What minimum thickness of concrete must metallic underground ducts be encased in?

• A. 1 inch
• B. 2 inches
• C. 3 inches
• D. 4 inches

Answer: (B)

The correct answer is that metallic underground ducts must be encased in a minimum thickness of 2 inches of concrete. This requirement is in place to ensure adequate protection against physical damage and to provide structural integrity. The concrete acts as a barrier that can resist external forces, such as those that may arise from soil movement, traffic loads, or other environmental factors.

By encasing the ducts in this specified thickness, the risk of corrosion and physical impact on the metallic surfaces is considerably reduced, thus enhancing the longevity and safety of the underground duct systems. This guideline aligns with industry standards that prioritize safety in installation practices, ensuring that infrastructure can withstand various stresses encountered underground.

While the other thickness options are greater than the minimum required, they do not comply with the specified standards, as the 2-inch encasement strikes a balance between adequate protection and practicality in installation.