Understanding Electric Shock: The Path of Current Through the Body

Electric shock incidents pose a serious safety risk, particularly for workers operating electrical tools. The flow of current through a person's body during an electric shock can be outlined by specific resistance values and circuit principles. When a worker is exposed to a 120-volt circuit, the current flow and its potential effects can be calculated by considering the resistances involved in the human body and the surrounding environment.

The total current flow through the body is influenced by various resistances, including that of the skin, internal body resistance, and the shoes worn by the worker. For instance, a person standing in wet soil, wearing leather shoes, may have an estimated total resistance of around 5,700 ohms. This significant resistance leads to a current flow of about 21.1 milliamperes (mA), which is enough to induce a phenomenon known as an "electrical hold." In this scenario, the worker's muscles contract, making it impossible for them to release their grip on the electrical source, potentially leading to severe injury or fatality.

Understanding the effects of different current levels on the human body is crucial. Current flows as low as 30 mA can paralyze respiratory muscles, while 75 mA can cause heart fibrillation, leading to life-threatening situations. These values highlight the necessity of implementing stringent safety measures when working with electricity, especially in environments where the risk of electric shock is elevated.

Resistance values vary significantly depending on the conditions. For example, dry skin can offer a resistance of up to 1 megohm, whereas wet conditions can reduce this drastically to a mere 5-20 kilohms. Knowing these resistance levels aids in assessing the risk of electric shock under various circumstances. Tables detailing nominal resistance values for different body parts and materials provide insight into how easily electricity can pass through.

The implications of electric shock extend beyond immediate physical effects, as prolonged exposure can lead to lasting damage. If a worker remains in contact with an electrical source, the heat generated by the current can lower resistance, resulting in increased current flow and higher chances of severe injury. Therefore, recognizing these risks and understanding the mechanics of electric shock is essential for promoting safety in the workplace.

Ultimately, the complexities of electrical safety necessitate diligent education and adherence to guidelines. Calculating current flow and understanding the bodily impacts of electric shock are foundational for engineers and safety professionals, highlighting the critical nature of risk management in environments where electrical tools are in use.