30 CFR § 57.4505
Fuel lines to underground areas.
Fuel lines into underground storage or dispensing areas shall be drained at
the completion of each transfer of fuel unless the following requirements are
(a) The valve at the supply source shall be kept closed when fuel is
not being transferred.
(b) The fuel line shall be--
(1) Capable of withstanding working pressures and
(2) Located to prevent damage; and
(3) Located in areas free of combustible materials or in
areas where any exposed combustible materials are coated with one inch of
shotcrete, one-half inch of gunite, or other noncombustible material with
equivalent fire protection characteristics.
(c) Provisions shall be made for control or containment of the entire
volume of the fuel line so that leakage will not create a fire hazard.