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> Imagine an air dive to 25msw and a nitrox-36 dive to 30msw. [...] > someone should run a series of test profiles, using all four > combinations of depth and gas sequence (keeping all else constant), Well, I have nothing better to do, so I'll take a stab at it. All the numbers here (in particular, %CNS) are from standard tables in the IANTD EANx Student Workbook. Somebody else can calculate %CNS out exactly if they want :-). For each combination, I maximized the no-stop bottom time on each dive, assuming a 2 hour SIT between each pair of dives. Note that for the 25MSW dive, I used the 27MSW column on my (American) dive tables. Dive 1: Dive 2: Totals: 30MSW, Air 25MSW, EAN36 Group J BT: 25 mins 24 mins 49 mins %CNS: 8.3 20.0 28.3 25MSW, Air 30MSW, EAN36 Group I BT: 30 mins 17 mins 47 mins %CNS: 6.7 16.7 23.4 30MSW, EAN36 25MSW, Air Group H BT: 40 mins 6 mins 46 mins %CNS: 33.3 2.2 35.5 25MSW, EAN36 30MSW, Air Group H BT: 50 mins 3 mins 53 mins %CNS: 33.3 2.8 36.1 Assuming that these numbers are right :-), the best overall results seem (to me, anyway) to be obtained by doing Air on the first dive, whether that is the deep or shallow dive. This gives decent bottom times on the repetitive dives, as well as the overall lowest total %CNS. Since we teach that O2 is less forgiving than N2, that seems to be the safest sequence to follow. I might give a slight advantage to doing Air/Shallow first, since you only sacrifice two minutes of bottom time to gain a one letter group improvement in the N2 loading, combined with the lowest total %CNS. It's pretty much a toss-up, though. Any other comments or observations? -JimG
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