Question on the Padi RDP

[brnt999]

I have a question on the Padi RDP. After the first dive of a series, and after the surface interval, you arrive at a new pressure group. You move to table 3 and match your new pressure group to the depth of your next dive and it tells you your residual nitrogen time and your adjusted no decompression limits. The residual nitrogen time in any pressure group gets smaller the deeper you dive. Why is that? Why should the nitrogen in your system be less the deeper you dive?

 

[WheelsUSN]

The pressure group letter indicates a theoretical amount of nitrogen in your system. The number that you are looking at in table three isn't a direct representation of the amount of nitrogen in your system, it is the amount of time that you would have to spend at that depth to get that amount of nitrogen in your system. The deeper you go and the more pressure you are under, the faster your body absorbs nitrogen so the less time it takes to get to the same level.

Another way to look at it is to choose a pressure group, for example 'N', and look at table Three. At 50 feet your RNT is 44 minutes. Now look at table one and see how long it would take to get to pressure group 'N' on your first dive of the day, the answer will also be 44 minutes. Staying with pressure group 'N', if you look at table three for the RNT at 100 feet it is 19. If you look at table one to see how long it would take you to be in pressure group 'N' on the first dive of the day it will also be 19 minutes.

 

[Easdem]

Great answer.

The pressure group letter indicates a theoretical amount of nitrogen in your system. The number that you are looking at in table three isn't a direct representation of the amount of nitrogen in your system, it is the amount of time that you would have to spend at that depth to get that amount of nitrogen in your system. The deeper you go and the more pressure you are under, the faster your body absorbs nitrogen so the less time it takes to get to the same level.

Another way to look at it is to choose a pressure group, for example 'N', and look at table Three. At 50 feet your RNT is 44 minutes. Now look at table one and see how long it would take to get to pressure group 'N' on your first dive of the day, the answer will also be 44 minutes. Staying with pressure group 'N', if you look at table three for the RNT at 100 feet it is 19. If you look at table one to see how long it would take you to be in pressure group 'N' on the first dive of the day it will also be 19 minutes.