What is the vapor density of air?

The vapor density of air is considered to be 1, as it is the reference point against which other gases are compared. In this context, vapor density is defined as the mass of a certain volume of gas relative to the mass of an equal volume of air at the same temperature and pressure. Since air is the baseline standard, its vapor density is normalized to 1.

Other gases can have vapor densities greater than or less than 1, indicating whether they are heavier or lighter than air. For example, a vapor density less than 1 suggests that the gas will rise in air, while a vapor density greater than 1 indicates it will sink. This characteristic is crucial in firefighting and safety, as it affects how gases behave in the atmosphere, influencing both detection and ventilation strategies during a fire. Understanding that air serves as the reference point makes recognizing the significance of vapor density in fire behavior and gas behavior more intuitive.