Certified Fire Investigator Practice Exam

What does the term "vapor density" refer to?

1. The weight of vapors released by a substance

2. The relationship of a substance's vapor to air density

3. The temperature at which a substance ignites

4. The speed at which vapors disperse in air

The correct answer is: The relationship of a substance's vapor to air density

Vapor density refers specifically to the relationship of a substance's vapor to the density of air. It is a crucial concept in understanding how gases and vapors behave in the atmosphere, particularly in terms of their potential to accumulate or disperse in a given area. When the density of a vapor is compared to the density of air, it helps to predict whether the vapor will rise, remain suspended, or settle; for instance, if the vapor density is less than that of air, the vapor will tend to rise, while if it is greater, the vapor will tend to sink. Understanding vapor density is important for fire investigators and safety professionals because it plays a significant role in determining how flammable vapors may behave in different environments, especially in enclosed spaces. This knowledge can inform decisions regarding ventilation, fire suppression strategies, and risk assessments in situations involving combustible materials.