Question 13

The Correct Answer is C 1. **Why option C (30 mA) is correct:** The human body's tolerance to electrical current is heavily dependent on the pathway and duration, but specific thresholds are established for dangerous physiological effects. The range of 20 mA to 50 mA is typically cited as the zone where breathing becomes difficult or impossible due to sustained muscle contraction (tetany) in the chest wall and diaphragm—a condition known as respiratory paralysis. At $30 \text{ mA}$, most people will be unable to overcome the contraction of their chest muscles and will be unable to breathe or pull themselves away from the energized conductor, leading to rapid asphyxiation if the contact is sustained. This level represents a minimum threshold for this life-threatening paralysis condition. 2. **Why the other options are incorrect:** * **A) 3 to 7 mA:** This range represents the "let-go" current threshold for women and the pain/tingling threshold. While painful, the person can still control their muscles and usually pull away from the conductor; respiratory paralysis is not typically the primary effect at this low level. * **B) 10 to 16 mA:** This range represents the "let-go" current threshold for men (around $16 \text{ mA}$) and the point where muscle contraction starts to become severe, potentially preventing voluntary release. While breathing may be labored or difficult, complete respiratory paralysis is not generally guaranteed until higher current levels are reached. * **D) 75 mA for 5 sec:** While $75 \text{ mA}$ is certainly sufficient to cause respiratory paralysis, this option also includes a fixed duration ($5 \text{ sec}$). The question asks for the *minimum threshold* of current needed to *produce* the condition, not the specific current-time combination required to ensure ventricular fibrillation or severe injury. $30 \text{ mA}$ is a better representation of the minimum current threshold for respiratory paralysis itself.