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Residential-style sprinklers are specifically designed & tested for their response and ability to "enhance survivability" in the room of fire origin. [NFPA 13 2002-07 126.96.36.199, 2010-13 188.8.131.52, 2016 184.108.40.206]
What makes them so attractive to use in residential occupancies?
Specifically Designed Spray Pattern
First, their spray pattern is specifically suited to residential hazards. Unlike light hazard office spaces, dining areas of restaurants, meeting rooms or lobbies, residential rooms regularly contain much of the fire hazard along the perimeter of the room. This hazard often presents itself as bookshelves, cabinetry, curtains, furniture, and an assortment of other potential fuel sources.
Unlike standard-spray fire sprinklers, residential-style sprinklers throw more water to where it's needed-along and up the edges of a room.
Residential-style sprinklers are specifically designed to throw along the outer boundaries of rooms, which better aligns with locations of typical residential hazards. Sprinkler throw data above is of the Victaulic V2738 residential sprinkler.
Residential-style sprinklers are also fast to respond, with the intent to fight the fire earlier in its incipient stages.
While light hazard areas are already required to use one of several specific sprinkler responses, including the option for quick-response sprinklers (NFPA 13 2002-16 220.127.116.11), residential-style sprinklers are still considered 'fast-response'.
The term Fast-Response is defined as a sprinkler with an RTI (Response Time Index) of 50 √m-s or less. It incorporates three specific styles of sprinklers - "Residential Sprinklers", "Quick Response Sprinklers" (including standard and extended coverage), and "Early Suppression Fast Response (ESFR)." Each of these sprinklers qualify as Fast Response, but they are not interchangeable. [Viking Technical Article by Scott Martorano, July 2006]
Based on the ability to better fight a residential fire, the use of residential style sprinklers has a hydraulic kickback that dramatically helps the hydraulic calculations for a residential area.
As residential sprinklers are not quick response sprinklers, the remote area reduction for the use of quick-response sprinklers does not apply.
However, NFPA 13 and NFPA 13R only require that the most hydraulically demanding four adjacent sprinklers be calculated, while NFPA 13D only requires the most hydraulically demanding two adjacent sprinklers be calculated. [NFPA 13 2002 18.104.22.168.1, 2007-16 22.214.171.124, NFPA 13R 2002 126.96.36.199, 2007 188.8.131.52, 2010-19 184.108.40.206, NFPA 13D 2002-10 8.1.2, 2013-19 10.2]
Additionally, NFPA 13R and NFPA 13D permit the design density to be as low as 0.05 gpm/sqft or the listed density of the sprinkler. [NFPA 13R 2002 220.127.116.11.2.2, 2007 18.104.22.168.1.2, 2010-19 7.1.1, NFPA 13D 2002-10 8.1.1, 2013-19 10.1.1]
These reductions can significantly reduce the flow for a remote area, resulting in less friction loss and ultimately a smaller system demand, even with smaller pipe sizes.
It's important to note that due to the different spray pattern, residential sprinklers have their own obstruction rules which differ from standard spray. Try out the Obstruction Calculator with residential-style sprinklers to see the difference.
Where Can Residential Sprinklers Be Used?
Residential style sprinklers are permitted in "dwelling units and their adjoining corridors, provided they are installed in conformance with their listing." [NFPA 13 2002-16 22.214.171.124]. Their limited to wet pipe systems unless listed for use in dry or pre-action, but this is often not a major inhibitor.
Residential sprinklers are allowed to be used in wet systems within dwelling units and their adjoining corridors.
Also of note is new verbiage in the 2013 edition of NFPA 13 annex which includes that "Residential sprinklers can only be used in corridors that lead to dwelling units. However, the corridors that lead to dwelling units can also lead to other hazards that are not dwelling units and can still be protected with residential sprinklers" [NFPA 13 2013-16 A.126.96.36.199].
This verbiage was included to clarify that just because other hazards might be adjacent to these same corridors does not mean residential style sprinklers cannot be used.
Residential sprinklers differ from standard spray in their response categorization and their water distribution. Both of these elements align with residential hazards, and their use offers some positive kickbacks to designers looking to use them in and around residential areas in buildings.
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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 188.8.131.52.3, 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.