A gas generator has an igniter and a compressed gas container which contains a first filling gas and has an outflow opening that is closed by a first bursting diaphragm. Upon activation of the gas generator the igniter produces a shock wave which runs at least in part through the compressed gas container before destroying the first bursting diaphragm. The compressed gas container is filled with a mixture of the first filling gas and at least one second substance having a molar mass higher than that of helium, the proportion of the second substance being between 1 and 13 mole percent of the total filling quantity or reaching, at maximum, the total mass of the first filling gas, and the first filling gas being helium, hydrogen, or a mixture of the two gases.