The fire department connection: A primer

It's important to understand the hows and whys of FDCs long before the alarm goes off; here's a closer look at these connections


The Fire Department Connection, also commonly known as the siamese connection, is an important component found on most sprinkler and standpipe systems.

When a fire sprinkler system activates, the FDC provides a means for firefighters to connect hose lines to supplement the fire sprinkler system’s domestic water supply.

NFPA 13: Standard for the Installation of Sprinkler Systems is the industry benchmark for design and installation of automatic fire sprinkler systems, and component options.

 The purpose of the FDC is to supplement the water supply, not necessarily provide the entire sprinkler system’s demand. (Photo/Greg Friese)
The purpose of the FDC is to supplement the water supply, not necessarily provide the entire sprinkler system’s demand. (Photo/Greg Friese)

NFPA 14: Standard for the Installation of Standpipe and Hose Systems, provides requirements for the installation of standpipes and hose systems to ensure that systems will work as intended to deliver adequate and reliable water supplies in a fire emergency.

The periodic inspection, testing and maintenance of both fire sprinkler systems, standpipe systems, and combination sprinkler standpipe systems are all addressed in NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.

NFPA 13E: Recommended Practice for Fire Department Operations in Properties Protected by Sprinkler and Standpipe Systems, provides information and procedures for fire department operations in properties equipped with fire sprinkler and standpipe systems.

Why NFPA 13 systems have a FDC

Fire sprinkler systems that are designed and constructed in compliance with NFPA 13’s requirements receive their water supply from the building’s domestic water supply. If necessary, a dedicated fire pump may be included as part of the system to ensure adequate water flow and pressure for proper system performance in the event of a fire.

FDCs are not intended to deliver a specific volume of water. The purpose of the FDC is to supplement the water supply, not necessarily provide the entire sprinkler system’s demand.

There are three common reasons why this additional water supply may be necessary.

  • A closed valve on the domestic water supply leading to the sprinkler system.
  • Inadequate domestic water supply being delivered to the sprinkler system.
  • A change to the occupancy of the building that presents a hazard greater than the sprinkler system was designed to handle.

Basic FDC components

The FDC can be thought of as only consisting of the inlet body. However, the FDC is made up of the inlet (what we see and connect hose lines to), a check valve (to prevent backflow from the sprinkler system’s domestic water supply) and piping connecting to the sprinkler system riser or main.

NFPA 13 specifies that the FDC must be located so that water flow from the FDC enters on the system side of the water supply check valve (see Figure 1). This provision refers to the inlet, piping, check valve, etc. as being one unit.

The sizing of all these components, from the FDC to the sprinkler system to the inlet, are based upon the designed size of the fire sprinkler system and the requirements of NFPA 13. 

Figure 1. A simple engineering diagram of fire sprinkler system's water supply including the FDC.

The required number of inlets on the FDC varies depending on the type and demand of the system being served. For most fire sprinkler systems, NFPA 13 requires a 4-inch pipe for the FDC and the FDC is required to have two inlets. There is no other criterion in NFPA 13 requiring more than two connections.

You might, however, encounter a FDC with a single-outlet when the FDC’s piping goes into a 3-inch or smaller riser.

For standpipe systems with no fire sprinkler system, NFPA 14 requires each FDC to have at least two 2½-inch internal threaded swivel fittings. Additionally, NFPA 14 requires standpipe systems to be designed so that the system demand can be supplied by both the attached domestic water supply, where required, and the FDC.

A less common type of FDC, but one that’s becoming more prevalent, has a single Storz-type inlet for use with large diameter hose. It is important that the hose lines between the pumper truck and the Storz connection are properly rated for the higher pressures produced by the pumper truck.

Where to look for the FDC

The FDC is most commonly located on the side of buildings, but may also be located remote from the building. These are known as freestanding or sidewalk FDCs.

NFPA 13 requires the fire department connection to be located on the street side of buildings; some individual state fire marshal offices further require that the FDC be located on the address side of a building.

There are situations where locating the FDC in those areas is impractical, such as with large shopping malls. This is where the authority having jurisdiction, your city or county government, gets involved during the planning process for such construction to ensure that the FDC is in an appropriate location.

NFPA 13 stipulates that the FDC should be located at the nearest point of access for fire apparatus or in a location that’s approved by the local authority. This could be a remote or free-standing FDC.

If a FDC only provides a water supply to a portion of a structure or building complex, a sign must be placed with the FDC that indicates which portions of are served by that FDC.

NFPA 13 also specifies that each FDC must have a sign – using raised or engraved lettering at least 1-inch tall on a plate or fitting – that identifies what type of system the FDC is supplying. Some examples are AUTOSPKR, OPEN SPKR and STANDPIPE.

There should also be a sign that indicates the water pressure required at the FDC inlets to deliver the greatest system demand. For example, it may read 150 psi.

Know FDC locations, operations

Getting out in your response district and conducting a pre-incident plan inspection for occupancies with FDCs is the only way to identify and correct problems before an emergency response is needed. Here are four of those common issues.

  • Connection threads on an FDC that are incompatible with the threads on your hose lines. There’s always an oddball building, or one that’s much older, that has a different thread than the rest of the area.
  • Missing inlet caps that will allow rainwater or debris to enter the FDC.
  • Connection swivels that are corroded and don’t move freely or don’t move at all.
  • FDCs that may be hidden by overgrown bushes or shrubbery.

Pre-fire inspections will enable you to discover the locations of valves, how they operate, their required fire flow, your department’s ability to provide that flow and the maximum occupancy the sprinkler system is designed to protect.

Pre-fire inspections also provide the opportunity to identify systems where a change in the building’s occupancy – without changes to the sprinkler system’s design – may threaten the system’s design. For example, a light retail store that’s now a carpet and flooring showroom.

Your fire department should have a SOG for supporting sprinkler/standpipe systems via the FDC. That SOG should address at least these four critical issues.

  • Supplying the FDC because doing so ensures that the system has an adequate water supply if the sprinkler heads have been activated by a fire.
  • Ensuring that the sprinkler supply valves are properly open and can supply the system.
  • Supplying the FDC for a standpipe system ensures that firefighters will have an adequate water supply when they hook up hoses inside the structure.
  • Ensuring that water being used to supply the FDC is not taking away water pressure from the domestic water supply that’s supplying the system.

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