56/Plumbing Engineer February 2020
The garden hose is the standard piece of equipment and flushing method for many underground water main installers. From NFPA 13, Chapter 6, 2019 edition: "6.10.2.1.1 Underground piping, from the water sup- ply to the system riser, and lead-in connections to the system riser, including all hydrants, shall be completely flushed before connection is made to downstream fire protection piping." Also from NFPA 13, the actual minimum flow rates for flushing must achieve 10 feet/second: 6-inch pipe, 880 gallons/minute; for 8-inch pipe, 1,560 gpm; for 10-inch pipe, 2,440 gpm; and for 12-inch pipe, 3,520 gpm. These are not achieved by flushing for domestic plumbing compliance. Assuming the dry sprinkler system is designed and installed correctly, the acceptance test procedures should include all the following. Coordination Between Fire Alarm, Sprinkler System Contractors A common mode of failure of dry sprinkler systems is the failure of the fire alarm contractor and fire sprinkler contractor to work together to test the automatic fire- extinguishing system operation devices (e.g., pressure switches and tamper switches). They also need to ensure the proper signals are sent to the fire alarm panel, coordinate the message the signals need to convey, and ensure that the appropriate signals are sent from the fire alarm control panel and received by central station monitoring. A low-air supervisory signal must be reported as a low-air supervisory signal and not as a trouble or alarm signal. Likewise, a dry system water-flow pressure switch signal must be reported as a fire alarm dry system water flow signal, not a trouble or supervisory signal. Makes sense, seems easy, right? Frequently, it does not work that way. If these two contractors don't work together when the sprinkler fitter installs the switches and the fire alarm technician wires the switches and programs the panel, the possibility of failures increases. Along these same lines, if the fitter and technician aren't both in attendance at the same time for acceptance testing, the likelihood of failure increases. Dry Sprinkler System Testing Acceptance testing of dry sprinkler systems under NFPA 13 includes the following, at a minimum: Pneumatic testing. 40 psi (2.7 bar) of air pressure for 24 hours measuring the pressure drop that cannot exceed 1.5 psi (0.1 bar). Hydrostatic testing. 200 psi (13.8 bar) or 50 psi (3.4 bar) above static pressure in excess of 150 psi (10.3 bar) for two hours. How do you do this in October through March in most of the northern half of the United States? If you try to do it in cold weather or with cold weather imminent, there is not any way you can get all the water out of the system. If it doesn't freeze and break, you are starting the corro- ground pipe, fittings, valves and their acceptance testing because if the testing is not done properly, it affects the owner, building, occupants and fire sprinkler systems within the building. NFPA 13 in Chapter 28.1 addresses these minimum requirements. The pictures in Figure 1 are from a new apartment building where the underground main blew apart a few months after occupancy, lifting the slab and breaking the roofline when the installing contractor put a PVC retainer flange on a ductile iron pipe. The photograph on the left is after repairs to the spigot piece. The elbow from the bottom of the spigot piece that was connected vertically to ductile iron and horizontally to PVC with PVC retainer flanges is on the right. Figure 2 shows some of what was found when an underground main was not properly flushed. The asphalt, sand, rocks and sticks were in the dry pipe valves, the two sprinkler systems in the attic that were removed piece by piece and flushed, the water softeners, the water heaters, the drinking fountains, the ice makers and so on - all had to be replaced. This was an existing building under remodeling that included installing new fire sprin- kler systems. Fire pumps, dry pipe valves and dry pipe systems (preaction and deluge, too) are very susceptible to dam- age when underground mains are not pressure-tested and flushed correctly. Acceptance testing of underground mains supplying fire sprinkler systems requires water flushing with flows not achieved through a garden hose.
FPE Corner
Fig. 1 Fig. 2
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