ON 4/17/00 WHILE WELDING ON THE MR-1-7 CHUTE IN THE CONCENTRATOR, A WELDER EXPERIENCED BACK PAIN. HE REPORTED THE INCIDENT ON 4/18/OO. HE IS UNCERTAIN AS TO THE EXACT CAUSE OF THE BACK PAIN, B UT BELIEVES IT MAY BE DUE TO BODY POSITIONS AND POSSIBLY PREVIOUS MOVEMENT OF A WELD MACHINE. HE RECENTLY BEGAN CHIROPRACTIC CARE.