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The term fail-safe is used to describe:
A device which, if (or when) it fails, fails in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Examples include:
Safety glass used in modern automobile windows, designed to shatter into small pieces rather than in the long jagged shards created when common window glass breaks.
Air brakes on railway trains. The brakes are held in the 'off' position by air pressure created in the brake system. Should a brake line split, or a carriage become de-coupled, the air pressure will be lost and the brakes applied. It is impossible for the train to be driven with a leak in the brake system.
Avionics using redundant systems to perform the same computation with voting logic to determine the "safe" result.
Motorized gates - In case of power outage the gate can be pushed open by hand with no crank or key required. See also fail-secure.
An operation which ensures that a failure of equipment, process, or system does not propagate beyond the immediate environs of the failing entity.
A system which has been structured such that it cannot fail (or that the probability of such failure is extremely low) to accomplish its assigned mission regardless of environmental factors. Examples include:
A precautionary secondary mechanism that achieves the same task as the primary mechanism.
The activation of grenades when the primary detonator is destroyed.
A device that activates explosives that releases lethal gas when destroyed.
A key seen in the very popular TV-Serie Lost by JJ. Abrams.
Fail-safe (fool-proof) devices are also known as Poka-Yoke devices. Poka-yoke, a Japanese term, was coined by Shigeo Shingo, a quality guru.
Fail-Safe is also the title of a novel, movie, and made-for-television play about a possible accidental nuclear war.
People also usually abide by the rules of 'fail-safe', succeeding only if it feels safe to do so.
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