Question 64 GLI03 - Master-LT 500-1600 GRT

The Correct Answer is A. **Explanation for A (Correct Answer):** Asphyxia is caused by a deficiency of breathable oxygen. The normal atmospheric concentration of oxygen is approximately $20.9\%$ to $21\%$. If $21\%$ of oxygen is present, the air is considered normal and fully breathable, meaning there is no oxygen deficiency, and therefore, asphyxia will **not** occur under this condition. **Explanation for B (Incorrect Option):** Where large quantities of inert gas (such as nitrogen or carbon dioxide) are present, these gases displace the oxygen, lowering its concentration below the safe limit (typically below $19.5\%$). This oxygen displacement leads to an oxygen-deficient atmosphere, causing asphyxia. **Explanation for C (Incorrect Option):** When large quantities of cargo vapor are present, these vapors displace breathable air (including oxygen). Similar to inert gases, this displacement lowers the partial pressure and concentration of oxygen in the enclosed space, leading to an oxygen-deficient atmosphere and causing asphyxia. **Explanation for D (Incorrect Option):** The rusting (oxidation) of internal tank surfaces is a chemical reaction that consumes oxygen from the atmosphere within the enclosed space to form iron oxides (rust). This consumption significantly depletes the available oxygen, creating an oxygen-deficient atmosphere that will cause asphyxia.