30 CFR 57.4462 - Storage of combustible liquids underground.
The requirements of this standard apply to underground areas only.
(1) Capable of withstanding working pressures and stresses and compatible with the type of liquid stored;
(2) Maintained in a manner that prevents leakage;
(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; and
(4) Separated from explosives or blasting agents, shaft stations, and ignition sources including electric equipment that could create sufficient heat or sparks to pose a fire hazard. Separation shall be sufficient to prevent the occurrence or minimize the spread of fire.
(b) Storage tanks shall be vented or otherwise constructed to prevent development of pressure or vacuum as a result of filling, emptying, or atmospheric temperature changes. Vents for storage of Class II or IIIA liquids shall be isolated or separated from ignition sources.
(d) All piping, valves, and fittings shall be:
(1) Capable of withstanding working pressures and stresses;
(2) Compatible with the type of liquid stored; and
(3) Maintained in a manner which prevents leakage.