Combination Systems: You Might be Surprised

Understanding combination sprinkler standpipe systems is simple. The fire sprinkler and standpipe systems share a common riser. The 2019 edition of NFPA 14 Standard for the installation of Standpipes and Hose Systems, Section 3.3.20.3 defines a combined system as: “A standpipe systems that supplies both hose connections and automatic sprinklers”. That definition also holds a hidden clue to understanding the design implication of a combined system. While it states “automatic sprinkler” it does not reference to the type of required standpipe activation. That leads us to a discussion of the different types of standpipes and their unique characteristics.

The 2019 edition of NFPA 14 defines seven different types of standpipes systems.

  • Automatic dry standpipe system
  • Automatic wet standpipe system
  • Combined system
  • Manual dry standpipe system
  • Manual wet standpipe system
  • Semiautomatic dry standpipe system
  • Wet standpipe system

When we determine which standpipe system will be required in our combination system, we can quickly eliminate a manual dry standpipe system, as it does not have a permanent water supply capable of supplying our automatic sprinkler design. The combined system and wet systems are obvious choices and only indicates that the risers are shared wet risers. The semiautomatic standpipe system is simply eliminated by the “automatic” sprinkler requirements found in NFPA 13 Standard for the Installation of Sprinkler Systems. This essentially leaves us with a choice between automatic dry standpipe, automatic wet standpipe, and a manual wet standpipe system. The key difference being the choice between automatic and manual. The term “automatic” simply means that the system will automatically provide required pressure and flow, while in contrast the “manual” system water supply is only required to meet sprinkler demand.  The manual standpipe side of the system will require supplemental pressure and flow to be supplied by the fire service.

One must also understand that for the purpose of this discussion that while hose connections are found in combination systems, hose connections may not always be required to meet both the flow and pressure requirements of a class I or III standpipe system. It must also be noted that combination systems are not allowed in all occupancies. Combined riser designed systems are typically found in large or multiple floor structures below the local jurisdictions height limitations for high-rises.

The choice of a manual wet supplementing a combination standpipe system over automatic wet is used to reduce total system cost, by relying on the fire service to provide pump pressure.  This allows a mid-rise building to be constructed without the need for a building fire pump. This often comes as a surprise to the fire service that often believes that all standpipe hose connections are created equal when it comes to pressure and flow requirements. There must be clear strategic plan for the use of combination systems and fire service tactical considerations must start with the buildings system design.

The local officials, both fire service and building officials, must understand local capabilities and have an in-depth understanding of the design differences and implications, to be able to adequately provide the best level of fire protection for their communities.