Surface Interval

The time spent at the surface between dives, during which the body releases residual nitrogen and no-decompression limits recover.

The surface interval is the time between surfacing from one dive and descending on the next. It is when your body off-gasses: the nitrogen absorbed during the dive leaves your tissues gradually while you breathe at surface pressure. The longer the interval, the less residual nitrogen you carry into the next dive and the more generous its no-decompression limits become. On tables the interval moves you to a better pressure group; on a computer it visibly rebuilds your available no-stop time.

Most operators structure the day around intervals of about an hour or more between dives, and many agencies suggest a minimum of 1 hour when diving close to the limits. The interval before flying is its own category: DAN's guidance of at least 12 hours after a single no-deco dive and 18 hours after repetitive dives is really a special surface interval requirement.

Use the time well: rehydrate, warm up, eat something, debrief the dive with your buddy, and plan the next dive together while conditions are fresh in your mind. Avoid heavy exertion and hot showers right after diving, both of which are thought to encourage bubble formation, and resist the temptation to shorten the interval because the boat schedule feels slow.