Electrical shock is often misunderstood, with many believing only high voltage determines injury severity. However, the human body’s reaction depends on multiple factors.
Beyond Volts: The Role of Current
The true danger in an electrical shock primarily comes from the electrical current, measured in amperes (amps), rather than the voltage, measured in volts. Voltage represents the electrical potential difference or the “pressure” that pushes electrical charge through a circuit. Think of voltage like water pressure in a hose: a higher pressure can push water with more force.
Electrical current, conversely, is the actual flow of charged particles, such as electrons, through a conductor over time. It is analogous to the volume of water flowing through that hose. Resistance, measured in ohms, is the opposition to this flow, similar to how the diameter of a hose or sand within it can restrict water flow. Ohm’s Law describes this relationship, stating that current is directly proportional to voltage and inversely proportional to resistance. Therefore, a high voltage can be dangerous because it has the potential to drive a high current through the body, especially if the body’s resistance is low.
Physiological Impact on the Body
When electrical current passes through the human body, it can disrupt normal physiological functions. The most concerning effect, particularly regarding the heart, is ventricular fibrillation. This occurs when electrical signals within the heart become chaotic and disorganized, causing the ventricles to quiver ineffectively instead of pumping blood. A current of 65 to 75 milliamperes (mA) of alternating current (AC) can induce ventricular fibrillation, while direct current (DC) requires higher levels, around 90 to 130 mA.
Beyond cardiac effects, electric shocks can cause involuntary muscle contractions, often making it impossible for a person to release the electrical source. This “let-go” threshold is around 10 to 15 mA for AC. Currents exceeding 10 mA can lead to respiratory paralysis, where muscles controlling breathing become rigid, potentially causing suffocation. Higher currents, particularly those above 5 amps, can result in severe burns at the points of contact and along the current’s path through the body due to the heat generated.
Key Determinants of Electrical Hazard
The extent of injury from an electrical shock is influenced by several factors beyond the current’s magnitude. The path the current takes through the body impacts the severity. Currents that pass through vital organs, such as the heart or nervous system, are more dangerous than those that do not. For example, a current traveling from one hand to the other poses a greater risk to the heart than a current flowing from a finger to the same hand’s foot.
The duration of contact with the electrical source also impacts the outcome. Longer exposure times allow more current to flow through the body, increasing the likelihood and severity of injury, even at relatively low voltages. The type of current, AC or DC, affects the body differently. AC is more hazardous than DC at the same voltage, partly because it can induce sustained muscle contraction (tetany), making it difficult to let go, and it is more likely to cause ventricular fibrillation. In contrast, DC often causes a single convulsive muscle contraction that might throw a person away from the source.
The body’s electrical resistance is another variable, largely determined by the skin. Dry skin offers high resistance. However, wet or perspiring skin drastically reduces this resistance, allowing more current to flow at a given voltage. When skin is broken or burned, its resistance is further reduced, increasing the danger.