The mine foreman or superintendent shall, once each week, direct and see that the methane content of the ventilating current or currents is determined by analyses or by an instrument capable of accuracy to .1%. The samples or the determinations shall be taken on the return end of the air circuit or circuits just beyond the last working place, unless otherwise directed by the department, and a correct report of these determinations shall be promptly furnished to the department. The determinations or samples shall be taken on days when individuals are working and recorded in a book provided for that purpose.
52 P.S. § 690-238