Sprinkler head clearance

[kurnal]

Does anybody have access to Factory Mutual technical background info in respect of ESFR sprinkler heads?

ESFR heads (in this case K360) require a  1 metre clearance to allow a proper spray formation beneath the head. I am working on a proposal to build a new ligh level mezz in an existing warehouse with ESFR and goods will be stored on top of the mezz up to 500mm of the heads.

The ESFR was originally designed for high rack storage ST5 category 3 goods, it will now be about 3m high racking  Cat 3 goods. The underside of the mezz wll have a  HHS system installed, the question is should we go to the expense and trouble of replacing the ESFR  roof heads, range pipes with XHH to comply with the necessary head clearance set out in the rules?

My gut tells me a K360 ESFR head will have a much better chance of suppressing the fire than the minimum alternative req - a 7.5mm XHH installation with K80 heads, even if we break the 1000mm rule.   I have been trying to find out from FM system design data exactly why they stipulate 1000mm clearance without success.

Any comment please?  Happy to give more detail on the design by PM if necessary

[wee brian]

That's a big deviation.  I wouldn't risk it myself.

As you say, I think it's to allow the spray pattern to spread. You could increase the number of heads maybe but I doub't anybody will insure it.  The 1m is probably from full scale trials, not cheap to replicate.

[Phoenix]

Hi kurnal,

Can't help you with the FM background I'm afraid.

I think you're likely to need the 1m clearance anyway. All HHS systems need this clearance.  You refer to XHH but, correct me if I'm wrong, I think that went out with the old 5306 part 2 a year or more ago.

The clearance is required to stop shielding of the fire and to allow the spray to cover a sufficient area instead of (with, for example, a 500mm clearance) all falling on an area of approximately 1 sq m.  With a clearance of 1m or more the spray pattern will fall on a larger area and have many more opportunities to penetrate through the storage down to the fire.  With a reduced clearance all the water is hitting a relatively small area and it will have less opportunities to penetrate down to the fire.  Indeed, it is very possible that no water will find its way to the fire at all until the fire has grown considerably.

You might be able to justify the retention of the ESFR system with this minimal clearance (I'm not saying that the system cannot function as required - a lot depends on the precise nature of the storage) but you will have to find a sympathetic sprinkler installer.  As a rule, the industry is more likely to recommend compliance with the 'Rules.'

Can't the building users find that extra half metre?

I wouldn't recommend losing the ESFR system as this is bound to have the best chance of any system of dealing adequately with the fire.  But you might find that replacing the ESFR system on the upper level has financial benefits for the future in reduced tank sizes and pump capacities.


Stu

[CivvyFSO]

Another problem you have is that you are going from something that is likely to put a fire out, to something that is only really accepted as controlling the fire. You might also run into problems with pipe size and pressures as there is a greater volume of water supplied to the ESFR.

[Phoenix]

The 'LPC Rules' is the only standard commonly used in fire safety in the UK that is, as it states, a book of rules.  It is guarded and preserved by the sprinkler industry - and rightly so (to a certain extent).  But it is anomalous when compared with the rest of the fire safety standards because it is rules and they are guidance.  The rules don't fit neatly into a risk assessment world.  Having said that there is capacity for risk assessment in the sprinkler world and, perhaps, a more liberal attitude is growing.

Stu

[kurnal]

Thanks guys and sorry for the drivel last night-  thats where posting too late at night the wrong side of a bottle of wine gets you.

Yes the fundamental issue is that an existing warehouse cannot extend due to site constraints and planning. They need more space so a storage mezz on top of an existing structural mezzanine  (it is topped by a concrete compartment floor so will be classed as a simgle level) is the only answer. We are talking about a 3000 sq m new storage mezz but headroom is pretty limited.

An LPC approved company has specced a system for beneath the mezz but have not commented on what goes on above the mezz. Beneath the mezz will be the HHS system (yes thanks Stu) cat 3 goods in racks. Top of the mezz- it is hoped to rely on the existing roof sprinklers. The existing roof sprinklers are ESFR and all the infrastructure is in place  and will continue to be required elsewhere.

Looking in more detail today at the proposal I find we are actually looking at Cat 2 goods on top of the mezz on slatted shelf storage 800mm mode  ST5 on top of the mezz.

To make it viable we need to store to 2.4m high - thats at the worst case clearance 500mm beneath heads at eaves but rising to 1000mm for about 50% of area.

In terms of volume of water the ESFR has huge capability but at 500mm clearance the fire may be shielded. The head data describes a parabolic curve for the spray pattern but gives no data or graph. I am sure this is available through FM but requests for further advice seems to fall on deaf ears.

In terms of flow and the BSEN12845 tables we are well over the top. But will a much increased volume of water capability compared to the level of fire loading   be a reasonable compensation for the low clearance?
 
Thats the imponderable.
I am suggesting to the insurers that where we cant achieve the clearance we might leave 2.4m fire breaks between each block of racks, the maximum size of the block of racks to equate to the AMNOSO. This should limit the effect of fire spread as a result of shielded fires. We will see what they say.

[patrickhamblin]

Kurnal: if you email me your address, I can help you.
Patrick.

[kurnal]

Thanks Patrick
email sent.