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Hi Steve, > So.....the $64,000 question...is there anyone out there with experience > with mutliple Trimix dives in a single day ? I had heard that some groups in > the USA might be doing this & would like some feedback, either positive or > negative on how well it works out. I'll have to check my log book to confirm, but off the cuff I would say that the MAJORITY of trimix dives I have done (both open circuit and with the rebreather) have been dives where I have done more than one trimix dive in a single day (does that qualify as enough real-world experience? :-) You see, a lot of the trimix diving I have done is in remote localities - mostly Rarotonga and Papua New Guinea. I have only a limited window of time to work on these expeditions, so I have tried to maximize the amount of exploration time in the windows. I have NEVER had any DCS-related problems on any of my multiple-trimix diving days. A couple of rules of thumb that I follow are: 1) never let the bottom time of any single dive on a multiple dive day exceed 60 minutes; 2) Go heavy on the helium - especially on the first dive (helium off-gasses faster during the surface interval); 3) Allow at least four, preferably 6 hours between dives; 4) go extra heavy on the deep stops and 20' O2 (or EAN80) stop on the first dive; 5) make the "harder-core" of the two dives on the first dive; 6) pad the O2 shallow stop on the last dive heavily (if possible, maybe use EAN80 on the first dive, then pure O2 on the second dive - but that all depends on what sort of O2 exposure you want to subject yourself to). Another rule of thumb I'm working on is whether to breathe O2 on the surface interval. It helps to purge extra nitrogen (the helium purges fine just breathing air), but I just don't know to what extent cumulative O2 exposure damages lung tissue or increases probability of convulsion. Until I feel more comfortable on the answers to those, I'm not sure whether O2 breathing on the interval is a good idea. I think in general you want to be much more "bubble-conscious" than "compartment-conscious" when making decisions about deco. The dissolved gas loading you start the second dive with will probably be nill compared with the bubble load you start the second dive with in terms of predisposing you to getting nailed after the second dive. In other words, go heavy on the deep stops on both dives, but particularly on the first dive. That's all I can think of for now. I'll let you know if I think of anything else. Aloha, Rich P.S. As with the deep stops article - you know the consequences of following decompression advice from a fish-nerd!
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