In the event of a fire, the doors to a stair tower must be closed to prevent the spread of fire by____________.

Correct Answer: Option A — convection

Stair towers act as chimneys for hot, buoyant gases during a fire. Closing fire doors prevents the movement of these heated gases and smoke, which spreads fire via convection. This containment strategy is essential for maintaining escape routes and protecting the integrity of the vessel's fire-rated bulkheads and decks.