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Slatted Ceilings and Sprinkler Protection
You asked the following questions: “We have a building that has wood veneer slat ceiling features. The slats are 5/8-in. wide and 3-1/4 in. deep with a 1-3/8 in. gap between the slats. The area above the slatted ceiling is constructed of noncombustible steel joist framing and roofing. Are sprinklers required above the slatted area?” In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is that sprinklers below the wood-slatted ceilings are not required. Sprinklers located below the decorative wood would be essentially ineffective unless the sprinkler is located directly in the fire plume. There is no ceiling to collect heat to activate sprinklers. Fire sprinklers opening above them at the floor or roof deck would cold solder the sprinklers located below. This application also does not appear to be a traditional grid ceiling. The NFPA 13 standard considers an open grid ceiling when the openings are ¼ in. or larger in the least dimension, where the thickness or depth of the material does not exceed the least dimension of the opening, and where such openings constitute 70 percent of the area of the ceiling material. The sprinkler discharge pattern can be affected by the open grid ceiling, so sprinkler spacing requirements are provided in section 8.15.14. The decorative wood is suspended with the longer leg vertical from the floor or roof deck above where the obstruction rules should be applied. If you use standard spray sprinklers and if the decorative wood is located more than 18 inches below the deflector, the wood obstruction can be ignored according to section 8.6.5.3.1. This applies to obstructions greater than 18 inches below the deflector, and sprinklers shall be installed under fixed obstructions over 4 ft wide. If the decorative wood falls within 18 inches of the deflector where water can spray above and below an obstruction or can spray on both sides of an obstruction such as a column, then section 8.6.5.2.1.3 applies. This is commonly known as the three-times rule. This section indicates that sprinklers shall be positioned away from obstructions a minimum distance of three times the maximum dimension of the obstruction (e.g., structural members, pipe, columns, fixtures). Thus, this could be a tedious process to verify each wood slat member is located according to this rule. The ceiling could be considered grouped obstructions, but NFPA 13 does not provide specific guidance. The committee did address a comment for grouped obstructions during the 2009 Report on Comments in 13-119 Log #234 with an action of Reject. The submitter proposed a new section 8.5.5.3.3.4 that stated, Grouped Obstructions. Closely spaced obstructions shall be considered a single obstruction when the space between individual obstructions is smaller than the width of the smaller adjacent obstruction. A.8.5.5.3.3.4 When there are more than two adjacent obstructions, the width of the grouped obstruction is intended to include any additional obstructions that do not meet the separation requirement. The committee rejected this proposal since insufficient material to inform a Committee Action on this item. This leaves us with the existing obstruction rules in NFPA 13. With that said, standard spray sprinklers are fairly tolerant of obstructions. The sprinklers have the ability to get water on both sides of the obstruction without allowing a significant dry shadow on the other side of the obstruction. This works for continuous and isolated obstructions where the sprinkler can throw water over and under the obstruction. This keeps the upper layer gases in the room cool, thus preventing flashover and controlling the fire. Additional factors to consider are the building construction and occupancy classification of the space: 1.The ceiling or roof deck is of noncombustible construction, and that is very tolerant of fire exposure. 2.The area where the wood-slatted ceilings are placed is a lobby and or a corridor (light hazard occupancy). 3.The quantity and/or combustibility of contents are low, and fires with relatively low rates of heat release are expected.
