Why should care be taken when topping off cargo on a cold day?

The correct answer is that care should be taken when topping off cargo on a cold day because of the risk of overflow due to temperature rise. When cargo is pumped into a tank, it may initially be at a lower temperature, especially on a cold day. As the liquid is filled into the tank, it can absorb heat from the surroundings or from the tank structure itself, and even the flow from the pump can generate heat.

When the temperature of the cargo rises after being topped off, it can expand, leading to a situation where the tank might be filled to capacity. If proper precautions and monitoring are not in place, this could result in an overflow, which poses safety risks and potential environmental hazards. Thus, understanding the thermal properties of the cargo and maintaining vigilance during the topping off process are vital for safe operations.

The other options, while relevant to tanker operations, do not specifically address the concerns associated with temperature fluctuations during topping off in cold weather. For instance, the risk of vapors escaping is more associated with pressure release or the characteristics of gaseous cargo rather than the direct impact of cold weather. Similarly, pressure build-up is a concern under different operational circumstances, not specifically tied to cold days. Lastly, the mixing of different cargo