A device for supporting a rupturable closure member of a pressure vessel, such as an airbag inflator has a hollow support with a tapered portion and an adjoining cylindrical portion. An exterior surface of the tapered portion has longitudinally extending grooves therein. An igniter is located adjacent the cylindrical portion of the support and a pyrotechnic substance is located in the cylindrical portion of the support between the igniter and the tapered portion of the support. A rupturable closure member being forced against an open first end of the tapered portion of the support by the gas in the pressure vessel such that a chamber is formed within the support. The igniter when activated ignites the pyrotechnic substance and the burning pyrotechnic substance generates gas under pressure that causes the tapered portion of the support to break along the longitudinally extending grooves and no longer support the rupturable closure member allowing the gas in the pressure vessel to rupture the unsupported rupturable closure member.