An apparatus for inflating an air bag (22) comprises a container (40) which holds an inflation fluid under pressure. The container (40) has an opening (44) through which the inflation fluid flows to inflate the air bag (22). A rupturable closure (80) is fixed to the container (40) and extends across the opening (44) to block the flow of inflation fluid through the opening when the closure is reinforced. The closure (80), when unreinforced, ruptures in response to pressure of the inflation fluid acting on the closure. A combustible member (100) is supported by the container (40) to reinforce the closure (80) and resist rupturing of the closure. The closure (80) becomes unreinforced upon a predetermined amount of combustion of the member (100). An actuatable initiator (120), upon actuation, initiates combustion of the member (100).