In compressed air tunneling, the volume of free air provided is______________?
In compressed air tunneling, the volume of free air provided is______________?
A. 6 mJ per second per m2 of face area
B. 6 m3 per minute per m2 of face area
C. 20 m3 per minute per m2 of face area
D. 6 m3 per hour per m2 of face area