Where can plastic pipe, tubing, and fittings used to supply fuel gas be utilized?

The correct choice reflects the specific applications where plastic pipe, tubing, and fittings can be safely and effectively used in the context of fuel gas supply. Plastic piping systems are designed to withstand certain environmental conditions and are specifically suited for outdoor installations, particularly when they are placed below ground.

When installed underground, these plastic pipes are protected from environmental stresses such as UV radiation, extreme weather conditions, and physical damage that could occur when they are above ground. The underground application allows for a direct and safe route for fuel gas without the risks associated with above-ground structures, such as accidental impacts or exposure to heat sources.

In contrast, options that suggest indoor usage do not align with the guidelines for plastic materials, as they typically require additional protections and are not rated for certain indoor applications where they may be exposed to higher temperatures or potentially damaging conditions. Additionally, the mention of above-ground installations, especially in outdoor settings, introduces concerns regarding the durability and exposure of plastic pipes to environmental hazards. Thus, the utilization of plastic pipe, tubing, and fittings specifically for outdoor and underground contexts is essential for ensuring safety and compliance with the codes associated with fuel gas supply.