When can routine communications resume after radio silence has been imposed?

Routine communications can resume after radio silence has been imposed when the Rescue Coordination Center (RCC) declares that emergency communications are concluded. This is the correct answer because the RCC is the authority that manages and oversees maritime search and rescue operations, including the coordination of communications during emergencies. Once the RCC has assessed that the emergency situation has been resolved and the need for prioritized communications has ended, they formally lift the radio silence, allowing vessels to resume routine communication tasks without the risk of interfering with ongoing emergency responses.

The other options, while they may seem plausible in ensuring effective communication, do not follow the established protocol regarding the lifting of radio silence. For instance, determining if the frequency is unused or assessing geographic distance for interference does not provide the authoritative clearance needed to ensure that routine communications can occur without jeopardizing active emergency situations. Additionally, the belief of the master that their communications will not interfere does not hold the same weight as a directive from the RCC, which is designed to ensure safety and effectiveness in emergency management.