29 CFR §1910.424

1. (a)General. Employers engaged in SCUBA diving shall comply with the following requirements, unless otherwise specified.
2. (b)Limits. SCUBA diving shall not be conducted:
   1. (1)At depths deeper than 130 fsw;
   2. (2)At depths deeper than 100 fsw or outside the no-decompression limits unless a decompression chamber is ready for use;
   3. (3)Against currents exceeding one (1) knot unless line-tended; or
   4. (4)In enclosed or physically confining spaces unless line-tended.
3. (c)Procedures.
   1. (1)A standby diver shall be available while a diver is in the water.
   2. (2)A diver shall be line-tended from the surface, or accompanied by another diver in the water in continuous visual contact during the diving operations.
   3. (3)A diver shall be stationed at the underwater point of entry when diving is conducted in enclosed or physically confining spaces.
   4. (4)A diver-carried reserve breathing gas supply shall be provided for each diver consisting of:
      1. (i)A manual reserve (J valve); or
      2. (ii)An independent reserve cylinder with a separate regulator or connected to the underwater breathing apparatus.
   5. (5)The valve of the reserve breathing gas supply shall be in the closed position prior to the dive.