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“combination.” Standalone systems are entirely independent from the potable system, although they may share a service entry. (See Figure 1). Standalone systems connected to a municipal system generally require a backflow valve to protect the potable supply. The system operates only when there is a fire. A combination system is one that—through a shared network of smaller supply lines (typically PEX)—shares fire protection and domestic service. The combination system is designed so that if a fire occurs while the domestic system is in use, there is adequate water reserve in the system to control a fire. The only valve required by the standards is a simple “main” drain so the system can be drained for service. This drain doubles as a testing orifice. RESIDENTIAL SPRINKLERS The entertainment industry has done no favors by the way it portrays fire sprinkler systems: Despite what one sees on television, if one sprinkler operates, they do not all start spraying water. Yes, there are commercial systems that operate that way—suitably called “deluge” systems—but these are used only to protect specific, high-hazard areas, such as flammable liquid or explosive manufacturing areas. Yes, television programs are entertaining, but they do not represent reality. Residential sprinklers are operated by heat—not smoke – and only the sprinkler or sprinklers nearest a fire will operate when they are reaching their opening temperature of about 155oF. Sprinklers installed in so-called warm zones—near furnaces, fire places or other heat-producing equipment—are set to operate at about 175oF to avoid accidental discharge. Sprinkler systems are designed so that two sprinklers will control a fire, and national fire data show in 84 percent of home fires where the sprinklers are used, just one sprinkler operates.5 Sprinklers come in many designs and configurations, driven by a variety of factors, such as coverage requirements, water pressure, pipe configuration and aesthetics. Generally, an individual sprinkler may cover up to 400 square feet, so it is possible many dwelling unit rooms can be protected by a single sprinkler. The technical committee that created the original NFPA 13D looked at fire data to determine where most fatal fires occur in dwell- Figure 1—This is the entire service entry for a residential sprinkler system: a potable water source, a backflow prevention device, a water pressure gauge and a drain valve. The pressure gauge is not required by IRC P2904 or NFPA 13D. Figure 2—“Tenting” batt insulation over sprinkler pipe allows heat from the conditioned space to keep the water from freezing. OCTOBER 2016 | 25


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