What is the rule of thirds in scuba diving?

The rule of thirds in scuba diving is a guideline for managing air supply effectively throughout a dive, ensuring safety during ascent and during any unplanned situations. According to this rule, divers allocate their air supply into three equal parts: one-third is used for the descent and bottom time, one-third is reserved for the ascent, and the final third acts as a safety reserve.

This approach promotes safety by ensuring that divers have adequate air for a safe ascent, as well as a buffer for unexpected circumstances, like needing to extend bottom time or dealing with unforeseen situations that may delay their return to the surface. By adhering to this rule, divers can minimize the risks associated with low air supply and ensure they can respond to emergencies while still enjoying their dive.