Abstract: An inflator (40) includes a chamber (220) for storing inflation (222) fluid under pressure. A first member (82) has an inner perimeter that defines an opening (92) for discharging the inflation fluid (222). A rupturable closure member (100) extends across the opening (92) and blocks inflation fluid flow though the opening. A second member (110) supports a central portion (302) of the closure member (100) against the pressure of the inflation fluid (222) in the chamber (220). Inflation fluid (222) flows through a passageway (270) defined by an outer perimeter of the second member (110) and the inner perimeter of the first member (82). An initiator (152) ruptures the closure member (100), forming petals (254) of the closure member that deflect into the passageway (270). The petals (254) slide along an outer surface (258) of a portion (132) of the second member (110) while deflecting into the passageway (270).