When fighting a shipboard fire, crew members securing doorways, hatches, and applying cooling water to adjacent decks and bulkheads, while monitoring the spread of heat and smoke, are setting a _________.

Correct Answer: Option C — fire boundary

A fire boundary is established to contain a fire by isolating the affected area. Crew members secure all openings and apply cooling water to surrounding bulkheads and decks to prevent heat conduction. This prevents the fire from spreading to adjacent spaces, protecting the vessel's structural integrity.