Abstract: An apparatus (20, 320) for inflating an inflatable vehicle occupant protection device comprises a container (22, 340) which defines a chamber (44, 348) for storing inflation fluid under pressure. The container (22, 340) has an opening (60, 360) through which the inflation fluid flows to inflate the protection device. A rupturable closure (102, 402) extends across the opening (60, 360) to block the flow of inflation fluid. A flow initiator (120, 322) is located in the chamber (44, 348) and is spaced from the closure (102, 402). The flow initiator (120, 322) comprises an ignition cup (122, 440) having a base section (142, 442) fixed to the container (22, 340). A movable section (146, 446) of the ignition cup (122, 440) is attached to the base section (142, 442) and is separable from the base section. The movable section (146, 446) has a vent (162, 464) which permits communication of the inflation fluid in the chamber (44, 348) with the interior of the ignition cup (122, 440).