The common residential voltage in North America, typically 110 to 120 volts (110V), has the capacity to kill a person. While a shock from a standard wall outlet may seem minor, the electrical potential is sufficient to cause fatal harm under the wrong conditions. Understanding the true danger requires shifting focus from the voltage itself to the flow of energy through the body.
Why Electrical Current Is the Killer
Voltage, measured in volts, represents the electrical potential difference or the “pressure” that drives the charge. Current, measured in amperes or milliamperes (mA), is the actual flow of electrons and is the true mechanism of physiological damage. The body is harmed by the passage of current, not the presence of voltage. A high voltage is only dangerous because it can push a high current through a person.
The relationship between voltage, current, and the body’s resistance is defined by Ohm’s Law. The amount of current flowing through the body equals the voltage divided by the body’s resistance. Even a low voltage like 110V can generate a fatal current if the body’s natural resistance is lowered significantly. The human body is sensitive to small amounts of current, especially those disrupting the heart’s rhythm.
Currents as low as 75 to 100 milliamperes are widely cited as the threshold for causing electrical fatality. This is a fraction of what a standard household appliance uses. For perspective, a typical 100-watt light bulb draws about 830 milliamperes. A relatively small flow of current, if sustained, is enough to interfere with the body’s electrical signaling.
Factors That Determine Severity
When a person contacts a 110V source, the severity of the resulting shock is determined by three variables that modulate the current’s flow. The body’s electrical resistance is the most significant variable, primarily located in the skin. Dry, intact skin can offer a resistance of 100,000 ohms or more, which limits the current flow from 110V.
If the skin is wet, sweaty, or broken, resistance can drop dramatically, potentially falling to 1,000 ohms or less. This reduction allows 110V to drive a lethal amount of current through the body, transforming a mild shock into a deadly one. This explains why electrical accidents are particularly dangerous in bathrooms or near water sources.
The pathway the current takes through the body is another determinant of the outcome. A current path that includes the chest, such as from one hand to the other or from a hand to a foot, is far more dangerous. This route places the heart and lungs directly in the electrical circuit, making it likely that the current will disrupt their functions. A path isolated to one limb is less likely to be fatal but can still cause severe tissue damage.
The duration of contact also plays a substantial role in determining the shock’s outcome. Even a current slightly below the lethal threshold can become deadly if the exposure is prolonged. A current flow of just 10 to 20 milliamperes can cause the involuntary contraction of muscles, known as tetany. This muscle “freezing” can prevent the victim from letting go of the conductor, which keeps the current flowing and increases the total energy delivered to the body.
Immediate Biological Consequences
Once a lethal current level is reached, the primary consequence is the disruption of the heart’s electrical system, leading to ventricular fibrillation. This condition causes the heart’s ventricles to quiver rapidly and chaotically instead of beating with a coordinated rhythm. The heart stops pumping blood, and circulation ceases, which rapidly leads to unconsciousness and death if not immediately corrected.
The current also affects the nervous and muscular systems, often causing severe, prolonged muscle contractions. If the current passes through the muscles that control breathing, it can lead to respiratory paralysis, causing the victim to stop breathing. Currents above 30 milliamperes are sufficient to cause this effect, even if the heart is not pushed into fibrillation.
In addition to electrophysiological effects, the body sustains thermal injury from the resistance it offers to the current flow. This heat generation, known as Joule heating, causes burns that are most severe at the points of electrical entry and exit. External burns may appear minor, but significant internal tissue damage to muscle, nerves, and organs can occur along the current’s path. Anyone who has experienced a significant electrical shock should seek medical attention, as internal damage and delayed heart rhythm issues may not be immediately apparent.