Standpipe systems comprise a network of pipes and hose connections installed throughout a building to ensure a reliable water supply for manual fire suppression by either the fire department or trained personnel. The design and installation guidelines for these systems are outlined in Chapter 6 of NFPA 14, Standard for the Installation of Standpipe and Hose Systems. These systems are categorized based on whether the pipes are filled with water (wet) or not (dry), and whether the water supply for firefighting is automatically provided by a water source, such as a city main or a tank and fire pump (automatic or semi-automatic), or needs to be supplied by a fire department pumper (manual). When designing a standpipe system, it is crucial to determine the appropriate fire suppression type pipe sizes, hose connection location, size, and pressure based on the system's classification. Standpipe systems are classified into three classes: Class I, Class II, and Class III.
Class I systems are designed for use by the fire department and are typically required in buildings with more than three stories above or below ground due to the challenges and time involved in laying hoses from fire apparatus to remote floors. These systems are also sometimes mandated in malls because these areas can be difficult to access directly with hoses from fire apparatus. Hose connections in Class I systems are generally located at:
Class I systems require a minimum residual pressure of 100 psi (6.9 bar) from the hydraulically most remote 2 ½ in. (65 mm) hose connection, with a flow rate of 500 gpm (1893 L/min) through the two most remote 2 ½ in. (65 mm) hose connections. A pressure-regulating device might be needed to limit the pressure at hose connections to less than 175 psi (12.1 bar) static (pressure when not flowing).
Class II systems are installed for use by trained personnel and are often required in large buildings without sprinkler systems. They may also be necessary to protect specific high-risk areas, such as exhibit halls and stages.
Historically, Class II standpipes were equipped with a hose, nozzle, and hose rack at each connection. Before the 2007 edition of NFPA 14, these systems were intended for use “primarily by the building occupants or by the fire department.” Due to concerns about untrained occupants using the hose safely and potentially choosing to fight fires rather than evacuate, the Technical Committee redefined Class II systems for use by “trained personnel or by the fire department.”
Class II systems must have enough hose stations to ensure that all areas of each floor level are within 130 feet (39.7 meters) of a 1 ½ inch (40 mm) hose connection with a 1 ½ inch (40 mm) hose, or within 120 feet (36.6 meters) of a hose connection with a hose smaller than 1 ½ inches (40 mm).
The minimum residual pressure for a Class II system is 65 psi (4.5 bar) from a remote 1 ½ inch (40 mm) hose connection with a minimum flow rate of 100 gpm (379 L/min). A pressure-regulating device might be necessary to limit the pressure at these hose connections to less than 100 psi (6.9 bar) residual (pressure when flowing) and 175 psi (12.1 bar) static (pressure when not flowing).
Class III systems combine the features of both Class I and Class II systems, providing for both full-scale and initial firefighting efforts. These systems are intended for use by fire departments and fire brigades. Because of their dual purpose, Class III systems include both Class I and Class II hose connections and must meet the placement, pressure, and flow requirements for both classes.
Pipe Sizing The minimum pipe size for Class I and III standpipes is 4 inches (100 mm). If the standpipe is part of a combined sprinkler system in a partially sprinklered building, the minimum size increases to 6 inches (150 mm). In fully sprinklered buildings, the combined standpipe size can be 4 inches (100 mm) if hydraulically calculated. The branch lines of the standpipe system must also be hydraulically sized but cannot be smaller than 2 ½ inches (65 mm).
Calculating Hydraulically calculating a standpipe system is similar to calculating a sprinkler system, as it involves determining the pressure loss in the system to achieve the required flow to the most remote hose connection. In addition to the required flow from the most remote hose connections, the system must also account for flow from connections on each standpipe based on the classification. For instance, when calculating a Class I standpipe system in a building less than 80,000 square feet (7432 m²), you need to calculate a flow rate of 500 gpm (1893 L/min) through the two most remote 2 ½ inch (65 mm) hose connections at 100 psi (6.9 bar). Additionally, you must calculate an extra 250 gpm (946 L/min) flowing from each standpipe in the building, with a maximum total flow rate of 1000 gpm (3785 L/min) for fully sprinklered buildings, and 1250 gpm (4731 L/min) for buildings that are not fully sprinklered.
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Important Notice: Any opinion expressed in this column (blog, article) is the opinion of the author and does not necessarily represent the official position of JIZHONG or its Technical Committees. In addition, this piece is neither intended, nor should it be relied upon, to provide professional consultation or services.
Fire sprinkler systems have traditionally used metal materials, but with the advent of CPVC, this plastic has become a popular alternative for wet pipe systems. Since CPVC fire protection systems were introduced in 1984, they have offered a viable alternative to steel pipes and fittings. CPVC's high melting point made it a favorable option, but additional benefits, such as its availability and lower cost compared to traditional carbon steel, have further enhanced its appeal.
Fire sprinkler systems are commonly designed as wet pipe systems. Historically, metal was the preferred material for these systems, but CPVC has emerged as a competitive alternative. Since its introduction in 1984, CPVC has provided a valuable substitute for steel in pipes and fittings. The high melting point of CPVC makes it a practical choice, but its advantages extend beyond this. CPVC is also more readily available and less expensive than traditional carbon steel, which has contributed to its growing popularity in fire protection systems.
CPVC is a lightweight thermoplastic created from PVC polymer with added chlorine molecules, making it a leading choice for non-metallic fire sprinkler systems globally. Its popularity stems from several key advantages over steel.
The additional chlorine and specialized additives in CPVC enhance its ability to endure high heat and pressure—critical attributes for fire sprinkler systems. CPVC's high limiting oxygen index of 60 means it resists burning and melting in high-temperature environments.
These properties make CPVC not only comparable to steel but often a superior option for fire sprinkler systems.
