29 CFR § 1910.425 - Surface-supplied air diving.
(a) General. Employers engaged in surface-supplied air diving shall comply with the following requirements, unless otherwise specified.
(1) Surface-supplied air diving shall not be conducted at depths deeper than 190 fsw, except that dives with bottom times of 30 minutes or less may be conducted to depths of 220 fsw.
(2) A decompression chamber shall be ready for use at the dive location for any dive outside the no-decompression limits or deeper than 100 fsw.
(3) A bell shall be used for dives with an inwater decompression time greater than 120 minutes, except when heavy gear is worn or diving is conducted in physically confining spaces.
(1) Each diver shall be continuously tended while in the water.
(2) A diver shall be stationed at the underwater point of entry when diving is conducted in enclosed or physically confining spaces.
(3) Each diving operation shall have a primary breathing gas supply sufficient to support divers for the duration of the planned dive including decompression.
(4) For dives deeper than 100 fsw or outside the no-decompression limits:
(i) A separate dive team member shall tend each diver in the water;
(ii) A standby diver shall be available while a diver is in the water;
(iii) A diver-carried reserve breathing gas supply shall be provided for each diver except when heavy gear is worn; and
(iv) A dive-location reserve breathing gas supply shall be provided.
(5) For heavy-gear diving deeper than 100 fsw or outside the no-decompression limits:
(i) An extra breathing gas hose capable of supplying breathing gas to the diver in the water shall be available to the standby diver.
(ii) An inwater stage shall be provided to divers in the water.
(6) Except when heavy gear is worn or where physical space does not permit, a diver-carried reserve breathing gas supply shall be provided whenever the diver is prevented by the configuration of the dive area from ascending directly to the surface.