What is the maximum allowable fill percentage for a cargo tank on a tank vessel?

The maximum allowable fill percentage for a cargo tank on a tank vessel is 98.5%. This regulation is in place to ensure safety during transportation and to prevent overfilling, which could lead to spills or other hazardous situations. The design of tank vessels incorporates safety margins to account for temperature variations, sloshing during transit, and the expansion of cargo, especially in the case of liquids that may change volume with temperature fluctuations.

Having a fill percentage capped at 98.5% allows for an adequate vapor space in the tank, which is crucial for accommodating the expansion of the liquid and preventing pressure build-up. This precaution not only protects the vessel and crew but also aids in safeguarding the marine environment from potential pollution should there be an incident.

Regulations derived from the International Maritime Organization (IMO) and the US Coast Guard (USCG) emphasize these safety limits. Thus, 98.5% is established as the threshold to maintain operational safety, making it the correct answer in this context.