What is vapor density?

• A. The weight of air compared to other gases
• B. The relative weight of a gas compared to air
• C. The speed at which a gas rises
• D. The temperature at which a vapor condenses

Answer: (B)

Vapor density is defined as the relative weight of a gas compared to air. This measurement helps determine how a gas behaves in the atmosphere, particularly in scenarios involving hazardous materials. Since air has a vapor density of 1, a gas with a vapor density greater than 1 will sink, while a gas with a vapor density less than 1 will rise. Understanding vapor density is crucial in HAZMAT situations as it impacts the dispersion of gases, enabling responders to predict how a gas might travel and accumulate in an environment.

The other options touch on related concepts but do not accurately define vapor density. For instance, measuring the weight of air compared to other gases looks at more general atmospheric properties, while the speed at which a gas rises deals with kinetics rather than density. The temperature at which a vapor condenses pertains to its phase change and behavior at specific temperatures, which does not align with the definition of vapor density.