Dry Hydrants and Static Water Supplies

Most rural areas growing in size have to address the critical need of establishing a water source for firefighting efforts, especially if they do not have an adequate municipal water system. Without the comfort of knowing that a pressurized fire hydrant is around the corner or just ahead, fire departments must develop a plan that will enable them to access a reliable water source and transport the water to the fire scene.

CONDITIONS AFFECTING WATER SOURCES

The following conditions affect the accessibility and reliability of water sources:

Excessive drafting height (static lift). Excessive drafting height reduces or prevents an adequate flow rate. The pumper is performing double duty: It is working to discharge water and also to draft water from a given height. The theoretical vertical lift of fire apparatus is 14.7 psi (atmospheric pressure at sea level) divided by .4332 lb./ft. equals 33.2 feet maximum vertical lift.

Even though we may theoretically draft from this height, other factors-such as static lift, elevation above sea level, and water vapor pressure-reduce the practical height to 15 feet. Also, five psi must be reserved for the pump. Fire apparatus are designed to pump at 100 percent capacity when drafting from 10 feet. Drafting water from 15 feet reduces the pump capacity to 70 percent and to 60 percent when drafting from 20 feet. It may be more practical to position the pumper to reduce the drafting height. Doing this may increase the hoselay, reducing the flow rate by increasing friction loss. However, this approach does not affect the flow rate as much as excessive drafting height. Here, preplanning is the key to determining the pumper position that will achieve the optimum flow rate.

Soft ground. Soft or moist ground may cause the apparatus to sink. Considering that the average piece of fire apparatus can weigh from 10 to 20 tons, the potential for getting stuck exists. Firefighters working on or around fire apparatus pulling the draft could be seriously injured, and the sinking apparatus could roll over and damage equipment as well.
Obstacles. Vehicles, trees, brush, and large rocks may prevent a pumper from reaching the water source or securing a draft. Often, a vehicle may be blocking a water source when a boat ramp is pres-ent. This could be the ideal spot to pull a draft as long as no land or watercraft is completely blocking you or delaying your getting the apparatus to the water. Natural obstacles, such as trees and rocks, may also prevent entry to the draft area. Brush that has to be cleared also delays drafting.
Steep inclines/declines. The incline or decline from the road to the water source may be excessive for fire apparatus. This brings you back to the predicaments of “How much lift will I need?” and “Do I have enough hard suction?” and “Is the pumper going to topple over?” Steep inclines could also have the water above the level of the pumping apparatus, necessitating that you carry the hard-suction hose up to the source.
Inadequate drafting depth. Drafting requires that two feet of water surround the strainer. Anything less may create a whirlpool effect or, worse, draw up debris. The whirlpool effect can also cause the loss of the draft, which might not be recoverable if the water level was reduced by drafting before the loss in the draft. If using a floating dock strainer, there must be two feet of water below the strainer for drafting.

Plant growth and silt. If not maintained, ponds will develop into swamps. This is a natural process caused by plant growth and silting from the surrounding terrain. This process at first begins around the edges of the pond and works its way inward. Drawing in plant growth will clog strainers, pump intake screens, and even nozzles, reducing the flow rate. Particles act as abrasives, causing deterioration within the pump and reducing drafting ability and pump capacity.

Ice and snow. Excessive snow covering will need to be cleared for the pumper to reach the water source. Once there, firefighters may have to break through thick ice to insert the suction hose and strainer. This is time-consuming and exhausting. In addition, firefighters may fall through thin ice or slip and fall when working on a frozen water source.
Drought. During droughts or even normal dry spells, water sources may become inaccessible because of lower water levels. The water source may shrink in size, leaving ground that cannot support the weight of fire apparatus. If the fire apparatus can park only at a specific location at normal water levels and cannot move closer to the water source, the reduction of the water level could mean that more hard suction is needed. This would indicate that the pump is working at a lower capacity.
Public parking violations. Parking in front of a fire hydrant is a traffic violation. Parking in front of an unmarked water source is not. It is not the person’s fault if the source is not marked; it is our own fault for not properly identifying it. At locations where signs have been posted, they may be stolen or destroyed by vandals. A hydrant is a hydrant, and it is a violation to park in front of it regardless of whether or not a sign is posted. Dry hydrants solve these problems.

DRY HYDRANTS

Dry hydrants are pipes permanently installed within a static water source, such as a pond, stream, river, or holding tank. Artificially created water sources use tanks constructed of fiberglass, concrete, or other materials.

Another type of artificial water source may be combined with natural water sources, such as creating a pond in a stream by constructing a temporary dam. A pond makes drafting from a small stream feasible. Natural water sources provide an almost inexhaustible water supply, but they are susceptible to weather and geological conditions. Artificial water sources are not affected by these conditions, but they contain a limited amount of water.

Among the considerations when installing dry hydrants for natural water sources are accessibility to the dry hydrant, pumper capacity, elevation above sea level, water vapor pressure, and static lift. Pipe installation factors include the type of pipe, horizontal length, vertical length, the number and type of elbows, the strainer, and any reducers, as well as whether standard hydrants will be used.

STANDARD HYDRANTS AS DRY HYDRANTS

Standard hydrants (the type used in pressurized water systems) should not be used as dry hydrants. The loss in psi may be minor in a pressurized system, but it will significantly decrease or prevent the expected gallons per minute. The friction loss is about four psi when delivering 1,000 gpm and increases as the gallons per minute increase.

The negative aspects of using standard hydrants include the following:

Mutual aid might think the hydrant is pressurized.
Adapters may be needed to connect the hard suction to the steamer connection, depending on the size of the suction hose and thread type.
The internal parts (operating stem and valve) will increase friction loss.
The drain could cause failure in drafting if the hydrant is not fully open because the valve is not covering the drain hole, preventing an adequate seal. This type of leak is not a big deal with pressurized water systems. However, it is disastrous when using a dry hydrant.

Some situations may dictate that a standard hydrant be used for drafting purposes-when the water level and the grade level of the land are within 41/2 feet, for example. With a dry hydrant, the water will stay in the pipe and at the same water level as the water source. If the water level is within 41/2 feet of grade, it could freeze in the cold months. It is best to keep the water level below the frost line to prevent freezing. Using a standard type hydrant will enable you to keep the water level below the frost line. The hydrant valve is low enough to keep water from freezing; and, if the hydrant is used, the water will drain out the drain hole and prevent freezing. A standard type hydrant should also be used when the water source is elevated above the hydrant. Then, a valve and drain must be used to prevent freezing.

BETHANY FIRE AND DRY HYDRANTS

The Town of Bethany, Connecticut, initiated the use of dry hydrants in the 1970s to ease the burden of securing a static water supply. Bethany is a rural town with a population of 4,600 and growing. The number of larger homes has been increasing, creating the need for greater volumes of water when fire breaks out. Three water companies own a great deal of the land. Homes and businesses are separated. The narrow, winding roads make securing and maintaining an adequate water supply challenging for the fire department.

To address the problem, pumpers are designed to carry 1,000 gallons of water and from 2,000 to 3,000 feet of large-diameter hose. Our three tankers carry 2,500 to 3,000 gallons of water. Tanker shuttle operations have been adapted and are an integral part of our firefighting operations. These operations require a great deal of personnel. They also create a nightmare on roads not intended to sustain this degree of traffic of large and heavy vehicles.

Installing dry hydrants facilitates tanker shuttle operations and drafting from a static water source. Dry hydrants reduce or eliminate the need for long-distance tanker shuttles because of the strategic planning of dry hydrants. This means that the chance of running out of a continuous water supply is reduced. Where tanker shuttles are not needed, firefighters may now perform actual firefighting duties. Locating a pumper at the hydrant and one at the fire scene and connecting them with large-diameter hose demonstrates a much more efficient operation.

In conjunction with Bethany’s Planning & Zoning Commission, Building Department, Fire Marshal’s Office, and Inland Wetlands Commission, we established procedures for installing dry hydrants throughout the town at no (or very minimal) cost to the taxpayer. At present, there are no plans to install dry hydrants using town funds. However, two town-owned parcels have dry hydrants installed on them. The fire department and the various town agencies are always looking for dry hydrant opportunities.

When developing the specs for dry hydrants in Bethany, the following resources were used as references:

NFPA (National Fire Protection Association) 24, Standard for the Installation of Standpipe and Hose Systems;
NFPA 1141, Fire Protection in Planned Building Groups;
NFPA 1231, Standard on Water Supplies for Suburban and Rural Fire Fighting;
The U.S. Department of Agriculture Dry Hydrant Manual;
The NFPA’s “Planning for Water Supply and Distribution in the Wildland/Urban Interface”;
The Town of Bethany’s “Local Inland/Wetland Rules”;
Rural Fire Fighting Operations, Book Two-Water Supplies and Water Delivery Techniques, Larry Davis (International Society of Fire Service Instructors, 1986); and
IFSTA’s “Water Supplies for Fire Protection” and “Pumping Apparatus.”

WATER SOURCE SPECIFICATIONS

The land developer should be responsible for the engineering and installation of dry hydrants. The fire department should give the developer its requirements, which should be written in an easy-to-read outline format without sacrificing important details. Bethany’s water source requirements or specs are organized as follows: I. Water Sources: A. Natural Water Sources, B. Storage Tanks; II. Fire Department Connection; III. Flow Requirement; IV. Access Lot; and V. Diagrams.

Water Sources-Natural and Storage Tanks

The number of subdivisions is ever increasing. We require a water supply within a subdivision for five or more homes. The developer is responsible for designing and paying for the subdivision’s dry hydrant installation(s). The developer may select a natural water source or install a storage tank. The water sources are to be no more than 4,000 road feet apart. This will allow for a maximum hoselay of 2,000 feet for building lots that use a common driveway or rear building lots. Distance from the dry hydrant cannot exceed 2,000 road feet.

Dry hydrants must also be installed for commercial and industrial occupancies. The dry hydrants must not be more than 1,000 road feet from the occupancy. For commercial and industrial areas having a multitude of building lots, the maximum allowable distance between the two dry hydrants is 2,000 road feet. Many factors dictate where dry hydrants should be located. Among the considerations here are any strategic needs related to the type of occupancies, ease of installation, accessibility, and conformance to specifications.

Natural Water Sources

When installing a dry hydrant in a natural water source, such as a lake or pond, the minimum capacity of water shall be 250,000 gallons. This may seem excessive, but the possibility of drought conditions, ecology, and aquatic life in the water must be considered. Taking water from the source should minimally disturb the ecosystem and the aquatic life of the water source. Water-retention capabilities must be demonstrated, including those for the 50-year-drought provision. (Bethany averages approximately 48 inches of rain each year. The 50-year-drought provision is a calculation representing the worst rain deficit that might be expected every 50 years. The Inland Wetlands Commission uses this statistic along with the 50-year-flood statistic in determining wetland permits. The developer must give this information to the Inland Wetlands Commission before he can obtain the necessary permits.)

Other requirements for natural water are the following:

Static lift shall not exceed 15 feet.
The pipe connecting the water intake with the dry hydrant shall be at least 41/2 feet deep, to prevent freezing. The pipe shall be installed level from the water intake to the hydrant’s 457 riser. The pipe shall have a minimum of a six-inch-diameter schedule 40 PVC or equivalent. Some conditions may dictate that a larger-diameter pipe be installed to satisfy the flow requirement.
The water intake shall be one of the following:-galley type. The galley shall be deep enough to provide a year-round water source, including the 50-year drought level, installed to prevent silting; installed on a cement pad, or equivalent, to prevent settling; and installed to prevent objects such as stones, fish, frogs, and plant debris from entering the intake.-strainer type. The strainer shall be corrosion-resistant screen with a clappered end cap. It shall be deep enough to provide a year-round water source, and the strainer must be encompassed by no less than two feet of water in all directions even when a severe drought is in progress.

Storage Tanks

The tanks shall be constructed of fiberglass by Owens-Corning (Model D-3 or D-6) or approved equivalent.

The tanks must be buried so that the top is 41/2 feet deep, to prevent freezing. The bottom shall be no more than 20 feet from the centerline of the dry hydrant head.
The tanks must be contiguous, not partitioned.
The tanks shall provide for one 22-inch-diameter “accessway” with a ladder, one dry hydrant connection, one fill connection, and a vent. A 48-inch-diameter riser pipe with concrete cover shall be installed over the accessway.
The water intake shall be placed six inches from the bottom of the tank.
The pipe connecting the water intake with the dry hydrant shall have a minimum of a six-inch-diameter schedule 40 PVC or equivalent. Some conditions may dictate that a larger-diameter pipe be installed to satisfy the specified flow requirement.
The vent shall be a schedule 40 PVC pipe and two 90° elbows with a perforated cap.
The fill connection shall be a six-inch schedule 40 PVC pipe with one 90° elbow. The fill connection shall consist of two 21/2-inch female national standard threads and plug.
The vent and fill pipes shall be painted green.
All connections must be airtight.
The tanks shall be initially filled to capacity with clean water.
Runoff from the surrounding terrain shall not enter the tanks.
A tank-full indicator or a visual hatch that will enable anyone filling or inspecting the tank to quickly see that the tank is filled must be installed.
Tanks shall be installed and tested according to the manufacturer’s instructions.
Tanks shall be a minimum of 20,000 gallons for residential locations.
Tanks shall be a minimum of 40,000 gallons for commercial and industrial areas.

Fire Department Connection

The dry hydrant should be designed so that adapters will not have to be used. Most six-inch-diameter hard-suction hose consists of national standard threads with a female connection on one end and a male connection on the other end. When the female end attaches to the pumper, the male end must attach to the dry hydrant. The dry hydrant must consist of a female connection and plug. The dry hydrant shall have two 457 elbows and a connecting pipe constructed of schedule 40 PVC pipe with airtight fittings. Support framework, bars or form, must be included to relieve horizontal and vertical strain on the dry hydrant. This may be combined as part of the barricades as described below. The dry hydrant must have a turn-off valve and a drain (should the water level rise to within 41/2 feet of the surface).

The hydrant shall be protected with at least two barricades painted green or brown, which must be positioned so they do not interfere with hydrant and fire apparatus operations. The barricades may be constructed of (but not limited to) four-inch steel cement filled tubes, fence, guard rails, boulders, or upright posts.
An access lot must be created so that the pumper can safely park off the road.
The hydrant must be elevated two feet from the center of the hydrant to the ground. The hydrant must face the access lot.
The hydrant must be close enough to the access lot to allow fire apparatus using 10 feet of six-inch suction hose to complete the connection.

Flow Requirement

The flow requirement is the most important specification. It is stated as follows: “The dry hydrant must provide 1,000 gallons per minute, with a fire department pumper operating at 100 percent capacity at 150 psi through 10 feet of six-inch suction hose.”

Access Lot

The access lot shall be at least 50 feet long and 15 feet deep, with the deepest point at the hydrant. It also shall support the weight of fire apparatus under all weather conditions. The lot must be shaped to allow easy access for fire apparatus traveling in either direction.

Documentation

An “as built” drawing shall be provided to the Bethany Fire Department describing the installed water source in its entirety. The drawing shall include the following information:

the manufacturer’s name, address, and phone number and the model and type of the hydrant;
the size, type, and full length of the connecting pipe;
the size, type, and number of the elbows;
the name, address, and phone number of the manufacturer and the size and type of the intake and/or strainer;
the name, address, and phone number of the manufacturer and the dimensions, capacity, location (including depth below-ground level) of the tank (if used);
the location and size of all inlets, outlets, inspection ports, and so on, pertaining to the tank (if used);
the height from the intake strainer to the center of the dry hydrant;
the height from the water level to the center of the dry hydrant; and
any other devices or procedures included in the hydrant setup, such as supporting devices, valves, drains, silt dams, tanks, pumps, cisterns, hatchways, piping, and so on.

Owner manuals and all other documentation shall be provided to the Bethany Fire Department.

Any device or procedure pertinent to the operation and maintenance of the water source shall be provided to the Bethany Fire Department.

FACTORS AFFECTING DELIVERY RATE

Natural limitations and design features affect the flow rate from a dry hydrant. The natural limitations of a site cannot be changed. They include the following:

elevation above sea level (measured in psi),
static lift (converted from feet to psi), and
water vapor pressure.

Design features can be changed to achieve the expected delivery rate and include the following:

pipe size in inches;
type of pipe;
total horizontal length of the pipe;
total vertical length of the pipe;
the number and types of elbows, usually 90° or 45°
strainers;
reducers; and
the type of hydrant-standard or dry.

Changing these features will affect the resulting gallons per minute. Increasing the pipe size will decrease the friction loss and increase the gpm. Using 45° elbows instead of 90° elbows will reduce friction loss. Reducers are used to adapt a larger pipe size to the standard six-inch hydrant. Reducers will increase friction loss; however, this is more than compensated for by the greater flow rate of the larger pipe. (The actual procedures for designing a dry hydrant are beyond the scope of this article.1)

BETHANY’S SPREADSHEET SYSTEM

The Bethany Fire Department developed a dry hydrant design EXCELT spreadsheet, which runs on an Apple Macintosh computer. By changing the number, the spreadsheet instantly reports whether a particular design will achieve the expected gallons per minute. If a design will not work, the spreadsheet displays helpful messages explaining the likely reasons. It also indicates which pumpers will take full advantage of the dry hydrant design. The results, with the hydrant identified, may be printed out and filed for later reference.

We believe that when developers create residential and commercial subdivisions, they should provide an impounded water source for fire protection. Fire hydrants are required in towns with municipal water systems. Areas without a municipal water system should not relieve the developer’s responsibility for the requirement. The cost of a dry hydrant may seem prohibitive initially; however, when factoring in the number of structures, the value of each structure, and the average monthly mortgage payment, the cost to the property owner is only a few dollars more per month. If the reduced insurance rates are also factored in, the property owner may benefit. This is a win-win situation for all involved parties: The property owner may reduce his insurance rates and gain peace of mind; the developer benefits from the public safety selling point; and the fire department wins because it operates with fewer personnel and greater efficiency.

Dry hydrants provide accessible and reliable natural water sources and reduce tanker shuttle travel time; eliminate tanker shuttle operations when the fire scene is within the reach of large-diameter hose; simplify and facilitate reliable water transportation to the fire scene; and require fewer personnel when drafting, making fire personnel available for other fireground assignments.

Endnote

1. Rural Fire Fighting Operations, Book Two-Water Supplies & Water Delivery Techniques, Larry Davis (International Society of Fire Service Instructors, 1986), explains these procedures in detail.

MICHAEL HANLEY is the fire department water source commissioner for the Town of Bethany, Connecticut, and drafted the water source specifications for the Bethany Fire Department. He reviews proposed residential and commercial subdivisions and issues requirements and recommendations to the Planning and Zoning Commission and the Inland Wetlands Commission. He works with the Zone Enforcement Office to ensure that all the public safety requirements are met. He is a Connecticut-certified Fire Department Pump Operator.

The water level dictates that a standard hydrant be used. This type of hydrant allows water to drain from the barrel, preventing damage from freezing.

DICK MURCHISON is a lieutenant with the Waterbury (CT) Fire Department and an inspector/estimator with Grinnell Fire Protection Systems in Hartford, Connecticut. He has an associate’s degree in fire technology and administration from Waterbury State Technical College and a bachelor’s degree in fire protection engineering from the University of New Haven in West Haven, Connecticut. He is a certified Fire Service Instructor I in the states of Connecticut and Maine; a certified instructor in incident command, hazardous materials awareness, and hazardous material operational; and an emergency medical technician.

This standard hydrant is gravity-fed from a reservoir, yielding about 800 gpm. A standard hydrant is necessary in this case to allow water to drain from the barrel to prevent damage from freezing. (Photos by author.)

This 45? dry hydrant is fed with an eight-inch PVC pipe, yielding 1,500 gpm. The strainer is protected by a cement galley surrounded by rip-rap (stones). A boulder in front of the hydrant allows the suction hose to rest, relieving stress on the hydrant. It also facilitates hookup when only the driver is present.

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Our first tank installation. It includes, in addition to the tank, a female dry hydrant, a fill pipe, a vent, and an accessway.