Failuresafe

Failuresafe is a design principle in safety engineering that refers to configuring systems so that, in the event of a fault, they default to a safe condition. The term is commonly encountered as fail-safe, though some texts and brands use the single word failuresafe. A safe condition can mean halted operation, isolation of hazardous functions, or a transition to a non-operational yet non-harmful state.

Origins trace to railway signaling and other critical systems where a fault must not create danger. In practice, failuresafe means that a fault cannot lead to unsafe behavior; rather, the system either prevents the hazard or minimizes risk.

Applications include rail signaling and braking systems, electrical power grids with protective relays, aircraft control systems, medical devices, and consumer electronics that implement safe defaults or power-down on fault.

Implementation techniques include redundancy of critical components, safe states and default-off design, isolation and fault containment, watchdogs and health monitoring, fail-safe interlocks, and safe shutdown procedures, as well as clear emergency overrides.

Limitations accompany failuresafe design. It can reduce system availability, increase cost, and add design and maintenance complexity. A failuresafe approach does not prevent all failures; instead, it aims to reduce the severity of consequences through careful risk assessment, testing, and clear operational procedures.

See also: fail-safe, fail-secure, fail-operational.