Which factor can cause a sunken floating roof?

• A. Improper management of rainwater
• B. Too much ventilation
• C. High ambient temperature only
• D. Excessive product in the tank

Answer: (A)

Sunken floating roofs happen when the roof loses enough buoyancy that it can no longer float on the liquid. The roof relies on the liquid it sits on to provide buoyant support. If rainwater isn’t managed properly, water can accumulate on or around the roof, especially in the roof well or annular space. That extra water adds weight to the roof, while the buoyant force from the stored liquid remains the same, so the roof can sink downward. Proper rainwater management—drains, seals, and rapid shedding of rain—prevents this added load and keeps the roof floating at the correct level.

Other factors don’t cause sinking in the same way. Ventilation mainly affects pressure and vapor losses, not the roof’s weight. A high ambient temperature by itself doesn’t add enough weight to overpower buoyancy. And having more product in the tank actually increases buoyancy, which would push the roof up rather than sink it.