Which of the following is NOT a type of pressure vessel?

A safety vessel is not recognized as a distinct type of pressure vessel in the standard classifications used in engineering and design. Pressure vessels are typically categorized based on their orientation and shape, which include vertical and horizontal vessels. Closed vessels are designed to hold substances at a pressure significantly different from the ambient pressure, ensuring they can contain pressurized liquids or gases safely.

Vertical and horizontal vessels are distinguished by their orientation, impacting factors such as design, space usage, and the handling of substances. Closed vessels are similar but have a specific characteristic of being sealed and able to maintain internal pressure. In contrast, the term "safety vessel" does not align with these established categories, highlighting why it is the correct choice in this context.