What does it mean if a tank has a "closed vent" system?

A tank with a "closed vent" system is designed to prevent the escape of vapors into the atmosphere, which is especially important for environmental protection and safety. When loading or unloading liquids, a closed vent system ensures that vapors generated inside the tank do not escape, thereby reducing air pollution and minimizing the risk of fire or explosion due to flammable vapors coming into contact with ignition sources.

This system essentially allows for the management of vapor space within the tank, capturing and reclaiming vapors rather than releasing them. This is critical for compliance with environmental regulations and helps to maintain the integrity of the load and protect public health.

The other options do not fully capture the primary function of a closed vent system, which is centered on safety and environmental concerns during the transfer of liquid cargo.