REPAIRMEN WERE REPLACING SUPPORT BARS IN #1 CINKER COOLER. THE COOLER GRATES HAD BEEN REMOVED SO THAT THE SUPPORT BARS COULD BE REPLACED, RESHIMMED, AND PROPERLY ALIGNED. INJURED EE WAS WALK ING ATOP SUPPORT BARS WHEN HE LOST HIS BALANCE AND TWISTED HIS LEFT KNEE, TEARING CARTILAGE IN THE PROCESS. WENT OFF ON 5-19-03 AS LTA.