A mechanism (10) for releasably confining pressurized fluid in a container (18) is provided. The mechanism includes a rupturable membrane (22) in fluid communication with an interior of the container (18), thereby exposing the membrane (22) to the fluid. The membrane (22) is configured to obstruct flow of the pressurized fluid when externally supported against pressure exerted by the fluid. The membrane (22) is also rupturable by pressure exerted by the fluid when not externally supported against the pressure exerted by the fluid. A support member (28) is provided for externally supporting the membrane (22) against pressure exerted by the fluid. The support member (28) is configured to be fracturable upon exposure to combustion products formed by activation of a gas generator (66) at least partially encased within the support member (28).