|Technical Hot Topics|
Following are questions answered by the engineering staff as part of the NFSA's Expert of the Day (EOD) member assistance program being brought forward as the "Best of August 2016."
It should be noted that the following are the opinions of the NFSA Engineering Department staff, generated as members of the relevant NFPA technical committees and through our general experience in writing and interpreting codes and standards. They have not been processed as formal interpretations in accordance with the NFPA Regulations Governing Committee Projects and should therefore not be considered, nor relied upon, as the official positions of the NFPA or its Committees. Unless otherwise noted the most recent published edition of the standard referenced was used.
Question 1 – Larger Orifice Sprinklers in Light Hazard Occupancies
A building contains a light hazard occupancy. Can ¾-inch fire sprinklers be used when protecting the building in accordance with NFPA?
Answer: Yes. First, NFPA 13 references sprinkler size by the nominal K-factor. Based on the NPT for the sprinklers in Table 18.104.22.168, this question refers to sprinklers with a K-factor of 8.0 and larger. NFPA 13 does not prohibit sprinklers with K-factors larger than 5.6 in light hazard occupancies. NFPA 13 does regulate the use of sprinkler with small K-Factors, those less than K-5.6 (see section 8.3.4), but does not prohibit the use of larger K-factor sprinklers in light hazard occupancies. In fact, there are many sprinklers that are listed for light hazard that have larger K-factors such as K-8. Section 22.214.171.124 even has an allowance for ESFR sprinklers to be permitted to protect light or ordinary hazard spaces and ESFR sprinklers are all larger K-factor orifices. What is important is that for a sprinkler to be used in a light hazard occupancy, it must be a quick response type sprinkler (see section 8.3.3).
Question 2 – Distance from a Ceiling Fan Obstruction
A ceiling fan is being installed with a dwelling unit of a building that is being protected in accordance with NFPA 13R. It was indicated that the ceiling fan in question will be suspended on a rod. Does the 3 ft distance from the center of the ceiling fan to the residential pendent sprinkler need to be maintained?
Answer: No. The 3 ft measurement was a decision of the technical committee based on practical installation conditions and common fan models that are installed tight to the ceiling. The distance is measured from the center of the fan since often the exact fan is frequently not known when the fire sprinkler system is being installed (or planned). The main obstruction created by a ceiling fan is the motor housing unit. If the motor housing unit is suspended via a rod, then the obstruction to the development of the fire sprinkler spray pattern is reduced. The rod and escutcheon would be considered noncontinuous obstructions. NFPA 13R does not offer much guidance on this type of obstruction.
As NFPA 13R provides minimal guidance on these types of obstructions, it would be wise to keep some distance between the ceiling fan support rod and its escutcheon. However, the length of the rod will alter how much of an impact the obstruction has on the sprinkler. Where the support rod is long, more than 18 inches, only a small amount of space would be necessary assuming the rod is a minimal diameter, such as an inch or so. If the support positions the fan only a few inches below the ceiling, then more distance will be needed so that the sprinkler spray pattern could develop. As always, it is important to discuss this issue with the authority having jurisdiction so that stakeholders agree on the appropriate distance to maintain since NFPA 13R does not specifically address this type of ceiling fan arrangement.
Question 3 – CMSA Hydraulically Remote Area
This scenario uses CMSA sprinkler protection criteria for Group A plastics on single- and multiple-row racks. The storage is up to 20 feet in a building with a maximum ceiling height of 25 feet. K-16.8 upright sprinklers have been selected to protect the arrangement. The design area includes the 15 most hydraulically remote sprinklers. Can the remote area rectangle can be based on the design area of the 15 sprinklers spaced at their maximum allowable coverage area of 100 square feet?
Answer: Yes. Following the guidance in NFPA 13 for K-16.8 CMSA wet sprinklers with a minimum operating pressure of 22 psi, 15 sprinklers need to be included in the remote area. It is acceptable to determine this design area based on the maximum spacing of these sprinklers when determining what the size of the design area would be. Assuming a maximum spacing of 100 square feet per sprinkler, the design area would appropriately be 1,500 square feet. This was further clarified in the 2016 edition of NFPA 13 under section 126.96.36.199.1 as follows:
188.8.131.52.1 For CMSA sprinklers, the design area shall be the rectangular area having a dimension parallel to the branch lines at least 1.2 times the square root of the area protected by the number of sprinklers to be included in the design area. The design area protected by the number of sprinklers to be used by the 1.2 rule shall be based on the maximum allowable area per sprinkler.