Scuba Diving: Calculating Maximum Allowable Time for a Second Dive

When planning a second dive following a surface interval, several factors need to be considered to determine the maximum allowable time underwater:

1. Depth of the Second Dive:

The depth of the second dive plays a crucial role in calculating the maximum allowable time. Deeper dives require shorter bottom times to mitigate the risk of decompression sickness.

2. Duration of the First Dive:

The duration of the initial dive impacts the residual nitrogen in your body. Longer dives result in higher nitrogen levels, affecting the allowable time for subsequent dives.

3. Surface Interval:

The surface interval between dives is crucial for allowing sufficient time for off-gassing nitrogen. Shorter surface intervals may require shorter subsequent dive times to stay within safe limits.

4. Residual Nitrogen Time:

Residual nitrogen time refers to the remaining nitrogen in the body after a dive. This residual nitrogen must be accounted for when calculating the maximum allowable time for a subsequent dive.

After a 30-minute surface interval following a 33-minute dive at 18 m/60 ft, the residual nitrogen time is approximately 25 minutes. For the second dive planned at 17 m/58 ft, the maximum allowable time can be determined by subtracting the residual nitrogen time from the no-decompression limit at that depth.

For the provided data, the maximum allowable time for the second dive at 17 m/58 ft is approximately 75 minutes. This calculation ensures that the diver stays within safe diving limits and minimizes the risk of decompression sickness.

It's important to note that these calculations are based on standard air diving and ideal conditions. Divers should always consult a certified instructor, use appropriate dive tables, and consider individual health factors when planning dives.