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Course Outline

The next limitation to consider, similar to the first dive, is the gas supply limit. This is the same as it was for the first dive.

In summary, the following are limitations for the second dive.

  • NDL: 33 min.
  • Gas supply: About 40–50 min.
  • TOD: 15 m/49 ft.

So, here is the plan for the second dive: maximum depth is 15 meters/49 feet for no longer than 30 minutes or 50 bar/750 psi, which is the first limit to reach. (Note: On pressure gauges, the closest reading you could see is 50 bar/700 psi.)

After the second dive of the day, what is the NDL pressure group designation? Let’s assume that the actual dive was to 15 meters/49 feet for 30 minutes. You know you had excess nitrogen carried over from the first dive before you started the second dive. Refer to Table 3. In the row for 18 meters/60 feet and column C, the excess nitrogen equated to 17 minutes (light blue cell).

To work out your pressure group designation after the second dive, take the 17 minutes of remaining nitrogen time (RNT) from the first dive, and add it to the actual bottom time (ABT) of the second dive—30 minutes. The total bottom time (TBT) is 47 minutes. Refer to Table 1.

Residual Nitrogen Time (RNT) + Actual Bottom Time (ABT) = Total Bottom Time (TBT)

The pressure group designation is now G.

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