According to NFPA 58, plastic pipe should be used where?

The correct answer pertains to the guidance provided in NFPA 58 regarding the use of plastic pipe. According to the code, plastic piping systems are specifically approved for outdoor and underground applications, which helps ensure safety and integrity in environments where metal piping might be subject to corrosion or environmental damage.

When installed underground, plastic piping has advantages such as resistance to corrosive soil conditions and the ability to reduce the risk of leaks. These properties make plastic an appropriate choice for underground distribution systems of liquefied petroleum gas (LPG), where weather and soil conditions can impact the longevity and reliability of the material used.

In contrast, indoor installations, commercial applications, and specific areas like residential kitchens may have requirements that favor different materials such as steel or copper, predominantly due to factors like fire safety, mechanical strength, and regulatory compliance in those specific environments. Thus, option B accurately reflects the standards established in NFPA 58 for the use of plastic piping in LNG applications.