During which type of purge is a vessel pressurized with inert gas and then the pressure is relieved?

The correct answer is a pressure purge. In this process, the vessel is first filled with an inert gas, which helps to displace any potentially hazardous vapors present inside. The purpose of using an inert gas is to create an oxygen-deficient environment, preventing the formation of flammable mixtures.

Once the vessel reaches the desired pressure with the inert gas, it is then relieved, allowing any residual vapors or gases within the vessel to escape. This step is crucial in ensuring that the remaining atmosphere in the vessel is safe for subsequent operations or maintenance.

In contrast, other types of purges focus on different methods of ensuring safety. For example, a vacuum purge would involve removing air by creating a vacuum, while a flame purge would use a flame to burn off flammable vapors. Scavenging purge might refer to a different technique where certain gases are drawn out or prevented from reacting. Each of these methods has its specific applications based on the nature of the cargo and the operational requirements, but the characteristics of a pressure purge specifically align with the process described in the question.