Which statement is true concerning inert gas systems on tank vessels?

The use of flue gases from the ship's boilers in inert gas systems is indeed a common practice, making this statement accurate. Inert gas systems are crucial for safety on tank vessels, particularly for preventing explosive atmospheres in cargo tanks. By diluting the oxygen concentration with inert gases, such as flue gases, the risk of combustion is significantly reduced.

Inert gas systems can either derive gases from flue gas emissions produced in the ship's boilers or generate inert gases through other means, but flue gases are a traditional and effective source. The system treats these gases to remove moisture and other harmful constituents before being introduced into the cargo tanks.

The other choices indicated are not correct as they do not accurately describe the function or requirements of inert gas systems on tank vessels. Inert gas systems do not rely solely on external air sources, nor are they primarily designed for cooling; their main function is to enhance safety by controlling the atmosphere in cargo holds. Furthermore, these systems are generally mandated by international regulations to ensure safety in tankers.