What is Vapor Density a comparison of?

Vapor density refers to the ratio of the weight of a vapor to the weight of an equal volume of air at a specific temperature and pressure. This measure is significant because it helps to determine whether a vapor will rise or sink in the atmosphere. If the vapor density is less than one, the vapor will rise in air, while a vapor density greater than one indicates that the vapor will sink. Understanding vapor density is essential for hazardous materials responders, as it aids in assessing how gases or vapors might disperse in the event of a leak or spill, influencing safety measures and response strategies.