30 CFR § 71.205 - Approved sampling devices; operation; air flowrate.
(a) Approved sampling devices shall be operated at the flowrate of 2.0 L/min, if using a CMDPSU; at 2.2 L/min, if using a CPDM; or at a different flowrate recommended by the manufacturer.
(b) If using a CMDPSU, each sampling device shall be examined each shift by a person certified in sampling during:
(1) The second hour after being put into operation to assure it is in the proper location, operating properly, and at the proper flowrate. If the proper flowrate is not maintained, necessary adjustments shall be made by the certified person.
(2) The last hour of operation to assure that it is operating properly and at the proper flowrate. If the proper flowrate is not maintained, the respirable dust sample shall be transmitted to MSHA with a notation by the certified person on the back of the dust data card stating that the proper flowrate was not maintained. Other events occurring during the collection of respirable dust samples that may affect the validity of the sample, such as dropping of the sampling head assembly onto the mine floor, shall be noted on the back of the dust data card.
(c) If using a CPDM, the person certified in sampling shall monitor the dust concentrations and the sampling status conditions being reported by the sampling device at mid-shift or more frequently as specified in the approved respirable dust control plan, if applicable, to assure: The sampling device is in the proper location and operating properly; and the work environment of the occupation being sampled remains in compliance with the applicable standard at the end of the shift.