EE WAS REMOVING AN OVERHEAD CHAIN FALL (HOIST) FROM THE RIGGING, STANDING ON 6' STEP LADDER TO REACH THE UNIT HANGING OVERHEAD. THE CHAINFALL SAFETY LATCH CAUGHT ON THE RIGGING CAUSING THE EE TO PULL ON THE UNIT. THE UNIT BACAME LOOSE CAUSING THE EE TO LOSE HIS BALANCE CAUSING HIM TO FALL APPROX. 4' FROM THE 6' STEP LADDER LANDING ON HIS RIGHT ARM.