If the depth of the passageway exceeds a certain threshold, what materials must line the walls?

When the depth of a passageway exceeds a specified threshold, it is crucial for safety and durability to line the walls with materials that can withstand various environmental stresses, including moisture, fire, and potential impact. Concrete or masonry is ideal in this context because these materials offer significant structural integrity and fire resistance. They are capable of supporting heavy loads, are non-combustible, and help prevent the spread of fire, which is critical in passageways where both people and equipment might pass.

Moreover, concrete and masonry contribute to the overall stability and longevity of the structure. They provide a solid, stable surface that is essential for areas of passageways that may see considerable foot traffic or equipment movement. This makes them suitable for use in both commercial and industrial environments where safety regulations dictate specific requirements for wall materials based on depth and usage.

Other materials such as wood or plastic would not provide the necessary fire resistance or structural stability required for deeper passageways, making concrete or masonry the appropriate choice for compliance with safety standards.