I referred to merchant ships in international trades subject to IMO/SOLAS rules and ITF requirements for crew accommodation.
Ships in national trade are built according national rules, which can differ considerably from SOLAS.
Military and coast guard ships are not built as per SOLAS. You can do whatever you like, e.g. fit flush hatches in decks without coamings and use them as escape routes. I wonder what ITF would say about USN accommodations.
Watertight doors are evidently only fitted in watertight bulkheads of the hull.
Passengers are today accommodated in deckhouses and thus not exposed to watertight doors.
Large numbers of crew are on the other hand accommodated in the hull, often below waterline, and may be exposed to watertight doors, if fitted.
Such watertight doors are not permitted by SOLAS unless an exemption certificate is issued and particular instructions issued how to use them, e.g. to always be closed at sea.
Many maritime administrations do not follow the IMO rules and permit watertight doors everywhere with catastrophic results! M/S Costa Concordia suffered a hull leakage incident, up-flooding some compartments causing total black out but floated safely 2012. However, when the crew abandoned ship, watertight doors were opened by them producing progressive flooding of intact compartments … so the ship lost stability … capsized … and sank hours after the incident took place. To cover up the defect it was decided to blame the Master alone for everything. I assume the Fitz commander will be treated the same. Just blame the senior officer on the ship.
It could be added that all compartments on different decks should be isolated from one another by fire doors, so that fire smoke in one compartment shall not spread to other compartments. Such doors can easily be closed by remote control. I have no idea how you remotely close a hatch in a deck.