Scenerio: You are going out on a boat for 2 dives. The plan is to do both dives at similar depths, with the second maybe a little shallower, max 70ft. Your two Nitrox tanks are 32 and 40. Which order do you use them and why.
Diving Nitrox
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underwasser bolt
Contributor
40 first because my nitrogen loading will be less; i am only doing 2 dives so a 24 hour PPO2 should not become an issue. the next dive i do the 32 to a more shallow depth. If i have some 40 left I could hang it on the line at 20 feet and do my safety stop with it in order to load even less nitrogen for the dive. the logic being that at these depths and percentages you are likely do me nitrogen limited and not o2 limited. actually, at these depths with a single tank you will probably run out of gas before you hit either limit.
OP
They are considered equal.
Doesn't really matter if both are shallow (70') and about the same depth. MODs are 111' and 82' (32 and 40%). The only thing I could think of making a difference is if one dive was shallow, in the 70' range, but was on a wall with an unlimited bottom, and one was a 70' with a defined 70' bottom. In this case I'd use the 32 on the wall dive, incase you had to go deep to rescue a buddy. Other than this unique case, I wouldn't worry about it.......
1_T_Submariner
Contributor
I would do the 32% first to make my EAD deeper on the first dive than the second.
I have done this with air and 32%. But in that case MOD was the limiting factor on the first dive.
I'm interested in other more experienced responses.
I have done this with air and 32%. But in that case MOD was the limiting factor on the first dive.
I'm interested in other more experienced responses.
If one dive was better than the other id maximise dive time on it by shortening the time on the better dive (and if needed doing some deco).
Both being equal id probably use the 40% last for no real reason.
Generally here though you get a decent deep wreck as your first dive and a ****ty drift for the 2nd.
Both being equal id probably use the 40% last for no real reason.
Generally here though you get a decent deep wreck as your first dive and a ****ty drift for the 2nd.
emttim
Contributor
I would do the EANx40 blend on the first dive too for the same reason...less nitrogen loading and it shortens the surface interval as much as possible to get back to a reasonable nitrogen level before the second dive. Obviously, the less nitrogen you load up on the first dive, the more bottom time you have on the second dive.
fppf
Contributor
I would plan my dives ahead of time and bring 2 tanks of 36.
But given your question, I would use the hotter mix on the second dive because you will have the higher risk of DCS on a repeditive dive.
But given your question, I would use the hotter mix on the second dive because you will have the higher risk of DCS on a repeditive dive.
emttim
Contributor
Why would that be enough of a risk to even affect your dive plans? If you do the recommended 3 minute safety stop at 15', and ascend no quicker than 60'/min or whatever your dive computer tells you, then there should be such a minimal amount of silent bubbles in your body that the risk of DCS is almost non-existent....especially after only 2 dives. Either way you will probably end in the same pressure group or close to it anyhow.
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