In regard to the installation of underground gas piping, what dictates an increase in cover from 12 inches to 18 inches?

The requirement for an increase in cover from 12 inches to 18 inches for underground gas piping is primarily dictated by the potential for external damage. When gas lines are buried, the depth to which they are placed serves as a protective measure against physical damage. If the location has a higher risk of heavy traffic, excavations, or any other potential hazards that could compromise the integrity of the piping, deeper installation is necessary. This additional depth provides an extra layer of safety and reduces the risk of accidental damage from above-ground activities.

As for other options that discuss different aspects like temperature fluctuations, proximity to electrical lines, or soil composition, they do not have a direct influence on the required depth of cover for protection against physical damage. While these factors might have relevance in other contexts within gas installation practices, they do not warrant an increase in cover on their own in the same way that the potential for external damage does.