Kill switch
safety mechanism to quickly shut down a system in an emergency, when it cannot be shut down in the usual manner
A kill switch, also known more formally as an emergency brake, emergency stop (E-stop), emergency off (EMO), or emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usual manner. Unlike a normal shut-down switch or shut-down procedure, which shuts down all systems in order and turns off the machine without damage, a kill switch is designed and configured to abort the operation as quickly as possible (even if it damages the equipment) and to be operated simply and quickly (so that even a panicked operator with impaired executive functions or a bystander can activate it). Kill switches are usually designed to be noticeable, even to an untrained operator or a bystander.
Some kill switches feature a removable, protective barrier against accidental activation, such as a plastic cover that must be lifted or glass that must be broken, known as a molly-guard. Kill switches are features of mechanisms whose normal operation or foreseeable misuse might cause injury or death; industrial designers include kill switches because damage to or the destruction of the machinery is less important than preventing workplace injuries and deaths.
A similar system, usually called a dead man's switch, is a device intended to stop a machine (or activate one) if the human operator becomes incapacitated or leaves the machine unattended, and is a form of fail-safe. They are commonly used in industrial applications (e.g., locomotives, tower cranes, freight elevators) and consumer applications (e.g., lawn mowers, tractors, personal watercraft, outboard motors, snow blowers, motorcycles and snowmobiles). The switch in these cases is held by the user, and turns off the machine if they let go. Some riding lawnmowers have a kill switch in the seat which stops the engine and blade if the operator's weight is no longer on the seat.
Vehicles
On railways, an emergency stop is a full application of the brakes in order to bring a train to a stop as quickly as possible.
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