Which feature identifies the vapor dome roof tank?

• A. Two roofs: Tank cover and floating roof
• B. Ladder to the center of the roof
• C. Giant bulge on top
• D. External drain on the bottom

Answer: (C)

Vapor dome roof tanks are identified by a domed, bulging shape on top of the fixed roof. That large bulge is the dome itself, which creates a controlled vapor space above the liquid and helps manage hydrocarbon vapors. The other options don’t define this roof type: a ladder to the center isn’t unique to a vapor dome, an external drain is a bottom feature, and the idea of “two roofs” isn’t how a vapor dome is described. So the giant bulge on top is the characteristic feature that signals a vapor dome roof tank.