A helmet has attached to its lower rim an inflatable bag which normally is folded so as not to restrict normal head and neck movements of the wearer but on inflation will fill the gap between the helmet rim and shoulders of a wearer. Carried by the helmet and preferably packed with the bag is a package including a conventional gas generator, igniter and battery. A switch to operate the igniter is located in the crown area of the helmet and is closable on an impact with a predetermined force on the crown of the helmet. When closed the bag is almost instantaneously inflated and fills the gap to transfer most if not all of the impact force to the shoulders and relieve the cervical spine of a damaging axial compressive force. In another version, the attachment is a rigid padded ring conforming to the contour of the lower rim or base of the helmet and the lower part of the face guard, if any. It is detachable from the helmet and can be driven downward into engagement with the shoulders of the wearer by a gas-operated piston and cylinder arrangement carried by the helmet.