Dry fire Hydrants
Planning for dry hydrants involves several
considerations and should
involve all affected agencies and private concerns so a coordinated
effort can take place. Some factors to consider are:
Current & future population.
Existing & future
buildings
Property values protected.
Potential for loss.
Fire history of the area protected.
Current water supply systems.
Other potential water sources.
Cost of project.
Equipment and personnel of the local
fire dept.
Training needs of the fire department.
Other specific factors of local concern.
Dry Hydrant Location and Design
The location of individual dry hydrants is also influenced by
several factors. Close proximity to an all-weather roadway between
10-20' from edge of roadway is ideal. For economical and
installation ease, a pond between 50-100' from the roadway edge is
preferred. It is extremely important to coordinate the exact
location with the local fire department.
Maximum distance of travel between dry hydrants.
This can vary for several reasons, but one target
distance could be one dry hydrant every 3 square miles. This would
produce a travel time of about 6 minutes between the water and the
fire, assuming an average safe constant speed for a loaded truck of
35 mph. NFPA
1231 contains numerous design criteria, such as a recommendation
for a 6-inch minimum inside diameter of the pipe and limit of 10 to
12 feet for static lift. Use a minimum number of elbows. NFPA
1231 also provides a work sheet for calculating various head loss of
the design.
Ownership of the land.
It is recommended the fire department should contact the legal
property owner to secure written permission (in conjunction with the
town or county attorney) to use the water source. If a possible dry
hydrant site is along a road right of way, you will need town,
county or state approval. In some cases Corps of Engineers approval
may also be needed. Obtaining written permission is an important
requirement that may take some time.
Depth of water at the source.
Careful note should be made about the useful depth of a lake or
pond, which is from the minimum foreseeable low-water surface level
to the top of the suction strainer (not the bottom of the lake). The
low-water mark considers drought, freezing and other effects, such
as where the water level is lowered to generate power. The absolute
lowest level must be not less than 2 feet, to prevent a vortex or
whirlpool, which could allow air to enter the pump and cause loss of
pump prime. You may need a minimum of 4 to 5 feet of water over the
suction screen and pipe during low water to prevent a freeze-up of
the screen. An overall depth of 8' is desired. With the intake
strainer being located 2' above the bottom.
Composition of the bottom material.
For long-term useful hydrant operation, the best composition for the
bottom of a lake, stream or pond is sand, gravel or rock or a
combination of these. Decaying vegetative matter could clog the
suction screen.
Ease of digging.
A backhoe will need to get close enough to the water's
edge to reach out and dig at least 5 feet below the surface of the
water to start the trench. Protection of the connection. A location
that is conveniently accessible to fire apparatus may also be
exposed to accidents from other passing vehicles. An impact barrier
constructed of partially buried posts may be needed to prevent a
vehicle from destroying a dry hydrant in a heavily traveled area.
Special markings may be necessary to avoid damage from snow plows.
Measurement for the proper amount of materials.
Use of a design worksheet will assist in calculating the materials
needed including total length of piping materials, couplings and
elbow. It is better to have too much pipe than too little. Use a
minimum number of joints. Design sheets are available at our
office.
Costs.
The expense of a dry hydrant installation depends on
local
practices and the length of pipe needed. Our experiences estimated
the cost there to be between $500 and $750, including the cost for
contractor labor and machines if the distance from hydrant head to
pond is between 50-75'.
Beware of other utilities in the digging area.
You must carefully check for the presence of buried lines and pipes
and notify utility companies before you start digging. Contacting
Ohio Utility Protection Service is a must.