EE WAS OPERATING A MANTRIP. HE WAS IN A CLOSE CLEARANCE AREA. A PIECE OF SLATE THAT HAD FALLEN OUT FROM BETWEEN THE LAST ROW OF BOLTS AND THE RIB WAS ANGLED OUTWARD INTO THE TRAVELWAY. THE ACC IDENT INVESTIGATOR AND THE INJURIES SUSTAINED INDICATE THAT HE WAS RESTING HIS ARM ON THE OUTER FRAME OF THE MANTRIP & WHEN HE PASSED THIS PIECE OF SLATE IT STRUCK HIS ARM CAUSING EVULSION