29 CFR 1910.426 - Mixed-gas diving.
(a)General. Employers engaged in mixed-gas diving shall comply with the following requirements, unless otherwise specified.
(b)Limits. Mixed-gas diving shall be conducted only when:
(1) A decompression chamber is ready for use at the dive location; and
(i) A bell is used at depths greater than 220 fsw or when the dive involves inwater decompression time of greater than 120 minutes, except when heavy gear is worn or when diving in physically confining spaces; or
(ii) A closed bell is used at depths greater than 300 fsw, except when diving is conducted in physically confining spaces.
(1) A separate dive team member shall tend each diver in the water.
(2) A standby diver shall be available while a diver is in the water.
(3) A diver shall be stationed at the underwater point of entry when diving is conducted in enclosed or physically confining spaces.
(4) Each diving operation shall have a primary breathing gas supply sufficient to support divers for the duration of the planned dive including decompression.
(5) Each diving operation shall have a dive-location reserve breathing gas supply.
(6) When heavy gear is worn:
(i) An extra breathing gas hose capable of supplying breathing gas to the diver in the water shall be available to the standby diver; and
(ii) An inwater stage shall be provided to divers in the water.
(7) An inwater stage shall be provided for divers without access to a bell for dives deeper than 100 fsw or outside the no-decompression limits.
(8) When a closed bell is used, one dive team member in the bell shall be available and tend the diver in the water.
(9) Except when heavy gear is worn or where physical space does not permit, a diver-carried reserve breathing gas supply shall be provided for each diver:
(i) Diving deeper than 100 fsw or outside the no-decompression limits; or
(ii) Prevented by the configuration of the dive area from directly ascending to the surface.