A released chemical with a vapor density greater than that of air will likely do which of the following?

A released chemical with a vapor density greater than that of air will likely do which of the following?

• A. It will rise to the ceiling.
• B. It will tend to settle near the floor because it is heavier than air.
• C. It will immediately mix with air.
• D. It will not disperse.

Answer: (B)

Vapor density relative to air determines where a released vapor tends to move. If a vapor is heavier than air, it won’t rise toward the ceiling; instead, gravity pulls it downward, so it tends to collect near the floor. Because it is denser than air, the vapor will pool in low areas—on the floor, along walls, in basements, manholes, and other low-lying spaces—where it can maintain higher concentrations. In enclosed or partially enclosed spaces, this can create a hazardous layer at floor level that responders must monitor and ventilate appropriately. Gases do mix with air over time, but the dominant immediate behavior of a heavier-than-air vapor is floor-level pooling rather than quick, uniform mixing. It will disperse eventually, but not in the way a lighter-than-air vapor would. It certainly does not remain completely localized or not disperse at all.

Vapor density relative to air determines where a released vapor tends to move. If a vapor is heavier than air, it won’t rise toward the ceiling; instead, gravity pulls it downward, so it tends to collect near the floor.

Because it is denser than air, the vapor will pool in low areas—on the floor, along walls, in basements, manholes, and other low-lying spaces—where it can maintain higher concentrations. In enclosed or partially enclosed spaces, this can create a hazardous layer at floor level that responders must monitor and ventilate appropriately.

Gases do mix with air over time, but the dominant immediate behavior of a heavier-than-air vapor is floor-level pooling rather than quick, uniform mixing. It will disperse eventually, but not in the way a lighter-than-air vapor would. It certainly does not remain completely localized or not disperse at all.