What Distance Under Sprinkler Is No Longer An Obstruction?

1/25/2021

When would you consider an obstruction no longer an obstruction, vertically below an ESFR sprinkler?

If the top of storage has to be 36" wouldn't 36" be the cut off? Or do the obstruction rules go the floor?

I have a warehouse that has 2 x 4 light fixtures which are 6'-0" below the roof deck, and am wondering whether these are considered obstructions. Thanks in advance.

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7 Comments

Sarah Swan link

1/25/2021 09:09:39 am

We have actually asked the NFPA 13 committee what their intent was for this. Unfortunately, the response was that anything can be considered an obstruction to and ESFR sprinkler, no matter the distance from it. We questioned if this applied to things like rails near the floor to protect walkways from forklifts, and were told that it does.

Bruce Seiler

1/25/2021 09:15:36 am

Obstruction rules still apply. ESFR sprinkler heads have very specific requirements. NFPA 13 2019 Edition Chapter 14. Section 14.2.1.2 would cover the light fixtures, specifically Item (2). "Additional sprinklers shall not be required where the obstruction is 2 ft. or less in width and the sprinkler is located horizontally 1ft. or greater from the nearest edge of the obstruction. Spacing of lights should follow this standard. The standard does not provide a specific distance below the sprinkler head that obstructions become a problem. It distinguishes between Obstructions at or Near Ceiling for non-continuous obstructions and continuous obstructions.

Mike

1/25/2021 09:24:19 am

Looking at the Tyco ESFR data sheet, under Obstruction Criteria they say to Refer to FM 2-0 Section 2.2.

https://www.fmglobal.com/-/media/Documentum/Data-Sheet-Individual/02-Sprinklers/FMDS0200.pdf?isGated=true&itemId={993E5163-0BFB-47CB-BD99-442324FE7F93}

This has been pretty strict. In the past I have had to add ESFR's underneath 4" and 6" roof drain lines.

There's always a trade off using ESFR and CMSA heads vs. standard spray heads. Might use less heads at the roof but you have to add heads for obstructions.

Franck

1/25/2021 11:02:29 am

For that reason, in my previous company, we were saying that you have to build a warehouse around an ESFR protection (to avoid all these issues).

Providing an ESFR protection within an existing building is most of the time a nightmare (air velocities, presence of heating devices near the ceiling, obstructions from the building structures, from the components (ligths, pipes...), from the draft curtains, presence of skylights...)

CJ Bonczyk

1/25/2021 10:50:04 am

Unfortunately all obstruction rules currently stated in code apply whether it be FM Global or NFPA requirements. I prefer to follow the installation guidelines as outlined in FM Global. They provide a clear pictorial view of what is required. In your situation it does not matter whether the obstruction is greater than 36" below the bottom of the deflector.

NFPA does not clearly call out a maximum cut off distance other than the following:

NFPA 13 2019 14.2.11.2 discusses isolated obstructions below elevation of ESFR sprinklers. Sprinklers are required below unless the obstruction is 2' or less in width and a minimum of 1' horizontally or greater from the nearest edge of the obstruction. It also states that additional sprinklers shall not be required where the obstruction is 2" or less in width and located a minimum of 2' below the elevation of the sprinkler deflector or is positions a minimum of 1' horizontally from the sprinkler. Note that it does state that sprinklers special obstruction allowances shall be installed according to their listing.

Check the cut sheet of the ESFR sprinkler and see what minimum code requirements are to be followed for both FM & NFPA. Ensure the elevation tolerances for the sprinkler can be met.

FM Global provides the following:
Also as stated previously FM Global provides guidelines for storage sprinklers (FM Data Sheets 2-0 & 8-9). 2-0 specifically address umbrella discharge patterns for ceiling level storage sprinklers in 2.2.3.5 & 2.2.3.5.1. The remaining information, tables and figures are of great information as well and should be strictly followed.

Word of advice is to provide a preliminary layout of the ESFR sprinklers with the steel background should be provided to the client/GC for in-depth coordination of lights/HVAC/plumbing/HVLS fans etc. The spacing of the sprinklers is critical obviously and many times you can have the MEP be adjusted to accommodate the ESFR spacing because the ESFR's are limited to the steel locations and code limitations.

Franck

1/25/2021 10:55:20 am

Same rule applies for all sprinklers (even though more restrictive in term of width with ESFR):

Whatever the distance below the deflector, any item can create an obstruction to the sprinkler water discharge pattern and prevent water to reach the fire.

This apply for lights, groups of cables/pipes, but also applies for wooden shelves within rack arrangements (difference between open and solid shelves).

Only acceptable exceptions are listed by NFPA, such as removable tables...

You have to check the obstruction rules within NFPA and provide sprinkler underneath if you don't fall under an exception.

Brian Hoole

1/25/2021 12:24:36 pm

2019 NFPA 13:8.12.6 Clearance to storage (Early Suppression Fast Response Sprinklers). The clearance between the deflector and the top of storage shall be 36 in. or greater.

Any obstruction large enough to cause an obstruction to the ESFR below the top of storage would hinder the ability to pick commodities from the shelving with fork lifts. Utilizing catwalks would likely require in-rack protection under the additional walkways.

What Distance Under Sprinkler Is No Longer An Obstruction?

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