Which of the following fittings is allowed for concealed gas installations?

The choice of couplings as the correct answer for fittings allowed in concealed gas installations is based on their specific design and function. Couplings are used to connect two sections of pipe in a straightforward manner, creating a seamless joint that is essential for maintaining the integrity of gas piping systems. In concealed installations, where connections are not visible and are typically enclosed within walls or floors, it is critical that the fittings used are reliable and capable of preventing leakage.

The use of couplings ensures that gas lines remain secure and less prone to potential gas leaks, which is a vital consideration for safety in gas installations. The materials and construction of couplings typically meet higher standards necessary for gas applications, making them suitable for hidden connections.

In contrast, other fittings such as tees and elbows may not be permitted in concealed applications due to the additional joints or changes in direction they introduce. Brazed fittings, while they can create strong joints, may not be ideal for situations where accessibility for future inspection or maintenance is limited. Their installation can also pose challenges in terms of ensuring proper techniques are used, which may not be feasible in concealed applications where visibility is compromised. Thus, couplings stand out as the safest and most appropriate choice for concealed gas installations.