A vented submersible dam barrier for use in a glass forming chamber to selectively interrupt the flow of glass supporting molten metal is disclosed. The disclosed barrier includes a dense inner body and an outer cover or shell with a space or interstices within the shell through which gases may move to an end of the dam barier at which there is mounted a facility for venting the enclosed portion of the dam barrier. Venting may be provided into a space above the surface of the pool of molten metal in which the dam barrier is placed.