When to Group Obstructions for ESFR Sprinklers?

9/11/2024

I have a project using ESFR under NFPA 13-2022 Edition.

Section 14.2.11.3.4 states that an obstruction will not be combined if the distance to the adjacent obstacle is greater than three times the width of the adjacent obstruction.

The appendix states the minimum distance to another obstacle as three times the diameter of the pipe.

For example, I am analyzing a 1 foot wide vent duct and a 2-inch pipe. Should they be 3 feet apart, or 6 inches apart, in order to consider each item it's own obstruction?

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3 Comments

Dan Wilder

9/11/2024 09:47:10 am

What is the position below and to the side of the sprinkler?

IMO 6" clear should be acceptable for the single additional conduit (this situation), but that section only discusses objects that individually would not trigger an obstruction issue but when combined, can become an obstruction.

You could apply 14.2.11.3.1(4) if the two are located more than 12" horizontally from the sprinkler and greater than 31" below (per table 14.2.11.1.1(a)). If it's less than that, the duct triggers the additional protection, regardless of the conduit. Also, the width goes from 1.5", 6", then 24".

If it's closer than that, the duct triggers additional protection.
<1½" width and >12" below deflector (no horizontal requirement)
<6" width and >6" horizontally (vertical requirement per table so >31" below)
<24" width and >12" horizontally (vertical requirement per table so >31").

I'm still looking for a good visual of this arrangement and since I still don't deal with ESFR on the regular so I'm open to learning!

Jack G

9/11/2024 10:03:35 am

I go to the fm guidelines for ESFR s. They have led the way on this. They have nice pictorial scenario s the describe and you can visualize the results.
NFPA criteria was really adopted from the fm criteria.

Casey Milhorn

9/12/2024 11:11:04 am

See link below:

https://www.nfpa.org/education-and-research/research/fire-protection-research-foundation/projects-and-reports/obstructions-and-early-suppression-fast-response-sprinklers

To add to Jack's comments, NFPA research foundation has conducted a two phase research project relative to obstructions effects on ESFR sprinklers. I didn't reread the results, but from memory they found that obstructions in certain arrangements and sizes, were a lot less detrimental to spray pattern and protection as previously thought.

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When to Group Obstructions for ESFR Sprinklers?

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