What is the minimum encasement requirement for metal ducts installed in or under concrete?

The minimum encasement requirement for metal ducts installed in or under concrete is typically set to ensure the protection of these ducts from physical damage and to maintain their integrity over time. Encasement helps to guard against corrosion, particularly in environments where moisture may be present within the concrete.

In this context, a minimum thickness of 2 inches for the encasement is necessary to provide adequate protection. This thickness ensures that there is sufficient concrete cover to shield the metal ducts from any potential impacts or stresses associated with the concrete structure.

The other choices represent insufficient encasement thickness, which may not offer adequate protection against the potential risks. A thinner encasement might expose the ducts to corrosion or physical damage, thus undermining the duct's performance and longevity. Therefore, adhering to the 2-inch encasement requirement is crucial for ensuring the durability and reliability of metal ducts in such installations.