EMPLOYEE WAS INSTALLING A CLEAN-UP SIEVE IN THE PLANT WHEN HE FELT PAIN IN THE LOWER PART OF HIS BACK. THEN ON 9/9/03 HE WAS LIFTING A 55 LB BAG OF MATERIAL WHEN THE PAIN GOT WORSE. HE WENT TO THE DOCTOR ON 9/10 AND MISSED TWO DAYS OF WORK. IT BECAME REPORTABLE 9/10/03.