30 CFR § 57.22315
Self-contained breathing apparatus (V-A mines).
Self-contained breathing apparatus of a duration to allow for escape from the
mine and sufficient in number to equip all persons underground shall be
strategically located throughout the mine. Such apparatus shall be approved
by MSHA and NIOSH under 42 CFR part 84 and shall be maintained in accordance
with manufacturers' specifications. This standard does not apply to double
entry mining systems where crosscut intervals do not exceed 250 feet.
[60 FR 30398, June 8, 1995]