Diving, Climbing to Altitude, and again diving.

[Niazi]

This is my second post after 4 years. Not sure if my question belongs here.


Here is my question:-


I dived at 100 feet at sea level for 25 minutes. That made my RGD 'H' as per US Navy Dive manual table 9-7. I was immediately ordered to fly to 3600ft above sea level for salvage dive in a lake. I had to fly in an uncompressed helicopter which would ascend to a maximum altitude of 4000ft above sea level . Therefore as per US navy dive manual table 9-6 I had to wait for 1 hours 6 minutes before rising to altitude of 4000ft.


After waiting 01:06 my RGD reduced to 'G' and I was air lifted and dropped near the lake.


Now as per table 9-5 repetitive group associated with initial ascent to altitude should be 'C' because I have climbed 4000 ft.


My question is will I take into consideration group 'G' or 'C' to calculate Residual Nitrogen Time for my next dive? Or will I be taking both Residual Nitrogen Time of both the groups and adding them? Or will I be only considering the larger of the two?


Thanks.

 

[ajduplessis]

Worst case (shorter dive) in my book always win.

 

[runsongas]

the two RNT should be treated as additive i believe. in the reverse situation where you climb to altitude first, you would start at group C and then add your bottom time for your dive, so it should be the same for the reverse.

 

[knotical]

Great question. Haven’t seen it covered in the books. The two pressure groups represent residual N2 pressures from two different causes, so as everyone (including you) has suggested, they need to both be considered. Is G + C = J the best approach? Not sure, but it seems reasonable. Maybe make it a K for unknowns. On the other hand, you were off-gassing during the flight and set-up at altitude, so that would tend to lower your pressure group a bit (back to J?). The longer you can wait while acclimating at elevation, the better.

 

[Niazi]

Yes..... sounds reasonable. When in doubt added safety is the best answer. Adding G +C to make it a J sounds perfect.