An inflatable air bag system having an inflatable curtain-like cushion element for inflated deployment away from a storage position along the roof rail portion of the vehicle frame to provide coverage over an expanded region of the vehicle interior. The cushion element is inflated by the rapid introduction of a substantially inert gas such as helium from an elongate gas storage receptacle extending at least partially along the roof rail portion of the vehicle frame. The gas storage receptacle serves as a profiling and stiffening support member for the cushion element in the storage position extending along the roof rail. The inflation gas may be discharged directly into an interior portion of the cushion element so as to promote rapid expansion and deployment of the cushion element over centralized regions of the surface to be covered.