The correct answer is A) immediately. On a Mobile Offshore Drilling Unit (MODU), control of fire should be addressed immediately as it poses a serious threat to the safety of the vessel and personnel. Fires can quickly spread and lead to catastrophic consequences, so the priority is to initiate firefighting efforts as soon as the fire is detected, before addressing other concerns like flooding or restoring vital services. Establishing fire boundaries can be important, but controlling the fire itself is the most critical first step. The other options are incorrect because they do not reflect the urgency required in responding to a fire on a MODU. Waiting to address the fire until after controlling flooding or restoring vital services could allow the fire to grow out of control and jeopardize the entire operation.