Which connection does not require nitrogen purge?

The final tie-in to an existing system does not require a nitrogen purge because it typically involves connecting the new section of the gas line directly to an already operational system. During this process, if done properly, the existing system should already be pressurized and filled with the appropriate medical gas. The use of nitrogen in purging is primarily to eliminate contaminants and ensure the purity of the gas in the newly installed sections. Since the existing system is already pressurized and in use, the need to purge it with nitrogen before the tie-in is unnecessary.

In contrast, joint fittings, branch connections, and initial line setups often require purging with nitrogen. This step is crucial in these contexts to prevent any contamination from entering the gas line, maintain system integrity, and ensure that the gas delivered is safe and meets quality standards. Thus, these connections necessitate nitrogen purging to mitigate the risks associated with the introduction of particulates or moisture that could compromise the entire medical gas delivery system.