failsafety

Failsafety refers to the design and assessment practices that aim to ensure a system behaves safely when faults occur. The goal is to prevent harm, limit damage, and move the system into a defined safe state in the presence of errors. In practice, failsafe design often results in a fault-triggered shutdown or safe-mode operation instead of continuing to function in an unsafe manner. The concept is central to functional safety across industries.

Key principles include the introduction of safe states, redundancy to tolerate faults, fault detection and isolation, health monitoring, and deterministic fault handling. Designers may use fail-safe, fail-safe-with-diagnostics, or fail-safe hard stops, and distinguish them from fail-operational approaches that maintain operation at reduced capability. Diversity, containment, and clear interfaces help prevent common-cause failures.

Common techniques include protective interlocks, watchdog timers, heartbeat monitoring, sensors and actuators with defined safe positions, and architectural separation that limits fault propagation. Safety integrity levels or similar risk-based classifications guide the required rigor of design, verification, and validation. Standards such as IEC 61508, ISO 26262, and DO-178C provide frameworks for assessing and assuring functional safety.

Limitations include trade-offs among safety, cost, complexity, and reliability. No system can be guaranteed completely fault-free; failsafety focuses on reducing risk to acceptable levels and enabling timely safe recovery through testing, certification, and ongoing safety management.