Sprinkler Protect Above & Below Narrow Baffles?

4/19/2021

How close can hanging baffles be spaced together before sprinklers are required below (and possibly above) them to provide full sprinkler coverage?

I have a situation where about 20 acoustical baffles will be hanging 6-12 inches below the ceiling. The baffles are 18-inches by 10-feet long, spaced 8-inches apart.

I've looked at providing sprinklers above them at the ceiling level, and it isn't clear cut; each individual obstruction is less than 4-feet wide, so I can see NFPA 13 (2019) Section 10.2.7.1.2(2) applying as long as you can sprinkler between them. But I think the baffles are located too close together to be considered non-continuous obstructions and their proximity would obstruct the sprinkler spray pattern development.

I've looked at Section 9.5.5.2, where continuous or non-continuous obstructions less than 18-inches below the sprinkler deflector prevent the sprinkler pattern from fully developing, but that section states that as long as no additional floor area is created then no additional sprinklers are required. Having a tough time believing that only sprinklering above the baffles will fully protect beneath them. Any help is appreciated!

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5 Comments

Dan Wilder

4/19/2021 08:44:49 am

Some missing info would be how wide are each baffle and how deep? As the upright sprinkler requires 1" clearance from deflector to roof, the spacing is actually 5"-11" and even worse with a pendent sprinkler if the piping is run within this space and not above it.

You may need to apply 9.3.10 as a more applicable section to address the lower baffles as an alternate. Using the spray patterns to reinforce a decision on spacing may also be helpful to avoid sprinklers below (i.e. space the sprinklers at 6x6 or up to 11x11 to allow spray distribution into each vertical channel).

I do not see a need for sprinklers below the baffles, they are spaced too far apart (assuming the width isn't obnoxiously wide).

For example:
https://www.reliablesprinkler.com/files/spray_distributions/Page%20F-12.pdf?x80029

4/19/2021 09:30:44 am

I initially read that there was 6-12" of clear space below a ceiling/roof THEN the baffles would start...

If the baffles are tight to the ceiling and hang down 6-12" max, that makes things very easy and just provide sprinklers where the deflectors are clear of the bottom of the baffles.

Casey Milhorn

4/19/2021 09:35:00 am

Yeah, definitely need some clarification. You might be right Dan. Maybe they start at 6" to 12" down and have some considerable depth to them.

Larissa M.

4/20/2021 02:23:16 pm

For clarification: each baffle is 1in wide, 18in deep, with a length of 10ft. The baffles will be suspended, with the top of the baffle 6-12in from the ceiling. So the bottom of the baffles will be 24-30" beneath the ceiling.
Entire assembly with an 8in spacing between the baffles would be 14'-4" x 10'-0".

Looking at section 9.3.10 I do think the baffle assembly would be more of an open-grid ceiling than individual obstructions. From reading this, the baffles would need to hang lower, 18in to ceiling minimum, and the baffle depth would need to decrease to 8in to match the spacing between them.

Kenneth Casey Milhorn

4/19/2021 09:22:54 am

If I'm understanding the situation correctly, I would say pendent sprinklers at 12" down from the higher ceiling would resolve any issues with the baffles being obstructions. Space the sprinklers in every 6th or 7th baffle (cloud), if they aren't tilted at too much of an angle. If the slope is too great to not be considered a flat ceiling, then you might have to install exposed heads in between the gaps instead. The main thing is to keep the deflectors a max of 12" down from the ceiling above and you should be compliant with NFPA 13. The only concern I could see would be heat collection and the baffles blocking heat moving back down past the baffles. If you are above the baffles I don't see how you would satisfy the obstruction rules in this scenario. BUT, I don't think this situation should warrant two levels of sprinklers if you can meet the 12" deflector distance requirement without obstruction to sprinklers.

Sprinkler Protect Above & Below Narrow Baffles?

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