Editing Fail-safe (section)

===Mechanical or physical===
Examples include:
*[[File:Pl control valve.jpg|thumb|upright|Globe control valve with pneumatic diaphragm actuator. Such a valve can be designed to fail to safety using spring pressure if the actuating air is lost.]]Safety valves – Various devices that operate with [[fluid]]s use [[fuse (hydraulic)|fuses]] or [[safety valve]]s as fail-safe mechanisms.
*Roller-shutter fire doors that are activated by building alarm systems or local smoke detectors must close automatically when signaled regardless of power. In case of power outage the coiling fire door does not need to close, but must be capable of automatic closing when given a signal from the building alarm systems or smoke detectors. A temperature-sensitive [[fusible link]] may be employed to hold the fire doors open against gravity or a closing spring. In case of fire, the link melts and releases the doors, and they close.
*Some airport [[baggage]] [[cart]]s require that the person hold down a given cart's handbrake switch at all times; if the handbrake switch is released, the brake will activate, and assuming that all other portions of the braking system are working properly, the cart will stop. The handbrake-holding requirement thus both operates according to the principles of "fail-safety" and contributes to (but does not necessarily ensure) the fail-security of the system. This is an example of a ''[[dead man's switch]]''.
*[[Lawnmower]]s and [[snow blower]]s have a hand-closed lever that must be held down at all times. If it is released, it stops the blade's or rotor's rotation. This also functions as a ''dead man's switch''.
*[[Air brake (rail)|Air brakes]] on railway [[train]]s and [[air brake (road vehicle)|air brakes]] on [[truck]]s. 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 uncoupled, the air pressure will be lost and the brakes applied, by springs in the case of trucks, or by a local air reservoir in trains. It is impossible to drive a truck with a serious leak in the air brake system. (Trucks may also employ [[Wig wag (truck braking systems)|wig wags]] to indicate low air pressure.)
*Motorized gates – In case of power outage the gate can be pushed open by hand with no crank or key required. However, as this would allow virtually anyone to go through the gate, a ''fail-secure'' design is used: In a power outage, the gate can only be opened by a hand crank that is usually kept in a safe area or under lock and key. When such a gate provides vehicle access to homes, a fail-safe design is used, where the door opens to allow fire department access.
*{{anchor|semaphore}}[[File:130330 Thomas ELC and Wansbeck Railtour Northumberlandia 030.jpg|thumb|upright|Railway semaphore signals. "Stop" or "caution" is a horizontal arm, "Clear to Proceed" is 45 degrees upwards, so failure of the actuating cable releases the signal arm to safety under gravity.]] A [[railway semaphore signal]] is specially designed so that, should the cable controlling the signal break, the arm returns to the "danger" position, preventing any trains passing the inoperative signal.
*[[Isolation valve]]s, and control valves, that are used for example in systems containing hazardous substances, can be designed to close upon loss of power, for example by spring force. This is known as fail-closed upon loss of power.
*An [[elevator]] has brakes that are held off brake pads by the tension of the elevator cable. If the cable breaks, tension is lost and the brakes latch on the rails in the shaft, so that the elevator cabin does not fall.
* Vehicle air conditioning – Defrost controls require vacuum for diverter damper operation for all functions except defrost. If vacuum fails, defrost is still available.