The invention relates to a protection device which defines a through hole (21) for the passage of a fluid which may be under overpressure conditions. In addition, the inventive device comprises: a stop plug (26) which can move between an open position and a position in which a first section of the hole (21) is sealed; a stop valve (28) which can move between an open position and a position in which a second section of the hole (21) is sealed; and means (22, 23, 27) for triggering both the movement of the stop plug (26) and the movement of the valve (28) from the open position to the sealing position in response to an overpressure (P2) in the hole (21). The invention is particularly suitable for self-contained equipment used to supply electrical power by means of a fuel cell.