Abstract: The invention relates to a safety device constituting a valve for releasing pressurized gas in the event of a dangerous situation, including a body defining a gas flow channel extending in a longitudinal direction between a first upstream end to be brought into contact with a pressurized gas source (G) and a second downstream end to be brought into contact with the outer atmosphere, wherein the device includes a plug located in the channel for preventing the flow of gas between the upstream end and the downstream end in a normal situation, the plug being shaped so as to release the passage for the gas in the event of a dangerous situation in which it is subjected to a pressure and/or a temperature exceeding a predetermined threshold, characterized in that, from the upstream direction toward downstream direction, the channel includes two upstream and downstream adjacent flow portions, respectively, having different respective transverse dimensions (d, D), the ratio D/d between the transverse dimension D of the