Electrocution, which is death resulting from electrical shock, is a phenomenon that depends on multiple factors, making the simple question of “how much electricity” complex to answer. The true measure of danger is not the potential difference, or voltage (V), but the electrical current (amperage, A) that flows through the body. The lethal current is highly variable because the human body is not a simple, fixed conductor. The final outcome is determined by the relationship between the applied voltage, the body’s internal resistance, and the path the current takes through the tissue.
The Distinction Between Current and Voltage
The amount of electrical flow that can pass through a person is governed by Ohm’s Law, which describes the relationship between voltage, resistance, and current. Voltage provides the electrical “pressure” or push, while resistance is the body’s opposition to the flow, and current is the resulting flow of electrons. Mathematically, \(I = V/R\) shows that for a fixed resistance, a higher voltage produces a proportionally higher, and thus more dangerous, current.
The key physiological danger is measured in milliamperes (mA), or thousandths of an ampere, because the human nervous and cardiac systems operate on tiny electrical impulses. A person can perceive an alternating current (AC) as low as 1 mA at the common power line frequency of 60 Hertz. As the current increases, it stimulates muscle contraction, leading to painful shocks.
A more hazardous threshold occurs when the current causes uncontrollable muscular contraction, often called the “let-go” current. This threshold is typically between 9 and 30 mA for men and 6 to 25 mA for women. If the current is above this level, the person cannot voluntarily release the energized conductor, which prolongs the duration of the shock. Extended exposure increases the total energy absorbed by the body, compounding internal damage.
The Body’s Resistance and Pathway
The amount of current passing through the body depends almost entirely on the body’s electrical resistance, which is not a fixed quantity. Resistance is composed of external (skin) and internal components, with the majority concentrated in the outer layer of the skin, the epidermis.
Dry, intact skin offers high resistance, ranging from 100,000 Ohms up to 500,000 Ohms, limiting current flow even at household voltages. This protective barrier is easily compromised by moisture, such as sweat or water. Wet skin can drastically reduce the resistance to as low as 1,000 Ohms, or even 150 Ohms if submerged.
Once the current bypasses the skin, the internal body resistance, composed of wet, salty tissues, is consistently low (300 to 1,000 Ohms). This means that if the skin is wet or punctured, even relatively low voltages can push a lethal amount of current through the body. High-voltage exposure can also cause the skin’s insulating properties to fail through dielectric breakdown, instantly lowering resistance and permitting massive current flow.
The current’s pathway is another determining factor in injury severity. Electricity flows along the path of least resistance between the entry and exit points. A path crossing the thoracic cavity is significantly more dangerous than one confined to a single limb. A hand-to-hand or hand-to-foot path is especially threatening as it directs the current through the heart and lungs, which are sensitive to electrical disruption.
How Electrical Current Causes Death
Electrical current causes death or severe injury through three primary mechanisms: disruption of the heart’s rhythm, paralysis of the respiratory system, and thermal damage to tissues. The most common cause of death in low-voltage electrocutions is ventricular fibrillation (VF). This occurs when the current interferes with the heart’s natural pacemaker signals, causing the ventricles to quiver rapidly and chaotically instead of contracting in a coordinated manner. VF is a failure of the circulatory system because the heart ceases to pump blood effectively. For alternating current, the threshold for inducing VF can be as low as 30 to 100 mA flowing through the chest for more than one second.
Current can also cause immediate death by respiratory paralysis, especially when the path involves the chest muscles or the brainstem. The current causes the muscles responsible for breathing, such as the diaphragm, to contract and lock in a sustained spasm (tetany). This prevents the victim from exhaling or inhaling, leading to asphyxiation. Currents of about 30 mA can be sufficient to cause respiratory arrest, particularly if the inability to “let go” prolongs the exposure time.
The third mechanism involves the conversion of electrical energy into heat, known as Joule heating. This thermal energy causes severe burns, both externally at the contact points and internally along the current’s pathway. High-voltage shocks, typically above 600 Volts, are more likely to cause catastrophic thermal injuries. These internal burns can damage blood vessels, nerves, and deep organs, often leading to delayed complications like tissue death, infection, and multi-organ failure. The damage from these internal burns is often far more extensive than what is visible on the skin’s surface.