If you work with sprinkler systems & review layouts, you've undoubtedly encountered sprinklers near ceiling fans. Today I'm taking a look at some of the requirements for sprinklers near fans, and the basis for those requirements.
Traditional Ceiling Fans
The chief concern with a typical residential-style ceiling fan is that the fan motor housing and fan blades could form an obstruction to proper sprinkler discharge.
Motor Housing Obstruction
NFPA 13 addresses the discharge from the motor housing by the Three Times Rule, where the sprinkler must be located three-times the width of the obstruction up to 24 inches (610 mm).
Fan Blade Obstruction
In terms of obstruction from the fan blades, NFPA 13 also allows sprinklers to be placed "without regard" to the blades of ceiling fans less than 60 inches (1.5 m) in diameter as long as the plan view is at least 50 percent open (NFPA 13 2010-19 under "Obstructions to Sprinkler Discharge Pattern Development" subsections in Chapter 8).
NFPA 13R 3 and 5-foot Rules
NFPA 13R takes a more straightforward requirement for positioning of sprinklers near ceiling fans - residential pendent sprinklers must be 3-feet and residential sidewalls must be 5-feet unless another sprinkler is positioned on the adjacent side, or, the sprinkler is positioned so that the fan is not considered an obstruction (NFPA 13R 2007 126.96.36.199.3, 2010-19 6.4.6).
Residential style sprinklers are impacted by ceiling-mounted obstructions, such as lights and fans, to a greater degree than obstructions down from the ceiling since residential sprinklers throw with more high-wall wetting
NFPA 13R Research Basis
The NFPA 13R guidance was driven by fire modeling, sprinkler response tests, distribution tests, and full-scale fire tests by the National Fire Sprinkler Association and the Viking Corporation in 2005 (Valentine and Isman, Interaction of Residential Sprinklers, Ceiling Fans and Similar Obstructions). These tests indicated that the fan blades where not significant obstructions as long as the sprinkler was far enough away from the motor housing, allowing the sprinkler to control a fire on the other side of the fan in a small room.
These tests also indicated that fans on low to medium speed did not significantly impact sprinkler performance, but high speed did. Despite the effect, the fire was still controlled in small rooms. Larger rooms, due to the size, would be expected to require additional sprinklers (NFPA 13R 2007 Annex).
High Volume Low Speed Fans (HVLS)
Fans moving larger volumes of air can have a significant impact on plume development and fire sprinkler response.
In 2009, a research project sponsored by the Property Insurance Research Group (PIRG) and other industry groups, coordinated by the Fire Protection Research Foundation (FPRF) ran a series of 10 full-scale fire test and limited scale testing to evaluate the impact on sprinkler system performance.
In 2011, a second phase was conducted by Factory Mutual Research Corporation.
Recommendations from Research
Based on the tests, effective sprinkler operation was obtained when the HVLS fans did not obstruct sprinkler discharge and were shut down upon the activation of the first sprinkler.
The research also included shutdown by air-sampling type detection and use of ionization type smoke detectors, with earlier fan shutdown resulting in less commodity damage. FM Global's recommendations even extend into smoke detection devices or heat detection devices as an acceptable means to conduct the fan shutdown (provided uniformly above the fan blade area, per Data Sheet 548).
Due to size and large air movement, High Volume Low Speed Fans (such as Big Ass fans) impact sprinkler discharge as both a potential obstruction and as a large air mover
NPFA 13 Requirements for HVLS Fans
NFPA 13 defines high volume low speed fans as ceiling fans approximately 6 feet (1.8 m) to 24 feet (7.3 m) in diameter, with a rotational speed of approximately 30 to 70 revolutions per minute (NFPA 13 2013-16 Section 3.3.14).
Beginning with the 2013 Edition of NFPA 13, NFPA 13 has required four principal items concerning these large fans (NFPA 13 2013-16 Section 11.1.7 and 12.1.4 for storage):
(1) The maximum fan diameter must be 24 feet (7.3 m)
(2) HVLS fans be centered approximately between four adjacent sprinklers
(3) The vertical clearance from the fan to the nearest sprinkler deflector must be a minimum of 3 feet (0.9 m)
(4) HVLS fans must shutdown (via interlock) immediately upon receiving a waterflow signal in accordance with NFPA 72.
While NFPA 13 suggests centering the fan between four sprinklers - trying to convince an architect or mechanical engineer to shift their equipment based on the sprinkler system can be difficult to do. I've had better success designing the sprinkler locations around the fan location.
Since sprinklers are designed to be sensitive to air temperature and movement, ceiling fans can impact performance. With small ceiling fans, the biggest concern is obstructing sprinkler discharge, while for larger HVLS fans this chief concern moves towards the movement of air and impacting the response. Fortunately, research-backed recommendations have been provided to still allow effective fire sprinkler protection alongside ceiling fans.
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.