eMedicine Specialties > Dermatology > Environmental

Burns, Electrical

Author: Erika Kis, MD, Assistant Professor, Burn and Plastic Surgery Unit, Department of Dermatology and Allergology, University of Szeged, Hungary
Coauthor(s): Lajos Kemeny, MD, PhD, DSc, Professor and Head, Department of Dermatology and Allergology, Albert Szent-Gyorgyi Medical Center, University of Szeged, Hungary
Contributor Information and Disclosures

Updated: Jun 25, 2008

Introduction

Background

The term electrical burn is used widely to describe the variety of injuries created by supraphysiologic electrical energy interacting with living tissue. Although thermal burns remain some of the most common results of such an interaction, this term does not adequately describe the range of effects they have in the human body. The term burn also does not encompass the special considerations required in the diagnosis and treatment of patients with these injuries.

Usually, electrical injuries are arbitrarily categorized into 1 of 3 groups: low-voltage injuries, high-voltage injuries, and lightning injuries (see Causes). Each has its own special concerns.

The following additional eMedicine articles on electrical burns may be of interest:

• Burns, Electrical (Pediatrics)
• Burns, Electrical (Plastic Surgery)

Additionally, the following Medscape resources may be helpful:

• Trauma Resource Center
• Wound Management Resource Center
• Critical Care Nursing Resource Center
• Disaster Preparedness and Aftermath Resource Center
• CME course - Different Treatment Strategies for Smoke Inhalation in the Burn Unit (Slides With Transcript)

Pathophysiology

Certain properties of electricity and tissue illustrate the mechanisms of electrical injury and the ability to predict patients' outcomes. These properties include voltage, current, resistance, and conductance. Voltage is the electromotive force or the difference in the electrical potential. The current is the flow of electricity. The resistance of a material is its opposition to the passage of an electric current through it, and its conductance is its ability to transmit a current. In addition, electricity can also form arcs and result in the creation of plasma.

Factors that determine the extent of tissue damage, morbidity, and mortality include the voltage, the type (alternating current [AC] or direct current [DC]) and path of the current, and the resistance or conductance of the tissue (especially the type and quantity of the tissue affected and its degree of hydration, orientation, contact surface area, and duration of exposure).

Voltage and current

The larger the voltage for a given conducting body of relatively fixed resistance, the larger the amount of current that can pass through it. Because voltages of generated electricity are usually known (and measured in volts) and because the resistance of the body is not, the current must be calculated.

Alternating current and direct current

AC is electrical energy that oscillates in each of 2 directions at a set rate, ie, the direction of flow through the conductor reverses. The standard frequency of alternation in the United States and Canada is 50-60 cycles per second (cps), or hertz. DC is electrical energy that flows in only 1 direction.

The inherent safety or injury consideration with low-frequency energy is that it is also within the range of physiologic stimulation of the neuromuscular action potential. As low as 1.1 mA may produce a tingling sensation. Put simply, with a current stronger than 15 mA, the muscles of a portion of the body that is involuntarily transmitting impulses can contract, also called tetany, as long as the current is applied. (The threshold of involuntary spasm is called the let-go threshold.) In practical terms, when a person touches his or her hand or forearm to a source of current, the extremity contracts and the person cannot release his or her hand or forearm from the source. This contact prolongs the exposure and thus the damage is more severe. At levels above 30-40 mA (ventricular fibrillation may be induced at 1-5 A), the heart goes into a continuous contraction and reverts back to sinus rhythm when the voltage has been released.¹

Increasing the duration of contact generally increases the tissue damage, at least until the conducting tissue carbonizes and becomes more resistant to further flow of the current. When the body becomes a part of an electrical circuit, the current frequently becomes more concentrated at the entry and exit points (with some exceptions). At these points, greater tissue damage can occur, especially in terms of thermal burns.

This muscular contraction effect, coupled with the increased ability of AC to penetrate the epidermal resistance barrier (see below), explains why lower AC voltages are as dangerous as the higher DC voltages and currents. AC is 3 times more dangerous than DC at the same voltage.

Effects on tissue

When an electrical current is transmitted by means of direct contact with a conducting material or an arc that reaches the tissue surface, the electrons begin to flow, as ions flow in a solution. Electrolysis and other exothermic electrochemical reactions occur, with the alteration of pH and oxygen levels and the release of toxic by-products into the surrounding tissue.²

In comparison, the phenomenon of electroporation is the more rapid effect of current passing through cellular tissue. This is strictly a cellular (or lipid bilayer) phenomenon resulting from the denaturing effects of the current on the negatively charged proteins in the cell membrane, especially those around the cell pores and gates. The proteins in the cell membrane can lose their 3-dimensional structure and distort or create intramembrane pores or gates. Consequently, intracellular contents can admix with the extracellular components. If not reversed in time, this phenomenon leads to cell death, which is not the effect of joule heating (which takes much longer to occur).

Direct flow occurs when a person touches a conductor. Indirect flow can be separated into arc, flash, thermal, and blunt injuries. Arc occurs when a spark occurs between 2 objects not in contact with each other. The arc injury occurs when the victim becomes part of the arc. The arc may then cause burns after igniting clothing. Flash burns occur when the flow of current proceeds along the external surface of the body and are enhanced by wet skin or clothing. Flash injury may cause partial-thickness burns.³ Flash (also called sideflash, flash discharge, splash, or spray) occurs when current begins down one path, such as a tree, then jumps to a grounded nearby person, following the path of least resistance. This mechanism is believed to be the most common in lightning strike injuries.⁴

In addition to lightning, step voltage is another high-voltage discharge phenomenon. When an electrical discharge (especially lightning) strikes a grounded surface, the current rapidly dissipates outward in a radial pattern along the surface. The resultant difference in the electrical potential between 2 points, even those separated by a relatively short distance (eg, length of a walking stride between the feet), may be tremendous. The dissipating current can often find a pathway of lower resistance. For example, the current may travel from one leg through the body to the other leg instead of passing along the ground, even though the legs are separated by only a few inches. The result can be devastating when large voltages are involved, as in lightning strikes. Because farm animals have longer strides, this kind of injury is more likely to occur in animals than in people.

Resistance and conductance

The passage of a given current generates more heat in a more-resistant conductor (eg, tissue) than in a less-resistant conductor. The direct dissipation of energy as heat is called joule heating, and this is the major cause of thermal burns to tissue. Therefore, tissues that are less conductive tend to heat up more as current passes through them. The order of tissues, from the most conductive (ie, least resistant) to the least conductive (ie, most resistant) is as follows: nerves, blood vessels, muscles, skin, fat, and bone.

Nerves, blood vessels, muscles, and bone

Nerves and blood vessels carry relatively more current with less heat generation, whereas bone tends to convert more of the electrical energy into heat. The difference in conductance is why high-voltage thermal damage has a significant deep component. In addition, because of its large volume, muscle carries the largest amount of current, which also heats the surrounding tissues.

Bone, which also dissipates heat more slowly than other tissues, heats the surrounding tissues even after current ceases to flow. For this reason, the thermal damage caused by a current passing up through an upper extremity is concentrated at the wrist and elbow, the places with less tissue cross-sectional area and more resistive structures (bone and tendon).

Skin

The epidermal barrier is effectively removed when the skin is immersed in a fluid-conducting medium such as water. With a fluid conductor, the flow of current is spread over a broader contact surface, and the water and its attendant ions can more effectively reach portions of the epidermis that are better conductors. For this reason, burns are not seen on the surface of skin immersed in water; in addition, more current flows through the body as a whole because the body becomes a whole-volume conductor. The classic example of this phenomenon is bathtub electrocution, which has a high mortality rate because the current can cross the myocardial and diaphragmatic muscles, often without leaving a surface burn of any kind.

When electrodes are applied to the skin, as in cardioversion, a perimeter effect can be seen.³ Usually, only a first-degree burn occurs at the perimeter, as demonstrated at histologic examination. In this peculiar phenomenon, the applied current passes through the center of the interface between the skin and the conducting pad or gel without causing significant thermal burn. However, the current arcs through the surrounding skin on which little or no conductive gel is placed and where the conducting pad has an abrupt edge. The result is a thermal burn through the less conductive epidermis. This effect has been largely eliminated with the use of electrode pads with a high-impedance perimeter.

AC energy does not meet the same initial resistance in the epidermis because the direction changes in the current act like alternating magnetic fields that induce an electrical field in the tissue. These magnetic fields (similar to those used in MRI) readily penetrate the body.² Compared with current conduction, current induction does not depend on surface skin resistance.

Arcs and plasma

An arc is one of the forms of electrical flow that produce the greatest amounts of current and heat. An arc results when a stream of plasma (a good conductor) is generated from the atoms in the conducting material. The electrical field strength of the material undergoes a huge change as it nears a high-potential pathway. The formation of an arc depends on the voltage and the dielectric properties of the insulating medium, usually air. In most people with a high-voltage injury, an arc is actually formed before they make physical contact with the electrical source. The dielectric breakdown strength of air is approximately 2 million V/m. This value is lessened by increased humidity or precipitation. At voltages below 300 V, physical contact must be made. An arc does not form in the air.²

Arc faults give off thermal radiation and bright, intense light that can cause burns to the body, especially to the skin and eyes. Next to the laser, the electric arc is the hottest event on earth, with recorded temperatures as high as 35,000°F (19,427°C).⁵ High-voltage arcs can also produce a considerable pressure wave by rapidly heating the air and producing a blast that may exceed 200 lb/ft² (978 kg/m²).This pressure burst can send molten metal droplets from melted copper and aluminum components in electrical equipment great distances at extremely high velocities. In addition to direct personal injury from these hot metals, arc blasts can throw a worker against nearby objects or walls, causing secondary injuries such as blunt force trauma, cuts, and abrasions. The impulse sound wave near the unprotected ear can also result in temporary or permanent traumatic hearing loss.⁶

The temperature of an arc is 4532-18,032°F (2,500-10,000°C). This resultant temperature can create such a shearing force that the tissue layers frequently separate. The large temperature gradient often results in full- or partial-thickness burns of the skin and deeper tissues. Additionally, the temperature of an arc (eg, lightning strike) can ignite clothing and even melt metal objects (eg, a coin in the pocket), which can then cause secondary thermal injuries. In addition, when large amounts of heat are generated (as in a lightning arc), superheating of the surrounding air can generate a thermoacoustic blast (thunder) that can cause blunt injuries.

Plasma, a highly ionized gaseous conductor, can be generated as a result of contact with metal power lines. The result is the formation of a peculiar coating of metal on the skin, or effectively, electroplating of the skin. Plasma can also be generated from within the body at the point at which an arc eventually contacts the body.

Frequency

United States

The number of patients with any type of electrical injury who present for treatment is estimated to be 5,000-52,000 per year.⁷ Most authors agree that hospital admissions resulting from an electrical injury represent 3-7% of all injuries primarily classified as burns. Approximately 3,000 patients who survive electrical shock are admitted to specialized burn units annually.⁸

The effect of electrical injuries on the US economy is staggering. For occupational injuries alone, the National Institute for Occupational Safety and Health estimated an impact of more than $1 billion on the economy.² Electrical burns are the fifth leading cause of occupational fatalities.⁹ See Media File 1.

As a separate category, lightning injuries cause 300-600 deaths annually in the United States, more than any other weather phenomenon (excluding hurricane Andrew).⁴ In fact, more deaths have been attributed to lightning than to any other natural disaster, and the rates do not take into account the fact that the annual frequency of nonfatal lightning injuries is 3-5 times that of fatal injuries.¹⁰ Furthermore, many injuries are unreported.

As a natural phenomenon, lightning is geographic and seasonal. Typically, lightning strikes affect individuals who participate in outdoor recreation or work outside, and 70% of fatalities occur in June, July, or August. More lightning injuries occur in the Southeast; the Rocky Mountains; and along the Mississippi, Hudson, and Ohio River valleys than anywhere else. The afternoon and evening are the most likely times for an injury to occur.¹⁰

In general, intentional electrical injuries (eg, those due to Taser devices) are not addressed in incidence and prevalence studies.

International

The increasing worldwide incidence of electrical injuries is the result of several factors. The population is growing, as is the percentage of people who use or have access to electricity. Developing nations are particularly affected; for example, one physician in the Dominican Republic noted that as many as 39% of admissions to the local hospital for burns were due to electrical injuries.¹¹ Increased reporting of these injuries also plays a role.

In China, the number of patients severely injured by electrical current, historically 3-4% of all burn unit admissions, has progressively increased as the amount of electricity generated has increased. In this decade, an additional large disproportional increase in the incidence of high-voltage burns has occurred in men fishing near electrical wires. When the fishing rod contacts with overhead high-voltage electrical lines, the fisherman sustains severe burns with true injuries, flash injuries, or both together.¹²

In a 2007 Iranian study, the most common cause of high-voltage injuries was climbing power poles to trap pigeons or access bird’s nests (both in adults and children).¹³ See Media Files 2-3.

Mortality/Morbidity

Electrical injury occurs in approximately 1000 deaths annually. Most of these occur in victims aged 15-40 years. Most electrical injuries are due to low-voltage energy, which also accounts for half of all deaths.³ Patients with low-voltage injuries have a disproportionately high mortality rate compared with those who sustain high-voltage injuries or lightning injuries.

• High-voltage injuries may cause relatively few deaths and relatively more morbidity because the energy involved can cause the individual to be thrown back from the point of contact or because it can cause a violent and sudden single muscle contraction, which also propels the individual away from the electrical source. In addition, in patients with high-voltage injuries, the high rate of limb amputations (45-71%) accounts for much of the resultant morbidity.
• In a 2007 Iranian study, the incidence of amputation in the high-voltage group was significantly higher than that reported in the low-voltage group (11.1% vs 3.5%, P = .05).¹³
• Patients with lightning injuries have a mortality rate of less than 30%. Factors that influence this rate can include the flash mechanism of injury (see Pathophysiology) and the lightning standstill phenomenon (see Physical).
• Bathtub electrocution has a high mortality rate because the current can cross the myocardial and diaphragmatic muscles, often without leaving a surface burn of any kind.

Sex

Nonlightning electrical injury has a male predilection approaching 93%, which reflects the preponderance of men in construction and electrical occupations. High-voltage injuries are most common in men.¹⁴

Age

Nonlightning electrical injury has a bimodal distribution with respect to age. In a 2006 Turkish epidemiological study of patients in an emergency department, the mean age was 21.1 years. The age range was 2.5-62 years. Most of these patients (57.6%) were adolescents and adults; the smallest percentage of patients (6%) was elderly persons.¹⁵

• The first peak, which represents approximately one third of the injuries, occurs in children younger than 6 years, in whom most injuries are the low-voltage type. Usually, low-voltage burns occur in toddlers who bite electrical cords or in slightly older children who place metal objects into electrical outlets.
• In young people aged 11-18 years, some accidents occur as a result of their touching high-voltage power lines.
• The second large peak occurs in persons aged 15-40 years as they enter or re-enter the workforce.

Clinical

History

Although the history of an electrical injury is well known in most patients, some patients are found unconscious and others may be unable to recall the history. If an electrical burn is suggested, certain clues to the type of injury (predominantly findings on the skin surface) may become evident during the secondary physical survey. If the history or extent of injury is unknown, a thorough physical assessment of the electrical injury is critical.

Physical

Specific surface-injury patterns may be of great importance in the diagnosis and treatment of patients with electrical burns. If the features of the history suggest an electrical burn, certain clues to the type of injury (predominantly findings on the skin surface) may become evident during the secondary physical survey.

Frequently, an electrical injury of significance, especially one to the extremities, seems more like a crush injury than a burn because the external signs of the injury often overlie a more serious and deeper injury.⁹

• High-voltage electrical injuries  
  • The entrance and exit wounds caused by the current may be small and otherwise overlooked, especially if they are on the scalp, on the soles of the feet, and in locations that are not typically examined. The tissue destruction results from the energy's conversion to heat as it meets resistance. Smaller body parts are likely to be completely destroyed. The trunk allows for enough dissipation of the heat to protect vital visceral organs.¹
  • Although small, the wounds typically extend deep into the underlying tissue, and they tend to be well circumscribed.¹⁴
  • The burn is commonly third degree, and, as such, it can have a central blown-out appearance with a leathery texture, a white-to-yellow coloration, and a hyperemic border.
  • Patients might also have injuries as a result of being thrown back from the point of contact.
• Thermal burns  
  • A flash-type thermal burn is often superficial and covers broad areas of exposed surfaces. These findings provide clues not only to the amount of current involved in the exposure but also to the other types of injury that may be present.
  • Thermal burns can be typical first-, second-, or third-degree burns, and the skin can appear punctate, belying the underlying tissue damage.
  • Burns in the flexor creases, such as at the axillae, elbows, wrists, popliteal fossae, and those between the fingers (most common), are a result of current flowing through the path of least resistance. When the current encounters a relatively resistant joint (ie, one with a small cross-sectional area or highly resistant tissue), the current seeks a surface pathway of less resistance, ie, it jumps across the joint and courses along the skin surface.
  • The oral commissure burn is a common thermal burn that occurs in young persons exposed to low-voltage household AC. This injury most often occurs when children suck on the end of an extension cord or chew on it. Severe oral mucosal, lip, and tongue injuries can occur. A common delayed complication of such an injury is staining of the teeth. Postinjury bleeding of the labial artery often occurs 2-3 days after this type of injury. The health care provider must be alert to this late complication and reassess the patient to detect it. The labial artery is most commonly involved in burns of the oral commissure and mouth because it is the conduit of least resistance and disperses the most amount of current or electrical energy. The bleeding occurs as a delayed manifestation of arterial injury as the scab matures and prematurely dislodges in the wet environment of the mouth.
• Lightning injuries  
  • These injuries may cause any of the skin manifestations seen with other electrical injuries, but they may also appear as linear burns in areas in which sweat was present on the skin surface at the time of the lightning strike.¹⁶
  • A peculiar and pathognomonic skin manifestation of lightning injury is the Lichtenberg figure. This sign is described as a fernlike, arborescent, or Christmas tree–like pattern. The feathery marking appears on the skin within hours after injury and usually disappears within 24 hours. It most likely represents an electron shower and not a true burn. As such, it requires no specific treatment.
  • An additional peculiar and perhaps pathognomonic sign of lightning injury is the tiptoe sign.¹⁷ In the case report describing this manifestation, all 10 patients with a simultaneous flash-type lightning injury had multiple, small, circular, full-thickness burns on the soles of their feet and on the tips of their toes. These signs were theorized to result from their wearing partially insulated, thick-soled shoes that prevented the current from exiting directly through the bottom of their shoes. Instead, the current exited the body through the sides of the shoe where the foot was closest to the ground.
  • Lightning can also superheat the surrounding air and create a resultant thermoacoustic blast (thunder) that can cause blunt injuries.
  • The large temperature gradient often results in full- or partial-thickness burns of the skin and deeper tissues. Additionally, the temperature of a lightning strike can ignite clothing and even melt metal objects (eg, a coin in the pocket), which can then cause secondary thermal injuries.
  • Some high-voltage injuries, especially lightning injures, are known to cause such localized and complete vasospasm of an extremity that the limb can appear cold and lifeless for hours; however, it eventually recovers completely.
  • Lightning standstill is likened to a state of suspended animation in which cell death does not occur immediately after apparent clinical death (see Medical Care).
• Low-voltage injuries (see Media Files 4-7)  
  • With low-voltage injuries, an edematous area surrounded by shriveled, depressed skin may be the most common finding.¹⁸
  • In contrast, after a high-voltage injury, the skin may appear dry and shriveled, and it is more likely to be charred.¹⁸

Causes

• Low-voltage injuries
  • Also called low-tension injuries, low-voltage burns are caused by voltages less than 1000 V.
  • This group includes most injuries caused by household current, as well as occupational injuries resulting from the use of small power tools.
• High-voltage injuries
  • These burns are also known as high-tension injuries, and they are a result of exposure to 1000 V or more.
  • These injuries are often the result of occupational or incidental exposure to outside power lines.
• Lightning injuries involve voltages higher than those of the other injuries and are usually categorized separately.
  • The typical lightning injury involves energy with high voltage and high amperage but extremely short duration.
  • Lightning is usually a unidirectional massive current impulse and is best understood as a current rather than a voltage phenomenon.
  • The largest flow of current tends to jump to the ground before much of it passes through the body.
  • Lightning injuries tend to be seasonal.
• Other electrical injuries
  • Intentional injuries include those due to the use of high-voltage Taser devices for rapid incapacitation, child and/or spouse abuse, and torture.¹⁹
  • The use of skin electrodes, as in cardioversion, can cause a perimeter effect (see Pathophysiology).³ Most electrode burns are related to the presence of high-frequency electric fields created either by an electrosurgical unit or an MRI scanner. A smaller number of lesions are produced by low-current, long-duration DC stimulation and during high-current stimulation such as defibrillation. Practitioners should pay special attention with patients in the presence of radiofrequency energy being generated by an electrosurgical unit or MRI scanner. The electrodes attached to a patient may act as an "antenna" bringing this energy to the electrode-skin interface and create a burn.²⁰

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