Question 45 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is D **Explanation for Option D (Correct Answer):** It is critical not to top off double bottom fuel oil tanks when loading fuel at cold temperatures because of the principle of thermal expansion. Fuel oil loaded at cold temperatures occupies less volume (it is denser) than it will when heated. When the ship moves into warmer waters, or when the fuel oil is heated in the tanks (either naturally by the surrounding environment or intentionally for pumping/use), its temperature rises significantly. This temperature rise causes the fuel volume to increase (expand). If the tank was filled completely—or "topped off"—at the colder temperature, the resulting thermal expansion will cause the fuel oil to exceed the tank's capacity, leading to an **overflow** through the tank vents or other openings. This is a primary cause of accidental spills during fuel operations. **Explanation of Incorrect Options:** * **A) Air pockets may cause the fuel to bubble out of the ullage hole.** This is incorrect. Air pockets might cause turbulence or minor pressure fluctuations, but they do not cause a persistent overflow issue related to temperature change. Furthermore, "topping off" (filling completely) is the action that removes ullage (empty space), making the thermal expansion problem worse, not better. * **B) Increased viscosity of the product needs higher loading pressure, which increases the chances of a spill.** While cold temperatures increase viscosity and may require slightly higher pressure, this is generally managed by standard pumping procedures and does not specifically create the overflow hazard associated with filling the tank completely. The main danger of topping off is thermal expansion, not loading pressure. * **C) Fueling valve may become stuck closed and cause the fuel oil to spill before the valve can be opened.** This is incorrect. Valve sticking is a maintenance or mechanical issue and is not directly related to the volume expansion problem that results from filling a tank too completely in cold weather. If a valve sticks closed, it would prevent loading, not cause a spill due to topping off.