An electric shock can occur upon contact of a human's body with any source of voltage high enough to cause sufficient current through the muscles or hair. The minimum current a human can feel is thought to be about 1 milliampere (mA). The current may cause tissue damage or fibrillation if it is sufficiently high. Death caused by an electric shock is referred to as electrocution.
When the current path is through the head, it appears that, with sufficient current, loss of consciousness almost always occurs swiftly. (This is borne out by some limited self-experimentation by early designers of the electric chair and by research from the field of animal husbandry, where electric stunning has been extensively studied) '''
The comparison between the dangers of alternating current and direct current has been a subject of debate ever since the War of Currents in the 1880s. DC tends to cause continuous muscular contractions that make the victim hold on to a live conductor, thereby increasing the risk of deep tissue burns. On the other hand, mains-frequency AC tends to interfere more with the heart's electrical pacemaker, leading to an increased risk of fibrillation. AC at higher frequencies holds a different mixture of hazards, such as RF burns and the possibility of tissue damage with no immediate sensation of pain. Generally, higher frequency AC current tends to run along the skin rather than penetrating and touching vital organs such as the heart. While there will be severe burn damage at higher voltages, it is normally not fatal.
It is sometimes suggested that human lethality is most common with alternating current at 100–250 volts, however death has occurred outside this range, with supplies as low as 32 volts and supplies at over 250 volts frequently causing fatalities.
Electrical discharge from lightning tends to travel over the surface of the body causing burns and may cause respiratory arrest.
The voltage necessary for electrocution depends on the current through the body and the duration of the current. Using Ohm's law, Voltage = Current × Resistance, we see that the current drawn depends on the resistance of the body. The resistance of our skin varies from person to person and fluctuates between different times of day. In general, dry skin is a poor conductor that may have a resistance of around 100,000 Ω, while broken or wet skin may have a resistance of around 1,000 Ω.
The capability of a conducting material to carry a current depends on its cross section, which is why males typically have a higher lethal current than females (10 amperes vs 9 amperes) due to a larger amount of tissue . However, death can reportedly occur from currents as low as 30 mili-amperes.
Using Ohm's law, we may derive the voltages lethal to the human body. This is given in the following table:
|Electric current (amperes)||Voltage at 10,000 ohms||Voltage at 1,000 ohms||Maximum power (watts)||Physiological effect|
|0.001 A||10 V||1 V||0.01 W||Threshold of feeling an electric shock, pain|
|0.005 A||50 V||5 V||0.25 W||Maximum current which would be harmless|
|0.01-0.02 A||100-200 V||10-20 V||1-4 W||Sustained muscular contraction. "Cannot let go" current.|
|0.05 A||500 V||50 V||25 W||Ventricular interference, respiratory difficulty|
|0.1-0.3 A||1000-3000 V||100-300 V||100-900 W||Ventricular fibrillation. Can be fatal.|
|6 A||60,000 V||6,000 V||400,000 W||Sustained ventricular contraction followed by normal heart rhythm. These are the operation levels for a defibrillator. Temporary respiratory paralysis and possibly burns.|
It is possible to have a voltage potential between neutral wires and the ground in the event of an improperly wired (disconnected) neutral, or if it is part of certain obsolete (and now illegal) switch circuits. The electrical appliance or lighting equipment might provide some voltage drop, but not nearly enough to avoid a shock. "Live" neutral wires should be treated with the same respect as live wires. Also, the neutral wire must be insulated to the same degree as the live wire to avoid a short circuit.
It should be mentioned that much care needs to be taken with electrical systems on ships and boats, especially steel or aluminum ones. Anyone standing on a metal deck or leaning against a bulkhead is automatically grounded, so great care must be taken that all live electrical wires are well insulated. As an example of the danger, during WW II, the battleship USS Washington had not one casualty due to enemy action. However, there were some sailors killed by electrocution while doing such things as using electric drills that had defects in them. For the details, see the official histories of this distinguished USN warship.
Electrical codes in many parts of the world call for installing a residual-current device (RCD or GFI, ground fault interrupter) in electrical circuits thought to pose a particular hazard to reduce the risk of electrocution. In the USA, for example, a new or remodeled residential dwelling must have them installed in all kitchens, bathrooms, laundry rooms, garages, and also any other room with an unfinished concrete floor* such as a workshop. These devices work by detecting an imbalance between the live and neutral wires. In other words, if more current exits through the live wire than is returning though its neutral wire (presumably via ground), it assumes something is wrong and breaks the circuit in a tiny fraction of a second. There is some concern that these devices might not be fast enough to protect infants and small children in rare instances.
The plumbing system in a home or other small building has historically used metal pipes and thus been connected to ground through the pipes*. This is no longer always true because of the extensive use of plastic piping in recent years, but a plastic system cannot be relied upon for safety purposes. Contrary to popular belief, pure water is not a good conductor of electricity. However, most water is not pure and contains enough dissolved particles (salts) to greatly enhance its conductivity. When the human skin becomes wet, it allows much more current than the dry human body would. Thus, being in the bath or shower will not only ground oneself to return path of the power mains, but lower the body's resistance as well. Under these circumstances, touching any metal switch or appliance that is connected to the power mains could result in severe electric shock or electrocution. While such an appliance is not supposed to be live on its outer metal switch or frame, it may have become so if a defective live bare wire is accidentally touching it (either directly or indirectly via internal metal parts). It is for this reason that mains electrical sockets are prohibited in bathrooms in the United Kingdom. However, the widespread use of plastic cases for everyday appliances, grounding of these appliances, and mandatory installation of Residual Current Devices (R.C.D.s) have greatly reduced this type of electrocution over the recent past decades.
A properly-grounded appliance greatly reduces the electric shock potential by causing a short circuit if any portion of the metal frame (chassis) is accidentally touching the live wire. This will cause the circuit breaker to turn off or the fuse to blow resulting in a power outage in that area of the home or building. Often there will be a large "bang" and possibly smoke which could easily scare anyone nearby. However, this is still much safer than risking electric shock, since the chance of an out-of-control fire is remote.
Where live circuits must be frequently worked on (e.g. television repair), an isolation transformer is sometimes used. Unlike ordinary transformers which raise or lower voltage, the coil windings of an isolation transformer are at a 1:1 ratio which keeps the voltage unchanged. The purpose is to isolate the neutral wire so that it has no connection to ground. Thus, if a technician accidentally touches the live chassis and ground at the same time, nothing would happen.
Neither ground fault interrupters (RCD/GFI) nor isolation transformers can prevent electrocution between the live and neutral wires. This is the same path used by functional electrical appliances, so protection is not possible. However, most accidental electrocutions, especially those not involving electrical work and repair, are via ground -- not the neutral wire.
The National Socialists are known to have used electrical torture during World War II. An extensive fictional depiction of such torture is included in the 1966 book The Secret of Santa Vittoria by Robert Crichton. During the Vietnam War, electric shock torture is said to have been used by both the Americans and Vietnamese. A scene of electrical torture in the American Deep South is included in the 1980 Robert Redford film Brubaker. Amnesty International published an official statement that Russian military forces in Chechnya tortured local women with electric shocks by connecting electric wires to their bra straps. Examples in popular modern culture are the electric torture of Martin Riggs in Lethal Weapon and John Rambo in Rambo: First Blood Part II. Japanese serial killer Futoshi Matsunaga used electric shocks for controlling his victims.
Advocates for the mentally ill and some psychiatrists such as Thomas Szasz have asserted that electroconvulsive therapy is torture when used without a bona fide medical benefit against recalcitrant or non-responsive patients. See above for ECT as medical therapy. These same arguments and oppositions apply to the use of extremely painful shocks as punishment for behavior modification, a practice that is openly used only at the Judge Rotenberg Institute.
Low- to moderately high-voltage electric shocks do not result in the type of pain felt at death or organ failure, nor have been proven to result in "significant psychological harm of significant duration, e.g., lasting for months or even years,".