- Actuator comprising a translation chamber defining a translation direction between a first blind end of the translation chamber and an opposite end in which at least one opening is provided, a trigger element carrying at least one projection extending along the translation direction being mounted for being movable in translation in the translation chamber between a retracted position and a triggering position, in which the at least one projection projects further through the at least one opening than in the retracted position, the actuator comprising: a first element and a second element mounted in the translation chamber, at least one of the two elements (22, 35) being made of a magnetic or magnetizable material, the two elements (22, 35) having a shape complementary to the internal shape of the translation chamber to enable the two elements (22, 35) to be guided and moved in translation in the translation chamber, the first element being located on the blind end side of the translation chamber and carrying on its periphery in contact with the inner surface of the chamber a sealing element to form a sealed space between the end of the first element on the blind end side of the translation chamber and the blind end of the translation chamber, the second element being located on the opposite end of the translation chamber upstream of the trigger element in the translation direction, an electromagnet configured to be electrically controlled by electromagnet control means, the electromagnet being disposed between the first element and the second element, an elastic recall element disposed in the translation chamber for, in the deactivated position of the electromagnet, moving the second element to place the trigger element in its triggering position, the actuator also being configured to be pneumatically controlled by pneumatic control means to create an overpressure in the sealed space to move the first element, then the electromagnet, the second element and the trigger element step by step in order to place the trigger element in its triggering position independently of the state of the electromagnet, and a stop in the translation chamber to limit the travel of the trigger element in the translation chamber. a first element and a second element mounted in the translation chamber, at least one of the two elements (22, 35) being made of a magnetic or magnetizable material, the two elements (22, 35) having a shape complementary to the internal shape of the translation chamber to enable the two elements (22, 35) to be guided and moved in translation in the translation chamber, the first element being located on the blind end side of the translation chamber and carrying on its periphery in contact with the inner surface of the chamber a sealing element to form a sealed space between the end of the first element on the blind end side of the translation chamber and the blind end of the translation chamber, the second element being located on the opposite end of the translation chamber upstream of the trigger element in the translation direction, an electromagnet configured to be electrically controlled by electromagnet control means, the electromagnet being disposed between the first element and the second element, an elastic recall element disposed in the translation chamber for, in the deactivated position of the electromagnet, moving the second element to place the trigger element in its triggering position, the actuator also being configured to be pneumatically controlled by pneumatic control means to create an overpressure in the sealed space to move the first element, then the electromagnet, the second element and the trigger element step by step in order to place the trigger element in its triggering position independently of the state of the electromagnet, and a stop in the translation chamber to limit the travel of the trigger element in the translation chamber.