Are Sprinklers Allowed Directly onto 3-inch Pipe?

11/14/2024

I designed an in-rack system, and due to the available pressure, I needed 3" diameter pipe feeding the sprinklers.

The fitter, who I respect as a knowledgeable person, thought that sprinklers were not permitted to be installed directly off of pipe greater than 2-1/2". He was not able to provide a code reference.

I searched NFPA 13 and came up with nothing to confirm or deny what he was saying. I'm wondering if anyone else is familiar with this limitation. Thanks!

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10 Comments

danefre

11/14/2024 07:33:53 am

It's in the obstruction subchapter of each sprinkler type. Reads like this:
"The requirements of xxxx shall not apply to sprinkler system piping less than 3 in. in diameter."

For example, the standard spray upright one is section 10.2.7.2.1.8 in the 2019 edition.

Keep in mind this is not universal and there are sprinkler types and design schemes that permit uprights installed directly on 3in. pipe. Quell comes to mind.

I haven't seen an in-rack specific section that overrules that requirement.

Taylor Schumacher

11/14/2024 08:07:59 am

It is an obstruction and falls in to the 3x/4x rules with certain exceptions for pipe sizes as your fitter pointed out. Mind also, that the max pipe size increases for CMSA and ESFR sprinklers where they can be installed on 3" pipe.

Dan Wilder

11/14/2024 08:05:34 am

Sometimes the easiest remembered section is the toughest to find...

Within the 13-19' Edition

SC - 10.2.7.2.1.8 allows less than 3" pipe (2½" max)
EC - 11.2.5.2.1.7 allows less than 3" pipe (2½" max)
RES - 12.1.11.2.1.6 allows less than 3" pipe (2½" max)
CMSA - 13.2.8.2.2 allows 4" and less (4" max)
ESFR - The way 14.2.11.3.1(2) reads, this could be a pipe with a max size of 1.5" (a 2" wide obstruction less than 2' below the deflector affecting 2 or more sprinklers). However, the little voice is telling me that 2½" is the max size but can't find a section to justify.

As to the in-racks, they are specifically exempt from obstruction rules in 9.5 (per 25.4.1), but there is nothing in 9.5 as to a pipe size max. I would then refer to the section that complies with the rack sprinkler type being used, for standard coverage-10.2.7.2.1.8 and a 2½" pipe max for uprights.

Glenn Berger

11/14/2024 08:07:06 am

I agree with Danefre. I believe that this restriction applies to upright sprinklers only.

Pete H

11/14/2024 08:11:33 am

Only uprights. Otherwise no obstruction is created (though good luck getting the deflector of a pendent to be within 12" of the deck if it was directly attached to the bottom of large enough pipe. So it's not like we just have carte blanche to use 6" branch lines and pendants even if that wasn't cost prohibitive.)

Adam (OP)

11/14/2024 08:13:28 am

Thanks, everyone!

For this system, we're going with pendants, so no issue there.

It's good to be familiar with this for future reference, though.

One strategy we had along the way was to increase the size of an existing branch to feed the in-rack system, which would have resulted in a 3" pipe with uprights above.

Jose Figueroa

11/14/2024 09:03:39 am

To ensure clarity, let’s rephrase the question to make it more direct: "What is the maximum permissible diameter for a branch line in an in-rack automatic sprinkler system?" Based on my understanding, I believe it to be 4 inches. Therefore, your hydraulic calculation appears to be accurate. I appreciate the work of the pipe fitter and their expertise in this area.

Jack G

11/14/2024 10:05:21 am

Agree with comments. Most important is to review the manufacturers data sheet for sprinkler head type used.

Franck

11/14/2024 10:10:26 am

Obstruction for upright sprinklers only, as mentioned above.

2 solutions: provide pendent sprinklers (no obstruction from the pipe) or place the sprinklers on sprigs or offset from the pipe to eliminate the obstruction that is created directly below the sprinkler (with a minimum distance of 3 times the pipe diameter, up to 2 ft, above the pipe).

I use quite often this rule in cable tunnels/galleries where large pipes are often provided with only one row of sprinklers (i.e. directly above the feed main).

For in-racks, you can put tem pendent (no obstruction) but I strongly recommend adding sprinkler guards (if you want to avoid water damages inside the racks with collision from the pallet loads).

Jack G

11/14/2024 11:01:12 am

Rack sprinklers have their own set of rules and can even be spaced closer than standard sprinklers,
For standard sprinklers I believe the 3 inch rule is for shadowing.
I ve always applied the 3 inches as a measurement and not a pipe size, 2.5 inch pipe is less than 3 inches.

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Are Sprinklers Allowed Directly onto 3-inch Pipe?

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