Use Intermediate Level/Rack with ESFR at Deck?

5/25/2021

At a tire store we currently have 25.2K ESFR at the roof, and they have some open grated flooring down at about 10-ft above finished floor where their tire areas are. We are currently protecting the areas that are wider than 4ft.

There are some other runs that are just under 4-ft wide and the AHJ is saying we need to protect those. They're 86% open grates, deeper than 1/4". I'm fine with adding the heads under these, however the AHJ is stating that we must protect below them with ESFR's instead of an intermediate level/rack style sprinkler. I've never seen this approach in 20 years nor can find any justification in the code to support this.

The AHJs comments suggest the water shields are necessary to prevent cold soldering from ESFR sprinklers above.

Is there a code basis to use intermediate level/rack style sprinklers under obstructions with ESFR at the deck?

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3 Comments

FIREPE25

5/25/2021 08:16:48 am

The open grating is essentially just an obstruction that is over 4'-0" in width. I believe NFPA 13 says that you need to protect under obstructions using the same sprinklers as above. NFPA also says you need shields below open grating. They actually do make certain ESFR sprinklers with guards and shields now that you could potentially use.

One way you could get out of it is if a smaller orifice sprinkler below the open grating would be able to protect what is under it.

Dan Wilder

5/25/2021 08:54:45 am

In 13-19 Ed.

9.5.5.3.3 indicates the same type of sprinklers shall be used below the obstruction (ESFR in this case) but does not state anything about matching the K-Factor, just the type (agreeing with FIREPE25)

14.2.11.3.4 States sprinklers installed below open grating shall be of the intermediate level/rack storage type or otherwise shielded

You can always coordinate with the owner to install sheet metal above the sprinkler locations to act as a shield, we've done this in the past when a listed guard/shield was not available.

AB link

7/25/2022 09:12:30 am

I was looking for some information today to pass on to an owner who wants to avoid having to put guardrails around an open grate walkway over a 240'-0 x 10'-0 tunnel/pit below finish floor- the open grate walkway is above at finish floor level. I digress.

I came across this in FM Data Sheet 2-0 (October 2021)

- It's possible the AHJ has a copy of FM Data Sheet 2-0 for reference in sticky situations. I mean - can't go wrong with the conservative option. It references matching K-Factors, etc.

Thought I'd share. All the best - AB

2.5.4.5.8 Obstruction to Ceiling-Level Storage Sprinkler Discharge Due to Open-Grid Walkways

2.5.4.5.8.1 Whenever possible, avoid the installation of an open-grid walkway (see definition in Appendix A). Instead, provide the walkway level with a solid flooring and install sprinklers under the solid flooring in accordance with Section 2.5.1.7.

2.5.4.5.8.2 Sprinklers may be omitted from the underside of an open-grid walkway that is a minimum of 70% open if:

A. The area below the walkway will be void of any storage, or other combustible materials, and

B. If the walkway is adjacent to rack storage, product from the racks is not expected to spill out onto the walkway during a fire event.

2.5.4.5.8.3 Sprinklers may be omitted from the underside of an open-grid walkway if:

A. The walkway is located adjacent to a storage rack, and

B. Face sprinklers are provided for the storage rack at the same level as the walkway.

2.5.4.5.8.4 If Sections 2.5.4.5.8.1 through 2.5.4.5.8.3 are not satisfied, install sprinklers under an open-grid walkway as follows:

A. Sprinkler Type: 160ºF (70ºC) nominally rated, quick-response Storage sprinklers equipped with water shields that have the same K-factor, coverage-type, and orientation as the sprinklers being installed at ceiling level.

B. Sprinkler Spacing: Install the sprinklers under the open-grid walkway using a maximum linear spacing
of 8 ft (2.4 m).

C. Sprinkler Design: Use the same branchline pipe size that is being installed at ceiling level.

2.5.4.5.8.5 As an acceptable alternative to the guidelines in Section 2.5.4.5.8.4, if the open-grid walkway is located adjacent to a storage rack that is protected with in-rack sprinklers, the sprinklers under the open-grid walkway can use the same sprinklers and in-rack sprinkler design that is being used for the in-rack sprinklers.

2.5.4.5.8.6, If sprinklers are installed in accordance with Sections 2.5.4.5.8.4 or 2.5.4.5.8.5, the sprinkler system under the walkway does not need to be hydraulically balanced with the ceiling-level sprinkler system.

Annex Definitions:

Open-grid ceiling: A ceiling that is installed between the sprinklers installed under a solid ceiling and the protected occupancy that consists of uniform openings that constitute at least 70% of the ceiling area.

Open-grid mezzanine: A mezzanine that consists of uniform openings that constitute at least 70% of the mezzanine area.

Open-grid walkway: A walkway that consists of uniform openings that constitute at least 70% of the walkway area.

Use Intermediate Level/Rack with ESFR at Deck?

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