INJURED HAD EXITED THE DECK OF THE MOBILE BRIDGECONVEYOR HE WAS OPERATING TO RETRIEVE A CHAIN. AS HE WALKED TOWARD THE FRONT OF THE MBC, THE NEXT MBC INBY BEGAN TO BACK UP PUSHING INJURED'S M BC AGAINST THE LO-LO BELT STRUCTURE CATCHING THEINJURED'S LOWER LEGS BETWEEN THE MBC AND THE LO-LO BELT STRUCTURE.