STANDPIPE SYSTEM DEFINITION: An arrangement of piping, valves, hose connections, and associated equipment installed in a building or structure, with the hose connections located in such a manner that water can be discharged in streams or spray patterns through attached hose and nozzles. PURPOSE: Extinguishing a fire, thereby protecting the building & occupants. CLASSES OF STANDPIPE SYSTEMS. CLASS I SYSTEMS.  A Class I standpipe system shall provide 21∕2 in. (65 mm) hose connections to supply water for use by fire departments and those trained in handling heavy fire streams. CLASS II SYSTEMS. A Class II standpipe system shall provide either 11∕2 in. (40 mm) hose stations to supply water for use by trained personnel or a hose connection for the fire department during initial response. A minimum 1 in. (25.4 mm) hose shall be permitted to be used for hose stations in light hazard occupancies where investigated and listed for this service and where approved by the AHJ. CLASS III SYSTEMS