(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.