An electrical shock occurs when an electric current passes through the body, potentially causing significant harm. The human body is naturally conductive, and its systems, including the heart, rely on electrical signals to function properly. When an external electrical current interferes with these natural processes, the consequences can range from mild discomfort to severe injury or even death.
Beyond Voltage: The Role of Current
While many people associate the danger of electricity with high voltage, it is actually the amount of electrical current, measured in amperes (A) or milliamperes (mA), that causes harm. Voltage represents the electrical “pressure” that drives current, but physiological effects are determined by the current flowing through tissues. The body’s resistance, measured in ohms, opposes this current flow.
Ohm’s Law states that current is directly proportional to voltage and inversely proportional to resistance, meaning lower resistance allows more current to flow for a given voltage. The majority of the body’s electrical resistance is concentrated in the skin. Dry, intact skin can offer significant resistance, potentially exceeding 100,000 ohms. However, wet skin, cuts, or punctures drastically reduce this resistance, allowing higher currents to pass through the body even at lower voltages. For instance, wet skin can reduce resistance to as little as 1,000 ohms, making a typical 120-volt household current capable of delivering a dangerous 120 milliamperes.
The Heart’s Response to Electrical Current
Electrical current interferes with the heart’s natural electrical rhythm, which coordinates its pumping action. The primary dangers to the heart from electrical shock are ventricular fibrillation and asystole. Ventricular fibrillation is a disorganized, rapid quivering of the heart’s lower chambers, preventing it from effectively pumping blood. This condition is the most common cause of death from electrical accidents.
Very small currents can be perceptible, with some individuals feeling alternating current (AC) as low as 1 milliampere. Currents above 10 milliamperes can cause muscles to freeze, making it impossible to let go of the electrical source. Respiratory paralysis can occur at currents as low as 20 milliamperes, becoming complete below 75 milliamperes. Ventricular fibrillation can be induced by alternating currents as low as 30 milliamperes if sustained through the chest for longer than one second. For adults, the threshold for ventricular fibrillation is typically estimated between 60 and 120 milliamperes, while direct current (DC) generally requires higher thresholds (90 to 130 milliamperes) for the same duration.
Factors Determining Shock Severity
Beyond the current level, several factors influence the severity of an electrical shock. The path the current takes through the body is highly significant, with a path through the heart being the most dangerous. For example, current flowing from one hand to the other, or from a hand to a foot, is more likely to traverse the heart, increasing the risk of cardiac effects.
The duration of contact with the electrical source also plays an important role; longer exposure increases the potential for severe injury or death. Rapid intervention, such as quickly turning off the power, can minimize harm. The type of current, alternating current (AC) or direct current (DC), also affects the outcome.
AC, which changes direction periodically, is generally considered more dangerous than DC at the same voltage. AC can cause continuous muscle contraction (tetany), making it difficult to release an energized object and prolonging exposure. AC also has a greater tendency to disrupt the heart’s rhythm and induce ventricular fibrillation. While DC can cause a single, forceful muscle contraction that might throw a person away, it is less likely to cause fibrillation compared to AC.
Safety Measures and Emergency Response
Preventing electrical shock involves adopting several safety practices around the home and workplace:
- Follow appliance instructions and avoid overloading electrical outlets.
- Replace or repair damaged electrical cords, and keep cords tidy, secure, and away from hot surfaces.
- Unplug unused appliances to reduce potential risks.
- Keep electrical devices and outlets away from water sources.
Ground Fault Circuit Interrupters (GFCIs) are safety devices that quickly shut off power when they detect an abnormal flow of electricity, such as a ground fault. They are particularly important in areas where water and electricity may come into contact, like kitchens and bathrooms.
In the event of an electrical shock, immediate and cautious action is necessary. Prioritize safety by never touching a person still in contact with the electrical source, as the current can pass through you. If possible and safe, turn off the power source immediately. If not, use a dry, non-conductive object (like a wooden broom handle) to separate the person from the source. Once the person is free, call emergency services immediately. Check for breathing and a pulse. If unresponsive and not breathing normally, begin cardiopulmonary resuscitation (CPR) if trained.