What is the vapour density of air?

The vapor density of air is defined as 1.0. This value is a reference point and serves as the baseline for comparing the densities of other gases. When discussing vapor density, it is typically in relation to air, which is why air is assigned a value of 1.0.

In practical terms, if a gas has a vapor density greater than 1.0, it is heavier than air and will tend to sink, while gases with a vapor density less than 1.0 are lighter than air and will rise. Understanding vapor density is crucial for fire fighters and others in emergency response to anticipate how hazardous gases will behave in the atmosphere, especially when assessing the risks of smoke or gas dispersion.

The other values provided do not correspond to the correct understanding of the vapor density of air. For instance, the values of 29.9 and 14.7 could refer to molecular weights of specific gases (like carbon dioxide and nitrogen, respectively), but they do not represent vapor density of air. The value of 0.0 is not applicable in this context, as it does not have a meaning within vapor density measurements.