What does the "thirds rule" refer to in diving planning?

The "thirds rule" in diving planning is a crucial concept that enhances safety during underwater excursions. This rule dictates that a diver should allocate their air supply into three equal parts: one-third for the outbound journey to the dive site, one-third for the return journey back to the entry point, and the final third to serve as a reserve for emergencies. This strategy ensures that divers maintain a safety margin in case they encounter unexpected situations, such as needing to ascend early or address unforeseen difficulties during their dive.

This approach encourages prudent air consumption and promotes awareness of the diver's air supply throughout the dive. By adhering to the thirds rule, divers can better prepare for safe ascents and contingency planning. This rule underscores the importance of having a plan that accounts for variables that may arise, reinforcing a culture of safety in diving practices.