THE EMPLOYEE WAS CARRYING A 4'-0"" PC OF 4"" DIA PIPE, APPROXIMATELY 45 PDS. THE 40 DEGREE FITTING WAS ATTACHED WITH A SMALL LENGTH OF PIPE ATTACHED, MAKING AN ""L"". THE EMPLOYEE WALKED THROUGH A DOORWAY AND THE PROTRUDING PIPE STRUCK THE DOOR FRAME CAUSING THE EMP TO TWIST SUDDENLY. EMPLOYEE REPORTED A DULL PAIN IN LOWER BACK.