To prevent the overflow of cargo tanks, how full should you top off the cargo?

The correct approach to preventing the overflow of cargo tanks is to fill them to within 1 percent to 3 percent of their total capacity. This practice accounts for thermal expansion, which can cause the liquid to expand as it warms up, particularly in the case of products that can experience significant temperature changes during transport. By maintaining this percentage buffer, operators can help ensure that any expansion does not lead to overflow, which is crucial for safety and compliance with regulations.

Filling to a specific physical measurement, like 1 to 3 inches from the top of the vent pipe, does not account for variables such as the specific liquid's properties or temperature changes, which can result in inaccurate assessments of the tank's capacity. Similarly, using the bottom of the expansion trunk does not allow for the necessary expansion accommodation and may not reflect the actual liquid level relative to tank capacity. Thus, the percentage guideline is the most effective method for preventing overflow during cargo operations.