Not every space in a structure is required to be protected by sprinklers—and NFPA 13 is very clear on what those spaces need to remain unprotected.
NFPA Journal®,November/December 2011
By Matt Klaus
Everyone wants to save money, builders and building owners included. One way they can do that is to omit sprinklers from areas where the codes say it’s okay to leave them out. But it’s important to know precisely what those areas are.
Automatic sprinkler systems installed in accordance withNFPA 13, Installation of Sprinkler Systems, are intended to serve two functions: property protection and life safety. In order for the systems to achieve these goals, the general rule is to provide sprinklers to protect all spaces within a building. However, there are several spaces in which sprinklers are not required, as their installation may not be practical based on building geometry. Similarly, there are other spaces where sprinklers can be omitted where the potential for ignition and fire development are not a great cause for concern.
The majority of the spaces from which sprinklers can be omitted from NFPA 13 designs center around the concept of concealed spaces. Concealed spaces are non-occupied spaces that are created by building construction. These spaces may contain piping and wiring for various building systems, or, in many cases, may be void of any and all combustible material. The starting point for all designers, installers, and enforcers who are trying to determine if sprinklers are required in a specific concealed space is that concealed spaces should be sprinklered unless Section 8.15.1 of the 2010 edition of NFPA 13 provides alternate direction.
One of the distinctions this section makes is the type of construction that is used to form the concealed space. Concealed spaces that are constructed of noncombustible or limited combustible material are not required to be protected with automatic sprinklers, provided there is minimal combustible loading and no access to the space. The presence of combustible loading increases the potential for fire growth within the space and would therefore necessitate sprinkler protection. Where access is provided to these spaces, it is common for building occupants to use them for storage, creating a fuel load that would otherwise not be present in the noncombustible space.
Where access to noncombustible or limited combustible concealed spaces is provided, sprinkler protection can be omitted, provided the space is not used for occupancy or storage of combustibles. Often, access panels into noncombustible concealed spaces are present so that maintenance can be performed on building equipment. In these instances, the presence of the access hatch is not intended to trigger a requirement for sprinklers in an otherwise noncombustible space where no goods are being stored.
Noncombustible concealed space without sprinklers
Where combustible concealed spaces are formed, there is a greater concern for fire growth in the cavity. There are, however, certain combustible concealed spaces from which sprinklers can be omitted. Due to the impracticability of installation, sprinklers can be omitted in concealed spaces formed by studs or joists with less than 6 inches (15 centimeters) between the inside edges. Similarly, concealed spaces formed by ceilings that are attached directly to, or within 6 inches (15 centimeters) of, wood joists do not require sprinkler protection.
Combustible concealed spaces formed where ceilings are attached directly to the underside of composite wood joists or onto metal channels no deeper than 1 inch (2.5 centimeters) do not require sprinkler protection where the joist channels are fire stopped at intervals of not more than 160 cubic feet (4.5 cubic meters) and where at least 3.5 inches (8.8 centimeters) of that installation is installed at the bottom of the joist channels. Where wood joist or composite wood joist construction is used in ceilings not attached directly to the joist, sprinklers can be omitted where insulation is used to fill the void from the ceiling to the bottom of the joist and where the joist channels are fire stopped at intervals not exceeding 160 cubic feet (4.5 cubic meters) to the full depth of the joist.
Other combustible concealed spaces from which sprinkler protection can be omitted include spaces that are filled entirely with noncombustible insulation and spaces where the exposed materials are constructed entirely of fire-retardant-treated wood.
It is important to note that where sprinklers are omitted from combustible concealed spaces there may be an impact on the hydraulic design of the system. Often, where buildings have unsprinklered combustible concealed spaces, the minimum design area that must be considered for that portion of the building is 3,000 square feet (279 square meters) or twice what is typically expected for light and ordinary hazard spaces. For more information on when the 3,000-square-foot (279-square-meter) design area comes into play for combustible concealed spaces, refer to Section 188.8.131.52.4 in the 2010 edition of NFPA 13.
Inside + Outside
Sprinkler omissions are not limited to combustible concealed spaces. Stair shafts of noncombustible construction are permitted to have sprinkler protection only at the top of the shaft and underneath the first access landing above the bottom of the shaft.
Other spaces that may remain unsprinklered include spaces beneath ground floors, exterior decks, and platforms. Sprinklers can be omitted from these spaces provided they are not accessible for storage, contain no equipment such as conveyors or fuel-fired heating units, the floor above is not used for handling or storing combustible or flammable liquids, and the floor construction is tight.
Sprinklers can be omitted from several exterior spaces as well. Canopies, balconies, decks, roofs, and porte cocheres that are constructed of noncombustible materials, limited combustible materials, or fire-retardant-treated wood need not have sprinkler protection. Another outdoor space from which sprinklers can be omitted is an exterior exit corridor where the exterior walls of the corridor are at least 50 percent open and the corridor is entirely constructed of noncombustible material. This is a very common egress system for motels and apartment buildings.
Where NFPA 13 systems are installed in residential applications, sprinklers can be omitted from bathrooms that do not exceed 55 square feet (5.1 square meters) in area as long as the walls and ceiling provide a 15-minute thermal barrier. This requirement does not apply to limited-care facilities and nursing homes or to bathrooms that open directly onto public corridors. Other residential applications from which sprinklers can be omitted are clothes closets, linen closets, and pantries in dwelling units in hotels or motels where the space does not exceed 24 square feet (2.2 square meters) and the smallest dimension of the space does not exceed 3 feet (0.9 meters). These closets and pantries must be surfaced with noncombustible or limited combustible construction.
Residential sprinkler standards
NFPA 13R, Installation of Sprinkler Systems in Residential Occupanciesup to and Including Four Stories in Height, andNFPA 13D, Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, also permit sprinklers to be omitted from certain areas. NFPA 13D and NFPA 13R are developed with a singular fire protection goal: life safety. For this reason, there are several additional areas that can be unsprinklered, as fires in these areas are not linked to a loss of life.
In addition to the permissible omissions already listed for residential applications where NFPA 13 systems have been installed, sprinklers can be omitted in NFPA 13R systems in attics, penthouse equipment rooms, elevator machine rooms, concealed spaces dedicated to dwelling unit ventilation equipment, and other concealed spaces that are not used or intended for living purposes or storage. Sprinklers are not required in closets on exterior dwelling unit balconies or breezeways regardless of the size of the closet, provided the closet does not have doors or unprotected penetrations directly into the dwelling unit. Where fuel-fired equipment is present, at least one quick response sprinkler must be installed above the equipment.
Similar to NFPA 13R systems and residential areas of NFPA 13 systems, sprinklers can be omitted from bathrooms less than 55 square feet (5.1 square meters) and closets no larger than 24 square feet (2.2 square meters) in NFPA 13D systems. Nor are sprinklers required in NFPA 13D systems in attics, penthouse equipment rooms, elevator machine rooms, and concealed spaces containing only dwelling unit ventilation equipment.
NFPA 13D also permits some unique portions of one- and two-family dwellings to omit sprinklers. For example, sprinklers are not required in covered, unheated projections at the entrance and exit as long as the dwelling has another means of egress. In addition, sprinklers are not required in garages, attached porches, carports, and similar structures.
Ideally, all spaces within a structure would be provided with automatic sprinkler protection. However that simply isn’t possible. The NFPA technical committees that prepare the sprinkler documents have scrutinized areas from which sprinklers can be omitted and limited them to the greatest extent possible.
Matt Klaus is a senior fire protection engineer at NFPA.
NFPA 13 permits sprinklers to be omitted from concealed spaces that are formed by noncombustible and limited combustible materials provided that they have “minimal combustible loading.” In other words, in a concealed space without sprinklers, the floor, ceiling, walls, and structural elements of the space must be ...
The minimum vertical clearance between sprinklers and material below shall be 18 inches (45.7cm).
5.2. 1 of NFPA 13, which states that the distance from the sprinkler to the wall can be no more than one-half the allowable distance between sprinklers. The max distance between standard spray sprinklers in light hazard settings is 15 ft. (4.6 m) (with exceptions for light-hazard, combustible concealed spaces).
In other words, NFPA 13R requirements provide for a level of protection that allows occupants to escape a building in the event of a fire. Conversely, NFPA 13 provides protection to not only get people out to safety, but also to control or extinguish the fire – saving the building and its contents.
315.3. 1 Ceiling clearance.
Storage shall be maintained 2 feet (610 mm) or more below the ceiling in non-‐sprinklered areas of buildings or a minimum of 18 inches (457 mm) below sprinkler head deflectors in sprinklered areas of buildings.
In short the “beam rule” states that there must be at least 1 foot (0.3048 m)of separation between the sprinkler and the obstruction if the deflector is any distance above the bottom of the obstruction.
|OCCUPANCY HAZARD||SQUARE FOOT PER HEAD||MAXIMUM SPACING BETWEEN SPRINKLERS|
|Light Hazard (Office, Educational, Religious, Institutional, Hospitals, Restaurants, Clubs, Theaters, etc.)||130-200 SF per head (based on obstructions and flow calcs)||15 ft|
Since fire sprinklers already have a design diameter, all factors other than the pressure can be combined into a "K-factor" for simpler calculations. This results in a more compact formula: Q = K x √P.
If your home's water capacity was 10 GPM, you could place 3 heads per zone.
OSHA does not impose penalties or require abatement of de minimis violations. Question 1: 29 CFR 1910.159(c)(10) in part states, "The minimum vertical clearance between sprinklers and material below shall be 18-inches (45.7 cm)." Does this apply only to materials placed directly below the sprinkler heads?
NFPA 13 requires sprinklers installed in light hazard occupancies to be listed as quick-response sprinklers and permits listed residential sprinklers to be installed in dwelling units and their adjoining corridors.
Mixing NFPA 13 and NFPA 13R systems in a building also significantly complicates installation for sprinkler contractors. With different fire protection goals, NFPA 13 and NFPA 13R systems maintain different requirements for such critical factors as water supply, system demand, and sprinkler density.
NFPA® 13, Standard for the Installation of Sprinkler Systems, provides the minimum requirements for the design and installation of automatic fire sprinkler systems and exposure protection sprinkler systems.
The purpose of the “18-inch rule” is to prevent storage or any other obstruction from interfering with the spray of water from a sprinkler head during a fire. It is intended to prevent a situation in which the obstruction is within 18-inches of the ceiling and might be between the sprinkler head and the fire.
The minimum vertical clearance between sprinklers and material below shall be 18 inches (45.7 cm). Hydraulically designed systems.
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.
Four-inch minimum spacing from walls and maximums vary with room shape and size, which is why standard spray sprinklers have four-inch minimum spacing from walls and maximums. The minimum sprinkler distance from walls is four inches for all standard sprinkler heads. The distance from an end wall is 10.
The sprinklers spray at an angle of approximately 45 degrees. So of your light fixture is 4 inches deep, then you should keep them at least 4 inches away from the sprinkler heads.
» All sprinklers need to be quick-response standard spray or extended coverage pendent or upright sprinklers. » The ceiling height cannot exceed 20 feet. » The maximum spacing and area of protection cannot exceed the maximum spacing requirements for light hazard occupancies provided in Table 10.2.
Consider the distance of each sprinkler head. If they distribute water in a circumference of 8 feet around, place them 4 feet apart to ensure every part of the lawn gets watered. Whatever the maximum spray distance of the sprinkler head, divide it in half to find out how far apart to place your sprinklers.
In fire protection engineering, the K-factor formula is used to calculate the discharge rate from a nozzle. Spray Nozzles can be fire sprinklers or water mist nozzles, hose reel nozzles, water monitors and deluge fire system nozzles.
Most spray and rotator heads are designed to work their best at about 30 psi. When pressure is lower, the watering radius will be reduced, so you may need to place your heads closer together to get the coverage you need. Higher pressures – those above about 40 psi – will cause the head to mist or fog.
What is the average flow rate? The standard sprinkler flow rates, in general, are from 4 gallons per minute (gpm) from a 5/32-inch nozzle at 30 pounds pressures to over 11 gpm from a 7/32-inch nozzle at 70 pounds pressures.
For instance, suppose that you have 20 sprinkler heads. You determine that each needs a GPM of 1.5. As such, you need a total of 30 GPM. If your sprinkler system is only able to handle 16 sprinkler heads, you must have two zones to cover the area.
The minimum vertical clearance between sprinklers and material below shall be 18 inches (45.7 cm). Hydraulically designed systems.
A minimum 3-foot clearance in front of the entire width of the fire sprinkler equipment and 1-foot clearance on the remaining 3 sides shall be provided.