Why is it important for double bottom fuel oil tanks not to be topped off when loading fuel at cold temperatures?

Correct Answer: Option B — A temperature rise of the fuel will cause an overflow from the tank vent.

Fuel oil expands as it warms. If a tank is topped off at a cold temperature, the subsequent rise in ambient or engine room temperature will cause the fuel volume to increase. This expansion can force oil out of the tank vents, resulting in a reportable pollution incident.