Metallic underground ducts without an approved protective coating must be encased in a minimum of how many inches of concrete?

The requirement for encasing metallic underground ducts without an approved protective coating in a minimum of two inches of concrete is in place to enhance the durability and protection of the ducts. This specification helps to prevent corrosion and damage from external forces such as soil movement or accidental impact from surface activities. The use of concrete provides a barrier that can shield the metallic ducts from moisture and other harmful environmental factors that may lead to deterioration over time.

By encasing the ducts in a minimum of two inches of concrete, the design supports compliance with safety and longevity standards stipulated in the mechanical code, ensuring that underground installations remain functional and codes are adhered to for the protection of infrastructure and public safety.