Open diving bells.

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 (2) Protected against and maintained free from injurious corrosion.