[MEP Center Engineering]

Starter question — a frequently asked question posted by the MEP Center team to open this forum. Share your own experience below.

A mid-rise building has a combined sprinkler and standpipe system. The sprinkler demand at the base of the riser is 1 900 L/min at 5.0 bar. The site plan shows the FDC on the rear façade next to the loading bay, about 70 m from the nearest hydrant.

• What rules govern the FDC location and mounting height?
• How many inlets are needed?
• What valves and piping must sit between the FDC and the system?

[MEP Center Engineering]

Put the FDC where the fire service can see it and connect quickly: on the street or fire-access side, near a hydrant and the appliance parking position, and unobstructed. A rear location 70 m from a hydrant will normally be rejected. The number of 65 mm (2½ in) inlets follows the system demand, and the piping needs a check valve and an automatic drain, with no shut-off valve in the FDC line.

Location

• NFPA 14 and many local codes require the FDC within 30 m (100 ft) of a hydrant connected to an approved supply, unless the authority agrees otherwise. Many fire services set their own distance and side of the building.
• UK and similar practice (BS 9990, Approved Document B): the fire appliance must be able to park within 18 m of the riser inlet, and the inlet must be visible from the appliance.
• Mounting height (NFPA 13/14): 457 to 1 219 mm (18 to 48 in) above finished ground.
• Keep it clear of loading bays, parked vehicles, falling glass and landscaping. Give it a sign stating the system and the zones served.

Inlets

Use the local rule. A common basis is one 65 mm (2½ in) inlet per 946 L/min (250 gpm) of demand. For 1 900 L/min: 1 900 / 946 = 2.0, so a two-inlet (Siamese) connection. High-rise standpipes often need two remotely located FDCs. Confirm the thread or coupling type with the fire service.

Worked check: pressure the fire service must supply

1. Demand at the base of the riser: 1 900 L/min at 5.0 bar.
2. FDC line: DN100 steel (internal diameter about 105 mm), 30 m equivalent length including the check valve and fittings, C = 120. Hazen-Williams: p = 6.05 × 10⁵ × Q^1.85 / (C^1.85 × d^4.87) = 0.0142 bar/m, giving 0.43 bar.
3. Elevation: the riser base is 4 m below the FDC, a gain of 4 × 0.098 = 0.39 bar.
4. Required at the FDC: 5.0 + 0.43 − 0.39 = 5.04 bar at 1 900 L/min. Put this figure on the FDC sign or in the fire strategy if the fire service asks for it.

Valves and piping

• A check valve in the FDC line close to the connection to the system. No shut-off valve between the FDC and the system (NFPA 13).
• An automatic drain (ball drip) between the FDC and the check valve, so the line does not freeze.
• Connect the FDC line on the system side of the main control valve, so the fire service can still supply the system if that valve is closed. Follow the arrangement the code shows for your system type.
• Where a backflow preventer is on the incoming supply, the FDC connects downstream of it. See Backflow Preventers on Fire Lines.

Common mistakes

• Locating the FDC for architectural reasons, out of sight of the access road.
• A gate valve installed in the FDC line “for maintenance”.
• No drain, so the line fills and freezes.

More detail: Fire Department Connection (FDC): Location and Arrangement.

For deeper study: Fire Protection Design course.

Check the edition of the code that applies to your project.

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