What is the objective of bringing a hand line down to bare mineral soil?

The objective of bringing a hand line down to bare mineral soil is to create a barrier against fire spread. When the ground is cleared to expose the mineral soil, it removes the combustible material such as grass, leaves, and debris that could otherwise allow a fire to continue moving. This bare line serves as an effective defensive measure to prevent flames from crossing to unburned fuel, effectively containing the fire within a designated perimeter.

While containing a fire is critical, the primary purpose of doing so is to halt its progression by eliminating the potential fuel that sustains it. Thus, clearing down to bare soil is a tactical maneuver that directly enhances fire control and protects surrounding areas from exposure to flames.