THE EMPLOYEE WAS CLEANING THE FLOOR UNDER THE PRIMARY PLANT SCREEN, REMOVING EXCESS MATERIAL WITH A MOBILE EQUIPMENT ""BOBCAT"". A PVC WATER PIPE WAS BROKEN AND THE EMPLOYEE UNBUCKLED HIS SAFETY BELT AND INCLINED HIS BODY UP TO LOOK AND AT THAT MOMENT THE UPPER BUCKET FELL TRAPPING HIM BETWEEN THE BUCKET AND THE FRONT HOOD EQUIPMENT. HE RECEIVED CONTUSIONS TO CHEST, SHOULDERS & BACK.