Electrical injury

Electrical injury
An electrical injury, (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs
on direct contact with an electric current.
The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or only produce a light tingling sensation. However, a shock caused by low and otherwise harmless current could startle an individual and cause injury due to jerking away or falling. A strong electric shock can often cause painful muscle spasms severe enough to dislocate joints or even to break bones. The loss of muscle control is the reason that a person may be unable to release themselves from the electrical source; if this happens at a height as on a power line they can be thrown off. Larger currents can result in tissue damage and may trigger ventricular fibrillation or cardiac arrest. If death results from an electric shock the cause of death is generally referred to as electrocution.
Electric injury occurs upon contact of a body part with electricity that causes a sufficient current to pass through the person's tissues. Contact with energized wiring or devices is the most common cause. In cases of exposure to high voltages, such as on a power transmission tower, direct contact may not be necessary as the voltage may "jump" the air gap to the electrical device.
Following an electrical injury from household current, if a person has no symptoms, no underlying heart problems, and is not pregnant further testing is not required. Otherwise an electrocardiogram, blood work to check the heart, and urine testing for signs of muscle breakdown may be performed.
Management may involve resuscitation, pain medications, wound management, and heart rhythm monitoring. Electrical injuries affect more than 30,000 people a year in the United States and result in about 1,000 deaths.
Signs and symptoms
Burns
Heating due to resistance can cause extensive and deep burns. When applied to the hand, electricity can cause involuntary muscle contraction, producing the "no-let-go" phenomenon, and increasing the risk for serious 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 or the square of the current multiplied by the resistance) available from the source. Damage due to current is through tissue heating and/or electroporation injury. 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.
Ventricular fibrillation
A domestic power supply voltage (110 or 230 V), 50 or 60 Hz alternating current (AC) through the chest for a duration longer than one second may induce ventricular fibrillation at currents as low as 30 milliamperes (mA). With direct current (DC), 90 to 130 mA are required at the same duration. 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, ventricular fibrillation is usually lethal, causing cardiac arrest, because all of the heart muscle fibres move independently instead of in the coordinated action needed for successful cardiac cycle to pump blood and maintain circulation. Above 200 mA, tetanic muscle contractions are so strong that the heart muscles cannot move at all, but this condition might even prevent fibrillation.
Short single DC pulses induce VF dependent on the amount of charge (in mC) transferred to the body, which makes the amplitude of the electrical stimulus independent of the exact amount of current flowing through the body for very short pulse durations. DC shocks of short duration are usually better tolerated by the heart even at high currents and rarely induce ventricular fibrillation compared to contacts with longer duration DC or AC. The amount of current can easily reach very high values as amperage is only of second order importance to fibrillation risk in the case of ultra short contact times with direct currents. But even if the charge itself is harmless, the amount of energy being discharged still can lead to thermal and chemical hazards if its value is high enough.
One example of high current electric shock which may be usually harmless is an electrostatic discharge as experienced in every day life on door handles, car doors etc. These currents can reach values up to 60 A without harmful effects on the heart as the duration is in the order of only several ns.
Mechanism
Mechanism of cardiac arrhythmias induced by electricity is not fully understood, but various biopsies have shown arrhythmogenic foci in patchy myocardial fibrosis which contained increased amount of Na+ and K+ pumps, possibly associated with transient and localized changes in sodium-potassium transport as well as their concentrations, resulting in changes in membrane potential.
Neurological effects
Electric current can cause interference with nervous control, especially over the heart and lungs. Electric shock which does not lead to death has been shown to cause neuropathy in some cases at the site where the current entered the body. The neurologic symptoms of electrical injury may occur immediately, which traditionally have a higher likelihood for healing, though they may also be delayed by days to years. The delayed neurologic consequences of electrical injury have a worse prognosis.
When the path of electric current proceeds 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.
If ventricular fibrillation occurs (as above), the blood supply to the brain is diminished, which may cause cerebral hypoxia (and its associated neurologic consequences).
Mental health
There are a variety of psychiatric effects that may occur as a result of electrical injuries. Behavioral changes can occur as well, even if the path of electric current did not proceed through the head. Symptoms may include:
Depression, including feelings of low self-esteem and guilt
Anxiety spectrum disorders, including posttraumatic stress disorder and fear of electricity
Moodiness, including a lower threshold for frustration and "losing one's temper"
Memory loss, decreased attention span, and difficulty learning
Arc-flash hazards
OSHA found that up to 80 percent of its electrical injuries involve thermal burns due to arcing faults. 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. 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
The minimum current a human can feel depends on the current type (AC or DC) as well as frequency for AC. A person can sense electric current as low as 1mA (rms) for 60Hz AC and as low as 5mA for DC. At around 10mA, AC current passing through the arm of a human can cause powerful muscle contractions; the victim is unable to voluntarily control muscles and cannot release an electrified object. 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, cause tissue damage or fibrillation which can cause cardiac arrest; of AC (rms, 60 Hz) or of DC at high voltage can cause fibrillation. 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. 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. 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.
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%.
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".
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):
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. 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
Macroshock: Current across intact skin and through the body. Current from arm to arm, or between an arm and a foot, is likely to traverse the heart, therefore it is much more dangerous than current between a leg and the ground. This type of shock by definition must pass into the body through the skin.
Microshock: Very small current source with a pathway directly connected to the heart tissue. The shock is required to be administered from inside the skin, directly to the heart i.e. a pacemaker lead, or a guide wire, conductive catheter etc. connected to a source of current. This is a largely theoretical hazard as modern devices used in these situations include protections against such currents.
Lethality
Electrocution
The earliest usage of the term "electrocution" cited by the Oxford English Dictionary was an 1889 newspaper reference to the method of execution then being considered. Shortly thereafter, in 1892, the term was used in Science to refer generically to death or injury caused by electricity.
Factors in lethality of electric shock
The lethality of an electric shock is dependent on several variables:
Current. The higher the current, the more likely it is lethal. Since current is proportional to voltage when resistance is fixed (ohm's law), high voltage is an indirect risk for producing higher currents.
Duration. The longer the shock duration, the more likely it is lethal—safety switches may limit time of current flow. Short high-current pulses, as from capacitors, are usually less dangerous than longer-lasting low-current shocks.
Pathway. If current flows through vital organs, like the heart muscle, it is more likely to be lethal.
High voltage (over about 600 volts). In addition to greater current flow, high voltage may cause dielectric breakdown at the skin, thus lowering skin resistance and allowing further increased current flow.
Medical implants. Artificial cardiac pacemakers or implantable cardioverter-defibrillators (ICD) are sensitive to very small currents.
Pre-existing medical condition.
Age, body mass, and health status.
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 do not stimulate the nerves strongly 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 frequencies (i.e., 50 or 60 Hz), and direct current has been a subject of debate ever since the war of the 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. 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 the Guinness Book of World Records, 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. 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 sustained burns over 40% of his body and was completely paralyzed except for his eyelids. The shock with the highest voltage reported survived was that of Harry F. McGrew, who came in contact with a 340,000 volt transmission line in Huntington Canyon, Utah.
The severity and lethality of an electric shock also depend on time and frequency of the current flow passing through the human body. For example a high frequency current has a higher ventricular fibrillation threshold than lower frequency. Also shorter pulses create a higher threshold, short pulses below 10 ms are usually believed to have a primarily charge dependent threshold and shock amplitude. Research shows that for very short electric pulse durations below 1 ms the threshold curve converges into a linear, constant charge criterion for muscle and nerve stimulation including the heart and the brain. Heating is primarily determined by the amount of energy. These principles have been defined in IEC 60479-2, in opposite to IEC 60479-1 for longer durations above 10 ms with DC or AC which use a current-time curve based classification. This code is also used to determine the safety of capacitors, electrical shock weapons, electric fences and other short pulsed low- and high-voltage electrical applications.
Prevention
Grounding the electrical enclosure of high-voltage machinery
Use of insulated gloves, insulated boots, mats and tools
Protecting electrical circuit with a residual-current device (RCD)
Following the five rules of electrical safety
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. 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. Workplace deaths caused by exposure to electricity in the U.S. increased by nearly 24% between 2015 and 2019, from 134 to 166. However, workplace electrical injuries dropped 23% between 2015 and 2019 from 2,480 to 1,900. In 2019, the top 5 states with the most workplace electrical fatalities were: (1) Texas (608); (2) California (451); (3) Florida (306); (4) New York (273); and (5) Georgia (207).
A recent study conducted by the National Coroners Information System (NCIS) in Australia has revealed 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.
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 the years 2007–2011.
People who survive electrical trauma may develop a host of injuries including loss of consciousness, seizures, aphasia, visual disturbances, headaches, tinnitus, paresis, and memory disturbances. Even without visible burns, electric shock survivors may be faced with long-term muscular pain and discomfort, exhaustion, 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. As with any traumatic and life-threatening experience, electrical injury may result in post traumatic psychiatric disorders. 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.
Deliberate uses
Medical uses
Electric shock is also used as a medical therapy, under carefully controlled conditions:
Electroconvulsive therapy or ECT, a psychiatric therapy for mental disorders
As a surgical tool for cutting or coagulation in electrosurgery. An electrosurgical unit (ESU) uses high currents (e.g. 10 amperes) at high frequency (e.g. 500 kHz) with various schemes of amplitude modulation to cut or coagulate
As a treatment for fibrillation or irregular heart rhythms: see Defibrillation and Cardioversion
As a method of pain relief: see Transcutaneous electrical nerve stimulation (TENS)
As a treatment for excessive sweating with a process called iontophoresis
Electrodiagnosis, for example nerve conduction studies and electromyography
Electroporation for gene delivery
Entertainment
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.
It is also used entertainingly for sex stimulation. This is usually done via the use of an erotic electrostimulator which induces erotic electrostimulation. These devices may include a violet wand, transcutaneous electrical nerve stimulation, electrical muscle stimulation, and made-for-play units.
Policing 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. 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 use 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.
Electrical torture has been used in war and by repressive regimes since the 1930s. The United States Army is known to have used electrical torture during World War II. During the Algerian War electrical torture was used by French military forces. Amnesty International published a statement that Russian military forces in Chechnya tortured local women with electric shocks by attaching wires onto their breasts.
The is a method of torture whereby the victim is strapped to a metal frame and subjected to electric shock. It has been used in a number of contexts in South America. The parrilla was commonly used at Villa Grimaldi, a prison complex maintained by Dirección de Inteligencia Nacional, a part of the Pinochet regime. In the 1970s, during the Dirty War, the parrilla was used in Argentina. Francisco Tenório Júnior (known as Tenorinho), a Brazilian piano player, was subjected to the parrilla during the military dictatorship in Brazil.
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.
The Judge Rotenberg Center in Canton, Massachusetts has been condemned for torture by the United Nations special rapporteur on torture for its use of electric shocks as punishment as part of its behavior modification program.
Japanese serial killer Futoshi Matsunaga used electric shocks to control his victims.
Capital punishment
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 from the 1990s onward due to the adoption of lethal injection. 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 death.
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 4 states (Florida, Alabama, North Carolina and Kentucky) of the United States.
See also
Electrical burn
Electromagnetism
Graduated electronic decelerator
Lichtenberg figure
Lightning injury
Milgram experiment
References
Cited sources
External links
National Institute for Occupation Safety & Health: Worker Deaths by Electrocution, a CDC study
Effect of Electric Shock Currents on Humans
Electrical injury and its effects
Corporal punishments
Electrical safety
Medical emergencies
Torture
Electrical injuries
Causes of death
Occupational safety and health
Effects of external causes