After a 15-minute dive to 40 meters (131 feet), what is the surface interval time needed for a repetitive dive to 20 meters (66 feet) for 25 minutes?

To determine the surface interval time needed for a repetitive dive after a previous dive, it is essential to understand the effects of nitrogen absorption and the necessary decompression requirements.

When a diver makes a dive to a depth of 40 meters (131 feet) for 15 minutes, the body absorbs nitrogen based on the depth and duration of the dive. Following this initial dive, the diver needs to allow sufficient time on the surface for the body to off-gas or eliminate the excess nitrogen before completing another dive. This is especially important at increased depths where nitrogen absorption is greater.

For a subsequent dive to 20 meters (66 feet) for 25 minutes, the diver is still diving within the moderate range of nitrogen exposure, but because the first dive was deeper and involved a longer exposure time, a careful assessment of the surface interval is crucial to avoid decompression sickness.

The established no-decompression limits as per diving tables or dive computers indicate a necessary surface interval to ensure the diver can safely conduct a follow-up dive. In this case, a surface interval of 60 minutes has been recommended based on standard dive safety practices. This period allows the body adequate time to effectively expel the absorbed nitrogen after the deeper dive before attempting another dive, thereby ensuring safety