What does 'fail-safe' mean in engineering terms?

'Fail-safe' in engineering refers to a design principle that ensures equipment or systems maintain safety in the event of a failure. This means that when a failure occurs, the system will revert to a safe state, minimizing the risk of accidents or harm. For example, in mechanical systems, this could involve mechanisms that prevent a machine from operating dangerously or that safely shut it down in case of a malfunction.

The design philosophy behind fail-safe mechanisms is to enhance reliability and ensure safety is prioritized, effectively protecting users and surrounding environments from hazardous outcomes. This is particularly important in critical applications such as aviation, medical devices, and industrial safety systems, where failures could lead to severe consequences.

The other options do not accurately capture the essence of what fail-safe means. While a mode where equipment fails to operate might suggest a lack of functionality, it does not account for ensuring safety during failure. Continuous operation is more aligned with redundancy rather than fail-safe principles, and requiring manual input does not relate to the concept of safety during a failure scenario. Therefore, the definition that encapsulates the core intent of fail-safe design is the one that emphasizes safety in case of failure.