How is specific gravity of a gas defined?

The specific gravity of a gas is defined as the ratio of the average molecular weight of the gas or vapor to that of air. This definition is critical in various applications, such as fire and explosion investigations, because it allows for the comparison of different gases based on their density relative to air. Air has an average molecular weight of approximately 29 g/mol, and knowing how a particular gas compares to this value helps investigators assess potential behaviors, such as whether the gas will rise or settle in a given environment.

Understanding specific gravity in this context is essential because it influences the dispersion of gases during a fire incident and can indicate how a gas may interact with its environment. For example, a gas with a specific gravity less than 1.0 will tend to rise in air, while one with a specific gravity greater than 1.0 will typically settle, impacting how fires spread and how smoke accumulates.

This understanding also provides a framework for assessing risk and formulating safety measures during fire investigations. Knowledge of specific gravities helps in predicting possible behavior of flammable vapors, which is pivotal for effectively managing fire hazards.