Layout Sprinklers to "Skip" Cloud Ceilings?

3/30/2022

The NFPA 13 sections on cloud ceilings continue concentrate on sprinklers above the cloud ceilings, not the sprinklers in the clouds themselves.

If the area above the cloud is sprinklered throughout, yet there are multiple clouds greater than 4-ft wide in the shortest direction (all at the same elevation plane), creating obstructions to the sprinklers above, does each cloud obstruction need to be treated independently for sprinkler coverage beneath, or can the designer “skip” clouds or portions of the clouds and gaps, as long as the overall pendent sprinkler spacing does not exceed the maximum spacing for the hazard?

I would think the opening width between the clouds would play a role in this as well, the heat's ability to skip the gap. And whether or not the sprinklers above are able to develop their spray pattern.

I often see designs with sprinklers in clouds spaced out 15' x 15' leaving some clouds without sprinklers. As far as I can tell, even the 2022 edition and handbooks are silent on this.

Thanks in advance.

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8 Comments

Alex

3/30/2022 07:36:13 am

Hi,

I have seen this issue come up a handful of times. As far as I know, it is not in the code. The issue is very similar to when you have two ducts, both under 4' (call it 3'6") running parallel with each other. The code doesn't outline a minimum distance they must be separated by before they are treated as one duct.

For scenarios like this, I make a judgment call. To me, if the clouds are spaced 6-8" apart, I would call it one cloud. When they are spaced greater than 8", I would then protect each cloud individually. Where are those numbers coming from, my head. Why 6-8, that's just my thought.

I'm looking forward to what others have to say and if there is a code section or white paper that addresses this issue! Awesome question to get the gears going this morning.

Alex

3/30/2022 08:18:08 am

The closest code reference I can find that addresses this issue is in FM DS 2-0, code reference 2.5.2.5.3.1. There is an equation that helps the designer determine if multiple objects can count as a "grouped object". I have not actually used this yet in practice, but I did notice it while designing another project.

3/30/2022 08:33:22 am

I think this hits the issue right on the money! Great reference.

Thanks,
Alex

Different Alex

3/30/2022 11:39:58 am

Adding a thought to this thread, there comes a point when protecting each cloud individually is not possible because it places heads closer than 6 ft to each other, causing cold soldering (e.g., 4' x 4' tiles with 9" gaps, heads centered in tiles, spacing would be 4'-9"). Of course, in that scenario, moving off center would be possible but only for a certain number of tiles before "falling off."

Dan Wilder

3/30/2022 08:53:34 am

When not providing protection above, you are able to "cloud skip" because the ceiling is capable of trapping heat to activate sprinklers (this is noted in the FPRF report as well). When the calculations indicate that above ceiling cloud protection is required, the individual clouds cannot trap heat thus requiring above and below as they become obstructions.

Taking that basic premise, assuming the gaps are similar throughout the space, each cloud (when over 48") would be its own obstruction to the overhead system and should be handled with sprinklers beneath per obstruction.

Just my take when breaking down the individual components. there may be something in the two reports about specific testing performed that passed/failed that could help you out linked below.

https://www.nfpa.org/News-and-Research/Data-research-and-tools/Suppression/Sprinkler-Protection-for-Cloud-Ceilings

Anonymous

3/30/2022 04:16:09 pm

Thanks once again again, Dan (and thanks Joe for posting the question). I read those two FPRF reports and they are very interesting, lots of variables were tested, I guess that's why it's hard to make a catch-all set of requirements. On this project they even threw in HVLS fans, lol. :-)

Glenn Berger

3/30/2022 09:54:13 am

Treat the cloud ceilings as standard obstructions and provide sprinklers below the obstruction in accordance with NFPA 13. THEN check with the architects; they may want to see a NFPA 13 compliant pattern for sprinkler placement to be achieved.

Jesse

3/30/2022 10:23:16 am

I hate clouds.

Treat it as contiguous and space pendents accordingly

Layout Sprinklers to "Skip" Cloud Ceilings?

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