In the context of fire safety, what is the term for the weight of gas compared to air?

The correct term for the weight of gas compared to air is vapor density. Vapor density specifically refers to the mass of a certain volume of gas compared to the mass of an equal volume of air at the same temperature and pressure. This measurement is crucial in fire safety as it helps determine how a gas will behave when released into the atmosphere, such as whether it will rise or settle.

Understanding vapor density aids fire officers in assessing the potential risks of different gases, particularly in situations involving leaks or explosions. For instance, a vapor density greater than 1 indicates that the gas is heavier than air and will tend to accumulate at lower levels, potentially posing a hazard. Conversely, gas density typically refers to the actual weight of gas molecules compared to its volume without direct comparison to air.

The other options focus on different concepts that don't directly define the relationship of a gas's weight to air. Gas pressure relates to the force exerted by gas molecules in a defined space, while air weight is not a standard term used in the context of gas measurements.