Technical Standards and Safety Authority (TSSA) G3 Practice Exam

By definition, the specific gravity of a gas (vapor) compares the weight of the gas to which of the following?

1. The weight of air

2. The weight of an equal volume of air

3. The volume of gas compared to the weight of an equal volume of air

4. The volume of gas as compared to the weight of air

The correct answer is: The weight of an equal volume of air

The specific gravity of a gas (or vapor) is defined as the ratio of the weight of that gas to the weight of an equal volume of air. This definition emphasizes that specific gravity is a dimensionless quantity, meaning it provides a relative comparison between the two substances based on their weights under the same volume conditions. When assessing gases, understanding specific gravity is crucial in various applications, including combustion and safety assessments, because it indicates whether a gas will rise or fall in the atmosphere. A specific gravity of less than one suggests that the gas is lighter than air and will rise, while a specific gravity greater than one indicates that it is heavier and will tend to sink. The other options either misinterpret or misstate the concept of specific gravity regarding the relationship between weight and volume. By correctly identifying the relationship as between the weight of the gas and the weight of an equal volume of air, the chosen answer accurately reflects the standard scientific definition and application of specific gravity in relation to gases.