UNDERGROUND FLUSHING: How Much Is Enough? Part 1
If you are a general contractor for commercial/industrial properties, here is a scenario that will seem familiar. The fire protection underground piping is complete and tested, but the fire sprinkler contractor refuses to connect their system to the underground pipe. And, you are left wondering, “Why is this fire sprinkler contractor giving me such a hard time?” The answer is – he/she is not just trying to be difficult. The fire sprinkler contractor is actually prohibited from connecting to the underground supply until provided with an underground material and test certificate, as there is a real liability associated with unflushed and inadequately flushed underground piping.
But, what is flushing and why is it so important? Simply put, flushing is running water through a piping network at a flow rate greater than what could be reasonably expected to flow through the pipe under design conditions. The water is allowed to flow for a duration long enough to remove foreign objects that could be present. Fire sprinkler systems utilize a network of comparatively small orifices, or sprinklers, on a piping network to control or suppress a fire. The number of sprinklers expected to operate, and the water supply to those sprinklers, are critical to the success of the system. For a commercial application, the outlets are as small as one half inch; even the largest outlets are less than one inch in diameter. If any of these outlets become plugged during a fire, the results can be catastrophic. The system sits dormant until called to service with no outward signs that a failure is possible. Flushing helps to remove those objects that could plug up the sprinkler system, or water supply, helping to mitigate the threat of a system failure.
Flushing is also essential in regards to fire pumps. If the fire sprinkler system in your facility relies on a fire pump to boost the water pressure, keep in mind that all water that flows through the fire pump is processed by the pump’s impeller. The pump’s impeller is made of brass, which contains small vanes. The impeller rotates at high speed to boost the water pressure and deliver water to the sprinkler systems. The impeller can be damaged or plugged by rocks or other debris that may have made its way into the underground piping network during the installation process. A damaged impeller may not be able to supply the required water supply to the fire sprinkler system. Once again, catastrophic failures are possible. And, once again, flushing can help to mitigate this risk.
Proper flushing can virtually eliminate the potential for these types of failures. A one-time flush at the minimum acceptable flow rate for an adequate duration should remove any objects and debris that could damage or impair the fire pump or the fire sprinklers, helping to ensure the system is ready to perform as designed when called to service.
Part 2 of this series will review where you can find information on flushing in NFPA codes.
 NFPA 13 (2016 edition) Section 10.10.2.1.1: Underground piping, from the water supply to the system riser, and lead-in connections to the system riser shall be completely flushed before connection is made to downstream fire protection system piping. [24:10.10.2.1.1]