During which type of purge is a vessel filled with liquid, then drained and filled with inert gas?

The process described involves filling a vessel with liquid, draining it, and then filling it with an inert gas. This method is characteristic of a siphon purge, where a liquid is initially used to displace any reactive gases within the vessel. After the liquid is drained, the introduction of an inert gas serves to create an atmosphere that minimizes the risk of fire or explosion by preventing the presence of oxygen or reactive gases.

In contrast, other purge types differ significantly in their approach and application. The pressure purge typically involves introducing an inert gas under pressure to push out potentially hazardous gases without the introduction of a liquid. A vacuum purge uses reduced pressure to remove contaminants, often without any initial liquid filling phase. Open purging refers to allowing airflow through the system, which is not applicable for scenarios where the aim is to eliminate reactions with the atmosphere.

Therefore, the correct choice reflects the specific method of introducing a liquid, then clearing it, and finally filling with an inert atmosphere to maintain safety.