Appropriate Sprinkler Height from Tall Roof?

6/15/2023

We have a production facility with a roof height of 55-ft. Someone has decided that storage sprinklers would be more appropriate.

How far from the roof would it be acceptable to install K11.2 (K160) spray sprinklers?

Is this approach even acceptable? Does the extreme height of the roof affect the best sprinkler height?

I vaguely remember Russ Fleming did a paper on the hottest point in the fire plume being some 10 % (?) of the ceiling height from the roof. Must have been 20 years ago or more.

Hopefully someone can help me with information or views on this subject on an appropriate height from the roof.

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

9 Comments

6/15/2023 08:08:16 am

NFPA is rather silent on this issue unless storage is mentioned. FM guidelines has different requirements for ceiling heights as they get higher within DS 3-26.

R Jackson link

6/15/2023 08:21:33 am

FM has their own guidelines on everything. It seems as if they are close to something I read a long, long time ago. 'They seem to be able to swallow a camel, but gag on a gnat.' Pretty much sums up all politicians as well. Just my 2 cents worth. (That and $5.00 will get you a cup of 25 cent coffee.)

moises OLMEDA

6/15/2023 08:25:11 am

I think your guess is reasonable, even though the hazard category is between OH & EH, a bigger droplets have a better chance to control de fire and avoid the heat and turn into steam.

Jesse

6/15/2023 08:38:12 am

Seems like you have a few questions. First, make sure that whatever sprinkler you use is listed for the hazard class. Most storage sprinklers carry listings for OH.

Second, the storage sprinklers don't necessarily provide a larger drop per se. Large drop sprinklers do. Standard spray sprinklers are just that regardless of the listing.

Third, except when avoiding beams upright sprinkles will need to be within 12-inches of the deck usually/

Todd E Wyatt

6/15/2023 08:38:15 am

2022 NFPA 13 includes the following references to “distance below ceilings” :

Chapter 9 — Sprinkler Location Requirements
9.5.4.1* Distance Below Ceilings.

Chapter 10 — Installation Requirements for Standard Pendent, Upright, and Sidewall Spray Sprinklers
10.2.6.1 Distance Below Ceilings.
10.3.5.1 Distance Below Ceilings and from Walls.

Chapter 11 — Installation Requirements for Extended Coverage Upright, Pendent, Sidewall Spray Sprinkler
11.2.4.1 Distance Below Ceilings.
11.3.5.1 Distance Below Ceilings and from Walls to Which Sprinklers Are Mounted.

Chapter 13 — Installation Requirements for CMSA Sprinklers
13.2.7.1* Distance Below Ceilings.

Chapter 14 — Installation Requirements for Early Suppression Fast-Response Sprinklers
14.2.10.1 Distance Below Ceilings.

2022 NFPA Chapter 26 Special Designs of Storage Protection “is new to the 2022 edition of NFPA 13, but the requirements are not new to the standard. The protection criteria for the unique hazards covered in this chapter have been developed through many different tests for different materials and storage arrangements with various sprinkler types. Instead of having those scattered throughout NFPA 13 in several different chapters, they have been gathered together to be provided in a single chapter to make the criteria easier to find.”

Chapter 26 goes on to state the following :

26.1* General.
26.1.1*
This chapter shall cover special sprinkler system designs for storage protection.
26.1.2
The requirements of Chapter 20 shall apply unless modified by this chapter.
ENHANCED CONTENT
Where Chapter 26 has criteria for protection of a specific commodity, arrangement, and sprinkler, this chapter can be utilized. For anything not directly addressed within this chapter, the general requirements for storage protection of Chapter 20 apply.

Todd E Wyatt

6/15/2023 08:38:47 am

2022 NFPA 13 Chapter 20 General Requirements for Storage states the following :

Using Chapter 20 to Determine Storage Protection
For the protection of any storage occupancy, the intent of NFPA 13 is for the user to start with Chapter 20 and determine the general rules that apply. Then, the user is to go to the appropriate chapter (Chapter 21 to Chapter 26) for the commodity and storage arrangement being protected to get the rest of the discharge criteria.

In general, the protection rules in Chapter 20 through Chapter 26 are designed to answer four basic questions, assuming that a fire is going to start in the occupancy:

1. What is a reasonable estimate of the flow that will be needed for the sprinkler system? (This includes consideration for the number of sprinklers that might open in a fire and the flow that will be used for fire department operations to extinguish the fire upon their arrival.)
2. At what pressure does that flow need to be available?
3. How long will the flow need to last?
4. If the storage is on racks, do sprinklers need to be placed in the racks, or can the storage be protected by sprinklers only at the ceiling?

When NFPA 13 is selected as the document to provide requirements for protecting occupancies from fire with sprinklers, it is important to follow all the requirements of NFPA 13. The user is discouraged from picking selected requirements from other documents and trying to use them with NFPA 13, because the fundamental assumptions that went into selected requirements from other documents might not be valid with NFPA 13. Users who want to select sprinkler design criteria from another standard are encouraged to use that standard in its entirety, including any additional standards referenced by that standard. The authority having jurisdiction is permitted to review the other set of standards and determine whether or not (as a package) it meets the same level of safety as that prescribed by NFPA 13. If the authority having jurisdiction is convinced that the other set of standards is sufficient, then that set of standards can be permitted to be used under Section 1.4 and Section 1.5 of NFPA 13 as an alternative that meets the same level of safety as NFPA 13.

While the storage chapters of NFPA 13 can seem daunting at first, they become easier to navigate once the pertinent information for a given facility is identified. For most storage facilities, only a few dozen individual sections of the standard are applicable. The trick is being able to identify which sections apply to a given storage arrangement and which ones can be ignored. That is done by finding the correct sections in each chapter to jump to after the requirements of Chapter 20 have been addressed and the pertinent information has been identified. This information should be identified by the designer prior to searching through the various storage chapters (Chapter 21 through 26) since that information will confine the search to only the pertinent chapters and sections. After the commodity classification and the storage arrangement have been identified, the next step is to determine the ceiling-only options, if any, that apply from Chapters 21, 22, 23, 24, or 26, followed by the ceiling and in-rack options that are available from Chapter 25.

Exhibit 20.1 is a checklist that should be used prior to navigating through the individual storage chapters of NFPA 13. Once the information has been identified on the form, finding an applicable design approach becomes much simpler. Many designers simply take the commodity class and storage type (rack, piled, etc.) and head into the storage design chapters looking for guidance. While that is certainly one approach, it is like starting to cook dinner without first checking to see what ingredients you need—you might have to replan or reassess once you realize that you do not have the ingredients you need to finish the meal. Failing to identify critical information such as storage height, clearance, storage arrangement, and ceiling height can lead to headaches later in the design process if they are not factored into the design decision up front. All the information in Exhibit 20.1 is needed to achieve an allowable design option, so it is helpful to start with this form.

20.1 General.
This chapter shall provide the necessary steps for identifying commodity, storage arrangements, storage heights, and clearances as well as general protection criteria for storage conditions relative to Chapters 21 through 25.
ENHANCED CONTENT
FAQ
Why was Chapter 20 written to apply to all storage arrangements?
Rather than repeat all the general rules that apply to all storage situations, the rules have been consolidated in one location so that they are easily found and uniformly enforced. If the rules were repeated in multiple chapters, they might be more difficult to find, and they unintentionally might be modified by the technical committee in one chapter while left alone or modified in a differe

Todd E Wyatt

6/15/2023 08:39:53 am

FAQ
Why was Chapter 20 written to apply to all storage arrangements?
Rather than repeat all the general rules that apply to all storage situations, the rules have been consolidated in one location so that they are easily found and uniformly enforced. If the rules were repeated in multiple chapters, they might be more difficult to find, and they unintentionally might be modified by the technical committee in one chapter while left alone or modified in a different way in another chapter.
FAQ
Why are systems designed in accordance with 4.3.1.4 through 4.3.1.6 and 25.2 exempt from the requirements of Chapter 20?
Sprinkler systems that protect miscellaneous storage or low-piled storage have more in common with ordinary hazard or extra hazard occupancies than they do with storage occupancies. Fires in those occupancies do not generate the same kind of forceful vertical fire plumes that can be found in other storage occupancies. Therefore, the discharge criteria for systems designed in accordance with 4.3.1.4 through 4.3.1.6 and 25.2 ultimately revert to criteria in 4.3.3 through 4.3.6 for ordinary or extra hazard systems; the more stringent criteria found in Chapter 20 do not apply.
The rules of Chapter 20 apply to all storage occupancies, except for miscellaneous storage (4.3.1.4), low-piled storage (4.3.1.5), miscellaneous tire storage (4.3.1.6), and the storage arrangements in 25.2. When planning a sprinkler system for a storage or warehouse occupancy, the user needs to make sure that all the rules of Chapter 20 are followed in addition to the applicable requirements of Chapter 21 through Chapter 26. Even though Chapter 26 is not listed in Section 20.1, 26.1.2 states that Chapter 20 requirements must be followed.

Dan Wilder

6/15/2023 08:42:35 am

If the question is to lower sprinklers below the standard NFPA written or Sprinkler listed deflector distances below the roof deck, no, there is no provision within NFPA for that.

This is where a FPE consultation would be very beneficial to establish both effectiveness of the sprinkler system at that height and type of sprinkler to best provide water to the ground with heat and smoke modeling.

FM Guidelines can also be useful with the buy-in from the approving entities for design approach if structured correctly.

I did a design for a large convention center with 105' ceilings where we provided closed head 11.2K sprinkler layout at the roof deck (with something like a +5000ft² remote area) and a supplemental system of open head deluge EC sidewalls that covered the floor area around the 50' elevation (with beam detection). All FPE detailed AHJ/Insurance approved, but the intent was to provide the lower sprinkler coverage for water onto the fire and the overhead as a secondary cooling at the higher roof if needed.

Pete H

6/15/2023 02:54:18 pm

55 foot building using storage heads?

Is it protecting storage? It sounds like it is. In which case, you're going to have to use FM (as other comments have pointed out).

That said, if you are protecting storage as per FM 8-9... no, you won't be able to use an 11.2k sprinkler for a 55 foot building with storage underneath. You'll more likely be using either 28.0K or 33.6K sprinklers.

Appropriate Sprinkler Height from Tall Roof?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES