If a diver performs a 20-minute dive to 40 meters (131 feet), what is the minimum surface interval required before a second dive at 10 meters (33 feet) for 25 minutes?

To determine the minimum surface interval required before the second dive, it is important to understand the implications of the first dive, which was to a depth of 40 meters for 20 minutes. At this depth, according to standard dive tables and the principles of decompression sickness risk, the diver would accumulate a significant amount of nitrogen in their tissues, necessitating a certain amount of time at the surface before safely diving again.

The planned second dive is to a shallower depth of 10 meters for 25 minutes. While shallower dives typically result in lower nitrogen absorption and thus might allow for shorter surface intervals, the diver must still observe safety limits based on the first dive's profile.

Referring to dive tables or using software for decompression calculations, divers can find that the maximum allowable surface interval (or the minimum surface interval needed to avoid decompression sickness) directly correlates with the depth and duration of both dives. In this scenario, the 20-minute dive at 40 meters establishes a baseline for required rest to allow for safe off-gassing of nitrogen.

In this case, a surface interval of 45 minutes is the minimal time suggested to allow adequate off-gassing and to mitigate the risk of decompression sickness before the subsequent dive. This