21 JANUARY 2003
Follow NFPA 30 for capacity of diked enclosures, except where NFPA refers to the volumetric
capacity of the tank or tanks. Instead, add the volume for a five-year, one-hour-duration storm, or
one-foot freeboard, whichever is greater. The standard Air Force dike for large vertical tanks is
constructed of earth with at least 76 millimeters (3 inches) of reinforced concrete paving on the top
and slopes (see MIL-HDBK-1022A). Proper joint placement with a fuel-resistant joint sealer is a
critical design and construction element. The dike floor is typically crushed stone with a concrete
work ring surrounding the tank ring wall. If a concrete floor is desired it must be justified on an
economic basis. Usually a liner is placed beneath the dike, but a spray-on coating is also acceptable
where a concrete floor is also installed. Individual tanks larger than 10,000 barrels should be
enclosed in individual dikes. Several small tanks (less than 10,000 barrels each) may be enclosed in
one dike, up to a total capacity of 15,000 barrels. Where two or more tanks are in one dike, subdivide
it using 0.45-meter-tall (18-inch-tall) intermediate dikes. Slope the dike to carry drainage to the dike
drain. A swing line or locked drain valve will be used depending on weather requirements. A swing
line that may be raised or lowered in the interior of the diked area will be used in cold-weather areas.
A drain with a locking gate valve will be used where freezing conditions do not present a problem.
This valve must stay in the closed and locked position until the dike is drained. The valve is staffed
during drainage operations to prevent possible discharge of fuel pollutants into sanitary systems or
bodies of water. Water from the dike will be discharged as required by governing environmental
regulations. All piping within the dike must be fire-resistant, such as steel or stainless steel. Avoid
aluminum within the diked area.
7.5.2. Alternate Diking Construction. Earth dikes and basins around fuel storage tanks require
continuous maintenance to prevent erosion and eliminate vegetation. Some installations have applied
a nonselective soil sterilizer to the top and inside surfaces of the dike to eliminate vegetation. The
surfaces are treated with at least 76 millimeters of crushed rock or pit run gravel. To hold the rock in
place, Geotextiles or sprayed-on asphalt can be used. Inspect the earth dikes according to
requirements outlined in paragraph 10.8.1.