The subject of the present invention is a pyrotechnic method for generating gas at two successive flow rates a first flow rate then a second flow rate, said first flow rate being higher than said second flow rate--which comprises: the combustion of a first pyrotechnic charge (10) in a first combustion chamber (1) discharging into a second combustion chamber (2) via at least one nozzle (3); and the combustion of a second pyrotechnic charge (20) in said second combustion chamber (2) discharging to the outside via at least one vent (21). Characteristically, said first chamber (1) operates at high pressure and said second chamber (2) operates at low pressure. Another subject of the invention is a pyrotechnic gas generator suitable for the implementation of said method.The invention is most particularly applicable in the context of side protection airbags ("curtain airbags"), used in automobile safety.