Dead man's switch
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/38/Dodemansknop_Linde.jpg/170px-Dodemansknop_Linde.jpg)
A dead man's switch is a
These switches are usually used as a form of
Dead man's switches are not always used to stop machines and prevent harm; such switches can also be used as a
A similar concept is the handwritten
This concept has been employed with computer data, where sensitive information has been previously encrypted and released to the public, and the "switch" is the release of the decryption key, as with Vault 7.[2]
A related device is a kill switch.
Background
Interest in dead man's controls increased with the introduction of
With modern urban and suburban railway systems, the driver is typically alone in an enclosed cab. Automatic devices were already beginning to be deployed on newer installations of the
The status and operation of both vigilance and dead man's switch may be recorded on the train's
Types
Handle
Many dead man's switches are mounted in the control handle of a vehicle or machine and engage if the operator ever loses their grip.[citation needed]
Vehicles
Handle switches are still used on modern trams and trains.
Though there are ways that this type of dead man's control could conceivably fail, in practice they have proven highly reliable. On some earlier equipment, pressure was not maintained on the entire controller, but on a large button protruding from the controller handle. This button also had to be pressed continuously, typically with the palm of the hand so that the button was flush with the top of the handle. Another method used, particularly with some lever-type controllers, which are rotated rather than pushed or pulled, requires that the handle on the lever be turned through 90 degrees and held in that position while the train is in operation. Some dead man's controls only work in the mid position and not with full pressure (see pilot valve).
In modern New York City Subway trains, for example, the dead man's switch is incorporated into the train's speed control. On the R142A car, the train operator must continually hold the lever in place in order for the train to move.
An example of a passenger vehicle using a dead man's switch is on
Machinery
Handle-mounted dead man's switches are also used on many hand-held tools and lawn equipment, typically those that rotate or have blades such as saws, drills, snow blowers and lawn mowers. On saws for example, they incorporate a squeeze throttle trigger into the handle. If the user loses grip of the saw, the springs in the throttle trigger will push it back out to the off or idle setting, stopping the blade from spinning. Some tools go further and have a trigger guard built into the handle, similar to firearm safeties. Only when the user presses in the trigger guard first will it then release its lock on the trigger and allow the trigger to be pressed in. Typically, trigger guards can only be pressed in while the user has a firm grip of the handle.[citation needed]
Every walk-behind mower sold in the US since 1982 has a dead man's switch called an "operator-presence control", which by law must stop the blades within three seconds after the user releases the controls.[9] Attached across the handle is a mechanical lever connected by a flexible cable to the kill switch on the engine. While mowing, the operator must always squeeze the lever against the handle. If the operator ever loses grip of the handle, the blade will disengage or the engine will stop, stopping the blades from spinning and (if equipped) any drive wheels from turning. On mowers where the engine stops, this switch configuration also acts as the engine's main kill switch; when the operator wants to stop the engine, he can release the dead man's switch intentionally.[citation needed]
Touch sensor
On some vehicles, including the diesel-electric railway locomotives in Canada, and on Nottingham Express Transit vehicles, the tram's speed controller is fitted with a capacitive touch sensor to detect the driver's hand.[citation needed] If the hand is removed for more than a short period of time, the track brakes are activated.[citation needed] Gloves, if worn, have to be finger-less for the touch sensor to operate. A backup dead-man's switch button is provided on the side of the controller for use in the case of a failed touch sensor or if it is too cold to remove gloves.[citation needed]
Pedal
![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/61/SIFA-Pedal.jpg/220px-SIFA-Pedal.jpg)
A pedal can be used instead of a handle. While some pedal switches must simply be held down in order for the machine to function (this system is often found on amusement rides, where the operator is likely to remain in a standing position for a lengthy period of time while the ride is in motion), this method has some shortcomings. In the
There are some solutions to this issue that are now used in modern pedal systems. The pedal can have a vigilance function built in (a dead-man's vigilance device, driver vigilance device or DVD),
Some types of locomotive are fitted with a three-position pedal, which must normally be kept in the mid position. This lessens the likelihood of accidentally defeating it, although it may still be possible to deliberately do so. Adding a vigilance function to this type of pedal results in a very safe system. However, isolation devices are still provided in case of equipment failure, so a deliberate override is still possible. These isolation devices usually have tamper-evident seals fitted for that reason.
Seat switches
The dead man's switch can also be located beneath the seat of a vehicle or machine and engages if the operator is not in the seat holding the switch down. On modern tractors, the switch will cut the engine while the transmission is engaged or the power take-off is spinning. On riding lawn mowers, the switch is often more extreme where the switch will cut the engine even if the mower is parked and the blades are not spinning. Seat switches can also be used to keep small children from even starting the vehicle since they would not weigh enough to completely hold down a switch adjusted to an adolescent's or adult's weight.
Key switches
On recreational vehicles such as boats,
Some luggage carts at airports and exercise treadmills have this feature. In the case of treadmills, the dead man's switch usually consists of an external magnet attached to a cord that clips to the user. If the user falls or walks away without turning off the treadmill, the switch cuts power to the treadmill belt.
In information security, kill cords are also used in computers to turn off the machine if the user is separated from it.[15][16]
Altimeter switches
Vigilance control
The main safety failing with the basic dead man's system is the possibility of the operating device being held permanently in position, either deliberately or accidentally. Vigilance control was developed to detect this condition by requiring that the dead man's device be released momentarily and re-applied at timed intervals. There has also been a proposal to introduce a similar system to automotive cruise controls.[18]
Software
Spacecraft
Many spacecraft use a form of dead man's switch to guard against command system failures. A timer is established that is normally reset by the receipt of any valid command (including one whose sole function is to reset the timer). If the timer expires, the spacecraft enters a "command loss" algorithm that cycles through a predefined sequence of hardware or software modes (such as the selection of a backup command receiver) until a valid command is received. The spacecraft may also enter a
While having some similarities to a dead man's switch, this type of device (a command loss timer) is not actually a dead man's switch, because it aims to recover from a hardware failure rather than the absence of human operators. It is generally called a watchdog timer, and is also used extensively in nuclear power control systems. System components on a spacecraft that put it into a safe mode or cause it to execute default behaviors when no command is received within a predefined time window can be considered a dead man's switch, but hardware or software that attempts to receive a command from human operators through an alternate channel is an auto-recovering or adaptive communications system, not a dead man's switch. Voyager 2 recovered from a command receiver failure with a command loss timer.[22]
Train
In most trains, a basic level of protection is provided by a "dead man's handle" or pedal. If the driver is taken ill and releases this, the power will be shut off and an emergency brake application will be initiated to stop the train.
More recent safety standards do not consider this to be adequate, as the driver may slump over the dead man's handle and continue to hold it down even though they are not capable of controlling the train. Modern trains overcome this risk with the addition of a vigilance system[23] to the dead man's system. A buzzer or bell sounds every minute or so in order to alert the motorman or engineer. If they do not respond by moving a controller, or releasing and then re-applying the dead man's handle, the system will automatically initiate an emergency brake application. Most major rail systems in the world use this equipment, both in their freight and passenger operations. It is also used on the R143 and other New York City Subway cars while under CBTC operation. In the US, older locomotives produced before 1995 did not originally carry this feature, but given the modular nature of the system it is not uncommon to find them retrofitted.[citation needed]
Aircraft
In 2019, the Garmin G3000 became the first general aviation avionics suite capable of automatically diverting an aircraft to the nearest airport and landing it in the event a pilot fails to interact with the aircraft's controls or respond to system prompts. This automation capability has been made possible by advancements in computing, control, and navigation technologies and is of particular importance in a general aviation setting since private aircraft are often flown by only a single pilot.
Blackmail
The term "dead man's switch" is sometimes used to describe a form of defensive blackmail or insurance file in which the release of damaging material is threatened if anything happens to a person.[25]
See also
References
- ^ Terry Gross & David Hoffman, Fresh Air, "'Dead Hand' Re-Examines The Cold War Arms Race" Archived 15 October 2017 at the Wayback Machine 12 October 2009.
- ^ "WikiLeaks Password Is an Anti-CIA JFK quote". News.com.au. March 10, 2017. Retrieved 2023-11-23.
- ^ "HAND OF CORPSE AT THROTTLE. Engineer Killed at His Post, but the Train Ran On". Indianapolis Journal. Vol. 53, no. 12. Indianapolis. 1903-01-12. p. 1 col. 6. Retrieved 2020-06-06.
Passengers on an Incoming Knoxville & Ohio River Railroad train rode several miles this afternoon with the hand of a corpse at the throttle of the engine. The train left Buckeye, Tenn., on time and ran through to Careyville, the next station. When Engineer A. C. Young ran through the latter town Fireman Matlock knew something was wrong and stepped to the engineer's side of the engine. He found Young dead and immediately stopped the train. There is a wound on the left side of the engineer's head, and the supposition is that a piece of rock fell from the side of a high cut through the mountains and killed him instantly. The train ran perhaps eight miles after Young was killed.
- ^ Newman, Andy (May 7, 2010). "Not the First Time the 'Dead-Man' Switch Did Its Job". The New York Times. Archived from the original on May 18, 2020. Retrieved May 7, 2010.
- ^ "Bach-Simpson". Wabtec. Archived from the original on 2021-06-21. Retrieved 2023-11-22.
- ^ "Autopilot and Full Self-Driving Capability". Tesla.com. February 13, 2019.
- ^ "Tesla: Technology Helps to Keep Drivers Alert After Autopilot Crash". Fortune.
- ^ O'Kane, Sean (May 14, 2018). "Tesla Rejected More Advanced Driver Monitoring Features on Its Cars". The Verge.
- ^ "SAFETY STANDARD FOR WALK-BEHIND POWER LAWN MOWERS". GPO.gov.
- ^ "Driver Vigilance Devices – Systems Review (T024)". RSSB.co.uk. Archived from the original on 2018-08-04. Retrieved 2018-08-04.
- ^ "Locomotive Repair Books, Record Cards, Manuals and Driver's Handbooks". LocoDocs.co.uk. Retrieved 2013-11-15.
- ^ "Use your kill cord". RYA.org.uk. Royal Yachting Association. Archived from the original on 2013-01-17. Retrieved 2013-05-07.
- ^ "Kill Cords". Chieftain Training. 2020-02-14. Retrieved 2020-06-03.
- ^ Morris, Steven (6 May 2013). "Cornwall speedboat accident: police pay tribute to rescuers". The Guardian. Retrieved 2013-11-15.
- ^ Shilov, Anton (15 Dec 2021). "BusKill USB Cable Now Available: A PC Kill Switch for Data Protection". Tom's Hardware. Retrieved 2022-07-02.
- ^ Aufranc, Jean-Luc (15 Dec 2021). "BusKill USB kill cord protects data on Linux, Windows, Mac OS devices". CNX Software. Retrieved 2022-07-02.
- ISBN 0-691-02101-5. Retrieved 2008-11-16.
- ^ "How to Install a Deadman Switch?". FordNews.org. Retrieved 2022-11-02.
- ^ "About Inactive Account Manager". Google Help. Retrieved 2019-07-05.
- ^ "Dead Man Tracker". deadmantracker.com. Retrieved 2019-10-12.
- ^ "Deadmanswitch". Deadmanswitch.com. Retrieved 2022-01-14.
- ^ Allen, J.; Nance, H. (1978). "Voyager Support. DSN Progress Report 42-49" (PDF). Jet Propulsion Laboratory. Retrieved 4 March 2009.
- ^ "DSD Vigilance Unit" (PDF). 2010. Retrieved 2017-08-17.
- ^ Bertorelli, Paul (13 April 2015). "Piper Bets Big on Envelope Protection". avweb.com. Aviation Publishing Group. Retrieved 15 April 2015.
- ^ Bertorelli, Paul (11 April 2009). "What Happened to Julian Assange's Dead Man's Switch for the WikiLeaks Insurance Files?". Heavy.com. Retrieved 8 January 2021.
Further reading
- "Section 9. Watchdog, Deadman, and Power-up Timers". PIC32 Family Reference Manual (PDF). Microchip Technology Inc. 2013. DS60001114G. Archived(PDF) from the original on 2024-01-10. Retrieved 2024-01-10. (26 pages)
External links
![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
- Kill Cords: Lessons from the Milly RIB Report Archived 2014-08-19 at the Wayback Machine
- FRA Regulations