System Working Pressure and Fire Department Connections
System Working Pressure is currently a defined term in NFPA 14, Standard for the Installation of Standpipe and Hose Systems. This term has changed and evolved over the last few cycles of the standard. These changes have continued to make the concept of system working pressure difficult to understand, not only what it is, but its implications to overall system design as it relates to pressure from the fire department connection (FDC).
The definition was originally added to the 2016 edition of the standard but excluded surge pressure and pressure from the FDC. It was added to simply define the term and correctly apply hydrostatic acceptance testing requirements. The exclusion of surge and pressure from the FDC has been extremely confusing and does not address the rating or pressure requirements needed to provide system demand from the FDC. The issue being, does an FDC need to be rated for the system working pressure, or is just surge pressure excluded from system working pressure?
This confusion led to a modification of the definition of system working pressure in the 2019 edition. This change would remove the exclusion of pressure from the FDC and stated that system working pressure is anticipated static (nonflowing) or flowing pressure applied to the standpipe system components but leaves the exclusion of surge pressure. This was once again justified by the technical committee as further clarification that the FDC and the associated piping is subjected to the hydrostatic test requirements of Chapter 11.
FDC System Acceptance Testing
NFPA 14 Chapter 11 – System Acceptance, Section 11.4.1, requires all FDCs to be tested hydrostatically at not less than 200psi or 50psi in excess of the system working pressure, whichever is greater for a duration of 2 hours. System Demand is defined as the flow rate and residual pressure required from a water supply, measured at the point of connection of a water supply to a standpipe system, to deliver the total waterflow rate and the minimum residual pressures required for a standpipe system at the hydraulically most remote hose connection, and the minimum waterflow rate and residual pressure for sprinkler connections on combined systems. This creates a problem at the FDC when the hydraulically calculated pressure required to provide that system demand from the FDC exceeds the system demand by 50psi. This creates the potential for designing and installing a portion of the system that is under rated for pressure need to provide system demand from the FDC.
What NFPA 14 – 2023 Says about System Working Pressure
The NFPA 14 Technical Committee seeking to clarify that system working pressure includes all components of a system, including those pressure from the FDC required to provide system demand, should be rated for that pressure, once again modified the definition in the upcoming 2023 edition of the standard.
This clarification states that the maximum anticipated static (nonflowing) or flowing pressure applied to standpipe system components exclusive of surge pressures and inclusive of the system design/demand pressure from the fire department connection. The committee justified this change, to provide clarity that the FDC is not considered part of the surge pressure and that system components shall be rated for all system design pressures. This includes system demand and the hydraulically calculated pressure required at the FDC to provide that system demand.
This change means we now must discuss the acceptance testing requirements for FDC’s. Moving forward to the next edition, the definition of system working pressure would indicate that FDC’s should be rated and tested for the hydraulically calculated pressure that is required to provide system demand. Consideration for acceptance testing should include requiring all FDCs to be hydrostatically tested at not less than the hydraulically calculated pressure required to meet system demand, for a duration of 2 hours. The alternative is for the fire department to verify that system demand can be met from the FDC through a flow test.