If a dive team went to 60 feet for 40 minutes and surfaced for one hour, how long can they dive if they want to do a second dive to 50 feet?

To determine how long the dive team can safely dive to 50 feet after spending time at 60 feet, it is necessary to understand the concept of residual nitrogen time or surface intervals in relation to the dive tables or a dive computer.

After the first dive to 60 feet for 40 minutes, the body retains nitrogen that needs time to off-gas during the surface interval. The one-hour surface interval does help reduce that residual nitrogen, but the time at 60 feet and the total nitrogen saturation will impact the allowable bottom time for the subsequent dive.

Considering the depth of the second dive is shallower (50 feet) than the first dive (60 feet), generally, a dive to a lesser depth tends to allow more bottom time. Dive tables indicate that the no-decompression limits at various depths dictate how long divers can stay at those depths.

Since the team has already spent time at a deeper depth, and they have allowed for some off-gassing during the one-hour surface interval, the conservative approach often taken in diving is to limit the second dive length accordingly to avoid exceeding safe nitrogen loading.

The recommendation of 30 minutes is based on these calculations and considerations using the dive tables. It's essential to always err on the side of safety