Every container built after December 1, 1965, designed to be filled volumetrically, must be equipped with what?

Every container designed to be filled volumetrically and constructed after December 1, 1965, must be equipped with a fixed liquid level gauge. This requirement is in place to prevent overfilling, which can lead to hazardous situations, including the risk of pressure buildup and potential leaks. A fixed liquid level gauge allows operators to monitor the liquid level within the container accurately, ensuring that it does not exceed safe limits during the filling process.

The other safety devices mentioned, while important in their own right, serve different purposes. A pressure relief valve is critical for handling excess pressure that might build up inside a container but does not provide a mechanism for monitoring liquid levels. An automatic shut-off valve is important for automatically stopping the flow of gas or liquid under certain conditions but does not offer continuous level monitoring. An overflow protection device adds an extra layer of safety in case of overfilling but does not serve the same function as a fixed liquid level gauge, which directly shows the fluid's current level.