Each open diving bell must--
(a) Have an upper section that provides an envelope capable of maintaining a bubble of breathing mixture available to a diver standing on the lower section of the platform with his body through the open bottom and his head in the bubble;
(b) Have lifting equipment capable of returning the occupied open bell to the dive location;
(c) Have an umbilical; and
(d) Be--(1) Made of corrosion-resisting material; or
(1) Made of corrosion-resisting material; or
(2) Protected against and maintained free from injurious corrosion.