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L ast month, we explained that without a clear understanding of flow rates from pressurized hydrants, firefighting operations that rely on them as a water source can turn into reckless gambles instead of calculated maneuvers. Measuring hydrant flow rate is virtually the only way to know the firefighting value of a water supply system. Now, we will review some planning considerations for hydrant flow testing.
Testing provides valuable information for pre-fire water-supply planning of target hazards in the test area. When collecting data, your goal is to produce a graph showing a hydrant water flow curve with a delivery rate in gallons per minute (gpm) available over a range of residual hydrant pressures.
Fire hydrants can be broadly classified into two groups – standard and non-standard. A standard hydrant has one large-diameter outlet called the pumper or steamer connection. It also has two 2½-inch discharges called hose connections. Non-standard fire hydrants, which may be installed based on local needs, come in different configurations and may have multiple 2½-inch discharge openings. The typical hydrant is coupled to the water supply system piping through a six-inch water main connection, which is where the hydrant’s service valve is located.
• Markings – National Fire Protection Association (NFPA) Pamphlet 291, Recommended Practice for Fire Flow Testing and Marking of Hydrants, 2013 edition, recommends color-coding for hydrants based on flow rate: 1,500 gpm or greater is light blue; 1,000 to 1,499 gpm is green; 500 to 999 gpm is orange; and less than 500 gpm is red. Color-coded covers installed on discharge caps are highly visible and are a good alternative to painting a hydrant; see Figure 1. It is also a good idea to install flags or markers to locate hydrants in snow and to prevent damage from plows. Inoperable or out-of-service hydrants should be written up for repair and clearly marked or covered as shown in Figure 2.
• Testing – It is important that hydrant testing be conducted by qualified personnel. In many areas, the water utility is the Authority Having Jurisdiction (AHJ) over the water-supply system, responsible for hydrant maintenance and flow testing. If this is true in your community, contact the AHJ and have a fire department representative present for flow-test verification. Before fire department personnel take on the task of conducting hydrant testing, contact the AHJ for approval and obtain and follow two essential documents: NFPA 291 and the American Water Works Association’s M17, Installation, Field Testing and Maintenance of Fire Hydrants.
• Tools – To perform a hydrant flow test, you will need a typical hydrant bag, which contains a hydrant wrench, rubber mallet and spanners, along with a curb valve key to shut off a hydrant’s service valve if problems develop. You can perform a hydrant flow test with a standard pitot tube, but a suitable hydrant test kit is a good idea as calibrated equipment increases accuracy and ease of calculating flow test results.
The test kit shown in Figure 3 is equipped with a hydrant wrench, pitot tube, 2½-inch stream shaper and 2½-inch hydrant cap with calibrated gauge and bleeder. It also includes several pressure gauges and tables to easily calculate flow rates.
• Site inspection – Inspect the site before testing and plan for a large volume of water discharge and subsequent runoff. Do not test during freezing weather. Plan to provide vehicle traffic control if water streams will discharge into streets.
Before testing, check hydrants for visible signs of problems and damage. These may include obstructions such as sign posts, fences or shrubbery; obvious strike damage; dented, ungreased or non-operational caps and threads; a stripped valve stem operating nut; or a leaking valve seat. With dry-barrel hydrants, check for a barrel full of water which indicates that the automatic drain is inoperable. Immediately document hydrant deficiencies and submit to the water utility company, as damaged hydrants must be repaired before testing.