EMPLOYEE WAS CONDUCTING A PRE-OP CHECK ON TR 897-LO-TRAC, WHEN HE RAISED THE ENGINE HOOD TO CHECK THE ENGINE OIL LEVEL, HE SLIPPED AND HIS LEFT ARM WAS CAUGHT BETWEEN THE ENGINE COMPARTMENT AN D THE HOOD. EMPLOYEE WAS EVALUATED AT MESA CLINIC AND THE X-RAY REVEALED A FRACTURE TO THE LEFT ARM.