In caves there is the &quot;rule of 6ths&quot; which means of your available gas, you plan to complete the dive with 5&#x2F;6ths left. Open water divers usually plan to surface with 1&#x2F;3rd remaining. There is a <i>lot</i> of redundancy built into any dive plan, every piece of kit has a backup, etc. No-one who actively enjoys or seeks out risks or adrenaline lasts long in the cave diving scene, because no-one will dive with them.