electrical injury electrical injury electrical injury is a physiological reaction caused by electric current passing through the body. the injury depends on the density of the current, tissue resistance and duration of contact. very small currents may be imperceptible or produce a light tingling sensation. a shock caused by low and otherwise harmless current could startle an individual and cause injury due to jerking away or falling. stronger currents may cause some degree of discomfort or pain, while more intense currents may induce involuntary muscle contractions, preventing the person from breaking free of the source of electricity. still larger currents result in tissue damage and may trigger ventricular fibrillation or cardiac arrest. consequences of injury from electricity may include amputations, bone fractures and orthopedic and musculoskeletal injuries. if death results from an electric shock the cause of death is generally referred to as electrocution. electrical injuryother nameselectrical shocklightning 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.specialtyemergency medicinecomplicationsburns, rhabdomyolysis, cardiac arrest, bone fracturesfrequency>30,000 per year (usa)deaths~1,000 per year (usa) electric injury occurs upon contact of a body part with electricity that causes a sufficient current to pass through the person's tissue. 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 second-degree burn after a high tension line accident 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) 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 fraction of a second may induce ventricular fibrillation at currents as low as 30 milliamperes (ma). with direct current (dc), 300 to 500 ma is required. 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 these conditions prevent fibrillation. 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 electrical 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 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 electrical 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 electrical 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 electrical current as low as 1 ma (rms) for 60 hz ac and as low as 5 ma for dc. at around 10 ma, dc 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. 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 of ac (rms, 60 hz) or 300–500 ma 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 voltage5%50%95% 25 v1,750 ω3,250 ω6,100 ω 100 v1,200 ω1,875 ω3,200 ω 220 v1,000 ω1,350 ω2,125 ω 1000 v700 ω1,050 ω1,500 ω 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 log-log graph of the effect of alternating current i of duration t passing from left hand to feet as defined in iec 60479–1. 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: 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 duration, the more likely it is lethal—safety switches may limit time of current flow pathway. if current flows through 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