What does vapor density refer to in the context of gases?

Vapor density is a critical property of gases that refers specifically to the weight of a gas in comparison to the weight of air. This measurement is important because it helps responders understand how a particular gas will behave in the atmosphere. If a gas has a vapor density greater than 1, it is heavier than air and will tend to sink, which can affect how it accumulates in low-lying areas and presents hazards during incidents. Conversely, a vapor density less than 1 indicates the gas is lighter than air and will rise, potentially dispersing into the atmosphere.

Understanding vapor density is essential for hazard assessment during emergency responses involving gases. It allows firefighters and hazardous materials responders to anticipate possible pathways of gas movement, informing decisions about ventilation, evacuation, and containment strategies.