Fail safe

In safety engineering and telecommunications, the term fail safe has the following meanings:

1. Of a device, the capability to fail without detriment to other devices or danger to personnel.

2. Pertaining to the automatic protection of programs and/or processing systems to maintain safety when a hardware or software failure is detected in a system.

3. Pertaining to the structuring of a system such that either it cannot fail to accomplish its assigned mission regardless of environmental factors or that the probability of such failure is extremely low.

The term fail-safe operation has the following meanings:

1. Operation that ensures that a failure of equipment, process, or system does not propagate beyond the immediate environs of the failing entity.

2. A control operation or function that prevents improper system functioning or catastrophic degradation in the event of circuit malfunction or operator error.

Sources: from Federal Standard 1037C and from the National Information Systems Security Glossary in support of MIL-STD-188