EMPLOYEE FILLING SUPERSACKS WITH LIMESTONE IN THE SCREEN STONE DEPT., GRABBED THE SACK W/HIS LT. HAND, BACK FACING SACK & PULLED TO SWIVEL SACK EVEN W/PALLET BELOW WHEN THE PIN FROM THE CLEVIS CAME OUT DROPPING THE SCALE, SACK FRAME & 2000 LB. SACK STRIKING THE EE ON THE BACK LEFT SHOULDER.