Vapors with density greater than air will tend to collect in low areas.

• A. Rise to the ceiling
• B. Diffuse evenly
• C. Dissolve in water
• D. Settle in low areas

Answer: (D)

Vapor density relative to air determines where a leak will pool. When a vapor is heavier than air, gravity pulls it downward, so it tends to flow along the floor and collect in the lowest areas—basements, depressions, pits, or along low spaces near walls. That’s why heavier-than-air vapors will settle in low areas and form hazardous pockets there. This differs from vapors that are lighter than air, which rise toward the ceiling. Density isn’t about dissolving in water—that’s a different property—so solubility doesn’t dictate why these vapors pool; it’s the relative weight in air that drives the behavior. In practice, expect low-lying accumulation and monitor or ventilate accordingly.