Virginia VDFP HazMat Awareness and Operations Practice Test

When a vapor density is greater than air, the vapor is heavier than air and will settle toward the lowest points due to gravity. It tends to pool in low areas such as floors, basements, depressions, trenches, or along drains where it cannot rise. This is why such vapors pose the greatest risk at floor level and in confined low spaces. In contrast, vapors lighter than air rise and collect in high areas, which is not the case here. Heat sources might increase vapor production, but they don’t change the tendency to pool in lower spots; vents can carry vapor but the first place it will accumulate is at the bottom.