Facility executives should not assume that the water supply was adequate at the time of original installation of the system. Oftentimes, an initial water distribution system flow test such as a hydrant flow test is overlooked during the initial inspection process after the building is constructed. Original data obtained well in advance of construction may not accurately describe the water supply strength when construction is complete or at the time of building occupancy.
Although a main drain test may repeatedly produce similar residual pressures at regular inspections, the system supply may have been inadequate from inception. Without calibration of the actual water distribution supply curve to the sprinkler system design criteria, an inadequate water supply can remain undetected despite performing the required main drain tests.
NFPA 291, Recommended Practice for Fire Flow Testing and Marking of Hydrants, addresses hydrant flow tests. For new building construction, a hydrant flow test should be performed at the time of initial acceptance testing for the sprinkler system, just prior to building occupancy. For an existing system, a water supply flow test should be performed at the next inspection interval, if the baseline test was not performed and recorded at the completion of construction. A water supply curve — hydraulic demand at a system reference point, such as the base of riser, compared to the available supply — can be used to validate the design flow data used to calibrate the main drain test residual pressures. If the as-built data does not agree with the design flow test figures or the supply is inadequate to satisfy the sprinkler system demand, facility executives should investigate the water supply immediately.
After the water supply curve is determined to satisfy the sprinkler system demand, future main drain test results can be checked against the baseline value to confirm water supply adequacy. With this foundation established, facility executives can be more confident in the results of the main drain test.
The Importance of Periodic Fire Sprinkler Testing and Inspection
Conduct an Initial Water Distribution System Analysis
Investigate Reductions in Main Drain Residual Pressures
Test Srinkler Pressure Gauges
Codes and Standards: Understanding NFPA 13