INVESTIGATION INDICATES EMPLOYEE WAS INSTALLING ROOF BOLTS IN THE FACE OF THE 3X4 ON THE 2 RT SECTION. HE HAD INSTALELED THE OUTSIDE ROOF BOLT AND WAS POSITIONING TO INSTALL INSIDE BOLT WHEN A RIB AND ROOF BROW ROLLED, THE BROW WAS APPROXIMATELY 10"" THICK BY 60"" LONG CONTAINING ROOF SHALE OF UNDETERMINED THICKNESS AND UP TO 43"" WIDE. THIS STRUCK THE HIM CAUSING INJURY