Which term is used to evaluate the weight of the gases based on the weight of air?

The term that is used to evaluate the weight of gases in relation to the weight of air is vapor density. Vapor density specifically refers to the mass of a gas compared to the mass of an equal volume of air at the same temperature and pressure. This measure is crucial in understanding how gases behave in different environments, particularly in the context of fire safety and inspections.

For instance, if a gas has a vapor density less than 1, it is lighter than air and will rise, whereas a vapor density greater than 1 indicates that the gas is heavier than air and will tend to settle at lower levels. This information is vital for identifying potential hazards in enclosed spaces where certain gases may accumulate.

In contrast, the density index typically relates to a broader concept and is not specifically tied to vapor or gas behavior relative to air. Gas weight ratio does not appear to be a standard term used in fire science, and vapor pressure pertains to the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases, rather than a direct comparison to air's weight. Understanding vapor density is essential for safety professionals in evaluating risks and implementing effective fire safety measures.