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

For concealed gas installations, couplings are the correct choice because they provide a secure and continuous connection between sections of pipe without creating abrupt changes in direction or branching, which is crucial for ensuring the safe and efficient flow of gas. Couplings allow for the extension of piping runs and are generally designed to be installed in walls or other concealed areas where maintenance access may be limited.

The use of couplings in concealed areas is also significant for maintaining the integrity of the gas line, as they eliminate potential weak points that could lead to leaks. This is especially important in building codes that focus on safety and compliance with gas installation standards.

Other fittings, although commonly used in plumbing and gas installations, may not be allowed for concealed applications due to safety concerns. For instance, tees and elbows can introduce potential leak points and create complications during inspections and repairs if the joints are not accessible. Brazed fittings, while strong, may require more exposure for installation and inspection, which could be problematic in concealed applications.