Abstract: The invention relates to the maintenance of safety devices. Valves and similar automatic, mechanical safety devices normally maintaining a fixed position are in danger of getting stuck, and consequently may not be fully operable in an emergency situation. In a system according to the invention, real-time data indicating the operability of, for example, a valve actuator, is provided. When a fault is discovered, it can be localized using online diagnostic tools. A standby state is continuously maintained, as the unit for activating the safety function is independent of the unit for monitoring the operability, and the latter is bypassed in an emergency situation.