inserted one into another and are welded ultrasonically along the weld seam 14 this weld seam 14 also being constructed so as to be closed all round and being gastight and protecting against the entry of moisture the electric igniter 18 can have a housing entirely of plastic or only a section of plastic such as for example the base or if the housing largely consists of sheet metal sections connected with each other of a plastic ring which connects sheet metal parts with each other and seals them the gas generator which is shown is distinguished by small dimensions and also a simple manufacture which can be carried out in few manufacturing steps whilst maintaining a manufacturing process ultrasonic welding the propellant charge does not have a filter chamber to save additional construction space in the embodiment illustrated in fig1 the igniter housing is self contained and forms a unit prefabricated separately from the outer housing in the embodiment according to fig2 the parts already mentioned in connection with fig1 which have remained functionally the same are given the reference numbers which have already been introduced the embodiment shown in fig2 differs from this first embodiment in that before fastening to the outer housing the igniter does not have an igniter housing which is self contained and hence also does not form a separately prefabricated unit rather the igniter housing consists of a cap 119 of plastic which is welded onto the cover 12 reference number 36 again designates the surrounding weld seam an igniter charge is filled into the cap 119 before placing onto the.