| Electrical injury | |
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| Classification and external resources | |
A person who was affected by a nearby lightning strike. Note the slight branching redness travelling up his leg from the effects of the current. |
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| ICD-10 | T75.4 |
Electric shock occurs upon contact of a (human) body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable.[1]
The minimum current a human can feel depends on the current type (AC or DC) and frequency. A person can feel at least 1 mA (rms) of AC at 60 Hz, while at least 5 mA for DC. The current may, if it is high enough, cause tissue damage or fibrillation which leads to cardiac arrest. 60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation.[2][3] A sustained electric shock from AC at 120 V, 60 Hz is an especially dangerous source of ventricular fibrillation because it usually exceeds the let-go threshold, while not delivering enough initial energy to propel the person away from the source. However, the potential seriousness of the shock depends on paths through the body that the currents take.[2] Death caused by an electric shock is called electrocution.
If the voltage is less than 200 V, then the human skin, more precisely the stratum corneum, is the main contributor to the impedance of the body in the case of a macroshock—the passing of current between two contact points on the skin. The characteristics of the skin are non-linear however. If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs.[4] The protection offered by the skin is lowered by perspiration, and this is accelerated if electricity causes muscles to contract above the let-go threshold for a sustained period of time.[2]
If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit through the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case. This is a concern in modern hospital settings when the patient is connected to multiple devices.
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Heating due to resistance can cause extensive and deep burns. Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage divided by resistance) available from the source. Damage due to current is through tissue heating.
A domestic power supply voltage (110 or 230 V), 50 or 60 Hz alternating current (AC) through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60 mA. With direct current (DC), 300 to 500 mA is required.[2] If the current has a direct pathway to the heart (e.g., via a cardiac catheter or other kind of electrode), a much lower current of less than 1 mA (AC or DC) can cause fibrillation. If not immediately treated by defibrillation, fibrillations are usually lethal because all the heart muscle cells move independently instead of in the coordinated pulses needed to pump blood to maintain circulation. Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all, but this conditions prevents fibrillation.
Current can cause interference with nervous control, especially over the heart and lungs. Repeated or severe electric shock which does not lead to death has been shown to cause neuropathy. Recent research has found that functional differences in neural activation during spatial working memory and implicit learning oculomotor tasks have been identified in electrical shock victims.[5]
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.)[6]
One major corporation found that up to 80 percent of its electrical injuries involve thermal burns due to arcing faults.[7] The arc flash in an electrical fault produces the same type of light radiation from which electric welders protect themselves using face shields with dark glass, heavy leather gloves, and full-coverage clothing.[8] The heat produced may cause severe burns, especially on unprotected flesh. The blast produced by vaporizing metallic components can break bones and irreparably damage internal organs. The degree of hazard present at a particular location can be determined by a detailed analysis of the electrical system, and appropriate protection worn if the electrical work must be performed with the electricity on.
The voltage necessary for electrocution depends on the current through the body and the duration of the current. Ohm's law states that the current drawn depends on the resistance of the body. The resistance of human skin varies from person to person and fluctuates between different times of day. The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms."[9]
The International Electrotechnical Commission gives the following values for the total body impedance of a hand to hand circuit for dry skin, large contact areas, 50 Hz AC currents (the columns contain the distribution of the impedance in the population percentile; for example at 100 V 50% of the population had an impedance of 1875Ω or less):[10]
| Voltage | 5% | 50% | 95% |
|---|---|---|---|
| 25 V | 1,750 Ω | 3,250 Ω | 6,100 Ω |
| 100 V | 1,200 Ω | 1,875 Ω | 3,200 Ω |
| 220 V | 1,000 Ω | 1,350 Ω | 2,125 Ω |
| 1000 V | 700 Ω | 1,050 Ω | 1,500 Ω |
The term "electrocution," coined about the time of the first use of the electric chair in 1890, originally referred only to electrical execution (from which it is a portmanteau word), and not to accidental or suicidal electrical deaths. However, since no English word was available for non-judicial deaths due electric shock, the word "electrocution" eventually took over as a description of all circumstances of electrical death from the new commercial electricity.
The lethality of an electric shock is dependent on several variables:
Other issues affecting lethality are frequency, which is an issue in causing cardiac arrest or muscular spasms, and pathway—if the current passes through the chest or head there is an increased chance of death. From a main circuit or power distribution panel the damage is more likely to be internal, leading to cardiac arrest..
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.
It is sometimes suggested that human lethality is most common with alternating current at 100–250 volts; however, death has occurred below this range, with supplies as low as 32 volts. Assuming a steady current flow (as opposed to static electricity), shocks above 2,700 volts are often fatal, with those above 11,000 volts being usually fatal. Shocks with voltages over 40,000 volts are almost invariably fatal. However, Harry F. Mcgrew came into direct contact with a 340,000 volt transmission line in Huntington Canyon, Utah, and survived. According to the Guinness Book of World Records, this is the largest known electric shock that was survived. Brian Latasa also survived a 230,000 volt shock in Griffith Park, Los Angeles, according to Guinness.
It should also be noted that as one's body is subjected to electrocution the skin burns and the natural resistance of the body decreases, thus increasing the amount of current flowing through the body over time, due to ohm's law.
There were 550 electrocutions in the US in 1993, which translates to 2.1 deaths per million inhabitants. At that time, the incidence of electrocutions was decreasing.[11] Electrocutions in the workplace make up the majority of these fatalities. From 1980–1992, an average of 411 workers were killed each year by electrocution.[9]
Electric shock is also used as a medical therapy, under carefully controlled conditions:
Electroshock weapons are incapacitant weapons used for subduing a person by administering electric shock to disrupt superficial muscle functions. One type is a conductive energy device (CED), an electroshock gun popularly known by the brand name "Taser", which fires projectiles that administer the shock through a thin, flexible wire. Although they are illegal for personal use in many jurisdictions, Tasers have been marketed to the general public.[12] Other electroshock weapons such as stun guns, stun batons ("cattle prods"), and electroshock belts administer an electric shock by direct contact.
Electric shocks are used as a method of torture, since the received voltage and current can be controlled with precision and used to cause pain and fear. In some cases with care it is possible to avoid obvious evidence on the victim's body although this is not always a priority.
Such torture uses electrodes attached to parts of the victim's body: most typically, while wires are wound around the fingers, toes, and/or tongue; attached to the genitals; or inserted in the vagina to provide a return circuit; the voltage source (typically some sort of prod) of precisely controllable pressure is applied to other sensitive parts of the body, such as the genitals, vagina, breasts, or head. The Parrilla is an example of this technique. Other methods of electrical torture (such as the Picana) do not use a fixed wire but the prod has two electrodes of different polarity a short distance apart so as to make a circuit through the flesh between them when it is placed on the body, thus making it easy for the operator to target the shocks accurately in the places that cause the victim most pain and distress, such as the genitals, vagina, breasts, or head. When the voltage and current is controlled (most typically, high voltage and low current) the victim feels the pain of electric shock but is not physically harmed. Repeated shocks to the genitals or vagina will result in the victim losing control of his or her bladder and unintentionally defecating, while extensive passage of the current through the buttocks will cause the victim to unintentionally defecate.
Electrical torture has been used in war and by repressive regimes since the 1930s:[13] The US Army is known to have used electrical torture during World War II;[14] Amnesty International published an official statement that Russian military forces in Chechnya tortured local women with electric shocks by attaching wires onto their breasts;[15] Japanese serial killer Futoshi Matsunaga used electric shocks for controlling his victims.[16]
Advocates for the mentally ill and some psychiatrists such as Thomas Szasz have asserted that electroconvulsive therapy (ECT) is torture when used without a bona fide medical benefit against recalcitrant or non-responsive patients—however such arguments do not apply to ECT when used after the patient has been anesthetized. See above for ECT as medical therapy. A similar argument and opposition apply to the use of painful shocks as punishment for behavior modification, a practice that is openly used only at the Judge Rotenberg Institute.[17][18][19]
Electric shock delivered by an electric chair is sometimes used as an official means of capital punishment in the United States, although its use has become rare in recent times. Although some original proponents of the electric chair considered it to be a more humane execution method than hanging, shooting, poison gassing, etc., it has now generally been replaced by lethal injections in states that practise capital punishment. Modern reporting has claimed that it sometimes takes several shocks to be lethal, and that the condemned person may actually catch fire before the process is complete. The brain is always severely damaged and inactivated.
Other than in parts of the United States, only the Philippines reportedly has used this method (1926–76). It was intermittantly replaced by the firing squad, until the death penalty was abolished in that country. It is legal in at least 10 states of USA.[20]