432-3
Natural Resources Conservation Service
Conservation Practice Standard
Dry Hydrant
(Each)
Code 432
SOUTH DAKOTA TECHNICAL GUIDE REVIEW
SECTION IV JULY 2004
432-3
Definition
A non-pressurized permanent pipe assembly system installed into water source that permits the withdrawal of water by suction.
Purpose
To provide all weather access and a connection to an available water source for fire suppression.
Conditions Where Practice Applies
At a location where a dependable source of water is available, where transport vehicles can access the site, and where a source of water is needed for fire suppression.
Criteria
Laws and Regulations. This practice must comply with all applicable federal, state, local, and tribal laws and regulations. Laws and regulations of particular concern include those involving water and drainage rights, pollution control, property easements, wetlands, Waters of the United States, preservation of cultural resources, and endangered species.
The hydrant owner shall obtain all necessary easements and permits prior to construction.
Site Conditions. All weather vehicle access to the dry hydrant must be provided. The dry hydrant must be reasonably close to the water source to minimize the length of suction line. The site should be selected in consultation with local fire officials. Special care and maintenance will be required when debris and fine soil particles are part of the water source.
Water Requirement. The water quantity considered available to a dry hydrant is the minimum available (at not over 15 feet total static lift) during a drought. A minimum of 30,000 gallons (1.1 acre-inches) of pumpable water or a minimum pump flow rate of 250 gallons per minute without interruption for 2 hours must be available.
Location and Access. A location map showing the exact site of the hydrant and vehicle access shall be furnished to the local fire department with a copy to the landowner. Letters of approval to use the site shall be obtained from the landowner and from any easement holders prior to construction. The local fire department should review the access, topography, and location prior to installation.
The fire truck connection shall be within 10 feet of the edge of a 12-foot or wider all weather access road. The all weather access road and fire truck pumper connection shall not be located in impoundment pool areas below auxiliary spillway elevation of constructed impoundments.
Fire truck pumping position adjacent to the dry hydrant should not be directly on a public road.
Water supply. The adequacy of the water supply shall meet local criteria. The adequacy of stream flow sources may be determined from analysis of stream gage data.
Pipe. The pipe material may be iron, steel or heavy duty plastic. Plastic pipe shall be schedule 40, SDR-26 (or equal) and protected from ultraviolet light. Pipe shall be 6 inches nominal diameter or larger. The pipe shall be fitted with intake screen or strainer and standard fire truck hose adapters for quick connect/release operations acceptable to the local fire department.
The depth at which the pipe is installed shall be below the frost-free depth for the area.
Pipe Intake and Strainer. Minimum pipe intake depth shall be the elevation needed to produce the water requirement plus two feet and one pipe diameter deeper. Where the intake is more than three feet off the bottom, a trash rack may be used in lieu of a screen or strainer.
Pipes shall be installed on a positive slope toward the water source. The intake screen or strainer shall be supported and secured at least two feet above the bottom of the water source. Surface water intakes shall be at least four feet beyond the earth slope.
The pipe intake entrance must be designed to pass the design pump flow rate at minimum design intake water level.
The strainer and related components shall be fabricated from durable, corrosion resistant material compatible with the pipe, soils, and water. Individual strainer inlet holes shall not exceed 3/8-inch diameter. Screens and strainers shall have a minimum total open area four times the pipe cross sectional area.
A strainer may be formed by drilling 1/4 inch to 3/8 inch diameter holes with a minimum of one hole diameter between the holes in heavy duty PVC pipe. Drill holes shall be deburred and the pipe cleaned before putting the strainer into service.
Screens or strainers shall be capped with a removable end cap. The end cap must be easily removed without unusual (special) tools. Perforations are recommended in the end cap.
Pump Lift. The top of the fire truck pumping connection or centerline of pump (whichever is higher) shall be no more than 15 feet in elevation above the elevation providing the water requirement. Suction hose connections that are not recessed in the ground should be approximately 24 inches above the ground surface, but lower than the fire truck intake.
The total lift (pumping suction head) shall not exceed 20 feet including all losses. Pumping suction head shall include head loss from screen or strainer, elbows, line friction, elevation (static head), and fire truck suction hose.
Dry Hydrant. Dry barrel (conventional) hydrants may not be used due to excess suction loss and the necessity that they be absolutely airtight.
A recessed or flush mount hydrant (below ground-level connection) may be specified for use in areas with special needs, such as in a high vandalism area or for low profile and esthetic needs.
The hydrant head sleeve shall be made of durable non-corrosive metal. The sleeve must be permanently affixed.
The hydrant head shall be able to accept a 6 inch NHT (American National Fire Hose Thread) connection to provide maximum supply. Hydrant (6 inch) head shall conform to ASTM 2466.
All hydrants shall contain a head strainer that can be removed without unusual (special) tools. All hydrants shall be air and water tight.
The dry hydrant cap shall be removable without unusual (special) tools. It shall be joined with a steel cable or chain and be permanently attached to the dry hydrant head. The cap shall be hard plastic or metal that is durable and will not corrode or cause corrosion.
Protection. After dry hydrant installation, the site shall be graded for surface drainage and vegetated or otherwise protected from erosion. Vegetation shall be in accordance with the Critical Area Planting (342) standard.
Considerations
Consider effects of hydrant use on water quantity and quality
Consider effects of sediment production caused by erosion during construction.
Plans and Specifications
Plans and specifications for installing this practice shall meet this standard and describe requirements needed to achieve the purpose.
Operation and Maintenance (O&M)
Prepare an O&M plan for use by the owner/operator. The plan should include the following as appropriate.
Keep the site clear of obstructions and mow the access area regularly to keep the area readily available for emergency use.
Pumper testing of the dry hydrant shall be done at least annually to verify site usability. This test shall include back flushing, followed by a pumper test at the maximum designed flow rate. Careful attention should be given to silt, debris, aquatic growth, or other interference that may limit full operation of the dry hydrant. Provide additional back flushing as needed to maintain immediate operability.
Checks of the intake screen should be made once every five years to identify any sediment build up and to provide information for a clean-out operation or control of aquatic growth.
SOUTH DAKOTA TECHNICAL GUIDE REVIEW
SECTION IV JULY 2004