Standpipes, hose valve connections supplied with water from a piping system that is always under pressure or can be rapidly supplied with water under pressure are the usual means through which firefighters are provided water to fight interior fires in large buildings such as malls and high-rises. NFPA 14, Standpipe, Hose Systems, is the recognized standard for the installation and design of standpipe systems.
Today, most standpipes installed are intended for use by the fire department; however, some are designed for occupant use. As with sprinkler systems, building codesgenerally dictate when and where standpipes are required.
Class of Service
Standpipe systems are classified into the following types:
Class I. For use by fire department personnel only. These systems are provided with 21â„2-inch hose valves located in building stairwells and other protected areas. Water supplies permit two hose streams to be fed simultaneously from a single riser. Each stream provides 250 gal /min at a minimum pressure of 100 psi.
Class II. For occupant use only. Provided with 11â„2-inch hose valves and hose racks with a minimum 100-feet length of 11â„2 hose, these standpipes are located in a building such that all areas of a building are within 130-feet of a hose valve (100- feet of hose plus 30-feet of water spray). It should be noted that most authorities having jurisdiction no longer permit hose to be attached to Class II systems since it is felt that the best option for occupants who are not trained in fire fighting procedures is to evacuate the building and report the emergency situation.
Class III. A combination of Class I and Class II systems with both 21â„2-in hose valves and 11â„2-in hose valves and hose racks with 100 ft of hose, installed as required for a Class I and Class II system. The calculated water supply at an outlet is the same as for a Class I system.
Riser Sizes. Standpipe pipe sizes can be established based on the performance of hydraulic calculations or for low rise buildings the NFPA 14 Pipe Schedule System, with the hydraulic procedure being the preferred method. The hydraulic calculations for a Class I system are based on flowing 500 gpm at 100 psi at the most remote standpipe and 250 gpm at the top hose connection of all other standpipes with a total not to exceed 1250 gpm.
Maximum Pressure. Standpipe systems should be designed so the maximum gage pressure at the inlet of any Class I hose connection does not exceed 175 psi and Class II hose connection, 100 psi. Where pressures exceed 175-psi, pressure limiting devices must be installed. Engineers must be extremely cautious in specifying pressure-limiting devices as they are frequently specified improperly.