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30" Round Spiral Ducts Under ESFR Heads

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Robert Gardner

Robert Gardner

Mechanical
Mar 1, 2018
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I thought I read some where that the spacing under the spiral Duct work was limited to 8 Ft. spacing. The building is under 30ft. storage to 20ft.
I also thought I read you need a Baffle above the sprinkler the same Dia. as the duct work for a heat shield.
Sprinklers on Br Lines at roof have a 8'4 x 12ft coverage.
We are still on 2010 Addition of NFPA 13, IF this true where is it in NFPA 13, what addition.
The duct work is directly below the Sprinkler line and runs parallel with the Br Line the total length of the bay.
 
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There is NOTHING in NFPA about heat collectors. They don't exist. Maybe you mean a water shield. Spacing shall be what your ESFR spacing is. Since bldg is <30', you can go 12' on center. I believe in the 2010 edition, you will have to calculate up to 2 additional sprinklers under the duct. So, your 12 sprinkler calc goes to 14 sprinklers now. The 2013 and newer allow you to omit those from the calculation, but you have to use the same size pipe as the branch line to supply the sprinkler under the obstruction.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC
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Where is it noted in FMDS 2-0? I looked and can't locate. I'm always down for learning something new.

Edit: I believe you are referring to FMDS 2-0: 2.2.3.5.2.1 (d) and Figure 40. But these are not heat collectors. They are water shields to prevent the sprinkler above from cooling and preventing the lower sprinkler to operate.



Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC
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Thanks I new I had seen something some were, I thought the shield was to help collect the heat better because the duct work was spiral.
Thanks for the HELP
 
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Was there a change that allowed the sprinkler to be placed at the side and not underneath??

If so does some one have a reference section.
 
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While FM doesn't call them heat collectors, that's effectively what they are doing. You have the choice of installing such to form a solid continuous flat obstruction such that the heat will collect and the sprinkler activate or else space the sprinklers at 4' spacing under a non flat, non solid obstruction (such as a round duct)(so the the activation of the sprinkler is not reliant on the heat accumulating at the sprinkler - rather at such spacing the sprinkler will be within the plume of the flame).
This applies to both storage and non storage sprinklers.
However, the OP's post did refer to NPFA so different animal as others have mentioned.
 
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The old "heat collector" is just a pet peeve. I still remember going to a shell building about 20 years ago. The deck was about 15'. The original sprinkler contractor installed pendent sprinklers at the anticipated ceiling height of 10' and just put 12" pie pans at every sprinkler stating that was the "heat collector" and all that was needed. Some days you don't even begin to question any more, just roll eyes and walk away.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC
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Have seen those 'pie pans' too Travis :). In fact you'll see them in Dublin (Ireland) airport - which is pretty embarrassing.

cdafd, no I wouldn't be calling those heat collectors. I'd consider those to be water shields. I was referring to the section in FM 2-0 that UFT12 referenced.

FM 2-0 Section 2.2.3.5.2.1 for storage sprinklers or Section 2.1.3.2.5.2 for non storage sprinklers - has options for dealing with obstructions for sprinklers. In looking at 2.1.3.2.5.2 there are four options for dealing with obstructions (a) through (d). Options (a) and (b) are only for dealing with Flat, Continuous, Solid objects. So round ducts, cable trays, etc. wouldn't fall into this category. Therefore you are left with (c) or (d).

(c) states "For non-flat, non-continuous, or non-solid type objects, install at flat, continuous, solid barrier under the object that equals the width of the object, and install sprinklers as recommended in options (a) and (b), depending on the width of the object. See Figure 12 for a diagram of this arrangement.
(d) states "As an alternative to option (c), install quick-response ceiling-level sprinklers under the object on a maximum 4ft (1.2m) linear spacing and a maximum 16ft2 (1.5m2) area spacing. See figure 13 for a diagram of this arrangement.

Therefore what I was referring to as a 'heat collector' (though not using that term), was using the option (c). In the classes I've taken from FM on this matter it was explained to me that having this barrier under non flat, non solid, non-continuous obstructions is to allow the heat to accumulate and the sprinkler to activate, which allows you to use regular sprinkler spacing under such obstructions. If you have a non-flat, non-solid, non-continuous obstruction without the barrier the heat won't accumulate and therefore the sprinkler spacing is reduced to the 4' linear so that the sprinkler will activate because it will be within the plume of the fire.

These barriers would be very different to just having a water shield type plate above the sprinkler. As per the FM text the barrier has to be the full width and length of the obstruction. They don't refer to them as heat collectors, I was just saying that the purpose of such was for heat collection and allows for regular spacing rather than the 4' spacing without them.

 
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kinda strange to me that by the alternative to the "heat collectors" 4 ft spacing the standard does not mention anything about baffles. Would that scheme work or did I miss the baffles somewhere?
 
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It is my understanding that baffles are not required. Logic being that with such close spacing if more than one sprinkler is being effected, that it is also going to basically be in the plume of the fire, and that it will therefore'overcome' the cold soldering effect. If it doesn't overcome the cold soldering effect, then it mustn't be that big a fire and the sprinkler causing the cold soldering is able to handle it. (or that the next over sprinkler will activate).
 
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