It shall be unlawful for any operator to operate an underground coal mine without the services of a mine manager. Further, it is unlawful for the operator of any coal mine to have in his service as mine manager at his mine, any person who does not hold a certificate of competency issued by the Mining Board of this State; Provided, that whenever any exigency arises by which it is impossible for any operator to secure the immediate services of a certificated mine manager, he may place any trustworthy and experienced man of the mine inspection district in charge of his mine to act as temporary mine manager for a period not exceeding 7 days, and with the approval of the State mine inspector of the district, for a further period not exceeding 23 days.