The agency said it was believed the operator removed the drill steel from the hole while rotation was still activated.
In its latest alert under its accident prevention program, MSHA suggests mines “ensure that mast type roof bolting machines have drill guides and deep wall chucks” and most importantly that rotation is stopped one foot before exiting the hole.
To avoid injuries, operators should never touch or hold onto a rotating drilling tool, wrench or bolt.
MSHA said mines should ensure that proper drill feed and rotation pressures were being used – only pushing pressures as high as necessary to efficiently drill the roof.
“To prevent the whipping drill steels, drill rotation speed should never exceed 700 rotations per minute, unless the manufacturer recommends a higher rate,” MSHA warned.
General tests and maintenance are also essential and emergency shut-off switches, drill guides and all other safety equipment should be routinely tested and maintained.
