What fitting is not allowed in a concealed location?

Unions are fittings that are specifically designed to provide a connection that can be easily disconnected. While this feature is advantageous in some applications, it also makes unions less secure compared to other fittings in situations where they may be subjected to moisture or other conditions that could lead to deterioration or failure over time.

In a concealed location, such as within walls or ceilings where access is difficult, it is crucial to minimize the risk of leaks or failures that might go unnoticed until significant damage occurs. Unions can become loose due to vibrations or temperature changes, making them a less suitable choice for these hidden applications.

On the other hand, caps, elbows, and tees are designed to create permanent connections or changes in direction in piping systems. These fittings tend to provide a more secure and stable assembly, reducing the risk associated with hidden connections. Therefore, the restriction on using unions in concealed locations prioritizes safety and reliability in the integrity of gas piping systems.