Electric shock

Electrical injury
Injury caused by a nearby lightning strike. The slight branching redness (sometimes called a Lichtenberg figure) travelling up the leg was caused by the effects of current.
Classification and external resources
Specialty emergency medicine
ICD-10 T75.4
DiseasesDB 4159

Electric shock is the physiological reaction, sensation, or injury caused by electric current passing through the (human) body.[1] It occurs upon contact of a (human) body part with any source of electricity that causes a sufficient current through the skin, muscles, or hair.

Very small currents can be imperceptible. Stronger current passing through the body may make it impossible for a shock victim to let go of an energized object.[2] Still larger currents can cause fibrillation of the heart and damage to tissues. Death caused by an electric shock is called electrocution. Wiring or other metalwork at a hazardous voltage which can constitute a risk of electric shock is called "live," as in "live wire."

Electric shock is often used to describe an injurious exposure to electricity.[3] Electrical currents can travel through the nervous system and burn out tissue in patches along the way. This can leave bizarre symptoms anywhere on the body and may lead to complex regional pain syndrome.

Shocks can be caused by direct or indirect contact. Contact with an exposed conductive part under fault conditions is called direct contact. IEC requires certain degrees of ingress protection against direct contact. Indirect contact protections can be achieved by earthed equipotential bonding and automatic disconnection of supply by using Residual Current Devices, for example.[4]

Introduction

The minimum current a human can feel depends on the current type (AC or DC) as well as frequency for AC. A person can feel at least 1 mA (rms) of AC at 60 Hz, while at least 5 mA for DC. At around 10 milliamperes, AC current passing through the arm of a 68-kilogram (150 lb) human can cause powerful muscle contractions; the victim is unable to voluntarily control muscles and cannot release an electrified object.[5] This is known as the "let go threshold" and is a criterion for shock hazard in electrical regulations.

The current may, if it is high enough and is delivered at sufficient voltage, cause tissue damage or fibrillation which can cause cardiac arrest; more than 30 mA[6] of AC (rms, 60 Hz) or 300 – 500 mA of DC at high voltage can cause fibrillation.[7][8] 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.[7] 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.[9] 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.[7]

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 with a probability of 0.2%.[10]

Signs and symptoms

Burns

Second-degree burn after a high tension line accident

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. For most cases of high-energy electrical trauma, the Joule heating in the deeper tissues along the extremity will reach damaging temperatures in a few seconds.[11]

Ventricular fibrillation

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 30 mA.[6] With direct current (DC), 300 to 500 mA is required.[7] 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, fibrillation is usually lethal because all of the heart muscle fibres move independently instead of in the coordinated pulses needed to pump blood and maintain circulation. Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all, but these conditions prevent fibrillation.

Neurological effects

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.[12]

When the current path is through the head, it appears that, with sufficient current applied, 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).[13]

Arc-flash hazards

OSHA found that up to 80 percent of its electrical injuries involve thermal burns due to arcing faults.[14] 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.[15] The heat produced may cause severe burns, especially on unprotected flesh. The arc blast produced by vaporizing metallic components can break bones and 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.

Pathophysiology

Body resistance

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".[16]

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):[17]

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

Voltage-current characteristic of human skin

The voltage-current characteristic of human skin is non-linear and depends on many factors such as intensity, duration, history, and frequency of the electrical stimulus. Sweat gland activity, temperature, and individual variation also influence the voltage-current characteristic of skin. In addition to non-linearity, skin impedance exhibits asymmetric and time varying properties. These properties can be modeled with reasonable accuracy.[18] Resistance measurements made at low voltage using a standard ohmmeter do not accurately represent the impedance of human skin over a significant range of conditions.

For sinusoidal electrical stimulation less than 10 volts, the skin voltage-current characteristic is quasilinear. Over time, electrical characteristics can become non-linear. The time required varies from seconds to minutes, depending on stimulus, electrode placement, and individual characteristics.

Between 10 volts and about 30 volts, skin exhibits non-linear but symmetric electrical characteristics. Above 20 volts, electrical characteristics are both non-linear and symmetric. Skin conductance can increase by several orders of magnitude in milliseconds. This should not be confused with dielectric breakdown, which occurs at hundreds of volts. For these reasons, current flow cannot be accurately calculated by simply applying Ohm's law using a fixed resistance model.

Point of entry

Lethality

Electrocution

The term "electrocution," coined about the time of the first use of the electric chair in 1890, originally referred only to electrical execution and not to accidental or suicidal electrical deaths. However, since no English word was available for non-judicial deaths due to electric shock, the word "electrocution" eventually took over as a description of all circumstances of electrical death.

Factors in lethality of electric shock

Log-log graph of the effect of alternating current I of duration T passing from left hand to feet as defined in IEC publication 60479-1.[19]
AC-1: imperceptible
AC-2: perceptible but no muscle reaction
AC-3: muscle contraction with reversible effects
AC-4: possible irreversible effects
AC-4.1: up to 5% probability of ventricular fibrillation
AC-4.2: 5-50% probability of fibrillation
AC-4.3: over 50% probability of fibrillation

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. Very high frequency electric current causes tissue burning, but does not penetrate the body far enough to cause cardiac arrest (see electrosurgery). Also important is the 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. Another factor is that cardiac tissue has a chronaxie (response time) of about 3 milliseconds, so electricity at frequencies of higher than about 333 Hz requires more current to cause fibrillation than is required at lower frequencies.

The comparison between the dangers of alternating current at typical power transmission frequences (i.e., 50 or 60 Hz), and direct current has been a subject of debate ever since the War of Currents in the 1880s. Animal experiments conducted during this time suggested that alternating current was about twice as dangerous as direct current per unit of current flow (or per unit of applied voltage).

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 42 volts.[20] Assuming a steady current flow (as opposed to a shock from a capacitor or from static electricity), shocks above 2,700 volts are often fatal, with those above 11,000 volts being usually fatal, though exceptional cases have been noted. According to a Guinness Book of World Records comic, seventeen-year-old Brian Latasa survived a 230,000 volt shock on the tower of an ultra-high voltage line in Griffith Park, Los Angeles on November 9, 1967.[21] A news report of the event stated that he was "jolted through the air, and landed across the line", and though rescued by firemen, he suffered burns over 40% of his body and was completely paralyzed except for his eyelids.[22]

Epidemiology

There were 550 reported electrocutions in the US in 1993, 2.1 deaths per million inhabitants. At that time, the incidence of electrocutions was decreasing.[23] 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.[16] A recent study conducted by the National Coroners Information System (NCIS) in Australia [24] has revealed three-hundred and twenty-one (321) closed case fatalities (and at least 39 case fatalities still under coronial investigation) that had been reported to Australian coroners where a person died from electrocution between July 2000 and October 2011.[25]

In Sweden, Denmark, Finland and Norway the number of electric deaths per million inhabitants was 0.6, 0.3, 0.3 and 0.2, respectively, in years 2007-2011.[26]

People who survive electrical trauma may suffer a host of injuries including loss of consciousness, seizures, aphasia, visual disturbances, headaches, tinnitus, paresis, and memory disturbances.[27] Even without visible burns, electric shock survivors may be faced with long-term muscular pain and discomfort, fatigue, headache, problems with peripheral nerve conduction and sensation, inadequate balance and coordination, among other symptoms. Electrical injury can lead to problems with neurocognitive function, affecting speed of mental processing, attention, concentration, and memory. The high frequency of psychological problems is well established and may be multifactorial.[27] As with any traumatic and life-threatening experience, electrical injury may result in post traumatic psychiatric disorders.[28] There exist several non-profit research institutes that coordinate rehabilitation strategies for electrical injury survivors by connecting them with clinicians that specialize in diagnosis and treatment of various traumas that arise as a result of electrical injury.[29][30]

Deliberate uses

Medical uses

Electric shock is also used as a medical therapy, under carefully controlled conditions:

Entertainment

Electrifying machine at Musée Mécanique that actually works with vibration[34]

Mild electric shocks are also used for entertainment, especially as a practical joke for example in such devices as a shocking pen or a shocking gum. However devices such as a joy buzzer and most other machines in amusement parks today only use vibration that feels somewhat like an electric shock to someone not expecting it.

Erotic electrostimulation involves the application of electrical stimulation to the nerves of the body, with particular emphasis on the genitals. Electrostimulation has been associated with BDSM activities, and erotic electrostimulation is an evolution of that practice. Erotic electrostimulation is the use of electrostimulation in an erotic or sexual manner versus the more sadistic or painful electric shocks in BDSM.

Law enforcement and personal defense

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.[35] Other electroshock weapons such as stun guns, stun batons ("cattle prods"), and electroshock belts administer an electric shock by direct contact.

Electric fences are barriers that uses electric shocks to deter animals or people from crossing a boundary. The voltage of the shock may have effects ranging from uncomfortable, to painful or even lethal. Most electric fencing is used today for agricultural fencing and other forms of animal control purposes, though it is frequently used to enhance security of restricted areas, and there exist places where lethal voltages are used.

Torture

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 without always visibly harming the victim's body.

Such torture uses electrodes attached to parts of the victim's body: most typically, while wires are wound around the fingers, toes, 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, 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. 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 will result in the victim losing control of his or her bladder and unintentionally urinating, 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:[36] The U.S. Army is known to have used electrical torture during World War II[37] and during the Algerian War electrical torture was a favorite method of French military forces;[38] Amnesty International published an official statement that Russian military forces in Chechnya tortured local women with electric shocks by attaching wires onto their breasts;[39] Japanese serial killer Futoshi Matsunaga used electric shocks to control his victims.[40]

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. 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.[41][42][43]

Capital punishment

Electric chair in Sing Sing

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 practice 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.

Other than in parts of the United States, only the Philippines reportedly has used this method, from 1926 to 1976. It was intermittently replaced by the firing squad, until the death penalty was abolished in that country. Electrocution remains legal in at least 5 states (Virginia, Florida, Alabama, North Carolina and Kentucky) of the United States.[44]

See also

Notes

  1. ↑ Boon, Elizabeth; Parr, Rebecca; 20,000Dayananda, Samarawickrama (2012). Oxford Handbook of Dental Nursing. Oxford University Press. p. 132. ISBN 0191629863.
  2. ↑ Leslie Alexander Geddes, Rebecca A. Roeder ,Handbook of Electrical Hazards and Accidents Lawyers & Judges Publishing Company, 2006 ISBN 0913875449, page 29
  3. ↑ Reilly 1998, p. 1
  4. ↑ Wright, Newbery & Institution of Electrical Engineers 2004, p. 196.
  5. ↑ John Cadick et. al (ed.) Electrical Safety Handbook Third Edition, McGraw Hill,2005 ISBN 0-07-145772-0 page 1-4
  6. 1 2 ucsb.edu - Electrical Safety Information - Physics Department, UCSB, 2012-01-09
  7. 1 2 3 4 Clifford D. Ferris, Electric Shock, chapter 22.1 in Jerry C. Whitaker (ed.) The Electronics Handbook, CRC Press, 2005, ISBN 0-8493-1889-0, pp. 2317-2324
  8. ↑ Electric Current Needed to Kill a Human
  9. ↑ Reilly 1998, p. 30
  10. ↑ Norbert Leitgeb (6 May 2010). Safety of Electromedical Devices: Law - Risks - Opportunities. Springer Science & Business Media. p. 122. ISBN 978-3-211-99683-6.
  11. ↑ Lee, R. C.; Canaday, D. J.; Hammer, S. M. (1993). "Transient and stable ionic permeabilization of isolated skeletal muscle cells after electrical shock". The Journal of burn care & rehabilitation. 14 (5): 528–40. PMID 8245107. doi:10.1097/00004630-199309000-00007.
  12. ↑ Mechanism of Electrical Injury Chicago Electrical Trauma Research Institute Archived May 3, 2015, at the Wayback Machine. Accessed April 27, 2010
  13. ↑ Electric Stunning of Pigs and Sheep
  14. ↑ "Industry Backs IEEE-NFPA Arc Flash Testing Program with Initial Donations of $1.25 Million". IEEE. 14 July 2006. Retrieved 2008-01-01.
  15. ↑ Arc Flash Protection
  16. 1 2 "Publication No. 98-131: Worker Deaths by Electrocution" (PDF). National Institute for Occupational Safety and Health. Retrieved 2008-08-16.
  17. ↑ Reilly 1998, p. 43
  18. ↑ "The Voltage Current Characteristic of the Human Skin" (PDF). University of Pretoria.
  19. ↑ Weineng Wang, Zhiqiang Wang, Xiao Peng, Effects of the Earth Current Frequency and Distortion on Residual Current Devices, Scientific Journal of Control Engineering, Dec 2013, Vol 3 Issue 6 pp 417-422
  20. ↑ "The Fatal Current". OSU Physics. Ohio State University. Retrieved 4 March 2015.
  21. ↑ "According to Guinness (comic)". Toledo Blade. 1978-04-28.
  22. ↑ "Firemen risk death to save teenager". Ocala Star-Banner. 1967-11-24.
  23. ↑ Folliot, Dominigue (1998). "Electricity: Physiological Effects". Encyclopaedia of Occupational Health and Safety, Fourth Edition. Archived from the original on 2007-02-28. Retrieved 2006-09-04.
  24. ↑ National Coroners Information System, NCIS
  25. ↑ Electrocution Related Deaths - National Coroners Information System (NCIS) Fact-Sheet, January 2012 Archived March 17, 2012, at the Wayback Machine.
  26. ↑ Kinnunen, Minna (2013). "Electrical accident hazards in the Nordic countries" (PDF). Master's thesis, Tampere University of Technology. p. 19. Retrieved 2013-06-10.
  27. 1 2 Pliskin, N. H.; Meyer, G. J.; Dolske, M. C.; Heilbronner, R. L.; Kelley, K. M.; Lee, R. C. (1994). "Neuropsychiatric Aspects of Electrical Injury". Annals of the New York Academy of Sciences. 720: 219–23. Bibcode:1994NYASA.720..219P. PMID 8010642. doi:10.1111/j.1749-6632.1994.tb30450.x.
  28. ↑ Grigorovich, Alisa; Gomez, Manuel; Leach, Larry; Fish, Joel (2013). "Impact of Posttraumatic Stress Disorder and Depression on Neuropsychological Functioning in Electrical Injury Survivors". Journal of Burn Care & Research. 34 (6): 659–65. PMID 23412330. doi:10.1097/BCR.0b013e31827e5062.
  29. ↑ http://www.cetri.org%5B%5D
  30. ↑ http://sunnybrook.ca/content/?page=sjr-patvis-prog-electrical%5B%5D
  31. ↑ Berrios, G E (1997). "The scientific origins of electroconvulsive therapy". History of Psychiatry. 8 (29 pt 1): 105–119. PMID 11619203. doi:10.1177/0957154X9700802908.
  32. ↑ Fink, M (1984). "The origins of convulsive therapy". American Journal of Psychiatry. 141 (9): 1034–41. PMID 6147103.
  33. ↑ Szasz, Thomas (2007). Coercion as Cure: A Critical History of Psychiatry. ISBN 978-1412810500.
  34. ↑ http://www.arcade-museum.com/game_detail.php?game_id=10550
  35. ↑ International Association of Chiefs of Police, Electro Muscular Disruption Technology: A Nine-Step Strategy for Effective Deployment Archived December 10, 2013, at the Wayback Machine., 2005
  36. ↑ Technological Invention and Diffusion of Torture Equipment The Strange Case of Electric Torture Instruments in the Early 20th Century Archived March 5, 2010, at the Wayback Machine.
  37. ↑ Rejali, Darius (2007-12-16). "Torture, American style: The surprising force behind torture: democracies". Boston Globe. Retrieved 2008-01-01.
  38. ↑ http://www.wsws.org/en/articles/2001/04/alg-a09.html%5B%5D
  39. ↑ "Russian Federation Preliminary briefing to the UN Committee against Torture". Archived from the original on May 16, 2009. Retrieved February 24, 2012.
  40. ↑ "Serial killer's death sentence upheld". Asahi Shimbun. 2007-09-27. Retrieved 2008-03-21.
  41. ↑ Israel, Matthew. "History and Basic Principles of JRC". Retrieved 2007-12-22.
  42. ↑ Gonnerman, Jennifer (20 August 2007). "School of Shock". Mother Jones Magazine. Retrieved 2007-12-22.
  43. ↑ Wen, P (2008-01-17). "Showdown over shock therapy". The Boston Globe. Retrieved 2008-01-26.
  44. ↑ Death Penalty Information Center Archived May 23, 2015, at the Wayback Machine.

References

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