Associate Safety Professional Practice Exam

What differentiates pounds per square inch absolute from pounds per square inch gage?

1. Psig is always higher than PSIA

2. Psig measures absolute pressure

3. Psig accounts for standard atmospheric pressure

4. There is no difference between the two

The correct answer is: Psig accounts for standard atmospheric pressure

The distinction between pounds per square inch absolute (PSIA) and pounds per square inch gauge (PSIG) lies in how each measurement relates to atmospheric pressure. Pounds per square inch absolute measures the pressure of a system relative to a complete vacuum, meaning it includes atmospheric pressure in its reading. This is useful for calculations that require an absolute reference point. On the other hand, pounds per square inch gauge measures the pressure relative to atmospheric pressure. Therefore, PSIG does not include the atmospheric pressure in its calculation and can show a reading of zero when there is no pressure above the ambient atmospheric pressure. When considering these definitions, the correct answer highlights that PSIG accounts for standard atmospheric pressure — it does not consider it in its measurement, while PSIA does. This fundamental difference is critical in fields such as engineering and safety, where accurate pressure readings are essential for system design, monitoring, and operations.