Here are the details for the third dive of the day.
- Surface interval time: 3.5 hr. (210 min.)
- Gas supply: 11.1 L/80 cu. ft. (Cylinder was re-filled to 200 bar/3000 psi.)
- TOD: 15 m/49 ft.
- Planned dive time: 30 min.
- SAC rate: 16 L p/m or 0.58 cu. ft. p/m (taken from the second dive)
Which is the limiting factor when calculating the maximum allowable dive time? It will be either the NDL or the gas supply. The planned dive time and SAC rate were taken from the last dive. Therefore, the estimated dive time should be the same unless environmental factors have changed. So, the NDL will be the controlling factor. After 210 minutes (3.5 hours ) surface interval time, what are the new NDL pressure group designation and the adjusted allowable dive time? To find out, refer to Table 2. Find row G, and go across the row to locate where 3.5 hours would fall—between 2:59 and 4:25 hours. The pressure group designation is C.
Next, refer to Table 3 to determine the maximum allowable dive time. Find column C and the row for 18 meters/60 feet. The maximum allowable dive time is 33 minutes.