Class I standpipe (Class 1): the fire department system
A Class I standpipe provides 2½-inch (65 mm) hose connections for use by the fire department and personnel trained in handling heavy hose streams. No hose or nozzle is stored at the outlet. The fire service arrives with its own hose and connects to the 2½-inch valve, usually in or near a stairwell, on the fire floor. It is the most common class in high-rise office, multifamily, and hotel construction.
This is the class most people picture in a high-rise: a crew climbs to the floor below the fire, connects to the standpipe, and advances a charged line. Because the connection is 2½-inch and the users are firefighters, Class I carries the highest flow demand of the three. The figures most people quote apply here: 100 psi residual at the hydraulically most remote 2½-inch outlet, with 500 gpm for the most remote standpipe. Class I is also the class most often supplied, or entirely charged, through a fire department pumper at the FDC.
Class II standpipe (Class 2): for occupants and on-site staff
A Class II standpipe provides 1½-inch (40 mm) hose stations intended for use by building occupants or trained staff, such as a fire brigade, during the early stages of a fire, before the fire department arrives. Historically these stations were fitted with hose and a nozzle attached.
Class II is far less common in new construction than it once was. Many jurisdictions no longer require occupant-use hose, on the reasoning that untrained occupants should evacuate rather than fight a fire, so Class II systems turn up mostly in older buildings, sometimes with hose valves capped off and the system reclassified. Where a Class II system exists, its required residual pressure is lower, typically 65 psi at the most remote outlet, because it was designed for a quick first-aid stream, not a fire-service attack. Always confirm what the adopted code requires before assuming a Class II hose is expected.
Class III standpipe (Class 3): both, from one system
A Class III standpipe provides both 2½-inch and 1½-inch hose connections, serving fire department use and occupant or first-aid use often from the same riser with a reducer. In practice a Class III system is engineered to the more demanding Class I criteria for the 2½-inch connections, with the 1½-inch outlets added where occupant use is intended.
Because Class III includes the 2½-inch fire-service connections, its testing looks like a Class I test: the system has to prove it can deliver the fire department flow and pressure at the remote 2½-inch outlets, not just the smaller occupant flow.
Why the class decides the test
The class is not a label. It sets the flow the system has to deliver and therefore what a compliant flow test actually requires. A 2½-inch (Class I or III) system is sized around the higher fire department demand. The commonly referenced figure is 500 gpm for the most remote standpipe plus 250 gpm for each additional standpipe, up to 1,000 gpm total in a building sprinklered throughout (1,250 gpm if it is not), at 100 psi residual at the most remote 2½-inch outlet. The exact figures depend on the adopted NFPA 14 edition and the approved design, and must be confirmed by calculation.
Proving that demand means flowing real water at real pressure from the remote 2½-inch outlets. On manual systems and many Class I systems there is no on-site supply capable of that flow, so the test, like a real fire response, depends on a pumper connected at the FDC. Identifying the class from the drawings is the first step in scoping the test correctly.
Class vs. type: the second way standpipes are sorted
Class describes the hose connections and who uses them. Type describes how the system gets water: automatic wet (the pipe is full and pressurized), automatic dry (the pipe holds pressurized air until a dry pipe valve admits water), semi-automatic dry (water is admitted when a remote control device is actuated), and manual wet or manual dry (there is no adequate supply of its own, so the fire department pumps into the FDC to charge it). The wet vs. dry standpipe guide covers each type in detail.
Type adds its own obligations. Dry and semi-automatic standpipes carry a recurring hydrostatic pressure test, and dry pipe valves carry trip tests that wet systems do not. Knowing both the class and the type is what tells you which tests you owe, how often, and what numbers you have to hit.
How to tell which class you have, and what test day looks like
Most owners do not know their standpipe class offhand, and that is fine. The riser diagram, the hose valve sizes, and the FDC signage tell us quickly. A 2½-inch valve with no hose points to Class I; a 1½-inch hose station points to Class II; both at the same location point to Class III.
On a Class I or III system, we set up at the most hydraulically remote 2½-inch outlet, flow water through calibrated equipment, and record static and residual pressure with flow. On a manual system, we bring the pumper truck and supply the fire department connection exactly as a fire crew would. The standpipe flow test page explains the full process.