Compartmentation places compartments, ship zones, and other volume objects within a ship. Compartments are physical spaces within the ship that cannot overlap, except for some limited cases where one compartment, such as a fuel oil day tank, is completely enclosed by another compartment (such as the main machinery space). In most instances, a compartment is completely defined in terms of topological boundary relationships with a plate system, a deck, a transverse bulkhead, a longitudinal bulkhead, or a hull shell object.