Fejlsikret

Fejlsikret is a design principle from safety engineering describing systems that are constructed to behave safely when faults occur. The aim is to prevent or limit harm by guaranteeing that a fault leads to a safe state or a controlled shutdown rather than unpredictable or hazardous operation. In Danish usage the term aligns with what in English is called fail-safe, and it is closely related to fault-tolerant design, though the emphasis is on safety of people and the environment.

Implementation relies on detection of faults, isolation of faulty elements, and a predefined safe-state logic. Common methods include redundancy (duplicate sensors, processors, power supplies), diverse or voting architectures, watchdog timers and self-diagnostics, safety interlocks, and safe shutdown procedures. Degraded operation may be allowed if it remains within safe limits.

Standards and analysis underpin fejlsikret design. Functional safety frameworks such as IEC 61508 and ISO 26262 guide the specification of safety requirements, safety integrity levels, and validation of fault-handling capabilities. Railway, process, and aerospace domains also use dedicated standards that stress safe-state behavior and fault containment.

Applications span critical infrastructure and equipment: railway signaling and braking systems, power distribution, chemical and petrochemical plants, medical devices, and aerospace controls. In each case the goal is to ensure that, even in the presence of faults, the system remains predictable and does not endanger users or operators.

Limitations: no system can be completely fault-free. Fejlsikret design concentrates risk reduction through safe-state behavior, robust diagnostics, and disciplined maintenance.