All mines, except those mines or locations in a mine that are too wet or too high in incombustible content to propagate an explosion, shall be rock dusted. The rock dusting shall be done with such regularity and frequency that all surfaces required to be rock dusted shall be kept in such condition that the incombustible content of the adhering and lodging dust is not less than sixty-five per cent. When methane is present in any ventilating current, such incombustible content shall be not less than sixty-five per cent plus one and four-tenths per cent for each one tenth of one per cent of methane so present.

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The rock dust to be used shall be pulverized limestone or any other material containing less than five per cent combustible material. All dust shall be so pulverized that it will all go through a sieve that has twenty openings to the linear inch and at least fifty per cent of such dust shall pass through a sieve with two hundred openings to the linear inch. The rock dust shall not contain more than four per cent free silicon and silicon dioxide.

The rock dust shall be distributed on top, bottom, and sides of all haulageways, traveling ways, developing entries, and rooms to within forty feet of face. Back entries shall be rock dusted for at least one thousand feet out by the junction with the first active entry.

In coal mines where rock dusting is required, the superintendent shall see that a representative sample of dust is gathered at each sampling point from the roof, sides, and floor of all entries by a competent person once each sixty days and tested to determine if any part of the mine requires redusting, and a record shall be kept in a book furnished by the division of mineral resources management for that purpose. Such books shall be kept in the mine office. Such record shall show the location at which samples have been taken and the results of the analyses or tests. The distance between sampling points on haulageways and traveling ways shall not exceed two thousand feet, but in developing entries and in entries producing coal from rooms or pillars and their parallel entries the distance between sampling points shall not exceed five hundred feet.

No operator of a mine shall refuse or neglect to comply with this section.