While the US Mine Safety and Health Administration did not identify the location or the identity of the injured worker, it did confirm the operator was struck by an unrestrained rotating steel drill, and investigators believe the drill steel was removed from the hole while rotation was still activated.

In hopes of preventing other similar accidents, MSHA stressed that bolters stop drill rotation one foot before exiting the drill hole, and never to touch a rotating tool, wrench or bolt.

Mines should ensure the proper drill feed and rotation pressure are being used, as the pressure should only be as high as needed to drill the roof efficiently.

Both well guides and deep well chucks should be on board mast-type bolting machines, and the guides should be well maintained. All units also should have operational emergency shut-off switches.

As with any other piece of equipment underground, the agency said, all bolters, including drill guides and safety equipment, should be thoroughly examined on a regular basis. Additionally, all workers with access to the machine should be task trained, including the use of drill guides and proper overall drilling processes.

Finally, MSHA said, mines should always take care to prevent whipping steel drills.

Drill rotation should never exceed 700 revolutions per minute unless the manufacturer recommends a higher rate.

More information on drilling safety and regulations can be found on MSHA’s web site.