Not all standpipe systems serve the same purpose, which is why NFPA 14 divides them into three classes. If you manage a multi-story commercial building, knowing which class you have (or need) matters for both code compliance and fire department response.
Class I: For Fire Department Use
Class I standpipes have 2.5-inch hose connections intended for use by trained fire department personnel, not building occupants. They’re the most common type in commercial high-rises and are typically what a fire department connects large-diameter hose to during a fire.
Class II: For Occupant Use
Class II standpipes have 1.5-inch hose stations meant to be used by trained building occupants or first responders arriving before the fire department, though many modern commercial buildings have moved away from occupant-use hose stations in favor of relying on extinguishers and professional response.
Class III: Both
Class III systems combine both connection sizes on the same standpipe, providing both an occupant-use hose station and a fire-department-use connection, and are common in taller buildings where code requires the broadest coverage.
The class required for a given building depends on height, occupancy, and local amendments to the fire code. See our full Standpipe Systems guide, and our related page on Fire Department Connections for how these systems connect to outside water supply.