A vapor with density greater than air tends to accumulate near the floor.

A vapor with density greater than air tends to accumulate near the floor.

• A. Near the ceiling
• B. In the middle of the room
• C. Near the floor
• D. In vents

Answer: (C)

When a vapor has a density greater than air, gravity pulls the heavier molecules downward and they don’t mix quickly with the surrounding air. As a result, the vapor tends to pool at the lowest point in a space—the floor. It can seep under doors, collect in basements, low corners, or other low-lying areas, creating a higher concentration there even if higher areas seem clear. This is why detectors for heavier-than-air vapors are often placed near the floor, and why ventilation strategies focus on removing gas from low areas first. The other locations—near the ceiling or in the middle of the room—are more typical of vapors that are lighter than air, which rise. Vents can serve as pathways, but the primary accumulation pattern is tied to density, not just where vents happen to be.

When a vapor has a density greater than air, gravity pulls the heavier molecules downward and they don’t mix quickly with the surrounding air. As a result, the vapor tends to pool at the lowest point in a space—the floor. It can seep under doors, collect in basements, low corners, or other low-lying areas, creating a higher concentration there even if higher areas seem clear.

This is why detectors for heavier-than-air vapors are often placed near the floor, and why ventilation strategies focus on removing gas from low areas first. The other locations—near the ceiling or in the middle of the room—are more typical of vapors that are lighter than air, which rise. Vents can serve as pathways, but the primary accumulation pattern is tied to density, not just where vents happen to be.