What term describes the weight of a gas compared to air?

The term that describes the weight of a gas compared to air is vapor density. Vapor density is a measure of how heavy a gas is relative to air, which can have important implications for safety and handling of hazardous materials.

When a gas has a vapor density greater than 1, it is heavier than air and may settle in low-lying areas, creating potential hazards in confined spaces. Conversely, a gas with a vapor density less than 1 is lighter than air and will rise. Understanding vapor density is critical for Hazmat operations, as it helps responders anticipate the behavior of gases in the environment and implement appropriate safety measures.