Which hazard is associated with a sunken floating roof?

• A. Leaking product and product carryover from leaking seals or blow by
• B. Increased structural strength
• C. Decreased vapor pressure below safe levels
• D. No hazard present

Answer: (A)

When a floating roof sinks, the seals around the rim cannot meet the tank wall properly. Those seals are what keep liquids and vapors from escaping into the vapor space or out of the tank. If the roof is sunken, gaps appear and the liquid product can leak around the rim while vapors can bypass the seals—this is often called blow-by. The result is both product leakage and vapor carryover into the vapor space or to venting systems, creating emissions and ignition risks. That combination of leaking liquid and vapor bypass is the hazard associated with a sunken floating roof. The other options don’t reflect the typical hazards from this condition: it doesn’t inherently strengthen the structure, it doesn’t reliably lower vapor pressure to safe levels, and there is indeed a hazard present.