Which term describes the comparison of vapor density?

• A. Relative humidity
• B. Specific gravity
• C. Weight ratio
• D. Concentration ratio

Answer: (B)

The term that describes the comparison of vapor density is specific gravity. Specific gravity is defined as the ratio of the density of a substance to the density of a reference substance, typically water for liquids and air for gases. When applied to vapors, specific gravity indicates whether a vapor is lighter or heavier than air. A specific gravity less than 1 means the vapor will rise in air, while a specific gravity greater than 1 indicates that the vapor will sink. Understanding this concept is crucial in hazardous materials situations, as it helps in assessing potential risks, such as accumulation in low areas during a leak.

Relative humidity refers to the amount of moisture in the air compared to the maximum amount of moisture the air can hold at that temperature and does not relate directly to vapor density. Weight ratio relates to the comparison of weights of two substances, but it does not specifically address density or vapor density. Concentration ratio gives information about the amount of a substance in relation to a volume or mass but does not convey the same information as specific gravity regarding density comparisons.