DUAL LEVEL GAS GENERATOR

In order to allow for at least two different rates of air bag inflation a gas generator (100) is provided with a single pyrotechnic charge (101) which is disposed in a chamber (116) in which argon or a similar type of non-toxic inert gas is stored under pressure. The chamber (116) is closed off by two or more burst discs (118, 120), only one of which is not exposed to a selectively ignitable squib (122). The non-exposed burst disc (118) is arranged to breach when the pyrotechnic charge is ignited and increases the gas pressure in the chamber (116) to a predetermined pressure. Each other disc (120) is arranged to withstand the predetermined pressure and requires weakening by exposure to the heat from an associated squib (122) before breaching will occur. The hybrid compressed gas/pyrotechnic pressure generation is such that the rate of air bag inflation varies essentially in proportion to the area of the exit port or ports which are opened by the breach of the burst disc or discs (118, 120). By limiting the number of burst discs (118, 120) which are breached, the exit port area and the rate of air bag inflation/deployment can be controlled for slow speed collisions. Breaching all or more of the discs (118, 120) maximizes port area and increases the rate of pressurization to a level suitable for high speed collisions.