Abstract: The invention relates to a pressure-relief device in a PFBC power plant with a combustor (12) enclosed in a pressure vessel (10). The device is intended to limit the pressure difference between the combustor (12) and the surrounding space (22) in the pressure vessel (10) and to initiate pressure relief of the pressure vessel (10) out into the atmosphere. Via a conduit (54) with a rupture disc (56), the combustor (12) communicates with one or more blow-off valves (42). If the rupture disc (56) bursts, a sensor (62) indicates this and effects opening of the blow-off valve (42) via signal processing and operating equipment (64). Between the rupture disc (56) and the combustor (12) a perforated diaphragm (60) is provided. In the space between this diaphragm and the rupture disc (56) a layer of particulate, heat-insulating material (58) is provided, which restricts the heating of the rupture disc (56).