An electric shock occurs when a person becomes part of an energized electrical circuit, allowing current to flow through the body. This flow interferes with the body’s own bioelectrical signals. The resulting injury severity is determined by the amount of electrical energy delivered to the tissues. Understanding these processes is essential, as even common household electricity can be dangerous.
The Essential Mechanism: Current Flow Through the Body
The destructive agent in an electric shock is the flow of current, measured in Amperes, not the voltage alone. Voltage represents the potential force available to push the charge, but damage results from the energy transfer as current moves through the body. The body acts as a conductor, completing the circuit between two points of different electrical potential.
The amount of current that flows is controlled by the body’s resistance to electricity. Skin provides the majority of this resistance, acting as an outer barrier. Dry skin can have a high resistance, potentially exceeding 100,000 Ohms, which limits current flow. Conversely, wet, sweaty, or broken skin drastically reduces resistance to as low as 1,000 Ohms or less.
When the skin barrier is compromised, voltage drives a much higher current into the body’s interior. Internal tissues, such as blood, nerves, and muscle, are rich in water and electrolytes, making them excellent conductors with low resistance, typically around 300 to 500 Ohms. The relationship between applied voltage, resistance, and resulting current flow determines the level of injury.
The Path and Duration of Electricity
The severity of an electric shock depends on the route the current takes and the length of time it flows. Current follows the path of least resistance through the body. A path that crosses the chest—such as hand-to-hand or hand-to-foot—is more dangerous because it directly involves the heart and lungs.
When electrical energy traverses the thoracic cavity, it can disrupt the heart’s electrical rhythm. A current path confined to one limb, such as finger-to-finger, may cause severe localized injury but is less likely to be immediately fatal. The duration of contact is also important, as a small current can be lethal if the exposure is prolonged.
Alternating current (AC), particularly the 50 to 60 Hertz frequency used in household electricity, is hazardous due to its cyclic nature. This frequency increases the probability that the current’s peak will coincide with the heart’s vulnerable repolarization period, a brief window when a small electrical stimulus can trigger a chaotic rhythm. Even a sustained low-voltage shock can deliver enough energy to cause serious harm.
Physiological Responses to Electric Current
Sufficient current flow causes damage through three primary mechanisms: cardiac disruption, thermal injury, and neuromuscular effects. The most common cause of death from electrocution is ventricular fibrillation, where the electrical signal overrides the heart’s natural pacemaker. This chaotic quivering of the ventricles prevents the heart from pumping blood, leading to circulatory collapse within seconds.
For an adult, an alternating current as low as 60 to 100 milliamperes (mA) passing through the chest can induce fibrillation. Direct current (DC) requires a higher threshold, typically 90 to 130 mA or more, to cause the same effect. Another immediate, life-threatening reaction is the tetanic contraction of skeletal muscles, often called the “no-let-go” phenomenon.
Currents above the “let-go threshold,” typically around 10 mA for AC, cause the flexor muscles in the hand to contract, locking the victim onto the conductor and prolonging exposure. Simultaneously, electrical energy converts to heat as it encounters resistance, a process known as Joule heating. This thermal effect causes severe burns, which can be minor externally but catastrophic internally, destroying tissue along the current’s path.