Water Supplies for Sprinkler and Standpipe Systems

Water supplies for sprinkler and standpipe systems must be reliable. When a municipal water supply has been identified as unreliable or incapable of meeting the demand of a sprinkler or standpipe system, fire pumps and water storage tanks or reservoirs may be required. Even in instances where a water supply is reliable and the protected area is of high value, a secondary water supply employing water tanks and fire pumps is often provided.
In determining the size and elevation of tanks, site conditions should be of primary concern. Often times water storage tanks can be located advantageously at the higher elevations of a property. Other times penstocks, flumes, rivers or lakes may serve as a water supply. In these cases approved strainers must be provided on the water supply inlets to prevent obstructions from entering system piping. In all cases, whether the water supply is from a municipal source or raw source as described above, consideration must be given to the potential effects of Microbiological Influenced Corrosion (MIC) which can rapidly damage sprinkler piping.
While water supply adequacy is heavily reliant on the presence of sufficient flow and pressure, water supply duration is also important. For sprinkler systems the minimum water supply duration is 30, 60 and 90-minutes for light, ordinary and extra hazard areas, respectively. Standpipe water supply duration is 30-minutes.
Water supply duration is mandated to ensure that adequate time is available to achieve fire control.
Fire Department Connection. With the exception of small sprinkler systems, all sprinkler and standpipe systems must be provided with a fire department connection (FDC). The FDC, often referred to as the siamese connection, is a means through which fire hoses may be connected to a system to support the hydraulic requirements of the system to which it is attached. In most cases, the FDC is a backup water supply. It should be noted that often times the FDC for standpipes in lowrise buildings is the only source of water supply. These systems are referred to as  manual standpipes. Before specifying a manual standpipe the AJH should be consulted.
Depending on the AJH, FDCs may be installed on a side of a building or they may be free standing. Whatever the case, the FDC should be 18- to 36-inches above grade, and within clear sight of a fire department access-way. To speed fire ground operations it is good practice to locate FDCs within 75 feet of a fire hydrant. In addition, high rise buildings should be provided with two remotely located FDCs.
While not a code requirement, as a rule of thumb, for each 250-gpm required, as determined in the hydraulic calculations, one 21⁄2-inch FDC outlet should be provided.
For a 600-gpm-system demand three 21⁄2-inch FDC outlets should be provided.
As it is becoming common place for fire departments to use quick connecting FDCs, Stortz Connections, and since the fire department is the FDC end user, in all cases the local fire official should be consulted regarding FDC type and location.

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