What action is taken to prevent vapor loss when a fixed roof tank’s temperature exceeds the limit?

• A. Blanket with nitrogen
• B. Vent to atmosphere
• C. Drain completely
• D. Pressurize with air

Answer: (A)

Nitrogen blanketing creates an inert layer over the liquid in a fixed roof tank. When the liquid heats up, vapors form and tend to escape. Filling the headspace with nitrogen reduces the amount of oxygen and limits the pathways for vapor to transfer to the atmosphere, thereby minimizing vapor loss and lowering ignition risk because hydrocarbons are less likely to form an explosive mixture with air.

Venting to atmosphere would simply release vapors to the environment, draining would waste product, and pressurizing with air would introduce oxygen and raise both vapor release and fire/explosion risk.