Fail-safe
From Wikipedia, the free encyclopedia
For other uses, see Fail-safe (disambiguation).
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:
- Luggage carts in airports in which the hand-brake must be held down at all times. If it is released, the cart will stop. See dead man's switch.
- Air brakes on railway trains and trucks. 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.
- The automatic protection of programs and/or processing systems when a hardware or software failure is detected in a computer system. See fail-safe (computer).
- A control operation or function that prevents improper system functioning or catastrophic degradation in the event of circuit malfunction or operator error.
- 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:
- The hardening of a nuclear missile bunker or the dispersion of nuclear bombers to multiple secret locations
- 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.
Fail-safe (foolproof) devices are also known as Poka-Yoke devices. Poka-yoke, a Japanese term, was coined by Shigeo Shingo, a quality guru.
