August 15, 2016
Mattress Storage - Solid Shelves “We have mattresses stored on racks with open wire grated shelves. The warehouse has ESFR K-17 sprinklers designed at 52 psi to a maximum 35-foot ceiling height, maximum 30-foot storage of Class I - IV commodities and Group A plastics. The proposed racks for a new tenant are double-row with 72 in. wide shelves on each side separated by a 30 in. flue space between the racks. When the racks are loaded with the mattresses, the mattresses will hang over the back of the racks so the flue space will actually be less than the 24 in. maximum flue space. The mattresses will be stored both on their side and lying flat. When the mattresses are stored on the shelves, the product will create a barrier on the shelves that is more than 20 sq. ft. that could be classified as solid shelving. Are in-rack sprinklers required?” We have reviewed NFPA 13, 2013 edition that you indicated as the applicable standard. Our informal interpretation is that in-rack sprinklers are required at every level. The definitions indicate how to determine the size. First, the rack shelf area is defined in 3.9.3.7.6 as the area of the horizontal surface of a shelf in a rack defined by perimeter aisle(s) or nominal 6 in. (152 mm) flue spaces on all four sides, or by the placement of loads that block openings that would otherwise serve as the required flue spaces. The definition of solid shelving in 3.9.3.8 indicates that solid shelving is fixed in place, slatted, wire mesh or other type of shelves located within racks. The area of a solid shelf is defined by the perimeter aisle or flue space on all four sides. Solid shelves having an area equal to or less than 20 sq. ft. shall be defined as open racks. Shelves of wire mesh, slates, or other materials more than 50 percent open and where the flue spaces are maintained shall be defined as open racks. The definitions tell us that the area of the solid shelving is the perimeter aisle or flue space on all four sides. If transverse or longitudinal spaces were not provided, the measurements would have to be taken to the perimeter aisle. For example, if the longitudinal space were covered by mattresses and the transverse flue was left open at each rack upright, the measurement would be the front and back solid shelves plus the covered longitudinal space. The definition of double-row racks in 3.9.3.7.1 has an aggregate depth up to 12 ft with an aisle width of at least 3.5 ft between loads on racks. Multiple-row racks in 3.9.3.7.3 are greater than 12 ft in depth or single- or double-row racks separated by aisles less than 3.5 ft wide having an overall width greater than 12 ft. The actual solid shelving size has to be determined for this application to see if 17.1.5.1 applies. This section states, “Where solid shelving in single-, double-, and multiple-row racks exceeds 20 sq. ft. but does not exceed 64 sq. ft. 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 apart vertically.” For standard spray sprinklers, this section allows in-rack sprinklers to be omitted from some levels if the in-rack sprinklers are spaced no more than 6 ft apart vertically. This applies where solid shelving is located close together. With ESFR sprinklers, this section may not apply (still needs to be clarified by the standard). An example provided in the NFPA 13 Handbook commentary indicates where solid shelving is provided 18 in. vertically between solid shelving that in-rack sprinklers located up to 6 ft vertically and not located at every tier can contain the fire size. This could result in several levels of storage between levels of in-rack sprinklers. In-rack sprinklers provided at every other level would be located greater than 6 ft apart vertically and would not meet Section 17.1.5.1. Regardless of the ambiguity regarding ESFR systems, in-rack sprinklers are needed at each tier as indicated by Section 17.1.5.2. Previously, ESFR sprinklers could not be used when solid shelving existed. Starting with the 2013 edition, this changed though poorly presented within the standard. The 2016 edition states: 17.1.5.5 Ceiling design criteria for CMDA, CMSA, and ESFR sprinklers shall be an applicable option for open racks combined with in-rack sprinklers installed in accordance with the criteria for solid shelving. There are still some unanswered issues that you will need to resolve with the AHJ regarding the placement of the in-rack sprinklers. The rack assembly could be called single-row racks with too narrow of an aisle (if the AHJ ignores the placement of the mattress when defining flue width in order to account for empty tiers of the rack) and it becomes a multiple-row rack. If they accept the flue as 24 inches, you are still a multiple-row rack (due to overall width as discussed above) but you have a flue. We are told to protect them as multiple-row racks as reminded in 17.1.2.3 Storage with aisles less than 3.5 ft (1.1 m) shall be protected as multiple-row rack storage. The problem is that there is no valid guidance for in-rack sprinklers. The guidance for a multiple-row rack is basically a maximum spacing along the transverse flue combined with a maximum area of coverage. This does not translate to a hybrid multiple-row rack that now has defined openings that allow vertical growth of the fire. Expect to provide an in-rack sprinkler within each individual 72 in. rack assembly and one in the flue. ------------ Technical Update is prepared by the Technical Services Dept. of the AFSA: Roland Huggins, a PE registered in fire protection engineering, Vice President of Engineering and Technical Services; and Tom Wellen, a PE registered in fire protection engineering. This is provided with the understanding that the AFSA assumes no liability for this opinion or actions taken on it and they are not to be considered the official position of the NFPA or its technical committees. Copyright 2016, American Fire Sprinkler Association. All Rights Reserved. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.firesprinkler.org/private.cgi/sprinklernotes-firesprinkler.org/attachments/20160815/f9d495d7/attachment.htm>
