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Storage Issues Got You Stumped?

Informal Interpretations Offer Solutions and Savings

The informal interpretations featured in this issue of Sprinkler Age address storage issues. AFSA’s informal interpretations are provided to AFSA members by Vice President of Engineering & Technical Services Roland Huggins, PE; Senior Fire Protection Engineer Russ Bainbridge, PE; and Technical Programs Specialist Tom Noble, CET. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them.

QUESTION: “Would unexpanded Group A plastics stored in wooden crates be considered cartoned?”

ANSWER: In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is unexpanded Group A plastics stored in wooden crates would be considered cartoned. This is a really interesting nuance that has mostly been ignored. Crates are a separate packing assembly that are explicitly addressed by Chapter 5 for defining the commodity classification. The problem is that the discharge criteria in Chapters 15 and 17 discuss only cartoned and exposed. In reality, we have two questions on the use of wooden crates with group A plastics. The first is what criteria to apply (cartoned or exposed) and the second is a more subtle nuance on what is the impact on the commodity classification.

The commodity classification is very explicitly addressed for Class I and II commodities. This is because the wood crate itself becomes the primary fuel load for a noncombustible product (making it a Class II whereas it would otherwise be a Class I). The definition of a Group A plastic says cartoned or within a wood container beyond specified amounts are a plastic. The packaging doesn’t contribute much to the fuel load (relatively speaking), so the product itself drives the decision. This doesn’t answer the question of whether or not to treat it as cartoned. Fortunately, we have an answer in Table A.5.6.1.1: General Guide to Identifying the Commodity Class for Solid Combustibles. Under the category Entirely Unexpanded Group A plastic, it identifies the packaging as corrugated cartons, wooden crates, and wooden boxes and assigns a commodity of cartoned unexpanded Group A plastic. As such, we can apply the cartoned criteria from Chapters 15 and 17.

Unfortunately, this same section of Table A.5.6.1.1 misleads us on defining the commodity. The aspect that is missing is how to treat multiple layers of corrugated cartons. This variable is addressed regarding Class II commodities but isn’t addressed for Group A plastics. The reason for this is that the table was based on the criteria from Chapter 5. Multiple layers of corrugation are part of the definition of Class II commodities in Chapter 5. It is not mentioned elsewhere in Chapter 5. You have to go back to Chapters 15 and 17 where the Decision Trees (Figures 15.2.2 and 17.1.2.1 of the 2013 edition) identify this variable. The note states:

“Note: Cartons that contain Group A plastic material are permitted to be treated as Class IV commodities under the following conditions: (1) There are multiple layers of corrugation or equivalent outer material that would significantly delay fire involvement of the Group A plastic.

“(2) The amount and arrangement of Group A plastic material within an ordinary carton would not be expected to significantly increase the fire hazard.”

As the criteria tells us, if the outer material is able to significantly delay the involvement of the Group A plastic inside the container, it can be classified as a Class IV commodity. This only requires two layers of corrugated cardboard which is typically wet (except for the initial burning pallets that activate the sprinklers). This includes equivalent outer material. Although cardboard will absorb more water, even dry wood provides more of a delay than wetted cardboard. Now, combine this with the fact that wetted wood does absorb some water and its burning characteristics are certainly reduced when continually wetted. Thus, solid wood crates are equivalent. I emphasize “solid” since this does not apply to slatted wood crates since a solid barrier is needed to slow down the exposure of the Group A plastic to the fire.

I’m perplexed by the identified note being deleted from the 2016 edition. Historically, it has been part of the solid pile (Chapter 15) criteria for decades and came from the old NFPA 231, Standard for General Storage. It wasn’t initially part of the rack criteria because it came from the old NFPA 231C, Standard for Rack Storage of Materials. Two separate committees controlled the two standards, and the question of why there a difference never came up. With the text being combined into a single document (NFPA 13, Standard for the Installation of Sprinkler Systems, in the 1999 edition), such differences become more apparent. It was added to the rack criteria starting with the 2007 edition since the storage arrangement does not impact the determination of the commodity classification. Since I cannot find a public input initiating the removal of this text from only Chapter 17 and I do not remember it being addressed (which would have stood out for me since I am the one who triggered having it added to the 2007 edition), I believe it was an inadvertent mistake. In reality, this criteria belongs in Chapter 5 and will be addressed in the next cycle.

As already stated, but worth repeating, the assignment of classification is a function of the burning characteristics of the load (that being a single load as can be tested under a calorimeter assembly). The aspect of storage arrangement is separately addressed in the assigned design basis for a specific commodity.

QUESTION: “We are installing systems with ESFR sprinklers into a 564,000 ft2 speculative rectangular warehouse. The building is 42-ft 2-in. tall at the ridge and 36-ft 6-in. at both eaves which means 43 percent the building has a roof deck above 40 ft and 57 percent of the building has a roof deck below 40 ft. Can we install sprinklers with different K factors in the portion above 40 ft (ESFR K-22.4) and the portion below 40 ft (ESFR K-16.8)? Can the sprinklers with different K factors be on the same system? This is a speculative building so there are no storage aisles established.” 

ANSWER: In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is that such combination of sprinklers with different K-factors on a single system is allowed by NFPA 13. Many contractors and Authorities Having Jurisdiction (AHJs) take an excessively conservative view on this issue based mostly on concerns about restoring the system and making a mistake on replacing the correct sprinkler type. The base criteria of Section 23.4.4.9.2 is that different orifices cannot be used to balance a system. Some exceptions were provided to indicate typical examples where different orifices were acceptable. This was not intended to be an all-inclusive list of where having different orifice sizes is acceptable. There are several references to using different types of sprinklers (which often have different size orifices) within the same compartment such as Section A.8.4. While explicitly saying when different types of sprinklers are used in the same compartment, it’s mainly emphasizing that they should have the same response characteristics (i.e., standard or quick response). Section A.23.4.4.9 is even more applicable in that it identifies different orifices sizes in foyer and room areas, which are not separate enclosures or one of the other listed examples identified in Section 23.4.4.9.2. As such you can mix ESFR sprinklers of differing orifice sizes but can’t mix ESFR and standard spray sprinklers. When calculating the system be sure to complete calculations confirming the most demanding system or providing calculations proving both K-factors will work at their required pressures. I suggest you come up with a detailed installation drawing to make sure the installer correctly installs the sprinklers in the correct locations.

QUESTION: “I have a project with storage of exposed, unexpanded Group A plastics in racks to a height of 20 ft with a building height of 40 ft 7 in. Is Section 12.1.3.4.8 requiring an acceptable clearance from storage to the ceiling with in-rack sprinklers or does it remove the acceptable clearance requirement from storage to the ceiling if in-rack sprinklers are installed? If I were to install in-rack sprinklers per Section 12.1.3.4.8 would I be able to use any of the rack configurations described in Section 17.2.1.4? For example, could I use any of the rack options for 20 ft of storage in a 25-ft building or 20 ft of storage in a 30-ft building? Also, Figure 17.2.1.4(j) shows a line of sprinklers directly over the top level of storage. Would this configuration require a solid barrier above the top of the storage?”

ANSWER: In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is Section 12.1.3.4.8 negates the excessive clearance. There are multiple sections that have to be referenced when determining a design criteria when the acceptable clearance between the top of the storage and ceiling is exceeded. The main section to review is Section 12.1.3, which covers the requirements pertaining to storage height and building height. Section 12.1.3.3 requires the design to be based off of the storage configuration that routinely or periodically is found in the building requiring the greatest water demand. The clearance from storage to ceiling requirements are contained in Section 12.1.3.4. Then Section 12.1.3.4.2 states: “for spray sprinkler criteria where the clearance to ceiling exceeds those identified in this section, the requirements of 12.1.3.4.3 through 12.1.3.4.8 shall apply.”

Since the term “through” is used, every applicable part of those sections has to be adhered to. With the storage commodity being exposed, unexpanded Group A plastics stored to a height of 20 ft, Section 17.2 contains the design requirements. Thus, Sections 12.1.3.4.5, 12.1.3.4.7, and 12.1.3.4.8 are applicable. Section 12.1.3.4.5 requires the protection criteria to be determined by using a storage height that would result in clearance to the ceiling of 10 ft or installing a supplemental row of in-rack sprinklers. For example, use the design requirements for a storage height of 31 ft for a building height of 40 ft 7 in., even if the storage height is only 20 ft. An equally acceptable approach is to install one level of supplemental, quick-response in-rack sprinklers located directly below the top tier of storage at every flue space intersection to be provided instead. Then Section 12.1.3.4.7 in conjunction with the supplemental in-rack sprinklers dictates the ceiling density to be based upon the given storage height as if the acceptable clearance to the ceiling were met. In other words, the supplemental in-rack sprinklers negates the excessive clearance. Next, Section 12.1.3.4.8 states if the design criteria already requires in-rack sprinklers for a certain storage configuration, provide those in-rack sprinklers as well as the supplemental in-rack sprinklers required by Section 12.1.3.4.5. After reviewing Figure 17.2.1.4(j) it is believed the line of sprinklers shown above the top level of storage is an error (effectively a typo) and those sprinklers are to be installed directly below the top tier of storage. This is supported by the configuration in the 2019 edition being shown without the sprinkler above the top tier (Figures 25.9.3.3(g) and 25.9.3.3(i)).

These topics should be discussed with the local AHJ and a written agreement with these interpretations should be obtained (or at least an email sent to the AHJ identifying the outcome of the discussion) before proceeding further with the project.

QUESTION: “We have a customer who owns four unheated warehouses that he uses for tiered baled cotton storage. These buildings currently do not have fire sprinkler systems installed. He is wanting to install fire sprinkler systems in these buildings, but the pitch of all of the roofs is 6:12. According to NFPA 13 2016 edition, Section 12.1.2, the sprinkler system criteria specified in Chapter 12 and Chapters 14-20 are intended to apply to buildings with ceiling slopes not exceeding 2:12 unless modified by a specific section in these chapters. Is there some sort of modification that can be made to the design density/area for baled cotton storage that would allow for a fire sprinkler installation under these steeply pitched roofs? Also, what is the theory behind limiting the ceiling slope to 2:12 for storage applications?”

ANSWER: In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is that there is no identified design basis for the protection of the storage with a sloped ceiling. Chapter 12 is a general chapter for storage that begins by indicating that the requirements of Section 12.1 are applicable to all storage arrangements and commodities other than miscellaneous storage (Chapter 13) and as modified by specific sections in Chapter 14 through Chapter 20. Then Section 12.1.2 says that the sprinkler system criteria specified in Chapters 14 through 20 are intended to apply to buildings with ceiling slopes not exceeding 2 in 12. The design area modifiers in Chapter 11 are not applicable to storage occupancies. This is why Section 11.2.3.2.4 ends with sloped ceilings in non-storage applications. Chapter 12 has its own section (12.5.1) addressing design modifiers and the only design modifier is for dry pipe and preaction systems. In order to use NFPA 13 design criteria for storage occupancies, the ceilings in these areas must not exceed a slope of 2 in 12. In the 2016 handbook there is commentary that explains why we limit the ceiling pitch in storage applications: “All of the testing used to develop storage protection requirements was done under flat roofs. A 1/6-scale model of a full-scale test facility was used to investigate the effects of varying ceiling slopes. These investigations indicated that sprinkler operating patterns and sequences will not be adversely affected when slopes do not exceed 2 in 12 (16.7 percent). Where the slope exceeds 16.7 percent, the sprinkler operating area and sequence can be skewed. Unless the fire occurs directly under a row of sprinklers, sprinklers nearest the fire may not operate. Heat from the fire will collect at the peak and result in the operation of an excessive number of sprinklers and loss of fire control. The design criteria for storage buildings having ceiling or roof slopes exceeding 2 in 12 are outside the scope of Chapter 12 and Chapters 14 through 20.

For storage buildings that have sloped ceilings greater than 16.7 percent, consideration should be given to larger design areas combined with skewed operating patterns. A good example of this concept is the construction type commonly referred to as “sawtooth roof,” in which generally only two or three sprinklers run up a section of roof with a slope greater than 16.7 percent. These sprinklers can be calculated as if all the sprinklers running up the slope will operate for the width of the hydraulic remote area. Experienced judgment will have to be used for small portions of the ceiling/roof that exceed 16.7 percent slope. Large roof/ceiling slopes over 16.7 percent are outside the scope of this chapter. If a storage application is addressed by Chapter 13, sloped ceilings are not a problem (since the Chapter 11 modifiers are applicable). Unfortunately, baled cotton is not viewed as simply a Class III commodity due to it being bailed (which greatly impacts the burning characteristics, much like rolled paper). That’s why it has its own section in Chapter 20. The only possible alternative is to add a ceiling in the area above the storage.

QUESTION: “We have an agricultural vegetation room in a commercial grow facility with double stacked tables that slide for access (like a rolling library stack) to maximize space/light utilization. The top table is 82.5 in. above the finished floor and the tables are 61.5-in. wide. The room is protected with an ordinary group 1 overhead system. The AHJ is concerned about the obstruction to discharge by the upper level of the tables. Would the fact that the tables slide make an argument for exemption in NFPA 13, 2016 edition Section 8.5.5.3.2? If the tables were considered racks would Table 13.2.1 allow its use as is under an ordinary group 1 without in-rack sprinklers?”

ANSWER: In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is the upper table cannot be ignored.

Section 8.5.5.3.2 allows us to ignore items like typical tables because they are the contents of the room and they don’t have significant fuel loads beneath them. Your situation is effectively a storage rack. Let’s first start with Chapter 13. Even though Table 13.2.1 does not require in-rack sprinklers for Class I or Class II, we have to meet the requirements of Section 13.1.3.1: “for storage of Class I through Class IV 12 ft (3.7 m) or less in height that does not meet the definition of Miscellaneous Storage that is on solid shelf racks, in-rack sprinklers shall be provided in accordance with 16.1.6, and ceiling sprinkler protection shall be provided in accordance with Chapter 13.” As Section 13.1.3.1 states, the design area and/or density doesn’t change but in-rack sprinklers are required if the solid shelf racks meet the criteria in Section 16.1.6. Within Section 16.1.6 there are two sections that apply to this configuration that require in-rack sprinklers and they are Sections 16.1.6.1 and 16.1.6.2. Section 16.1.6.1 states: “where solid shelving in single-, double-, and multiple-row racks exceeds 20 ft (1.9 m ) in area but does not exceed 64 ft (5.9 m ) in area, sprinklers shall not be required below every shelf but shall be installed at the ceiling and below shelves at intermediate levels not more than 6 ft (1.8 m) apart vertically.” And, Section 16.1.6.2 states: “where solid shelving in single-, double-, and multiple-row racks exceeds 64 ft (5.9 m ) in area or where the levels of storage exceed 6 ft (1.8 m), sprinklers shall be installed at the ceiling and below each level of shelving.” If they had built the tables with 6-in. flues every 5 ft. (or mechanical stops between tables to maintain a gap when moved), the ceiling-only protection would have been fine.

Since the upper tables are movable, depending on how much they move poses a problem for in-rack sprinklers. That leaves the only option of calling them significantly shielded and treat it as an extra hazard group 2. The main restriction on this approach is that you cannot have unlimited lengths for the obstruction. Although there is no defined size to said shielding, the fuel arrangement would need to fit inside the bigger remote area. This last approach would require consulting with the AHJ to determine the allowed maximum length for the racks. 

QUESTION: “Is there a minimum aisle width associated with a Table 21.3.1 (extended coverage CMSA K25.2) design?”

ANSWER: In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is there is no minimum aisle width requirement.

The aisle width is a variable that applies to the design basis of only single or double racks. When the criterion is applicable to all racks (single,- double-, and multiple-row racks) then there is no applicable aisle width. When the aisle is too narrow for a double-row rack, then by definition, it becomes a multiple row rack. That’s why Section 21.3.1 does not address aisles. The same is true for CMSA and ESFR in Chapters 16 and 17.

EDITOR’S NOTE: These interpretations were prepared by AFSA’s Technical Services Department in answer to specific questions from contractors and/or AHJs. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them. AFSA members can access past informal interpretations online. Visit firesprinkler.org, click on “Technical Services” and then “Informal Interpretations.” (Member user name and password required to gain entry.)

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