THE EMPLOYEE WAS HELPING CHANGE OUT A SLURRY LINE. HE WAS ON ONE END OF THE PIPE, WELDING A FLANGE ON THE END. AS HE WAS CHANGING SIDES HIS LEFT BOOT GOT STUCK IN THE MUD. WHEN HE TRIED TO FRE E IT HE COULDN'T ON THE FIRST ATTEMPT. HE THEN PULLED HARDER. THE NEXT TIME HE FREED HIS BOOT BUT IN THE PROCESS INJURED HIS LOWER BACK. HE DIDN'T REPORT IT UNTIL 4/19 & SEE DOCTOR 4/22.