30 CFR § 33.32 Determination of dust concentration.
(a) Concentrations of airborne dust in the test space shall be
determined by sampling with a midget impinger apparatus, and a light-field
microscopic technique shall be employed in determining concentrations of dust
in terms of millions of particles (5 microns or less in diameter) per cubic
foot of air sampled.
(b) Before a drilling test is started the surfaces of the test space
shall be wetted; the test space shall be cleared of air-borne dust insofar as
practicable by mechanical ventilation or other means; and an atmospheric
sample, designated as a control sample, shall be collected during a 5-minute
period to determine residual airborne dust in the test space.
(c) A sample of airborne dust, designated as a test sample, shall be
collected in the breathing zone of the drill operators during the drilling of
each test hole. Time consumed in changing drill steel shall not be considered
as drilling time and sampling shall be discontinued during such periods.
[Sched. 25B, 25 FR 6473, July 9, 1960, as amended at 26 FR 2599, Mar. 28,