What is a common characteristic of a permit-required confined space?

A permit-required confined space is characterized primarily by the potential to contain a hazardous atmosphere. This means that within such spaces, there may be harmful gases, vapors, or dust that can pose a danger to individuals entering the area. The identification of this characteristic is crucial because it dictates the safety protocols and procedures necessary before employees can enter the space.

In contrast, the other options do not correctly define a permit-required confined space. For example, having safety monitors on-site can be part of safety procedures, but it is not a defining characteristic of a permit-required space itself. Similarly, these spaces are not designed for open-air work; rather, they are often enclosed and may require special safety measures. Lastly, while a permit-required confined space can be used for storage, this is not a common or defining characteristic and does not necessitate an entry permit. The focus on hazardous atmospheres underscores the need for proper training and safety measures when working in confined spaces.