Question 36 QMED04 - Boiler Technician-Watertender

The Correct Answer is C 1. **Explanation of why option C ("30 mA") is correct:** A current of approximately **30 milliamps (mA)** passing through the torso is generally cited as the minimum threshold that can cause respiratory paralysis (inability to breathe) in most adults. This level of current affects the muscles of the chest and diaphragm, causing tetanic contractions (sustained, involuntary muscle spasms). If the person is still in contact with the energized conductor at this current level, they cannot physically release their grip or move to break contact, leading to prolonged exposure and potential suffocation. While effects can vary, 30 mA is the critical point for severe respiratory distress and paralysis. 2. **Explanation of why each of the other options is incorrect:** * **A) 3 to 7 mA:** This range represents the threshold of sensation and perception. People would feel a shock, but this level of current is generally considered harmless and insufficient to cause respiratory paralysis or an inability to let go (the "no-let-go" threshold). * **B) 10 to 16 mA:** This range defines the "no-let-go" threshold for most adult males (it is lower for women and children). While currents in this range cause painful, sustained muscle contraction in the hand/arm, making release difficult or impossible, they are usually below the level required to cause immediate, widespread respiratory paralysis (which typically requires the current to pass through the chest cavity efficiently). * **D) 75 mA for 5 sec.:** While 75 mA is a dangerous current level, the critical effect associated with this magnitude is ventricular fibrillation (VF), especially with extended exposure. Ventricular fibrillation can be induced by currents starting as low as 50 mA. Furthermore, the question asks for the minimum threshold for respiratory paralysis, which occurs significantly earlier (at about 30 mA) than the minimum current associated with guaranteed cardiac arrest.