(a) Except as allowed in paragraph (b) of this section, a tank with a diameter of—

(1) 6 feet or less must have a shell and head of 3⁄16 inch thickness or more; or

(2) More than 6 feet must have a shell and head of 1⁄4 inch thickness or more.

(b) If the tank has additional framework to guard against accidental puncturing of the tank, the shell and head thickness must be 1⁄8 inch or more.