What is the purpose of roof seals?

• A. To seal the roof to prevent product leakage
• B. To move up and down to minimize vapor loss
• C. To purge the tank with nitrogen
• D. To support the roof structurally

Answer: (B)

Roof seals work with the floating roof to keep vapors from escaping as the roof changes with the liquid level. A floating roof rises and falls as product is added or withdrawn, and the seals around the rim maintain a tight barrier between the roof and the tank wall during that movement. This seal while moving is what minimizes vapor loss. Purging with nitrogen or providing structural support aren’t related to the sealing function, so they don’t describe what the seals are for.