Nitrox and repetitive dives, what mix first?

[treywilly]

doing !!

 

[b1gcountry]

You could always plug the numbers into a deco program and see which has you coming out cleaner.

To me, however, the question is somewhat moot. If I'm heading out for two dives, I'm going to be diving the same gas on both dives. It just makes everything a whole lot easier, and it minimizes the risk of grabbing the wrong tank for a deeper dive.

Tom

 

[b1gcountry]

You could always plug the numbers into a deco program and see which has you coming out cleaner.

To me, however, the question is somewhat moot. If I'm heading out for two dives, I'm going to be diving the same gas on both dives. It just makes logistics a whole lot easier, and it minimizes the risk of grabbing the wrong tank for a deeper dive.

Tom

 

[scubafanatic]

I'm late to the party and I haven't the experience to back up my opinion, but FWIW I would dive the richer mix on the deeper dive (up to appropriate PO2 limits et cetera). My reasoning has nothing to do with the accumulation of nitrogen in the tissues during the dive itself, rather it's a question of having a slightly better gas gradient when ascending from depth. I'm going to do more ascending and reducing more ambient pressure on the deeper dive, so adding in an improved gradient is going to give me more than using nitrox on a dive with very little deco.

Assuming I stay within minimum deco limits (and I have no business doing anything else), I am going to be doing stops from 30' on a shallow dive and from 50% of average depth on a deeper dive. Perhaps from 50'. So on the deeper dive I'm going to be spending at least 66% more time decompressing, so I'm going to pull a figure out of my a-- and say I'll get 66% more benefit diving Nitrox on the deeper dive.

Okay, I know this is just conjecture, but this is my thinking.

...well, in Cozumel, when I dove with Liquid Blue ( a high-end advanced diver oriented dive op), the custom for a 2-tank outing was EAN 32 for the first/deeper dive...and EAN 36 for the 2nd, shallower dive.....I 'logic' being, no reverse profiles and reduced risk of violating a mixes MOD.

Karl

 

[Reg Braithwaite]

...well, in Cozumel, when I dove with Liquid Blue ( a high-end advanced diver oriented dive op), the custom for a 2-tank outing was EAN 32 for the first/deeper dive...and EAN 36 for the 2nd, shallower dive.....I 'logic' being, no reverse profiles and reduced risk of violating a mixes MOD.

I may have misunderstood the original question, I thought the scenario was that you had one tank of air and one tank of Nitrox, and neither dive violates the Nitrox's MOD. But given access to Nitrox on both dives and your choice of mix, conventional wisdom is to dive the "best mix" for each dive.

The minority point of view is that even when you can have any mix you like up to 40%, for the vast majority of dives within recreational limits the additional benefit of a richer mix on a shallower dive is insignificant compared to the consequences of accidentally exceeding a mix's MOD and suffering O₂ Toxicity convulsions and drowning, or the trouble of having to fiddle with different no-stop limits/minimal deco limits for each dive. This lowers the risk of accidentally mis-planning a dive.

Therefore some folks choose to only dive one Nitrox mix at all times. There is only one MOD to remember and one "table" to dive. I subscribe to this theory: I was also in Cozumel with Aldora last week, and I requested two tanks of EAN32 for my dives. That way there was no need to worry about the possibility of accidentally selecting the wrong tank for a dive or of exceeding the dive limits.

I could be misrepresenting the reasoning, but those two reasons are good enough for me, so I'm a full-time EAN32 man now.

 

[Blackwood]

To me, however, the question is somewhat moot. If I'm heading out for two dives, I'm going to be diving the same gas on both dives. It just makes logistics a whole lot easier, and it minimizes the risk of grabbing the wrong tank for a deeper dive.

I'll keep that in mind next month when I'm doing a 165' dive followed by an 85' dive.

 

[Reg Braithwaite]

I'll keep that in mind next month when I'm doing a 165' dive followed by an 85' dive.

We were talking about diving Nitrox in single tanks Let me sit at your feet and learn how to dive on the Internet from you, O Master. What mix of Nitrox will you be diving to 165' and what size of tank do you use that might be interchangeable between 165' and 85' dives?