(a) Diesel fuel tanks used underground shall—

(1) Have steel walls of a minimum 3/16-inch thickness, or walls made of other metal of a thickness that provides equivalent strength;

(2) Be protected from corrosion;

(3) Be of seamless construction or have liquid tight welded seams;

(4) Not leak; and

(5) For stationary tanks in permanent underground diesel fuel storage facilities, be placed on supports constructed of noncombustible material so that the tanks are at least 12 inches above the floor.

(b) Underground diesel fuel tanks must be provided with—

(1) Devices for emergency venting designed to open at a pressure not to exceed 2.5 psi according to the following—

(i) Tanks with a capacity greater than 500 gallons must have an emergency venting device whose area is equivalent to a pipe with a nominal inside diameter of 5 inches or greater; and

(ii) Tanks with a capacity of 500 gallons or less must have an emergency venting device whose area is equivalent to a pipe with a nominal inside diameter of 4 inches or greater.

(2) Tethered or self-closing caps for stationary tanks in permanent underground diesel fuel storage facilities and self-closing caps for diesel fuel tanks on diesel fuel transportation units;

(3) Vents to permit the free discharge of liquid, at least as large as the fill or withdrawal connection, whichever is larger, but not less than 1 1/4 inch nominal inside diameter;

(4) Liquid tight connections for all tank openings that are—

(i) Identified by conspicuous markings that specify the function; and

(ii) Closed when not in use.

(5) Vent pipes that drain toward the tank without sagging and are higher than the fill pipe opening;

(6) Shutoff valves located as close as practicable to the tank shell on each connection through which liquid can normally flow; and

(7) An automatic closing, heat-actuated valve on each withdrawal connection below the liquid level.

(c) When tanks are provided with openings for manual gauging, liquid tight, tethered or self-closing caps or covers must be provided and must be kept closed when not open for gauging.

(d) Surfaces of the tank and its associated components must be protected against damage by collision.

(e) Before being placed in service, tanks and their associated components must be tested for leakage at a pressure equal to the working pressure, except tanks and components connected directly to piping systems, which must be properly designed for the application.

(f) Safety cans must be:

(1) Limited to a nominal capacity of 5 gallons or less;

(2) Equipped with a flexible or rigid tubular nozzle attached to a valved spout;

(3) Provided with a vent valve designed to open and close simultaneously and automatically with the opening and closing of the pouring valve; and

(4) Designed so that they will safely relieve internal pressure when exposed to fire.