A fail-safe is a device or system that is designed to remain safe in the event of a failure. A fail-safe isn't designed to prevent failure but mitigates failure when it does occur. The following are examples.
ElevatorsElevators are typically designed with special brakes that are held back by the tension of the elevator's cable. If the cable snaps the loss of tension causes the brakes to be applied.
TrainsRailway trains commonly have air brakes that get applied automatically with the failure of the main brake system.
EarthquakesElevators and trains in earthquake prone regions such as Japan are often configured to detect earthquakes and automatically stop. Elevators may be designed to stop at the nearest floor and open their doors. In some cases, such systems are hooked up to earthquake early warning systems and can potentially stop seconds before an earthquake arrives.
Flight ControlFlight control computers are typically designed with redundancy so that if one goes down another kicks in. They may also be designed to detect a flight control computer that suffers from "insanity" meaning that it appears to be dysfunctional due to damage or other factors.
Electronic LocksElectronic locks that are designed to be unlocked by default in the event of power failure. Some vehicles don't have this feature and it's possible to get locked in a car that loses power.
Traffic LightsTraffic lights may be designed to blink red in all directions if their controller goes down.
Deadstick LandingAircraft are designed with some ability to glide and can be landed without any engine power. This isn't completely safe but is certainly possible with a competent pilot if there is a suitable landing spot within range.
SubmarinesSome submarines are designed to automatically drop their ballast in the event of power failure causing the submarine to surface.
Shut OffMany machines are designed to shut off if they detect something is wrong.
Fail OverComputer services are commonly designed with redundant servers. When one server fails, another replaces it almost instantaneously. This allows many services to maintain an uptime of 99.999% or greater.
This is the complete list of articles we have written about safety design.
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