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When this "traffic model" of dry-barrel hydrant is not in use, an integral drain automatically empties water from the barrel, so it will not freeze and block flow.
Photo credit: Photo courtesy of the author
Performing fire hydrant flow testing in small communities is critical to understanding the water-delivery rate available for firefighting. Flow tests can also uncover distribution system problems while also verifying that hydrants are in proper working order.
Photo credit: Photo courtesy of pollardwater.com
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.
• Dry barrel – In areas of the country that regularly experience below-freezing temperatures, the dry-barrel hydrant is most common. As the name implies, when the dry-barrel hydrant is not in use, it has a barrel that automatically drains so it will not freeze and block water flow. The valve seat is at the bottom of the hydrant, which keeps water below the frost line.
The dry-barrel hydrant must be operated in either the fully open or fully closed position. In a partially open position, the automatic barrel drain lets water continuously escape underground at the hydrant base, causing soil erosion and catastrophic damage.
The traffic model of dry-barrel hydrant is designed to shear, or break in half at ground level, in case of vehicle impact. Its design usually lets the base hydrant water valve stay seated on impact, preventing uncontrolled water release.
• Wet barrel – Wet-barrel hydrants have a barrel that is normally filled with water. They are found where temperatures rarely drop below the freezing point. Each hydrant outlet has its own stem and valve seat. Hydrant outlets can be open, closed or throttled in a partially closed position.
Life of a hydrant
Consider the plight of the pressurized fire hydrant, standing idle for long periods, subject to weather and damage from people and cars, but needing to operate correctly and preferably at a high-gpm delivery rate when called upon in a fire emergency.
Damage from unauthorized use, such as by construction workers, street-cleaning trucks or children trying to keep cool in hot weather, can seriously compromise the function of a hydrant. Unique locking hydrant hardware and hydrant operating nuts and caps that can only be operated with special wrenches can solve this problem.
Even authorized non-emergency hydrant use can be damaging to a fire hydrant’s well-being. Following are three real-life examples of “authorized” abuse:
• Broken valve stem – It was almost quitting time at a fire industry trade show, where we were operating an engine from a supply line in a demonstration area. A co-worker shut off the hydrant without notifying me. This hydrant was left-hand, meaning that the stem nut closed the hydrant valve in a counter-clockwise rotation. Intending to close the valve, he ignored the arrow cast into the hydrant’s top indicating the direction of operation. Using the hydrant wrench to force the stem in the wrong direction, he broke it, so the valve was stuck in the open position.
• Water hammer – Several years ago, a fire commissioner from a rural district was fundraising and performing community service by filling swimming pools using the fire department’s 3,000-gallon tanker. He drove the tanker to a neighboring district to use its pressurized hydrant system to top off the tank before making his next stop. He found a hydrant, connected a short length of three-inch hose and filled the apparatus with a direct tank fill. When the tank was full, he slammed the direct-tank-fill butterfly valve closed. Immediately, the fire hydrant “rocketed out of the ground.” He used an axe to cut the hose, and then got out before he and the tanker could be swallowed by the ensuing sinkhole.
• Partially open hydrant – At a northeastern U.S. state fire academy, we were doing new-product development tests on an engine. The academy had the typical dry-barrel hydrants found in geographic locations that experience freezing temperatures. We were accompanied by a new associate who had “lots of fire service experience.” We asked him to connect a short length of 2½-inch hose from a dry-barrel hydrant to the pony suction on the fire pump, and then to open the hydrant valve.
Thirty minutes later, I glanced at the hydrant and noticed water bubbling out of the ground around it. The valve was only partially open, which leaves the integral barrel drain at the hydrant’s base in the open position, undermining the surrounding rock and soil fill, and causing damage.
To ensure that the water-supply system is fit for firefighting, it is essential to have a suitable fire hydrant-maintenance and flow-testing program in your small community, preferably conducted by the water utility.
The primary purpose of flow testing fire hydrants is to determine pressure and flow-producing capabilities for manual fire suppression within the water distribution system. The tests also determine the general condition of the distribution system and provide information to fire insurance underwriters who set insurance rates. Test results can also be used by mechanical fire protection contractors in the hydraulic design of commercial fire sprinkler systems. n
• National Fire Protection Association 291, Recommended Practice for Fire Flow Testing and Marking of Hydrants, 2013 edition
• American Water Works Association M17: Installation, Field Testing and Maintenance of Fire Hydrants
• Wieder, Michael. Fire Service Hydraulics and Water Supply, second edition