Which location is most likely for vapors from a liquid with density greater than air to accumulate?

• A. High elevations.
• B. Low areas and below grade places.
• C. In the open air.
• D. Away from sources.

Answer: (B)

When vapors are denser than air, they don’t rise to disperse; they sink and collect in the lowest available spaces. That’s why heavier-than-air vapors tend to pool in low areas such as basements, pits, below‑grade rooms, trenches, and other depressions where airflow is limited. In these spots the vapor can reach higher concentrations and create a serious hazard, especially if ventilation is poor and ignition sources are present. The other options don’t support pooling: high elevations are less likely because the air is thinner up high; open air tends to dilute and disperse vapor quickly; and being away from the source doesn’t encourage accumulation since the vapor will settle toward the lowest available space rather than away from where it’s released.