Gas piping that is not protected can be installed above grade in which approved locations?

Gas piping that is not protected can be installed above grade in recesses or channels as these locations provide some degree of protection against physical damage and environmental factors. Recesses or channels allow the piping to be somewhat shielded while still being accessible for maintenance or inspection. The design of these areas can help to mitigate risks associated with exposure, such as accidental impact, which could compromise the integrity of the gas piping.

In contrast, open fields may not offer any protection from environmental hazards or physical damage, making them unsuitable for unprotected gas piping. Basements, while enclosed, are typically considered indoor environments where proper protective measures must be applied to prevent issues like corrosion or accidents. Greenhouses might also expose the piping to unique conditions such as increased humidity or physical interactions that could lead to deterioration or damage over time. Thus, utilizing recesses or channels presents a balanced approach to ensuring safety and functionality in the installation of gas piping.