Dead man's switch

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A dead man button (for another name, see alternate name) is a switch that is automatically operated if the human operator becomes incapable, such as through death, loss of consciousness, or physically removed from the control. Originally applied to switches on vehicles or engines, it has since been used to describe other intangible uses as in computer software.

These switches are typically used as a form of failure-safely in which they stop the machine without the operator from potentially harmful actions or crippling the device as a result of accidents, malfunctions, or misuse. They are common in applications such as in locomotives, aircraft refueling, freight elevators, lawn mowers, tractors, private boats, outboard motors, saws, snowblowers, tread engines, snowmobiling, amusement rides, and many medical imaging equipment. On some machines, this switch simply brings the machine back to safety, such as reducing the throttle to idle or applying the brakes while letting the engine still running and ready to resume normal operation once the controls are rebuilt.

The switch of the dead is not always used to stop the machine and prevent danger. This switch can also be used as a lethal switch. A spring-operated switch can also be used to complete the circuit when it is no longer retained. This means that the switch of the dead can be used to activate malicious devices, such as bombs or IEDs. Users (victims) hold such buttons in the hands of those who are arming the device. The device will activate when the switch is released, so if the user (victim) is knocked out or killed while holding the switch, the bomb will explode. The Special Weapon Distortion Separation System is the application of this concept in the field of nuclear weapons. The more extreme version is the Russian Dead Hand program, which allows the automatic launch of nuclear missiles if a number of requirements must be met, even if all Russian leaders must be killed. Similar concepts have been used with computer data, where previously sensitive information has been encrypted and released to the public, and "switch" is the release of the decryption key, as with the "insurance file" WikiLeaks.

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Interest in the dead-man controls increases with the introduction of electric trams and especially electrically powered trains, although dead-man equipment is scarce on US trams to successful PCC cars, which have left-footed legs operated on the left along with right-handed brakes and pedal power. This layout continues to be used on some modern trams around the world. In conventional steam railway trains, there's always a second person with an engineer, a firefighter, who can almost always take the train to stop if necessary. For decades this practice has continued in electric and diesel locomotives, although one person can theoretically operate them.

With modern urban and suburban rail systems, drivers are usually alone in closed cabins. Automated devices have begun to be used on the new installation of New York City's Subway system in the early 20th century. Malbone Street Wreck on the Brooklyn Rapid Transit system in 1918, though not due to driver disability, did spur the need for the universal deployment of the device to stop the train in terms of operator disability. According to the Manhattan borough historian, there are at least three examples where the dead-person switch was successfully used - in 1927, 1940, and 2010.

The status and operation of both alertness and the human dead-button can be recorded on railway recorder (commonly known as black box ).

Maps Dead man's switch

Type

Handle

Most human dead switches are mounted on the vehicle or engine control grip and engage if the operator loses its grip.

Vehicles

Grip switches are still used on modern trams and trains. Pneumatically or electrically connected dead-man control involves a relatively simple modification of the handle controller , the device that regulates traction power. If pressure is not maintained on the controller, the emergency brake train will be applied. Typically, the controller handle is a horizontal bar, rotated to apply the power required for the train. Attached to the bottom of the handle are the bars that when pressing the solenoid contact or switching inside the control house. The spring handle if the pressure is removed, release the rod contact with the internal switch, instantly cut off the power and apply the brake.

Although there are ways that this type of human-death control can fail, they prove very reliable. In some previous equipment, the pressure is not maintained on all controllers, but on the large button protruding from the control handle. This button must also be pressed continuously, usually with the palm of the hand so that the button is flush with the top of the handle. Other methods used, especially with some lever type controllers, which are rotated rather than pushed or pulled, require that the handle on the lever be rotated 90 degrees and held in that position while the train is operating. Some dead-man controls require the motorman to hold it in the center position rather than applying full pressure (see pilot valve).

In the modern New York City railway train, for example, the switch of the dead is inserted into the train speed control. In an R142A car, the carriage operator must continue to hold the lever in place for the train to move.

It is also common for many motor boats, especially ribs with outboard motors, to have a killcord. It is a switch of the dead in the form of a wire attached to the boat and the steering wheel (generally their wrists). If the helmsman falls from their seats, the rope will be pulled to cut the machine.

Machine

Hand-mounted switches are also used on many hand tools and lawn tools, usually rotating or having knives such as saws, drills and lawn mowers. On a saw for example, they insert a throttle trigger push to the handle. If the user loses the chainsaw grip, the spring on the throttle trigger will push it back to the off or idle setting, stopping the blade from spinning. Some tools move further and have a trigger guard built in the handle, similar to firearms safeties. Only when the user presses on the trigger trigger first then releases the key on the trigger and allows the trigger to be pressed. Typically, the trigger guard can only be pressed while the user has a firm grip handle.

Every walking mower sold in the US since 1982 has a dead switch called "operator-attendance control", which by law must stop the blade within 3 seconds after the user releases the control. Attached to their grip is a mechanical lever connected by a flexible cord to a lethal switch on the machine. When cutting, the operator should always press the lever to the handle. If the operator loses the handle of the handle, the machine will die, stop the propeller from the spinning and if equipped, every wheel drive from the turn. This switch configuration also serves as the main shut off switch for the machine. When the operator wants to stop the machine, they deliberately release the dead man's switch.

Touch sensor

In some vehicles, including diesel-electric train locomotives in Canada, and on Nottingham Express Transit vehicles, tram speed controllers are equipped with capacitive touch sensors to detect the driver's hand. If the hand is removed for more than a short time, the track brake is activated. Gloves, if worn, should be finger-less for touch sensors to operate. Back-up switch buttons are supplied on the control side for use in cases of touch sensors that fail or if it is too cold to remove gloves.

Pedal

Pedals can be used instead. While some pedal switches must be held for the engine to function (this system is often found on the amusement rides, where the operator tends to remain in a standing position for long periods of time while the vehicle is in motion), this method has some drawbacks. In a waterfall railway disaster, south of Sydney, Australia, in 2003, it appeared that the driver was slumped in his chair, letting the pedal depressed when he died suddenly of a heart attack. This also happened to Canada's National Railway Railliner passenger train in the 1970s, but the problem was noticed by other crew members and trains stopped safely.

There are several solutions to this problem that are now used in modern pedal systems. The pedal can have a built-in vigilance function, in which the driver must release and repress the pedal in response to audible signals. This prevents it from being overtaken by the above circumstances and is a standard feature on most UK DSD systems.

Some types of locomotives are equipped with three-position pedals, which should normally be kept in the center position. It also reduces the chance of accidentally defeating him, though it may still be possible to do so on purpose. Adding a vigilance function for this type of pedal produces a very secure system. However, the isolation device is still provided in case of equipment failure, so intentional replacement is still possible. This insulation device usually has a clear-seated tamper mounted for that reason.

Chairs switch

The switch of the dead can also be located under the seat of the vehicle or the engine and moves if the operator is not in the chair holding the switch. On a modern tractor, the switch will cut the engine while the transmission is active or the power take-off spins. When driving a lawn mower, the switch is often more extreme where the switch will cut the engine even if the mower is parked and the blade does not spin. The seat switch can also be used to keep young children from even starting the vehicle as they will not be heavy enough to fully hit the switch adjusted to the teen or adult weight.

The key switch

In recreational vehicles such as boats, personal watercraft and snowmobiles, and at the control panel of many amusement rides, the user or operator has a cable or lanyard attached to the wrist or life jacket which in turn is attached to a key mounted on the switch of the dead. If the rider falls from the vehicle or the operator at least away from the control, the cable will be pulled out of the switch of the dead, turn off the engine or set the throttle position to "idle". On powered vessels in particular these cables are often called "wiring kills" (use around the wrist is not recommended). If the skipper goes to sea or is forced away from control, the machine will be cut off. This prevents the ship from continuing under power but out of control, the risk of injury to anyone inside or out of water including passengers who may have fallen out or may still be on board, and collision damage to the property on the way out of this control vessel. It is a common and dangerous practice to defeat the killer cable by fixing it to the boat part instead of the operator; for convenience. This has been the cause of accidents, some of which are fatal, and/or which have caused losses to limbs.

Several luggage trains at airports and treadmill drills have this feature. In the case of a treadmill, a dead person's switch usually consists of an external magnet attached to the cable clamping to the user. If the user falls or walks away without turning off the treadmill, the switch cuts the power to the treadmill belt.

Altimeter switch

The Strategic Air Command developed the turn of the dead for its nuclear bomber, known as the Special Weapon Distortion Separation System (SWESS), which ensured nuclear charge was detonated when the crew became helpless by enemy action. The purpose of this device, unlike other examples mentioned above, is failing-off rather than fail-safe. Once armed, the system will blow nuclear weapons onboard if the plane falls below a predetermined level, usually due to being shot down.

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Blindness control

The primary security that fails with a dead human basic system is the possibility that the operating device is permanently detained in its position, either intentionally or unintentionally. Vigilance control is developed to detect this condition by requiring that the dead device be released momentarily and reapplied at a time interval. There is also a proposal to introduce a system similar to automotive cruise control. The combination of the switches of the dead and the alertness control device is a device of vigilance of the dead.

Software

The version of the switch software of the dead is generally only used by people with technical expertise, and can serve multiple purposes; such as sending notifications to friends or deleting and encrypting data. The "non-event" triggers can be virtually anything, such as failing to log in for 7 consecutive days, not responding to automated emails, pinging, GPS-enabled phones not moving for a period of time, or just failing to type code in minutes from the computer boot. An example of software based on the dead button is the Dead Man Switch which starts when the computer boots and can encrypt or erase user-specified data if unauthorized users should gain access to a protected computer. Google Inactive Manager Accounts allow account holders to nominate others to access their services if they are not used for long periods (default is three months). Killcord is a switch off the sensor resistance to release the encrypted charge in case the project owner stops checking.

Spacecraft

Many spacecraft use the shape of the switch of the dead to guard against the failure of the command system. A timer is formed which is usually reset by receiving a valid command (including whose only function is to reset the timer.) If the timer expires, the spacecraft enters the "lose command" algorithm that pedals through a predetermined set of hardware previous. and/or software modes (such as the selection of the receiver of the backup command) until a valid command is received. The spacecraft can also enter safe mode to protect itself while waiting for the next command.

Although it has some similarities to the switches of the dead, this type of device (timer loss of command) is actually not a human dead switch, as it aims to recover from a hardware failure rather than the absence of a human operator. These are generally called watchdog timers, and are also widely used in nuclear power control systems. The system components on the spacecraft that put it in safe mode or cause it to perform default behavior when no commands received within the specified time window can be considered a dead switch, but hardware or software that tries to receive commands from human operators via alternative channels is an automatic or adaptive recovery communication system, not a dead switch. Voyager 2 recovers from a command receiver failure with timer loss of command.

Train

In most trains, basic level protection is provided by "Deadman's hold" or pedal. If the driver is sick and releases it, the power will be turned off and the emergency brake application will begin to stop the train.

Newer safety standards do not consider this enough, because the driver may slump over the hand of the commander and continue to hold it even if they are unable to control the train. The modern train overcomes this risk by adding the vigilance system to a deadly system. A bell or bell rang every minute or so to alert the motorman or engineer. If they do not respond by moving the controller, or releasing and then reapplying the deadman handle, the system will automatically start the emergency brake application. Most major rail systems in the world use this equipment, both in shipping and passenger operations. It is also used on R143 and other New York City Subway cars while under CBTC operations. In the United States, older locomotives produced before 1995 did not carry this feature, but given the modular nature of the system it was not uncommon to find them retrofitted.

Planes

Some aircraft use vigilance controls to minimize hypoxia; down to a lower altitude if the pilot is unresponsive.

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Alternate name

• Replacement of "switch" with "control" or name indicating certain switch type, for example , "button", "trigger", "throttle", "pedal", "handle" , or "brake"
• Dead man's or dead-man replacements with "enabling" or "live-man" (usually used in the robot industry)
• "Driver's Safety Device" ("DSD") (the official UK term for this type of switch as used on railroad trains)
• "Operator Attendance Control" ("OPC")
• "Dangerous control"
• "Alerter System" (in the top-level system where the switch is enabled to sound an alarm rather than disable to disable high-level systems)
• "Kill the cable" on the boat.

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See also

• Emergency brake
• Handbrake
• Kill the switch
• Railway protection system
• Supervisory watchdog

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References

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External links

• Deadmans on French tram and guided bus (trolley) (PDF)
• Kill Cords: Lessons from Milly RIB Report

Source of the article : Wikipedia