Scope

• Source: the public water main, or a private tank or pump supply
• Delivery: a dedicated fire line from the main, usually with its own valve and backflow protection, to the building riser and to site hydrants
• Interface: sprinkler systems and the fire department connection are covered in the fire protection codes; see the related notes

Terminology

• Underground fire main / private fire service main: piping from the water supply to the building riser
• Hydrant: fire department water outlet on the main
• Fire flow: water supply rate the fire department needs for the building
• Flow test: field test of the available pressure and flow at a hydrant
• Depth of cover: distance from the top of the pipe to grade
• Thrust block: concrete that restrains fittings against water pressure
• Post indicator valve (PIV): valve with an external indicator
• Detector check valve: check valve with a meter bypass that detects flow

Components

• Tap and isolation valve at the main
• Underground pipe, fittings, and thrust restraint
• Backflow and check valves, and a detector check where required
• Hydrants and hydrant valves
• Building riser and fire department connection

Coordination

• Cover depth: NFPA 24 Section 10.4.2 is cited for pipe at least 1 ft below the frost line; where frost is not a factor, 2-1/2 ft of cover is cited in one fire department guide and 30 in. in a campus standard; secondary guides give 3 ft under drives and roads; confirm against the adopted edition
• Private mains: they need more cover than public mains because water does not circulate in them
• Hydrant feeds: no line smaller than 6 in. serves a hydrant
• Hydrostatic test: a study guide gives 200 psi or 50 psi above maximum static pressure, whichever is greater, held for 2 hours; confirm the adopted edition
• Water supply and flow test: request a hydrant flow test from the water utility early to confirm the available supply
• Hydrant locations and access: set with the fire marshal; see the fire code notes
• Tap and meter: the utility sets tap, detector assembly, and fees for the fire line
• Locates: call 811 before excavating

Relocation and disconnection

• Fire protection is life safety: keep an approved water supply in service; do not shut off or abandon a fire line without the fire marshal and the building owner's agreement
• Moving a hydrant or main: public hydrants and mains are the utility's and the fire department's; a private hydrant and main are the owner's, but changes need the fire marshal's approval and often a flow test
• Relocating a main: the owner pays where private development requires the move, under the general utility relocation rules
• Phasing: keep temporary fire protection or hydrant access during construction
• Abandonment: a fire line is cut off at the tap or main as the water utility requires and then capped
• Impairments: many fire departments require notice before the system is out of service

Sources

• Colorado Division of Fire Prevention and Control: underground fire main white paper, https://dfpc.colorado.gov/sites/dfpc/files/Underground Fire Main White Paper RES Revisions 3-4-2020.pdf
• Presidio Trust: underground fire service and fire hydrant standard, https://wp.presidio.gov/wp-content/uploads/2024/12/FDA-007-Underground-Fire-Service-and-Fire-Hydrant-8.7.2023-accesible.pdf
• San Francisco Fire Department: underground fire service guidance, https://sf-fire.org/media/3853
• Meyer Fire: NFPA 24 questions and answers, https://meyerfire.com/daily/category/nfpa-24
• Minnesota Lawyer: developers pay the cost of relocating utility lines, https://minnlawyer.com/2025/06/23/minnesota-becomes-the-latest-state-to-require-developers-to-pay-the-cost-of-relocating-utility-lines/