46 CFR § 197.334 - 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;
(c) Have an umbilical; and
(d) Be -
(1) Made of corrosion-resisting material; or
(2) Protected against and maintained free from injurious corrosion.