Which of the following is a direct indicator that an ASME tank has reached its maximum liquid level and will stop the flow?

• A. A steady white mist is emitted from the fixed maximum liquid level gauge
• B. The gauge reads full
• C. A whistle sounds
• D. The overfill protection device stops the flow

Answer: (D)

When managing an ASME tank, the feature that directly enforces the limit and stops the flow is the overfill protection device. This safety device is designed to sense the maximum liquid level and automatically shut off the flow as soon as that level is reached, preventing overfill and the associated hazards. The other cues—gauge reading full, a whistle, or any visible mist from a gauge—are warnings or indicators of high level or venting, but they do not themselves stop the flow. Only the overfill protection device provides that automatic, direct stoppage of flow.