ATOMIC SPRINKLER SYSTEMS: What the fine Department Need to Know
Sprinklers are by far the most widely used and reliable means of automatic fire protection. Sprinkler systems automatically detect a fire, transmit an alarm, and control or suppress the fire. Yet too often devastating fires occur in buildings that are fully sprinklered.
There are three major reasons for destructive fires in sprinklered buildings: a design deficiency in the sprinklcr system, either in the original design or due to changes in the building’s contents; an impairment to the sprinkler system before a fire, such as a closed valve or sprinkler obstruction; and an impairment to the system during a fire, usually caused by someone prematurely closing a sprinkler control valve. These reasons can be attributed to human error.
One way to reduce the chances of such costly errors is knowledge. Members of the public fire service and building owners should conduct prefire planning sessions to discuss the building’s layout and contents and the types and locations of fire protection features. These planning sessions may save not only the facility but also the lives of responding firefighters.
TYPES OF AUTOMATIC SPRINKLER SYSTEMS
Firefighters should know which buildings are sprinklered and with what types of systems. There are four main types of automatic sprinkler systems: wet-pipe, dry-pipe, preaction, and deluge. Decisions on which type of system to install depend on the area being protected.
Wet-pipe system. This system is the most common. Sprinkler piping is filled with water under pressure. When the individual sprinklers operate, the water immediately discharges and continues to flow until the system is shut off.
Dry-pipe system. This is used in unheated areas where water in piping would be susceptible to freezing. Instead of water, the piping contains pressurized air. The air holds the water behind a dry-pipe valve, which is located in a heated area. When a sprinkler activates, the drop in air pressure in the pipes allows the drypipe valve to open, which then lets water into the pipes. A dry-pipc system is less efficient than a wet-pipe system because of the time it takes to deliver water to activated sprinklers. However, the time can be decreased by using air exhausters or accelerators.
Preaction system. This is similar to a dry-pipe system but is considered slightly more efficient. It’s used where an alarm is desired in advance of sprinkler operation and where it is particularly important to prevent accidental discharge of water. Heat or smoke detectors are installed throughout a protected area. When a detector actuates, an automatic water control valve admits water into the sprinkler piping, where it remains until a sprinkler head operates.
Deluge system. This system operates in much the same manner as the preaction system but with one exception: Every sprinkler is open so that water will discharge from all sprinklers simultaneously when a heat or smoke detector activates, wetting down the entire protected area. This system is used in buildings where the immediate application of large quantities of water is needed.
SPRINKLER SYSTEM PIPING
A sprinkler system’s water supply is connected to the sprinklers through a network of pipes. The various types of piping and their functions include:
- yard mains—a system of large pipes, usually underground, that distribute water around the exterior of a building;
- lead in — the pipe that supplies water from the yard main into the building;
- feed mains—pipes that come from risers (which carry water to a higher level) and supply cross mains;
- cross mains—the pipes that directly supply the branch lines in which the sprinklers are placed; and
- branch lines—the lines of piping that are suspended and attached to the cross mains. Sprinklers are threaded into fittings directly in the branch lines.
In most industrial fires, the major source of fuel is the building’s contents. There are two kinds of piping systems used to determine the most appropriate pipe sizes for a specific building and its contents: the pipe schedule system and the hydraulically designed system.
Pipe schedule systems. These systems use three standard layouts (based on type of occupancy) of preengineered piping. A standard number of sprinklers is designed for each of the three pipe sizes.
- The system with the smallest -diameter piping is the light-hazard pipe schedule system, which is used in locations where there is very little fuel present, such as churches and institutional facilities.
- The ordinary-hazard pipe schedule system has slightly larger-diameter piping, which allows more water to flow. This system is used where there is a moderate amount of fuel, such as in machine shops.
- The extra-hazard pipe schedule system has the largest-diameter pipe. This system can deliver a large volume of water to protect areas containing flammable liquids and rubber tirestorage.
The same light-, ordinary-, and extra-hazard occupancy classifications are used in hydraulically designed systems.
Hydraulically designed systems. Most systems installed today are of this type. Sprinkler contractors use a computer to custom-design the exact protection configuration to meet a specific building’s needs. This system is preferred for two reasons: It generally requires smaller-diameter pipes than a pipe schedule system does, which saves on cost, and the design of the system often utilizes a grid or loop network of pipes that brings water in from several directions, which reduces friction loss of water. On the other hand, pipe schedule systems allow for more flexibility when a building’s occupancy changes, such as from light hazard to ordinary hazard —hydraulically designed systems are more customized and they’re also more costly to alter.
TYPES OF SPRINKLERS
The type of sprinkler head that is installed also depends on the area being protected. The upright standard sprinkler is one of the most common types of heads seen in industrial facilities. It is installed only in the upright position, on top of the piping.
The pendent standard sprinkler hangs below piping. It is just as effective on a fire as the upright but is used only where it is impractical to install upright sprinklers. Uprights are preferable because pendent sprinkler piping cannot be quickly and completely drained in a cold-weather emergency. Also, sediment can collect in pendent sprinklers.
Flush, recessed, and concealed sprinklers do the same job as standard sprinklers but are more attractive. They are installed in the pendent position with the operating elements either concealed or extending a short distance below the ceiling. They usually are found in light-hazard occupancies.
The sidewall sprinkler is designed for installation near the junction of the ceiling and the wall of narrow offices, corridors, and rooms containing light-hazard occupancies. It is equipped with a deflector that directs most of the water forward.
Window and cornice sprinklers are designed to protect windows and combustible cornices against fire exposures from other structures and fuel sources. These sprinklers are not automatic. Their operation depends on the manual opening of a control valve or on a thermostatically operated deluge valve. Thus they are less reliable and desirable than automatic protection.
Areas containing high-piled rack storage should contain rack storage sprinklers in addition to ceiling sprinklers. Rack storage sprinklers are installed within the racks, and a water shield protects them, like an umbrella, from water discharged from the ceiling sprinklers. This is necessary because otherwise the water spray would cool the rack storage sprinklers and delay their operation.
Certain high-challenge fires that require a high rate of water application are controlled by large-drop sprinklers, which deliver as much as 40 percent more water than standard sprinklers.
Severe fire hazards, such as rack storage of plastics, should be protected by the early suppression-fast response (ESFR) sprinkler— a new concept in sprinkler design. It has a more sensitive fusible element that makes it respond more quickly and a larger orifice to deliver a heavy sprinkler discharge directly on the fire.
Fast-response technology is being expanded into other areas as well. In addition to the ESFR sprinkler, there are several other types of quick-response sprinklers including standard and large-drop sprinklers with quickresponse links as well as new, specially developed residential sprinklers.
SPRINKLER TEMPERATURE RATINGS
Water is automatically released from a sprinkler when the sprinkler’s fusible element—usually a metal link or glass bulb —is heated to its predetermined temperature rating, as determined by NFPA 13 Chapter 3-11.6. For example, a sprinkler rated at 160°F will operate when the bulb or link is heated to that temperature. The rating usually is marked on the sprinkler’s operating element. Sprinkler frames and the liquid in glass bulbs also are color-coded according to temperature so that their rating can be determined from a distance.
One set of criteria that determines a sprinkler’s temperature rating is the occupancy it is protecting. Light-hazard occupancies should be protected by sprinklers with a rating of 135° to 170°F; ordinary-hazard areas, such as parking garages, restaurant service areas, and machine shops, should be protected by sprinklers with a range of 175° to 225°F; and extra-hazard occupancies that can produce fires with a high heat release, such as highpiled combustible storage areas, should be protected by sprinklers that range from 250° to 300°F.
The other important criteria for determining sprinkler temperature rating are the ambient temperatures that normally will surround the sprinkler. Sprinklers near unit heaters, skylights, or heating ducts often require higher temperature-rated heads to avoid accidental discharge.
VALVES
Throughout the sprinkler system is a variety of valves that retain the system’s water supply and minimize the areas that are put out of service during repairs to the system. For example, the water flow from a public water supply to the yard system is controlled by the supply control valve. Water that is maintained within the yard system at a higher pressure than that of the water supply will flow back into that supply unless a check valve is installed. The check valve is located between two supply control valves so that it can be isolated for maintenance.
Divisional valves also are located on the yard system. By closing two divisional valves, maintenance can be done on a specific part of the yard main without shutting down protection to the entire facility.
Sprinkler systems that require fire pumps usually have two valves: a suction valve, which isolates the fire pump from its static water supply, and a discharge valve, which controls the flow of water from the pump to the fire protection system. Closing the discharge valve isolates the pump from the yard system when pump maintenance is required. The suction and discharge valves should be open at all times, except during maintenance or annual pump tests.
The water supply for individual sprinkler systems can be turned on and off with sprinkler control valves.
These valves should be locked in the open position to ensure maximum effectiveness of the sprinkler system.
A shut valve can leave an entire section of a building unprotected. One of the first actions the fire department should take after arriving at a fire is to check to ensure that control valves are locked open. Firefighters can lose valuable time searching for these valves unless they review the locations during prefire planning sessions.
During planning sessions firefighters and facility management also should agree that sprinkler control valves will not be closed until a fire is completely extinguished (and fire companies have stretched hoselines to the seat of the fire and a firefighter is standing by the control valve, ready to open it at moment’s notice). Prematurely closing the valves allows the fire to accelerate and open more sprinklers. When the valves eventually are reopened, the water supply may be overtaxed because so many sprinklers have activated.
Following are some common types of sprinkler control valves and their respective inspection procedures.
- Post indicator valve (PIV) — this valve’s target will read “open” or “shut.” However, targets are not failsafe. To ensure that the gate did not drop off the valve stem and produce
1991. Factory Mutual Engineering Corporation. Reprinted with permission.
- an incorrrect reading, physically try the valve hy turning the operating rod beyond the wide open position. If the valve is completely open, the rod will spring back slightly.
- Wall post indicator valve— this valve is similar to the PIV except that it is mounted horizontally on a wall and operated by a wheel, not a handle. Again, physically try the valve: Turn the wheel and “spring test” it.
- Post indicator valve assembly— unlike the PIV, the PIV assembly’s target will give a true reading of whether the valve is open. The assembly can be visually inspected.
- Indicating butterfly valve (IRV)–A. visual inspection of this valve also is adequate. If the target indicates “open,” then so is the valve.
- Outside screw and yolk valve (OS&Y) — the most common type of valve. A fully extended stem indicates that this valve is fully open, and a completely retracted stem indicates
- that it is fully shut. Still, a visual inspection is not fail-safe. The valve still should be checked by hand.
- Curb box/roadway valve—a valve that usually is installed in the connection to the city water supply. An arrow on the cover plate indicates the direction in which to open this valve. Physically try this below-grade valve with a long tee wrench.
CONNECTIONS
A facility’s fire protection system also will feature a fire department connection, fire hydrant, and 2-inch drain. The fire department pumper connection, which is usually called a Siamese connection, enables the fire department to pump water from a public hydrant or suction source into the yard system. The National Fire Protection Association recommends that one of the first pumpers to arrive at a fire scene be connected to the pumper connection (NFPA 13E:13-5). The pumper increases the pressure and, in some cases, the volume of water delivered to the yard system.
Increasing water pressure enables automatic sprinklers to deliver more water to a fire. Increasing water volume permits the use of additional hoselines from yard hydrants. Yard hydrants provide a connection to the water supply that can be used (with handlines attached directly to the hydrant) to fight exterior fires that endanger the structure. Yard hydrants, however, should never boused to supply pumpers. Yard hydrants usually have two 2’/2-inch connections—they have no steamer connection. Firefighters should know the locations and types of all hydrants in the vicinity, including municipal hydrants that can supply pumpers.
The 2-inch drain, which is located on the riser, is used for draining a system when repairs are necessary. The drain also can be used to provide temporary protection. A coupling can be used to attach one end of a hose to the drain and the other end to a hydrant. This temporary hookup enables the fire department to supply water to sprinkler systems that are out of service.
