Understanding Electrical Currents: Thresholds and Dangers

Electric currents, especially those at 60 Hz, have profound physiological effects on the human body. The response to different magnitudes of current varies widely, depending on the intensity and duration of exposure. At a mere <1 milliampere (mA), the sensation is imperceptible, causing no harm. However, as the current increases to just 1 mA, individuals begin to experience a mild sensation, marking the threshold of perception.

The dangers escalate quickly with higher currents. At 10 mA, a person may experience paralysis of the arms, making it impossible to release their grip. This effect could potentially throw the individual clear from the source of the shock. As the current reaches 30 mA, respiratory paralysis can occur, often resulting in cessation of breathing, which can be fatal. At 75 mA, the risk of heart fibrillation rises dramatically, with a mere 0.5% chance of the heart's action becoming discoordinated.

As the current continues to escalate to 250 mA, the likelihood of experiencing heart fibrillation grows to a staggering 99.5% if exposed for five seconds or more. A current of 4 amperes (A) can lead to heart paralysis, halting the heart's function for the duration of the current passage. Interestingly, while this may not be immediately fatal, the short bursts of shock can cause serious complications when the current is interrupted.

Beyond the direct physiological effects of electric currents, electric arcing poses additional risks. Defined as a discharge of electricity through a gas, arcing occurs when the voltage surpasses the dielectric strength of the air, which can lead to dangerous conditions. This phenomenon can result from various scenarios, such as overvoltages from lightning strikes or the melting of conductors due to excessive current, creating a superheated environment that can lead to injuries.

The temperatures generated during electrical arcing can be staggering. Terminal points of arcs can reach temperatures as high as 50,000 Kelvin, while the surrounding air may still be extremely hot, causing second-degree burns at distances up to 12 feet. Furthermore, many common clothing materials are susceptible to ignition at these temperatures, leading to serious burns that can persist even after the arc source is removed. Understanding these thresholds and the nature of electric arcs is crucial for ensuring electrical safety and minimizing risks.