How is vapor density defined?

• A. The temperature at which vapor forms
• B. The weight of vapor compared to dry air
• C. The amount of gas released under pressure
• D. The volume of vapor produced during a chemical reaction

Answer: (B)

Vapor density is defined as the weight of vapor compared to dry air. This measure indicates how heavy or light a vapor is relative to air. If the vapor density of a substance is greater than 1, it means the vapor is heavier than air and will tend to settle in lower areas. Conversely, if the vapor density is less than 1, the vapor will rise above the level of air. Understanding vapor density is crucial for hazardous materials response because it helps responders anticipate the behavior of vapors during spills or leaks, particularly in terms of potential exposure pathways and the effectiveness of ventilation measures.

The other definitions do not accurately reflect vapor density. The temperature at which vapor forms pertains to boiling points or vaporization temperatures, while the amount of gas released under pressure relates more to gas laws than to vapor density specifically. Finally, the volume of vapor produced during a chemical reaction is concerned with the reaction's stoichiometry, not the comparative weight of that vapor to air.