The present invention relates to a gas generator (10) comprising a body (12) delimiting at least one part of a combustion chamber (20), said part housing a primary pyrotechnic charge (16) adapted to generate gases in the combustion chamber (20) when said charge is initiated in combustion, and a slide valve (60) located outside said body (12) and defining with the latter a second chamber (66) housing a secondary pyrotechnic charge (74) whereof the self-ignition temperature is less than that of the primary pyrotechnic charge (16). A gas flow channel (50) for flowing gas out of the combustion chamber (20) is formed in the body (12). According to the invention, the slide valve (60) blocks this channel when it is in a first position, and under the effect of gases released by said secondary pyrotechnic charge (74), the slide valve is adapted to move to a second position wherein the channel (50) is no longer sealed off, allowing the gases contained in the combustion chamber (20) to flow outwards to the exterior.