Where must CNG appurtenances and equipment be listed?

Answer: C — By a nationally recognized testing laboratory

The correct answer highlights the importance of CNG appurtenances and equipment being listed by a nationally recognized testing laboratory. This is crucial because these laboratories have established standards and protocols that ensure the safety, reliability, and performance of CNG equipment. Being recognized on a national level indicates that the laboratory operates under stringent guidelines set by authorities such as the American National Standards Institute (ANSI) or the Occupational Safety and Health Administration (OSHA), ensuring that the equipment meets regulatory compliance and industry standards. In the context of CNG safety and operation, using equipment that has been certified by a nationally recognized testing laboratory helps to reduce the risk of accidents or failures. It also promotes consistency across different regions and suppliers, as these laboratories follow uniform testing procedures recognized throughout the country. This is important not only for operational safety but also for public confidence in the use of CNG as an alternative energy source.