If you are diving at a depth of 20 meters (66 feet) for 40 minutes, what is the minimum surface interval required for a second dive to 30 meters (98 feet)?

To determine the minimum surface interval required after a dive to 20 meters for 40 minutes before conducting a second dive to 30 meters, it's essential to consider factors such as residual nitrogen from the first dive and the increased depth of the second dive.

When divers ascend after a dive, nitrogen absorbed in the body during the dive must be released, and this process takes time. The deeper the first dive (20 meters) and the longer it is (40 minutes), the more nitrogen remains in the tissues upon surfacing. The second dive to 30 meters (98 feet) increases the risk of decompression sickness due to increased nitrogen uptake at that greater pressure.

According to dive tables or dive computers, specific surface intervals are necessary to allow the body sufficient time to off-gas excess nitrogen before descending to a deeper level. A minimum surface interval of 45 minutes would typically allow for a safer transition between dives, particularly with the increased risk associated with a deeper second dive.

In this scenario, the total time and depth of the previous dive combined with the depth of the upcoming dive necessitate a longer, more conservative surface interval for optimal safety. This ensures that the diver minimizes the risk of decompression sickness and other related issues. Thus, a minimum surface