What do the heavy lines on Damage Control Diagrams indicate?

The heavy lines on Damage Control Diagrams indicate watertight and airtight boundaries. These lines are crucial as they help identify the structural divisions within a ship that maintain the integrity of compartments in the event of flooding or fire. Watertight boundaries prevent the ingress of water into a compartment, while airtight boundaries help contain smoke and fire, enhancing the overall safety of the vessel during damage control situations. Understanding these boundaries is essential for personnel to effectively plan and execute damage control strategies, protecting both the crew and the ship itself.