In which of the following applications is the use of type HDPE conduit allowed?

Type HDPE (High-Density Polyethylene) conduit is specifically designed for durability and resistance to various environmental factors, making it suitable for specific applications. Its use in cinder fill is permissible because the material can withstand the abrasive nature of the cinder and provides adequate protection for the conduits that carry electrical cables or communication lines.

Using HDPE conduit in cinder fill offers advantages such as resistance to moisture, chemicals, and temperature variations, which are essential in maintaining the integrity of the installations. This application ensures that the conduits remain effective and safe for long-term use in environments where traditional conduits may fail.

In contrast, other options such as direct burial of water lines, above-ground installations, and hazardous locations may not be suitable applications for HDPE conduits due to factors like exposure to varying environmental stresses, potential for damage, or compliance with specific code requirements that may dictate the type of conduit necessary for those situations.