Standpipe System Design and Calculations

Standpipe systems consist of piping and hose connections installed throughout a building to provide reliable water for the manual suppression of a fire by either the fire department or trained personnel. NFPA 14, Standard for the Installation of Standpipe and Hose Systems, Chapter 6, outlines design and installation requirements for standpipe and hose systems. Standpipe systems can be broken down into different types of systems to delineate whether the piping is full of water (wet) or not (dry) and whether the water supplied for firefighting is automatically provided by a water supply, such as a city main or a tank and fire pump (automatic or semi-automatic), or needs to be provided by a fire department pumper (manual). When designing a system, you first need to determine the supply pipe size, hose connection location, size, and pressure based on the standpipe classification. There are three classes of standpipe systems, they include Class I, Class II, and Class II.

Class I

Class I systems are installed for use by the fire department and are typically required in buildings that have more than three stories above or below grade because of the time and difficulty involved in laying hose from fire apparatus directly to remote floors. Class I systems are also sometimes required in malls, because these occupancies contain areas that are difficult to access directly with hose from fire apparatus. Locations for hose connections in Class I systems include:

  • Each main floor landing or intermediate landing of required stairs.
  • On the roof if the stairwell does not have access to the roof.
  • Each side of exit openings in horizontal exits.
  • Exit passageways.
  • Additional hose connections should be available in unsprinklered buildings where the distance from a hose connection to the most remote part of the floor exceeds the limits in NFPA 14 based on the sprinkler system type and building type.

The minimum residual pressure required for a Class I system is 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 may need to be used in order to limit the pressure at hose connections to less 175 psi (12.1 bar) static (pressure when not flowing).           

Class II

Class II are installed for use by trained personnel and are often required in large un-sprinklered buildings. They might also be required to protect special hazard areas, such as exhibit halls and stages.

In the past, Class II standpipes were typically installed with a hose, nozzle, and hose rack on each hose connection. Prior to the 2007 edition of NFPA 14, Class II systems were defined as being for use “primarily by the building occupants or by the fire department.” Because of concerns regarding the ability of untrained occupants to safely use the hose and the encouragement of occupants to fight the fire rather than evacuate, the Technical Committee chose to define Class II systems as being for use by “trained personnel or by the fire department.”

Class II systems need to provide enough hose stations so that all portions of each floor level of the building are within 130 ft (39.7 m) of a 1 ½ in. (40 mm) hose connection provided with 1 1∕ 2 in. (40 mm) hose or within 120 ft (36.6 m) of a hose connection provided with less than 1 1½ ∕ 2 in. (40 mm) hose connection.

The minimum residual pressure required for a Class II system is 65 psi (4.5 bar) from a remote 1 -1/2½ in. (40 mm) hose connection with a minimum flow rate of 100 gpm (379 L/min). A pressure-regulating device may need to be used in order 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

Class III systems combine the features of Class I and Class II systems. They are provided for both full-scale and first-aid firefighting. These systems are generally intended for use by fire departments and fire brigades. Because of their multiple uses, Class III systems are provided with both Class I and Class II hose connections and must meet the placement, pressure, and flow requirements for both Class I and Class II systems.

Pipe sizing

The minimum size pipe for Class I and III standpipes is 4 in. (100 mm). If the standpipe is part of a combined sprinkler system in a partially sprinklered building, that is increased to 6 inches (150 mm). If the building is protected with an automatic sprinkler system, then the minimum combined standpipe size can be 4 in. (100 mm) if hydraulically calculated. The branch lines of the standpipe system are to be sized hydraulically but cannot be smaller than 2 -1/2½ in. (65 mm).

Calculating

Hydraulically calculating a standpipe system is very similar to that of a sprinkler system because we are calculating the pressure lost in the system to get the required flow to the most remote hose connection. In addition to the required flow from the most remote hose connections, based on the classification we are required to also calculate flow from connections on each standpipe. For example, when calculating a Class 1 Standpipe system in a building that is less than 80,000 ft2 (7432m2) we need to calculate the flow rate of 500 gpm (1893 L/min), through the two most remote 2 ½  in. (65 mm) hose connections at 100 psi (6.9 bar) and also calculate an additional 250 gpm (946 lpm) flowing from each standpipe in the building up to a maximum total flowrate of 1000 gpm (3785 L/min) for buildings that sprinklered throughout, and 1250 gpm (4731 L/min) for buildings that are not sprinklered throughout.

Take a look at this video taken from our soon to be released Online Certified Water-Based System Professional Learning Path discussing how to hydraulically calculate a standpipe system.

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Shawn Mahoney
Technical Services Engineer

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