On repeaters, in Ham Meetings, or when people talk about electricity in general, I hear the sentence, "It's not the voltage that will kill you, but the current."
The idea that "current, not voltage, kills you" oversimplifies electrocution. While current is crucial, voltage plays a critical role too. Understanding how voltage, current, and resistance interact in the body is key to debunking this oversimplified belief.
Resistance
Our bodies vary in how easily electricity passes through them. Different body parts have different levels of resistance: bones and fat resist electricity more. At the same time, nerves and muscles allow it to pass more quickly. The skin's outer layer, the epidermis, contributes significantly to this resistance. Dry skin resists electricity more, but wet, sweaty, or burned skin has a lower resistance. The body's resistance decreases when the skin is burned during an electric shock.
Another point to consider is that the skin also acts like a capacitor. With a DC voltage source, this capacitance has little importance. But with an AC source, the epidermis's natural resistance is "shorted out," allowing the current to bypass epidermis resistance and lowering the body's total body resistance.
Voltage's Role
A current of 50mA to 100mA through the entire body is enough to provoke a cardiac arrest or 6mA through the heart. While current is often emphasized as the danger, voltage is equally critical. The current flowing through the body depends on both the body's resistance and voltage, as Ohm's law describes.
For instance, considering a body resistance of 1500Ω, with 12V, the current through the body will be 8mA, but with 120V, the current will be 80mA. That amount of current can pose serious hazards.
Note
In this example, 1500Ω is the average dry, healthy skin value. This resistance will be lower if the skin is wet or blistered.
Muscle Response
AC can cause tonic muscular spasms. These involuntary muscle contractions can tighten the grip, making it hard to release from the electrical source. AC frequency of 50/60 Hz affects the heart's natural rhythm, inducing ventricular fibrillation, which can lead to cardiac arrest. At lower voltage, DC is less likely to cause ventricular fibrillation. The skin's resistance remains more consistent with DC.
High-frequency currents, typically associated with radio frequencies (RF), tend to have shallower penetration depths into the body. RF currents can cause heating of the skin. It can lead to burns or tissue damage on the skin's surface. High-frequency currents can induce immediate pain sensations due to nerve stimulation. Prolonged exposure can result in the heating of deeper tissues, which can potentially cause damage to underlying tissues.
Rethinking the Myth
During an electric shock, the magnitude of current flowing through the body is determined by the product of the voltage applied to the body and the body's electrical resistance. When the voltage increases, the current passing through the body also increases. These factors highlight the complex relationship between voltage, current, and resistance during an electric shock.