EE WAS CLEANING ROCK BUILD UP FROM UNDER FEED TUBE. THE TUBE WAS RAISED UP TO CLEAN ROCK FROM TOP OF ADJUSTMENT RING COVER. THE TUBE WAS HOOKED TO BOOM TRUCK WITH 2 WAY SPREADER CHAINS. WHEN ANOTHER EE CLEARED A ROCK THE TUBE ROCKED FORWARD AND STRUCK EE'S LEG, PINNING HIS LEG BETWEEN FEED TUBE AND ADJUSTMENT RING COVER.