What do we call the ratio of the weight of a volume of gas to an equal volume of dry air?

The ratio of the weight of a volume of gas to an equal volume of dry air is referred to as vapor density. This concept is important in the field of firefighting and hazardous materials handling because it helps determine how various gases behave in comparison to air.

When vapor density is less than one, the gas will rise and disperse in the atmosphere; when it is greater than one, the gas will tend to sink. This knowledge is crucial for assessing the potential hazards associated with gases, especially in the event of a leak or explosion. Understanding vapor density can aid in making informed decisions on ventilation, evacuation, and containment strategies during emergencies.

The other terms, such as gas density and air density, describe different properties and measurements. Gas density refers to the mass per unit volume of a specific gas, while air density is a measurement of the mass of dry air per unit volume, but neither specifically compares a gas to dry air in the way that vapor density does. Weight ratio is a more ambiguous term that does not specifically relate to gas behavior compared to air. Thus, vapor density is the precise term needed for this context.