What is the maximum distance at which external duct insulation must be legibly identified?

The correct answer is that the maximum distance at which external duct insulation must be legibly identified is 36 inches. This requirement is crucial for ensuring safety and maintainability in mechanical systems. Identifying the insulation helps technicians, inspectors, and any personnel working with or near the ductwork understand the type of insulation used and any related issues, such as potential hazards or the need for special handling during maintenance.

Proper identification aids in distinguishing between various types of insulation materials, which can vary in properties and requirements. By maintaining a standard of identification within this distance, codes ensure that individuals can quickly and accurately assess the ductwork without unnecessary delays or confusion, thereby enhancing safety standards and promoting effective maintenance practices.

In contrast, other distances indicated by the options are not aligned with the established practices outlined in the code, which specifically stipulates that 36 inches is the maximum for effective identification of external duct insulation. This standard is designed to balance practicality and safety in mechanical installations.