A kill switch, also known as an emergency stop or e-stop, is a safety mechanism used
to shut off a device in an emergency situation in which it cannot be shut down in the usual
manner.
Unlike a normal shut-down switch/procedure, which shuts down all systems in an orderly
fashion and turns the machine off without damaging it, a kill switch is designed and
configured to a) completely and as quickly as possible abort the operation, even if this
damages equipment and b) be operable in a manner that is quick, simple, and, usually,
c) be obvious even to an untrained operator or a bystander.
Many kill switches feature a removable barrier or other protection against accidental activation.
Kill switches are featured especially often as part of mechanisms whose normal operation
or foreseeable misuse may cause injury or death; designers who include such switches
consider damage to or destruction of the mechanism to be an acceptable cost of preventing that
injury or death.
Applications A similar system, usually called a dead man's
switch, as its name suggests, is a device intended to stop a machine in case the human
operator becomes incapacitated, and is a form of fail-safe.
They are commonly used in locomotives, tower cranes, freight elevators, lawn mowers, tractors,
jet skis, outboard motors, snowblowers and snowmobiles.
The switch in these cases is held by the user, and turns off the machine if they let go.
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, much like an emergency brake on a train.
This occurs either by a manual emergency stop activation, such as a button being pushed
on the train to start the emergency stop, or on some trains automatically, when the
train has passed a red signal or the driver has failed to respond to warnings to check
that he/she is still alert, which is known as a dead man's switch.
In large ships, an emergency stop button pulls the countershaft for the fuel pumps to the
stop position, cutting off the fuel supply and stopping the engines.
With a controllable pitch propeller, the stop button may declutch the engine from the propeller.
NASCAR requires all their stock cars to be equipped with a steering wheel-mounted kill
switch, in case the accelerator pedal sticks and the driver needs to shut down the engine.
Kill switches are also used on land vehicles as an anti-theft system and as an emergency
power off.
Such devices are often placed in bait cars and configured so that observing police can
trigger the switch remotely.
A related concept is the dead man's switch, where the operator must be holding a button
or lever any time the vehicle is operating.
A common example of this would be the kill switches used by boaters wherein a cord connects
the kill switch to the operator, and if the operator is thrown overboard in an accident,
the cord will pull the switch and immediately shut down the vessel's engine.
This prevents it from becoming a run-away vessel that could impose a danger to other
vessels or swimmers at sea, and allows the operator to swim back to the vessel and re-board
it.
Machinery
On large industrial machines, an emergency stop button is typically located on the panel,
and possibly in several other areas of the machine.
This provides a rapid means to disconnect the energy source of the device to protect
workers.
For fail-safe operation, the emergency stop is button is a normally closed switch which
ensures that a broken wire will neither accidentally activate the emergency stop nor prevent it
from being activated.
On machinery controlled by a Programmable Logic Controller, the emergency stop is designed
in a way that it overrides the output of the controller.
In some contexts, such as nuclear reactors or data centers, the emergency stop is known
as a scram switch.
In the European Union, most types of machinery are required to be equipped with an emergency
stop according to the Directive 2006EC.
Exceptions apply for machinery in which an emergency stop would not lessen the risk as
well as for portable hand-held/hand-guided machinery.
A kill switch is also used for gasoline pumps or any other device that pumps large amounts
of explosive or flammable chemicals.
Most vehicles nowadays also have a kill switch that cuts power to the fuel pump if the vehicle
is overturned.
There is commonly a single kill switch for all pumps at a pumping station.
The kill switch is also used on such things as industrial band saws and belt sanders.
Kill switches are also found on school-use electric powered tools such as drills and
wood/metal lathes.
Elevators and Escalators Elevators often have a red two-way button
on the control panel which is either marked "Emergency Stop" or "Run/Stop".
Normally, the button is in the "up" or unpushed position, allowing the elevator to "run" in
normal service.
When the button is pushed, the elevator comes to an immediate stop.
When the button is pulled back out, it resumes normal service, thus the reason for the use
of the phrase "Run/Stop".
In some cases the switch is similar to a light switch with the switch being in the up position
for the elevator to "run" in regular service, and thrown down to "stop" the elevator.
Escalators will typically have a key-operated control that will turn the escalator off,
or change its direction to up or down.
Next to the key switch will be a red "Emergency Stop" button, which is used in the event of
equipment failure, or where there is a potential for injury, such as when someone's shoe gets
stuck in the comb at the top or bottom of the escalator.
The key switch is used to return the escalator to service after it has been stopped.
Musical instruments An electric musical instrument, such as a
guitar or bass guitar, may have a kill switch, also known as a stutter switch.
It is used infrequently but most commonly in heavy metal music.
A kill switch works by switching between the hot signal from a pick-up and the ground signal,
and does not break the circuit.
A typical way of achieving this is by turning down the volume on one of the pick-ups then
alternating the pick-up selector switch between that pick-up and one with the volume turned
up.
They are sometimes used when a singer doubles as a guitar player and isn't playing or sometimes
used as an effect during a song.
Kill switches are rarely a feature in production model instruments, although they are mainly
an after-market modification and a feature on custom shop instruments.
The kill switch circuit can also be built into an effects pedal and controlled by a
foot switch.
Well known users of the kill switch circuit are Tom Morello of Rage Against the Machine
and Audioslave, Victor Smolski of Rage, Josh Elmore of Cattle Decapitation, Buckethead,
Ace Frehley of Kiss, and Jonny Greenwood of Radiohead.
Jack White uses a kill switch during some of his performances and in songs like "Icky
Thump".
Greg Ginn of Black Flag achieved the notorious feedback scream which opens most of the tracks
on Damaged with a kill switch.
More recently, Eddie Van Halen has been using a custom EVH Wolfgang guitar on which he has
had a kill switch installed.
Gym Treadmills often use a safety key that the
runner clips to his or her waist, so that the safety key is pulled out if the runner
falls, and the machine stops immediately.
In other cases treadmills have a more traditional kill switch, often mounted towards the rear
of one of the hand-railings.
Amusement rides The emergency stop on an amusement ride is
similar to that on industrial equipment.
Typically brakes on a ride are designed to be disengaged when power is applied; disconnecting
power will cause all brakes to engage.
Most amusement rides have a computer that can, similar to the rail example provided
above, engage the emergency stop when such a ride is determined to be out of operating
specification.
Computer software The concept of "kill switch" may also be applied
to software as an anti-piracy feature, most notably in Windows Vista.
It renders the software essentially useless to users running what is determined by the
software author to be an illegitimately obtained, or pirated, copy.
In the example of Microsoft Windows, the company developed a verification tool named Windows
Genuine Advantage, that originally activated a kill switch, or reduced functionality mode,
on what Microsoft's mandatory software deemed to be an unlicensed copy of the operating
system.
Software kill switches have been shown to have varying degrees of success, as false
positives have been known to occur, prompting some vendors like Microsoft to "turn off"
the software kill switch in response to market pressure.
There is some anecdotal evidence that some software vendors install kill switches in
their software to enforce planned obsolescence, also known as a forced update.
This can cause considerable disruption in said customer's business functions.
With the shift towards application stores for software distribution, particularly on
mobile devices, Apple, Google, and Microsoft maintain software kill switches which allow
software to be remotely removed from devices, most prominently to guard users against security
threats.
Smartphones There have been increasing calls for remotely
operated kill switches to be enabled on smartphones.
See also RF Shielded Cabinet
Hardware Trojan Internet kill switch
Blue Light Station References