MSHA - Code of Federal Regulations - 30 CFR 33.31
30 CFR § 33.31
(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.