Associate Safety Professional Practice Exam

What is the specific gravity of dry air?

1. 0.8

2. 1

3. 1.2

4. 1.5

The correct answer is: 1

The specific gravity of dry air is defined as the ratio of the density of air to the density of a reference substance, which is usually taken to be water. Since the density of air at sea level (approximately 1.225 kg/m³) is much less than that of water (which is approximately 1000 kg/m³), specific gravity is a comparative dimensionless number. In this context, the specific gravity of dry air is commonly approximated as 1 when compared directly to itself at standard reference conditions. This means that dry air, when measured against the standard density of air, essentially has a standard value of 1. Other values, such as 0.8, 1.2, and 1.5, do not accurately reflect the specific gravity of dry air under standard atmospheric conditions. They either imply densities that do not align with the characteristics of air or refer to different substances altogether rather than the density of air compared to itself.