An electrical shock occurs when the human body becomes part of a complete electrical circuit, allowing current to flow through tissues. This interaction is an involuntary physiological response, ranging from a slight tingle to fatal injury. The passage of electrical current disrupts the body’s normal electrical functions and causes physical damage. The severity of the trauma is determined by physical factors, including the amount of current, the path it takes, and the duration of exposure.
The Essential Physics: Current, Voltage, and Resistance
The extent of harm from an electrical shock is primarily governed by the current that passes through the body. Current is the flow of electrical charge and is the factor that directly disrupts biological processes and generates damaging heat. Voltage is merely the electrical force or “pressure” that drives the current, and it does not cause harm by itself.
The current flowing through a circuit is equal to the voltage divided by the resistance of the circuit. This means that a high-voltage source is dangerous because it possesses the force to push a significant amount of current through the body’s natural resistance. Conversely, a low-voltage source, like a car battery, is generally safe because it cannot overcome the body’s resistance to produce a damaging current.
The body’s resistance to current flow largely resides in the skin, specifically the outermost layer. Dry, calloused skin can offer a resistance as high as 100,000 ohms, significantly limiting current flow. However, the presence of moisture from sweat or water dramatically lowers this resistance, sometimes to as little as 1,000 ohms, allowing a much higher and potentially lethal current to pass through at the same voltage.
High voltages, typically above 500 volts, are especially hazardous because they can physically break down the skin’s resistance, effectively bypassing the body’s primary defense layer. Once the skin’s barrier is breached, the current encounters the internal tissues, which have very low resistance, allowing a massive and uncontrolled surge of electricity.
The Critical Role of Electrical Path and Duration
The severity of a shock is influenced by the route the current takes through the body and the length of time the exposure lasts. The path is important because some tissues are more sensitive to electrical disruption than others. Current passing across the chest, such as from one hand to the other or from a hand to a foot, is particularly dangerous because it directly affects the heart and lungs.
This path can trigger a malfunction in the heart’s electrical system, which is the most common cause of death from electrocution. A complete circuit must be formed, which often involves the person contacting a live source and a grounded object simultaneously. The current will follow the path of least resistance, which is often through the highly conductive internal tissues like blood vessels and nerves.
The duration of the electrical exposure is another factor. A short burst of current, even if moderately high, may be survivable, but prolonged exposure allows a greater total amount of energy to be transferred into the body. Even a relatively low current can be lethal if the contact time is long enough to coincide with the vulnerable phase of the heart’s electrical cycle. Furthermore, alternating current (AC) at household frequencies can cause sustained muscle contraction, making the person unable to let go of the source and prolonging the exposure.
How Electricity Damages Biological Systems
The passage of current through the body harms biological systems through three primary mechanisms: electrical disruption, thermal injury, and mechanical trauma. The heart relies on precise electrical signals to maintain its rhythmic pumping action.
Disruption of this rhythm by an external current can lead to ventricular fibrillation, where the heart muscle quivers ineffectively instead of contracting properly. This is the most frequent cause of death in low-voltage AC exposures. High-voltage shocks, however, are more likely to cause cardiac asystole, which is a complete cessation of the heart’s electrical activity.
The nervous system is also highly susceptible to electrical damage because it relies on electrical impulses for communication. Current flow can instantly disrupt these signals, leading to respiratory paralysis, which causes the person to stop breathing. Furthermore, the involuntary, violent muscle contractions caused by the shock can prevent the person from releasing the electrical source, and these contractions can be powerful enough to cause fractures and joint dislocations.
Thermal damage is caused by the conversion of electrical energy into heat as it encounters the body’s resistance, a process known as Joule heating. This can result in severe external burns at the points of entry and exit, but more dangerously, it can cause deep internal tissue destruction that is not visible on the skin’s surface. Deep burns to muscles, nerves, and organs can occur even with seemingly minor surface injuries, leading to long-term complications and tissue death.