; and (3) by adding at the end the following: (2) Methods of measurement (A) In general Each operator of an underground coal mine shall take accurate and representative samples which shall measure the total incombustible content of combined coal dust, rock dust, and other dust in such mine to ensure that the coal dust is kept below explosive levels through the appropriate application of rock dust. (B) Direct reading monitors In order to ensure timely assessment and compliance, the Secretary shall, not later than 180 days after the date of enactment of the Robert C. Byrd Mine Safety Protection Act of 2017 , require operators to measure total incombustible content (or an equivalent measure of explosibility) in samples of combined coal dust, rock dust, and other dust, using direct reading monitors that the Secretary has approved for use in an underground coal mine, such as coal dust explosibility monitors. (C) Regulations The Secretary shall, not later than 180 days after the date of enactment of the Robert C. Byrd Mine Safety Protection Act of 2017 , promulgate an interim final rule that prescribes methods for operator sampling of total incombustible content (or an equivalent measure of explosibility) in samples of combined coal dust, rock dust, and other dust using direct reading monitors and includes requirements for locations, methods, and intervals for mandatory operator sampling. (D) Recommendations Not later than 1 year after the date of enactment of the Robert C. Byrd Mine Safety Protection Act of 2017 , the Secretary of Health and Human Services shall, based upon the latest research, recommend to the Secretary of Labor any revisions to the mandatory operator sampling locations, methods, and intervals included in the interim final rule described in subparagraph (B) that may be warranted in light of such research. (3) Limitation Until a final rule is issued by the Secretary under section 502(b)(2) of the Robert C. Byrd Mine Safety Protection Act of 2017 , any measurement taken by a direct reading monitor