What is the primary characteristic of an atmospheric tank?

The primary characteristic of an atmospheric tank is that it operates at pressures ranging from atmospheric pressure up to 1.0 pounds per square inch gauge (psig). This means that such a tank is designed to handle the environmental pressure without requiring significant additional pressure from the tank itself. Atmospheric tanks are generally used for the storage of liquids and are engineered to withstand the pressure exerted by the liquid they contain, as well as any potential vapors that may develop, but they are not meant for high-pressure applications.

The other options do not accurately describe the function or characteristics of atmospheric tanks. Specifically, tanks that store liquids at high pressure would fall under different design standards and safety regulations, while vessels meant for solid materials or specific medical gases at elevated temperatures represent distinct categories with different structural requirements and safety measures in place.