Electrical shock

Anatomy or system affected: Heart, nervous system, skin

Definition: The physical effect of an electrical current entering the body and the resulting damage

Causes and Symptoms

Electrical shock ranges from a harmless jolt of static electricity to a power line’s lethal discharge. The severity of the shock depends on the current flowing through the body, and the current is determined by the skin’s electrical resistance. Dry skin has a very high resistance; thus, 110 volts produces a small, harmless current. The resistance for perspiring hands, however, is lower by a factor of one hundred, resulting in potentially fatal currents. Currents traveling between bodily extremities are particularly dangerous because of their proximity to the heart.

Electrical shock causes injury or death in one of three ways: paralysis of the breathing center in the brain, paralysis of the heart, or ventricular fibrillation (extremely rapid and uncontrolled twitching of the heart muscle).

The threshold of feeling (the minimum current detectable) ranges from 0.5 to 1.0 milliamperes. Currents up to five milliamperes, the maximum harmless current, are not hazardous unless they trigger an accident by involuntary reaction. Currents in this range create a tingling sensation. The minimum current that causes muscular paralysis occurs between ten and fifteen milliamperes. Currents of this magnitude cause a painful jolt. Above eighteen milliamperes, the current contracts chest muscles, and breathing ceases. Unconsciousness and death follow within minutes unless the current is interrupted and respiration resumed. A short exposure to currents of fifty milliamperes causes severe pain, possible fainting, and complete exhaustion, while currents in the one hundred– to three hundred–milliampere range produce ventricular fibrillation, which is fatal unless quickly corrected. During ventricular fibrillation, the heart stops its rhythmic pumping and flutters uselessly. Since blood stops flowing, the victim dies from oxygen deprivation in the brain in a matter of minutes. This is the most common cause of death for victims of electrical shock.

Relatively high currents (above three hundred milliamperes) may produce ventricular paralysis, deep burns in the body’s tissue, or irreversible damage to the central nervous system. Victims are more likely to survive a large but brief current, even though smaller, sustained currents are usually lethal. Burning or charring of the skin at the point of contact may be a contributing factor to the delayed death that often follows severe electrical shock. Very high voltage discharges of short duration, such as a lightning strike, tend to disrupt the body’s nervous impulses, but victims may survive. On the other hand, any electric current large enough to raise body temperature significantly produces immediate death.

Treatment and Therapy

Before medical treatment can be applied, the current must be stopped, or the shock victim must be separated from the current source without being touched. Nonconducting materials such as dry, heavy blankets or pieces of wood can be used for this purpose. If the victim is not breathing, artificial respiration immediately applied provides adequate short-term life support, though the victim may become stiff or rigid in reaction to the shock. Victims of electrical shock may suffer from severe burns and permanent aftereffects, including eye cataracts, angina, or disorders of the nervous system.

Electrical shock can usually be prevented by strictly adhering to safety guidelines and using commonsense precautions. Careful inspection of appliances and tools, compliance with manufacturers’ safety standards, and the avoidance of unnecessary risks greatly reduce the chance of an electrical shock. Electrical appliances or tools should never be used when standing in water or on damp ground, and dry gloves, shoes, and floors provide considerable protection against dangerous shocks from 110-volt circuits.

Electrical safety is also provided by isolation, guarding, insulation, grounding, and ground-fault interrupters. Isolation means that high-voltage wires strung overhead are not within reach, while guarding provides a barrier around high-voltage devices, such as those found in television sets.

Old wire insulation may become brittle with age and develop small cracks. Defective wires are hazardous and should be replaced immediately. Most modern power tools are double-insulated; the motor is insulated from the plastic insulating frame. These devices do not require grounding, as no exposed metal parts become electrically live if the wire insulation fails.

In a home, grounding is accomplished by a third wire in outlets, connected through a grounding circuit to a water pipe. If an appliance plug has a third prong, it will ground the frame to the grounding circuit. In the event of a short circuit, the grounding circuit provides a low resistance path, resulting in a current surge that trips the circuit breaker.

In some instances, the current may be inadequate to trip a circuit breaker (which usually requires fifteen or twenty amperes), but currents in excess of ten milliamperes could still be lethal to humans. A ground-fault interrupter ensures nearly complete protection by detecting leakage currents as small as five milliamperes and breaking the circuit. This relatively inexpensive device operates very rapidly and provides an extremely high degree of safety against electrocution in the household. Many localities now have codes that require the installation of ground-fault interrupters in bathrooms, kitchens, and other areas where water is used.

Bibliography

Atkinson, William. “Electric Injuries Can Be Worse than They Seem.” Electric World 214, no. 1 (January/February, 2000): 33–36.

Begum, Jabeen. “Minor Electric Shocks and Burns: Symptoms, Causes, and Treatments.” WebMD, 9 May 2023, https://www.webmd.com/first-aid/electric-shock. Accessed 27 July 2023.

Bridges, J. E., et al., eds. International Symposium on Electrical Shock Safety Criteria. New York: Pergamon Press, 1985.

Cooper, Mary Ann. "Electrical Injuries." Merck Manual Home Health Handbook, Jan. 2009.

Dugdale, David C., Michael A. Chen, and David Zieve. "Ventricular Fibrillation." MedlinePlus, 22 June 2012.

"Electric Shock." HealthyChildren.org. American Academy of Pediatrics, 10 July 2013.

Heller, Jacob L., and David Zieve. "Electrical Injury." MedlinePlus, 5 Jan. 2011.

Hewitt, Paul G. Conceptual Physics. 11th ed. San Francisco: Pearson Addison Wesley, 2010.

"Home Electrical Safety Checklist." US Consumer Product Safety Commission, July 2008. PDF.

Hogan, David E., and Jonathan L. Burstein. Disaster Medicine. 2d ed. Philadelphia: Lippincott Williams & Wilkins, 2007.

Liu, Lynda. “Pullout Emergency Guide: Electric Shock.” Parents 75, no. 1 (January, 2000): 65–66.

Mayo Clinic Staff. "Electrical Shock: First Aid." Mayo Clinic, 15 Mar. 2012.

US Department of Labor. Occupational Safety and Health Administration. Controlling Electrical Hazards. Rev. ed. Washington, D.C.: Author, 2002.