NEITHER OPERATOR NOR LABORER FOLLOWED PROPER LOCK-OUT PROCEDURE WHICH LEAD TO UNIT ACTIVATING. INJURED EE WENT IN TO FEEDER TO CLEAR ROCKS. OPERATOR SAW LABORER CLIMB OUT & LEANED OVER TO YEL L AT LOADER OPERATOR ON RADIO NOT TO DROP BUCKET OF MATERIALS. AS HE LEANED OVER, OPERATOR HIT FEEDER BUTTON & LABORER FELL ONTO BELT.