(a) Drilling tests shall be conducted in a test space formed by two curtains suspended across a mine opening in such a manner that the volume of the test space shall be approximately 2,000 cubic feet.
(b) No mechanical ventilation shall be provided in the test space during a drilling test, except such air movement as may be induced by operation of drilling- or dust-collecting equipment.
(c) All parts of a unit or system shall be within the test space during a drilling test.
source: Schedule 25B, 25 FR 6473, July 9, 1960, unless otherwise noted.
cite as: 30 CFR 33.31