Sidewall sprinkler in a hotel

Charts and code from NFPA help installers and facilities managers determine the distance required between fire sprinkler heads and objects

How much distance do fire sprinkler heads need from obstructions, whether permanent or temporary? It’s a concern with big impacts for every sprinklered building. Failing to place the proper distance between sprinklers and obstructions can stop the fire sprinkler from discharging on time—or will prevent sprinklers’ spray from reaching a fire or wetting materials that will burn.

In part two of our series on distances for fire sprinklers, we look at some of these sprinkler head obstruction distance rules for standard spray sprinklers—a common sprinkler type that uses different rates of discharge to defend against a wide range of hazards. We provide an overview of what the NFPA requires for obstructions—both permanent and temporary—and take a closer look at some fundamental rules on the subject:

This blog does not cover distances between sprinklers and walls (or between sprinklers)—for those, read Maximum and Minimum Sprinkler Distance Rules, Part 1: Standard Spray Fire Sprinklers.

If you’re in the process of installing or replacing sprinklers, we invite you to look at our selection of commercial fire sprinklers, including standard spray models, from industry-leading manufacturers like Senju, Victaulic, Tyco, and Reliable (RASCO).

Fire sprinkler head obstructions are covered in NFPA 13 and NFPA 25

What is an obstruction? NFPA 13: Standard for the Installation of Sprinkler Systems defines two types:

From the 2019 edition of NFPA 13

3.3.133 Obstruction.

3.3.133.1 Continuous Obstruction. An obstruction located at or below the level of sprinkler deflectors that affects the discharge pattern of two or more adjacent sprinklers.

3.3.133.2 Noncontinuous Obstruction. An obstruction at or below the level of the sprinkler deflector that affects the discharge pattern of a single sprinkler.

The NFPA 13 Handbook notes that these terms emerged to help installers better understand the NFPA’s intent regarding the placement and spacing of sprinklers. These definitions make it clear that it’s the impact on sprinklers, and not the design of the obstruction itself, that matters.

NFPA 13 deals largely with permanent obstructions—construction features that threaten to disrupt sprinklers’ spray patterns. But for those tasked with the ongoing care of fire sprinkler systems, there’s the matter of distances from temporary obstructions. We’ve taken a look at these in our multi-part series on what facility managers need to inspect on a fire sprinkler system.

In a nutshell, NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems says that objects that can block a sprinkler’s spray must be at least 18 inches away from the deflector. (That’s the small metal part at the sprinkler’s forward edge.) There is an exception, however: In-rack sprinklers that are specifically designed for storage racks don’t observe this minimum requirement.

Boxes too close to fire sprinklers

These boxes should be at least 18 inches away from the deflector. Source: City of Montgomery, Ohio

And in a few cases, 18 inches from obstructions isn’t enough. Sprinklers designed for specific hazards or features (special sprinklers) require three feet of clearance, as do those covering stored rubber tires. Further, state and local fire codes may override these sprinkler head obstruction distance rules and require greater clearance between sprinkler heads and storage.

All standard spray fire sprinklers must reduce risks from a variety of objects

While NFPA 13 addresses the subject of obstructions largely by sprinkler type, all standard spray sprinklers share a few common provisions presented in chapter nine.

Sprinklers must minimize obstructions to discharge in accordance with 9.5.5.2 and 9.5.5.3 or additional sprinklers must be added to provide adequate coverage (section 9.5.5.1). Further, if an obstruction is no more than 18 inches under deflectors—and if it prevents the sprinkler’s pattern from developing—nearby sprinklers must follow the minimum distance guidelines in chapter 10 (9.5.5.2)

If the obstruction is more than 18 inches below the deflector—and interrupts that discharge in a horizontal plane—it must comply with the guidelines of section 9.5.5.3, which addresses:

  • Sprinklers under obstructions. Obstructions over four feet wide, including open-grate flooring, require sprinklers underneath (9.5.5.3.1 and 9.5.5.3.1.1). However, grate sprinklers must be protected against discharge from other sprinklers (9.5.5.3.4). Sprinklers below an obstruction must have their deflectors placed directly under it or within 3 inches (horizontally) of the obstruction’s outside edge, and may be anywhere from 1 to 12 inches below it (9.5.5.3.1.2 and 9.5.5.3.1.4).
  • Noncombustible material. If the obstruction won’t burn, and its base is no more than two feet above the floor, sprinklers aren’t needed underneath (9.5.5.3.1.5).
  • Temporary obstructions. Section 9.5.5.3.2 states that large conference tables and other objects that aren’t fixed in place don’t need sprinklers beneath them.
  • One sprinkler at the highest ceiling level may serve a closet or compartment at or under 400 cubic feet in size—regardless of obstructions (9.5.5.4)
  • Sprinkler types. Excluding overhead doors—which may have standard spray sprinklers underneath them—sprinklers below obstructions must be of the same type as those installed at the ceiling (9.5.5.3.3 and 9.5.5.3.3.1).
Catwalk grating in a theatre

Grated floors like the ones found in theater catwalks may require fire sprinklers below them. Source: InCord

NFPA charts prescribe distances from obstructions to pendent or upright sprinklers

Each sprinkler must be positioned to minimize obstructions that prevent it from activating on time. Section 10.2.1.2 of NFPA 13 provides a few ways for pendent and upright sprinklers to comply with this requirement:

  • Place the sprinkler in accordance with table 10.2.7.1.2 (shown below).
  • For obstructions under four feet wide, installers may place sprinklers on opposite sides of the obstruction (so long as the distance between each sprinkler and the obstruction’s centerline doesn’t exceed half the distance allowed between sprinklers—see part 1 in this series).
  • If a soffit or similar obstruction against a wall is no more than 30 inches wide, the sprinkler’s deflector may be positioned in compliance with Table 10.2.7.1.2. If it’s less than 24 inches wide, the deflector may be as high above the bottom of the obstruction as the installer wants—provided that it remains sufficiently close to the wall (again, see our previous blog to determine that distance).

Most of these rules refer to table 10.2.7.1.2. This table determines an appropriate distance between the sprinkler’s deflector and the bottom of an obstruction. As the distance from the fire sprinkler head to the obstruction’s side increases, so does the permissible vertical distance. Note also that the distance between the deflector and the side of the obstruction is measured from the deflector’s center.

NFPA obstruction chart 1

The letters “A” and “B” in the table below refer to dimensions shown in these illustrations from NFPA 13. Click here or on the above image for a larger version.

From the 2019 edition of NFPA 13

TABLE 10.2.7.1.2 Positioning of Sprinklers to Avoid Obstructions to Discharge [Standard Spray Upright/Standard Spray Pendent (SSU/SSP)]
Distance from Sprinklers to Side of Obstruction (A) Maximum Allowable Distance of Deflector Above Bottom of Obstruction (B) [in. (mm)]
Less than 1 ft (300 mm) 0 (0)
1 ft (300 mm) to less than 1 ft 6 in. (450 mm) 2 1/2 (65)
1 ft 6 in. (450 mm) to less than 2 ft (600 mm) 3 1/2 (90)
2 ft (600 mm) to less than 2 ft 6 in. (750 mm) 5 1/2 (140)
2 ft 6 (750 mm) in. to less than 3 ft (900 mm) 7 1/2 (190)
3 ft (900 mm) to less than 3 ft 6 in. (1.1 m) 9 1/2 (240)
3 ft 6 in. (1.1 m) to less than 4 ft (1.2 m) 12 (300)
4 ft (1.2 m) to less than 4 ft 6 in. (1.4 m) 14 (350)
4 ft 6 in. (1.4 m) to less than 5 ft (1.5 m) 16 1/2 (415)
5 ft (1.5 m) to less than 5 ft 6 in. (1.7 m) 18 (450)
5 ft 6 in. (1.7 m) to less than 6 ft (1.8 m) 20 (500)
6 ft (1.8 m) to less than 6 ft 6 in. (2.0 m) 24 (600)
6 ft 6 in. (2.0 m) to less than 7 ft (2.1 m) 30 (750)
7 ft (2.1 m) to less than 7 ft 6 in. (2.3 m) 35 (875)

Sprinkler head obstruction distances on an opposite, adjacent, or the same wall as a sidewall sprinkler are slightly different

Standard spray sidewall sprinklers are especially sensitive to obstructions. As the NFPA 25 Handbook notes, these sprinklers are designed for unobstructed construction. While some obstructions are unavoidable, nearby light fixtures and beams that can be accounted for can prevent proper coverage.

A sidewall sprinkler can’t be installed less than four feet from an obstruction unless:

  • The greatest dimension of the obstruction is less than two feet. In that instance, the sprinkler must be at least three times that dimension away from the obstruction. For example, a sidewall sprinkler requires 4 feet of distance from an obstruction that has a maximum dimension of 16 inches (10.3.6.1.1 through 10.3.6.1.2.1).
  • The bottom of the fixture is above the plane of the sprinkler’s deflector (10.3.6.1.2.2).
  • The obstruction projects from the wall where the sprinkler is mounted (10.3.6.1.4). These isolated obstructions must be located at least 4 inches from sidewall heads (10.3.6.1.4.1).

Installers may also place sidewall sprinklers on each side of an obstruction under four feet wide (10.3.6.1.5). But like pendent and upright sprinklers, the distance between sidewall heads and the obstruction’s centerline can’t exceed half the distance allowed between sprinklers (read more here). Additionally, when a sidewall head and the obstruction are on opposite walls, that obstruction may be as large as two feet deep and two feet wide (10.3.6.1.6).

NFPA 13 provides the required distances from standard spray sidewall sprinklers in tables 10.3.6.1.3 and 10.3.6.1.4. The first table provides the required distances for sidewall sprinklers located four feet or more from an obstruction. The second table addresses obstructions that share a wall with a sidewall sprinkler. In both instances, the distance between the deflector and the bottom of the obstruction is measured from the deflector’s center in a vertical line. The distance from the sprinkler to the side of the obstruction is measured in a horizontal line from the obstruction to the center of the sprinkler’s deflector.

NFPA obstruction chart sidewall sprinklers

The letters “A” and “B” in these images correspond with distances provided in two tables. The image on the right addresses obstructions on a wall shared with the sprinkler, while the left-hand image depicts a sprinkler and an obstruction on adjacent walls. Click here or on the above image for a larger version. Source: NFPA 13

 

Distances between sidewall heads and obstructions on adjacent walls (NFPA 13, 2019 edition)

 

TABLE 10.3.6.1.3 Positioning of Sprinklers to Avoid Obstructions (Standard Sidewall Spray Sprinklers)
Distance from Sidewall Sprinkler to Side of Obstruction (A) Maximum Allowable Distance of Deflector Above Bottom of Obstruction (B) [in. (mm)]
4 ft (1.2 m) to less than 5 ft (1.5 m) 1 (25)
5 ft (1.5 m) to less than 5 ft 6 in. (1.7 m) 2 (50)
5 ft 6 in. (1.7 m) to less than 6 ft (1.8 m) 3 (75)
6 ft (1.8 m) to less than 6 ft 6 in. (2.0 m) 4 (100)
6 ft 6 in. (2.0 m) to less than 7 ft (2.1 m) 6 (150)
7 ft (2.1 m) to less than 7 ft 6 in. (2.3 m) 7 (175)
7 ft 6 in. (2.3 m) to less than 8 ft (2.4 m) 9 (225)
8 ft (2.4 m) to less than 8 ft 6 in. (2.6 m) 11 (275)
8 ft 6 in. (2.6 m) or greater 14 (350)

 

Distances for sidewall sprinklers sharing a wall with an obstruction (NFPA 13, 2019 edition)

 

TABLE 10.3.6.1.4 Positioning of Sprinklers to Avoid Obstructions Along Wall (Standard Sidewall Spray Sprinklers)
Distance from Sidewall Sprinkler to Side of Obstruction (A) Maximum Allowable Distance of Deflector Above Bottom of Obstruction (B) [in. (mm)]
4 in. (100 mm) to less than 6 in. (150 mm) 1 (25)
6 in. (150 mm) to less than 1 ft (300 mm) 2 (50)
1 ft (300 mm) to less than 1 ft 6 in. (450 mm) 3 (75)
1 ft 6 in. (450 mm) to less than 2 ft (600 mm) 4 1/2 (115)
2 ft (600 mm) to less than 2 ft 6 in. (750 mm) 5 3/4 (145)
2 ft 6 in. (750 mm) to less than 3 ft (900 mm) 7 (175)
3 ft (900 mm) to less than 3 ft 6 in. (1.1 m) 8 (200)
3 ft 6 in. (1.1 m) to less than 4 ft (1.2 m) 9 1/4 (230)
4 ft (1.2 m) to less than 4 ft 6 in. (1.4 m) 10 (250)
4 ft 6 in. (1.4 m) to less than 5 ft (1.5 m) 11 1/2 (290)
5 ft (1.5 m) to less than 5 ft 6 in. (1.7 m) 12 3/4 (320)
5 ft 6 in. (1.7 m) to less than 6 ft (1.8 m) 14 (350)
6 ft (1.8 m) to less than 6 ft 6 in. (2.0 m) 15 (375)
6 ft 6 in. (2.0 m) to less than 7 ft (2.2 m) 16 1/4 (410)
7 ft (2.2 m) to less than 7 ft 6 in. (2.3 m) 17 1/2 (440)

We’ve just scratched the surface of NFPA 13’s sprinkler head obstruction distance rules

This concludes part two of our look at NFPA 13's rules regarding distances for sprinkler heads. We’ve covered the core sprinkler head obstruction distance rules for standard spray heads—and while they’re the most common type, they’re just one of several addressed by the standard. For more, check out part 1 in our series on distances for standard spray sprinklers, and stay tuned for our next entry in the series.

This article is just one small part of QRFS’s effort to help contractors, consumers, and fire safety professionals stay in compliance with standards and codes. If you’re on the hunt for new or replacement fire sprinklers, take a look at QRFS’s selection of commercial fire sprinkler heads. Our sidewall, pendent, and upright heads are available in temperatures ranging from 155 degrees to 286 degrees Fahrenheit, with a variety of finishes and cover plates to match buildings of all kinds.

Tyco sidewall sprinkler

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