Abstract: Ignition means being provided to ignite pyrotechnic materials, this ignition is produced by the activation of these ignition means. As long as the ignition means have not been activated, the casing is maintained firmly attached to a closing plug only by a first set of locking means so that at pressures within the casing in excess of a given pressure, the plug is ejected from the casing. As soon as the ignition means have been activated, the casing is maintained firmly attached to the plug by a second set of locking means at pressures within the casing in excess of the given pressure.