REPAIRMAN WAS NEGOTIATING INGRESS AND EGRESS TO DUCTWORK TO COMPLETE REPAIR OF MATERIAL HANDLING SYSTEM. REPAIRMAN TWISTED HIS BACK DURING THE INRESS/EGRESS ACTIVITIES. EE CONTINUED WORKING TH RU WEEK. ON 7-7, EE VISITED HIS CHIROPRACTOR AS HIS BACK HURT. BY 7-13, EE WAS UNABLE TO WALK. 7-9- HE DID NOT REPORT FOR WORK.