SIDEWALLS: THE “SUPERHUMAN” SPRINKLER HEAD?
BY GLENN P. CORBETT, P.E.
I`m always amazed at the new ways sidewall sprinklers are being used in the built environment–“superhuman” heads pointed in all directions, positioned behind obstructions, or installed under a variety of complicated ceiling types. Even more remarkable, many installers have found that these sprinklers, when used along with “smart water,” can perform amazing feats–even defying the laws of nature! Smart water, of course, is found only in certain areas of the country, but what a treasure! Water that can defy gravity and fly around corners and obstructions engenders envy in fire inspectors working in jurisdictions with just plain water.
Of course, my satirical look at sidewall sprinklers and smart water is just that–satire. Unfortunately, the reality is that many sidewall sprinklers are being installed–and in many situations are being asked to perform beyond their capabilities.
Before we look at their installation, let`s define the sidewall sprinkler. According to NFPA 13, Standard for Installation of Sprinkler Systems–1994, sidewall sprinklers are “sprinklers having special deflectors that are designed to discharge most of their water away from the nearby wall in a pattern resembling one quarter of a sphere, with a small portion of the discharge directed at the wall behind the sprinkler.”
Sidewalls may be one of three types–horizontal, pendent, or upright. Pendent and upright sidewalls look like their “normal” standard sprinkler counterparts except their deflectors have been “bent” to direct the discharge spray. Horizontal sidewalls are the most common.
Let`s take a look at listing laboratory (such as Underwriters Laboratories) testing criteria to gain a better understanding of the sidewall`s capabilities. They are tested in an environment using a flat ceiling and wall–not a “complex” ceiling/wall arrangement. If desired, manufacturers may include “obstructions,” such as beams, in the testing. NFPA 13 contains installation criteria concerning sidewalls and such obstructions, stating that these heads may be no closer than four feet to a beam or similar obstruction and must meet spray “clearance” criteria for those beams/obstructions over four feet away.
Also important is the placement of the sidewall near the juncture of the wall and ceiling. “Vertical” sidewalls (upright and pendent) cannot be placed in the “dead space” at the corner where the wall and ceiling meet–the dead space being four inches down from the ceiling and four inches out from the wall (this is the same dead space encountered for smoke detectors). Vertical sidewall deflectors also must be placed no more than six inches below a ceiling.
Horizontal sidewalls are given more leeway. Their deflectors may be closer than four inches from the wall on which they are located, and they may be placed as much as 12 inches below a noncombustible ceiling when they are listed for such a purpose.
Another fact concerning listing of sidewalls is the occupancy type in which they can be used. Unless specifically listed for use in ordinary hazard occupancies, sidewalls are restricted to use in light-hazard occupancies only (they are not listed for extra-hazard occupancies). Some sidewalls are listed for residential use–but not all of them.
Another important criterion for sidewalls is the need for a wall, draftstop, lintel, and so on “behind” the head to “collect” the heat and allow the head to operate promptly. In fact, NFPA 13 requires this “wall” to be a minimum of two inches greater than the distance from the ceiling to the deflector.
This lack of a wall is a common error found in the field. You may from time to time encounter heads “out in space” with nothing behind them (except for another sidewall pointed in the other direction!).
Another problem is the lack of a ceiling in some installations. The heads need a ceiling above them to collect heat–they won`t activate quickly (if at all) without the ceiling. I once encountered a large rotunda in a savings bank with a ring of sidewalls at the base of the rotunda with no way to collect heat at the heads. I doubt whether they ever would have activated in an actual fire.
Sloping ceilings are problematic. If used with such a ceiling, the heads must be placed at the top of the slope, pointed down, with the deflector parallel to the slope.
How much area can these heads cover? It depends on the occupancy and ceiling type. Basically, in light-hazard occupancies the coverage for “normal” (not extended coverage) sidewalls is 120 square feet for structures with combustible “sheathing,” 168 square feet per head for combustible construction (structural members) with noncombustible/limited combustible sheathing, and 196 square feet for noncombustible construction and noncombustible/limited combustible sheathing.
If listed by a testing laboratory for ordinary hazard, these normal sidewalls can be used to cover up to 80 square feet per head for compartments with combustible sheathing and 100 square feet for compartments with noncombustible or limited combustible sheathing.
The spacing between heads along a wall is 14 feet for light-hazard occupancies, 10 feet for ordinary-hazard occupancies.
In terms of maximum room width for a single row of “normal” (nonextended coverage) sidewall sprinklers, NFPA 13 sets a maximum room width of 12 feet for light-hazard occupancies with combustible sheathing or combustible construction and 14 feet for noncombustible construction with limited combustible/noncombustible sheathing. The maximum room width for a single row of sidewall heads in an ordinary-hazard occupancy (where listed) is 10 feet.
When the maximum room width must be exceeded, NFPA 13 allows the room width to increase to 30 feet for light-hazard occupancies and 20 feet for ordinary-hazard occupancies when two sets of sidewalls (on each side) are used. In this case, the heads must be staggered across the room.
How about the extended-coverage sidewalls that are loved by the hotel industry? Hoteliers like them because they can protect large bedroom areas while “hiding” the head and sprinkler piping in soffits at the perimeter of the room. Speaking of soffits, when a soffit exceeds eight inches in width, it must have additional heads for coverage below. This is often forgotten.
Extended-coverage heads can handle larger areas (approaching 400 square feet per head) and “throw” water farther. The coverage area and throw permitted is head specific–you must verify the actual coverage/throw by reading the technical data sheet prepared by the manufacturer. Use of these heads with sloped ceilings is also limited, typically to a maximum of two inches in 12 inches.
In addition, these extended coverage heads require tremendous pressure for the corresponding water “flow and throw.” (I once had a six-story hotel that used extended coverage sidewalls in conjunction with small branch lines that needed the building`s fire pump to properly supply the heads–even heads on the first floor–with nearly 100 psi residual pressure in the street!) Again, the technical data sheets must be consulted to determine the proper operating flows and pressures.
When conducting inspections of sidewall heads, come prepared by having reviewed the technical data sheet ahead of time–know the head`s limitations and listing caveats.
Specifically, look for the following:
obstructions that may block the sprinkler`s spray (including drapes, walls, etc.),
proper orientation/positioning of the head,
proper hanger support for the branch piping attached directly to the head (when the head activates, the head will be thrust backward toward the wall–don`t depend on the escutcheon to hold the head in place), and
misplaced wallpaper glue on the head (which has been found in some hotel renovation projects) that can prevent the head from operating. n
GLENN P. CORBETT, P.E., is a professor of fire science at John Jay College in New York City, a technical editor of Fire Engineering, and a firefighter with the Waldwick (NJ) Fire Department. He previously held the position of administrator of engineering services with the San Antonio (TX) Fire Department. Corbett has a master of engineering degree in fire protection engineering from Worcester Polytechnic Institute in Massachusetts. He authored two chapters on fire prevention/protection in The Fire Chief`s Handbook, Fifth Edition (Fire Engineering Books, 1995). Corbett has been in the fire service since 1978.