Disclosed are methods, systems, and apparatus for inflating airbags. In one embodiment, an initiator is deployed to open an exit gas port, through which the airbag is inflated. The airbag is primarily inflated via gas from a first gas chamber and is substantially maintained in an inflated state for a predetermined period of time primarily via gas from a second gas chamber. In one embodiment, an airbag inflator is provided which comprises a first gas chamber, a second gas chamber, and an intermediate chamber assembly. The intermediate chamber assembly comprises a first gas port positioned adjacent to and in fluid communication with the first gas chamber and a second gas port positioned adjacent to and in fluid communication with the second gas chamber. The inflator is configured to allow a greater flow rate of gas through the first gas port upon deployment than through the second gas port.