What is the purpose of the one-third rule in diving?

The one-third rule in diving is primarily used to manage gas usage, specifically by determining how to allocate the available air supply during a dive. According to this guideline, divers should use one-third of their available gas supply for the descent and bottom time, one-third for the ascent, and keep one-third in reserve for emergencies. This strategy helps ensure that divers have enough gas to safely complete the dive and return to the surface, while also preparing for any unplanned situations that may arise.

By adhering to the one-third rule, divers can maintain a safe approach to their gas consumption and minimize the risks associated with running low on air before completing the ascent. This practice emphasizes safety and contingency planning, which are essential components of responsible diving behavior.