by Jenny Knodell, IQS Editor
When I rolled out of bed this morning, one of the first things I did was turn on the overhead light. With the flip of a switch, my room transformed from a dark, quiet, peaceful sleeping chamber to a harsh, fully-lit, squint-inducing wake-up call in a tenth of a second. If you think about it, that technology, an on-off toggle switch, is pretty convenient, but no big deal since people have been using them for around 100 years. These handy devices aren’t just designed to turn lights on and off. Electric switches actually have some pretty important applications—life and death, in fact, and are found in heavy machinery, space crafts, trains, high-speed vehicles and military aircrafts.
In emergency situations, a device known as the dead man’s switch does what its name implies—takes over a system or machinery if the operator dies or become incapacitated. As morbid as the name sounds, it’s a vital part of modern security systems and will shut off and abort all operations at all costs, even if it means machinery damage. First used in locomotives, these switches were designed for emergency stops if the conductor was unable to fill his duties. Today, dead man’s switches are common staples in action flick climaxes—the hero always has to reach a detonating switch before the evil antagonist does, with no time to spare or something will blow up.
Photos courtesy of APEM Components, Inc.
Dead man’s switches are used in situations where if an operator dies, other people could too. Certain types need an alert individual to press or switch them on, and are activated in the small window of time between a deadly mistake and the catastrophe it ensues. In NASCAR, all race car steering wheels have pushbutton switches that shut the engine off in case the brakes fail or the accelerator petal sticks. Most gas station pumps are equipped with switches that shut off the gas flow in case of a fire.
Dead man’s switch on steering wheel of racecar.
In some cases, the operator stays in constant contact with a dead man’s switch, which will only activate if they fall limp. For example, some rotary switches are attached to an operator’s arm by a tether, and if they lose consciousness and fall, their body’s force activates the emergency switch. Others are located under foot-activated pedals. Many of these switches are connected to a data recorder to determine whether it was activated during a deadly accident or not.
Among all these life-saving functions, dead man’s switches have been used for exactly the opposite. Since the 1950s, the US military saw another application for emergency situation switches. Called Special Weapons Emergency Separation Systems (SWESS), Strategic Air Command installed nuclear bomb release systems into all aircraft bombers. These systems are activated by an altimeter switch. In war zones, if the pilot is killed or the aircraft controls fail, this switch automatically detonates nuclear weapons over enemy territory when the aircraft reaches a certain altitude. Because SWESS switches were designed for nuclear weapons, they aren’t used for missiles, which hit specific targets. However, missiles are often detonated by activating pushbutton or rotary switches.
Emergency stop pushbutton switch on control panel.