Which ANSI standard must PVC plastic pipe used for connecting gas pressure regulator vents conform to?

The correct answer is ANSI/UL 651, which is relevant for PVC plastic pipe used in gas applications. This standard focuses on the safety and performance requirements for underground rigid nonmetallic conduits and fittings designed for electrical and communication applications. In the context of connecting gas pressure regulator vents, it's essential that the materials used are certified for handling the specific pressures and potential chemical exposures associated with gas systems.

ANSI/UL 651 ensures that PVC pipes utilized in these applications provide the necessary structural integrity, durability, and resistance to environmental conditions, which is critical for maintaining safety standards in gas installations. Other standards listed, such as ANSI/UL 1002, ANSI/UL 737, and ANSI/UL 581, address different aspects of safety and performance for various types of piping and applications that are not specifically related to gas pressure regulator vent connections.