When workings are being driven toward any worked out and inaccessible or abandoned area or a shaft, that may contain accumulations of gases or water and cannot be inspected, they shall be narrowed to eight feet or less in width. Persons driving these workings shall constantly keep one bore hole near the center of the working and 20 feet in advance and one bore hole 15 feet deep in each rib at a 45 degree angle and at intervals of six feet as the face is advanced. These test holes shall not be used for blasting. Separate blasting holes, not over four feet deep, must be drilled. These precautions must begin at least 100 feet from the probable source of danger.