When should underground inspections be made according to the code?

Underground inspections should be made before backfill, as indicated by the correct answer. This requirement is crucial because it allows inspectors to evaluate the installation of underground piping and ensure that it meets all applicable codes and standards prior to being covered. Conducting inspections at this stage helps to verify that the materials and workmanship comply with the specifications laid out in the International Mechanical Code. If any issues are discovered during the inspection, they can be addressed before the excavation is filled in, preventing potential future problems that would be difficult and costly to resolve once the piping is buried. This process is essential for ensuring the long-term integrity and safety of the mechanical systems that rely on those underground installations.