EMPLOYEE WAS OPERATING A CHAIN SAW CUTTING A POST. THE POST WOULDN'T STAY STILL, SO HE CHOSE TO USE THE CHAIN SAW WITH ONE HAND & HOLD THE POST WITH THE OTHER; SAY KICKED, CUTTING THE ARM HOL DING THE POST. CAUSE OF INJURY--UNAWARENESS; COMPLIANCE W/RULES, MINE PROFICIENCY ARE FACTORS, PROTECTIVE EQUIPMENT COULD BE A FACTOR, MINING EQUIPMENT SYSTEMS NOT A FACTOR.