30 CFR § 70.300
Respiratory equipment; respirable dust.
Respiratory equipment approved by NIOSH under 42 CFR part 84 shall be made
available to all persons whenever exposed to concentrations of respirable
dust in excess of the levels required to be maintained under this part. Use
of respirators shall not be substituted for environmental control measures
in the active workings. Each operator shall maintain a supply of respiratory
equipment adequate to deal with occurrences of concentrations of respirable
dust in the mine atmosphere in excess of the levels required to be maintained
under this part.
[35 FR 5544, Apr. 3, 1970, as amended at 47 FR 28095, June 29, 1982; 60 FR 30398, June 8, 1995]