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When I ask fire officers across the country about their small towns’ fire hydrant and pressurized water supply system flow capabilities, their answers are often unclear, ranging from “marginal at best” to “totally inadequate for firefighting.”
Without a clear understanding of flow rates from pressurized hydrants, firefights 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.
When did your community’s water supply system last receive attention? Does the water utility operator perform a regularly scheduled hydrant maintenance program? How long has it been since hydrants were flushed, serviced and individually flow tested? Do you know the flow and pressure available from each hydrant in your community?
National Fire Protection Association (NFPA) pamphlet 291, Recommended Practice for Fire Flow Testing and Marking of Hydrants, 2013 edition, recommends that public fire hydrants be flow tested every five years to verify capacity and marking of the hydrant. They also recommend hydrants be flushed at least annually to verify operation and reliability, and to detect repair needs. Flow testing hydrants can uncover many water-supply system issues, including closed or partially closed hydrant service valves, tuberculation (the production of mounds of rust on the inside of pipes), foreign objects maliciously placed inside hydrant barrels and so on.
The key phrase here is “water-supply system,” which includes not only the hydrant, but all of the valves and piping upstream of the hydrant. All of the system’s components and its overall design impact fire hydrant performance.
There are generally three models of water distribution system ownership and operation: a municipal government, a public trust or authority and a private contractor. The owner/operator of the water distribution system, otherwise know as the water utility company, is usually the Authority Having Jurisdiction (AHJ) over its use. The AHJ sets policy on how, when or if the local fire department is authorized to conduct hydrant flow testing. Rules, regulations, policy and agreements can vary widely at the local level.
According to the American Water Works Association’s M17: Installation, Field Testing, and Maintenance of Fire Hydrants, “In many small communities, especially where the water purveyor is not the same political entity as the fire department, agreements have been made with the individual fire departments to maintain and test fire hydrants. While this practice is worthwhile, it should be remembered that unless there is a verifiable agreement, the owner of the hydrant retains responsibility for maintenance and inspection of the hydrant.”
To force water from the source to the consumer, water utilities use gravity, direct pumping or a combination of the two. Combination systems, those that use both gravity and pumps, are most common.
Water-distribution systems use various pipe sizes. Primary feeders are large pipes with wide spacing that convey water to various parts of the system for distribution to smaller mains. Secondary feeders are a network of intermediate-size pipes that reinforce the grid within various loops of the primary feeder system. Distributors are a grid arrangement of smaller mains serving individual fire hydrants and blocks of consumers.
Isolation valves, used for system repairs, are strategically installed throughout water-supply system piping. They can be a problem, as they may be accidentally left closed or partially closed, along with the hydrant’s service valve, which is located only a few feet from the hydrant. Hydrant testing can determine whether a water-supply system is operating as designed and whether a functioning water-supply system can provide an adequate flow of water for the target hazards in the testing area.