What is the vapour density of air?

What is the vapour density of air?

• A. 0.0
• B. 29.9
• C. 14.7
• D. 1.0

Answer: (D)

Vapor density, in safety and fire-service contexts, is the ratio of the density of a vapor to the density of air at the same temperature and pressure. Since air is the reference substance, its own vapor density is 1.0. This baseline lets you compare other vapors: a gas lighter than air has a vapor density less than 1.0, while a gas heavier than air has a vapor density greater than 1.0. The values like 14.7 or 29.9 come from a different convention that uses hydrogen as the reference, not air. So the correct answer, given the air-reference definition, is 1.0.

Vapor density, in safety and fire-service contexts, is the ratio of the density of a vapor to the density of air at the same temperature and pressure. Since air is the reference substance, its own vapor density is 1.0. This baseline lets you compare other vapors: a gas lighter than air has a vapor density less than 1.0, while a gas heavier than air has a vapor density greater than 1.0. The values like 14.7 or 29.9 come from a different convention that uses hydrogen as the reference, not air. So the correct answer, given the air-reference definition, is 1.0.