nozzle. So, what I wanted to demonstrate to the client is the normal typical fire size that would be required to activate such a device and then talk them through the problems with the proposed solution.

The system has MJC's linked to detectors but these have gone off inadvertently twice now at a cost of around £1million a throw!

[John Webb]

Is the purpose of the deluge nozzles to provide a water curtain to prevent spread into upper floors as the fire plume rises from a lower floor? Presumeably there is smoke venting in the atria roof?
And are there fire curtains (fixed or dropping) to channel smoke etc to the edge of the atrium and not allow it to spread across the floor of origin. Or are there other dividers from floor to ceiling breaking up the office space? Sorry for so many questions but I'm just trying to get things clear!

[Ashley Wood]

John, the deluge system is to project a water curtain. The easy answer to all your other questions is NO!

[John Webb]

In that case (IMHO) the spread of heat and smoke from a fire in an office will be so diluted by the time it reaches the perimeter of the atrium and starts spilling into it that you may not get sufficient heat past even a fast-response sprinkler to trigger it until there is a very sizable fire in the offices.

BRE 258 - the 1994 guide by Hansell and Morgan on 'Design approaches for smoke control in atrium buildings' - on page 22 onwards gives an explanation of using channelling screens to confine the spread of smoke to ensure, amongst other things, that there is not too much dilution of the hot gases so that they retain buoyancy and do not gain so much volume that large areas of vents are needed. (I think this Guide may have been revised more recently or a new one published - it may be worth checking www.bre.co.uk for information.)
But even if this is done to ensure sufficiently hot gases can set off the deluge system, I do wonder what will happen to the rising smoke plume as it passes through the deluge.

And if you spend money on smoke curtains would it be better to install these round the edges of each floor so that on activation of the FA they drop down (except on the fire floor) and isolate the non-fire floors from the atrium? You could then do away with the deluge system - just a thought!

[Ashley Wood]

John,

thanks for your responce. Food for thought.

Ashley

[wee brian]

Ashley - you are dead right - you would need some fairly sophistcated modeling or a hot smoke test to put a number on all this but clearly the sprinklers will be no use at all.

If they really want rid they should iether come up with an alternative to the water curtain (which always was a rubbish idea) or use a much beeter system to trigger the deluge valve.

This is a good example of what happens when fire negineers get carried away - an overcomplicated system that was destined to fail from the start.

[John Webb]

Rereading your post #4 I see that the office spaces are also sprinklered, which somehow I missed the first time around. I think these, particularly if they are changed to FR types, will keep any fire to such a small level that spread to another floor via the atrium is exceedingly unlikely. Bear in mind too that  if a part of a hot plume does encroach on a floor above, the nearest sprinklers there should operate and prevent further spread. So I think I'd probably dump the deluge system.
Main thing then would be to get good arrangements in place to clear the smoke away from the office floor(s) to limit smoke damage.

[Mark Probert - Southam]

There is potential of removing all of the sprinklers from this building but this is dependent upon the building size and height???

The use of a deluge system is a complete over design as sprinklers will contain, control and possible extinguish the fire and would concur with John about the effectivness of the system

There would be no need to go into too much detail about activation temps as the fire safety of the building could be made to work using passive fire protection allowing the building to be open without relying on an active fire protection system, however the use of sprinklers should be encouraged.