What is the minimum surface interval required after a double dive to 90 feet for 20 minutes followed by a dive to 80 feet for 20 minutes?

To determine the minimum surface interval required after a double dive, it is essential to consider the cumulative nitrogen loading from the two dives. In this scenario, a dive to 90 feet for 20 minutes is followed by a dive to 80 feet for another 20 minutes.

When divers engage in multiple dives, the nitrogen absorbed during each dive accumulates, which can lead to a greater risk of decompression sickness if the surface interval is not adequate. The required surface interval can be derived from decompression tables or dive computer calculations, which account for both the depth and duration of the dives.

For the dives in question, the recommended surface interval to allow for the safe elimination of nitrogen from the body is based on the total exposure. For a dive to 90 feet for 20 minutes, along with an immediate second dive to 80 feet for another 20 minutes, a minimum surface interval of 1 hour and 5 minutes would be necessary to ensure that the body can safely off-gas the accumulated nitrogen safely.

This calculation reflects a sound understanding of dive tables and the physiological factors at play, recognizing that dives at greater depths increase the amount of nitrogen absorbed and subsequently necessitate longer surface intervals to mitigate risks during subsequent dives or after surface intervals