30 CFR § 75.326
Mean entry air velocity.
In exhausting face ventilation systems, the mean entry air velocity shall
be at least 60 feet per minute reaching each working face where coal is being
cut, mined, drilled for blasting, or loaded, and to any other working places
as required in the approved ventilation plan. A lower mean entry air velocity
may be approved in the ventilation plan if the lower velocity will maintain
methane and respirable dust concentrations below the applicable levels. Mean
entry air velocity shall be determined at or near the inby end of the line
curtain, ventilation tubing, or other face ventilation control devices.
[61 FR 9828, Mar. 11, 1996; 61 FR 29288, June 10, 1996]