EMPLOYEE WAS STANDING ON LEVEL CONCRETE LIFTING A 70LB. SPOOL OF WELDING WIRE UP TO CHEST HEIGHT(5FT). HE WOULD HAVE SET THE SPOOL DOWN ON A FLAT SURFACE, BUT THE SPOOL SLIPPED AND HE LOST HIS GRIP. TRYING TO REGAIN HIS GRIP HIS BACK JAMMED. HE THEN LIFTED IT ON UP.