What does the term "vapor density" refer to with LPG and CNG?

The term "vapor density" specifically refers to the weight of the gas compared to air. Vapor density is a critical property for understanding how a gas will behave in the atmosphere. In the case of liquefied petroleum gas (LPG) and compressed natural gas (CNG), knowing the vapor density helps in assessing safety protocols, potential hazards, and proper ventilation requirements in environments where these gases are used.

For LPG, the vapor density is typically heavier than air, which means that if there is a leak, the gas will tend to settle in low-lying areas and poses a risk of accumulation and potential ignition sources. Conversely, CNG has a vapor density that is lighter than air, leading it to dissipate upwards in the event of a leak. Understanding the vapor density is crucial for the safe handling and storage of these gases in various applications, including automotive and industrial uses.