Vapour density is the density of a vapour in relation to that of air. It may be defined as mass of a certain volume of a substance divided by mass of same volume of air.

Vapour density indicates whether a gas is denser (greater than one) or less dense (less than one) than air. The density has implications for container storage and personnel safety - if a container can release a dense gas, its vapour could sink and, if flammable, collect until it is at a concentration sufficient for ignition. Even if not flammable, it could collect in the lower floor or level of a confined space and displace air, possibly presenting an asphyxiation hazard to individuals entering the lower part of that space.

[x] > 0