2 tanks: Nitrox and Air - Which one do you use first?

[GrierHPharmD]

I usually dive only Nitrox or only air on the typical 2-tank dive excursion, but today I have a nitrox fill and an air fill, and I'm going diving. As I was thinking things through, I began to wonder if there is an advantage to diving the nitrox tank first or saving it for the second dive.

I looked through my nitrox course materials (PADI and IANTD) and couldn't find any answers, so I thougth I'd post the question here.

The dives in question are shallow (~25 fsw), with long (90-120 minute) bottom times.

I realize that I may incur flames and peals of derisive laughter for this question, much as H2Andy did with his question about using water for weight, but it seems to me that exporing these little subtle applications of scuba knowledge is useful.

Thanks in advance,
Grier

 

[Charlie99]

The dives in question are shallow (~25 fsw), with long (90-120 minute) bottom times.

In this case of two shallow dives of the same depth, I'd dive air first, then nitrox. The 2nd dive on nitrox kind of works like a an extended safety stop to minimize the loading in the slow compartments.

OTOH, the last pair of dives where I used 1 tank of air and 1 of nitrox were the Key Largo wrecks Spiegel Grove and the Duane. In each case, the 110' wreck dives were followed by shallow reef dives. In this sort of sequence, I prefer to dive the wreck on nitrox, and use air for the 25' max shallow reef.


You can play around with various computer simulators or decompression programs, www.gap-software.com , for example to see the effect of your choices.

 

[matt_unique]

I usually dive only Nitrox or only air on the typical 2-tank dive excursion, but today I have a nitrox fill and an air fill, and I'm going diving. As I was thinking things through, I began to wonder if there is an advantage to diving the nitrox tank first or saving it for the second dive.

I looked through my nitrox course materials (PADI and IANTD) and couldn't find any answers, so I thougth I'd post the question here.

The dives in question are shallow (~25 fsw), with long (90-120 minute) bottom times.

I realize that I may incur flames and peals of derisive laughter for this question, much as H2Andy did with his question about using water for weight, but it seems to me that exporing these little subtle applications of scuba knowledge is useful.

Thanks in advance,
Grier

If the dives will be the same depth and time, use the Nitrox tank second since you will be surfacing with a greater NDL safety margin.

--Matt

 

[Don Burke]

I usually dive only Nitrox or only air on the typical 2-tank dive excursion, but today I have a nitrox fill and an air fill, and I'm going diving. As I was thinking things through, I began to wonder if there is an advantage to diving the nitrox tank first or saving it for the second dive.

I looked through my nitrox course materials (PADI and IANTD) and couldn't find any answers, so I thougth I'd post the question here.

The dives in question are shallow (~25 fsw), with long (90-120 minute) bottom times.

I realize that I may incur flames and peals of derisive laughter for this question, much as H2Andy did with his question about using water for weight, but it seems to me that exporing these little subtle applications of scuba knowledge is useful.

Thanks in advance,
Grier

The tables show an advantage to doing the dive with the deeper EAD first. Since both dives are to the same depth, air first and then nitrox would put you in a better position on the tables.

 

[glbirch]

If you're interested, DandyDon raised this point a while ago in this thread: http://www.scubaboard.com/showthread.php?threadid=54761&s=

 

[GrierHPharmD]

Thanks for the quick response. I suspected that I should use the Nitrox bottle second, but it's nice to see that somebody else had wondered about this.

Oops, it's time to dive,
Grier

 

[Scubaguy62]

Grier, trust me, do the nitrox last...If you don't you're going to end up with a greater amount of CO2 in your system and a splitting headache to go along with it.

It happened to me about 2 1/2 yrs ago when I did two dives to 40'. Why do you think I dive nitrox 100% of the time now???

Good luck tonight buddy...wish I could join you!!!

 

[glbirch]

Grier, trust me, do the nitrox last...If you don't you're going to end up with a greater amount of CO2 in your system and a splitting headache to go along with it.

It happened to me about 2 1/2 yrs ago when I did two dives to 40'. Why do you think I dive nitrox 100% of the time now???

Good luck tonight buddy...wish I could join you!!!

I'd be interested in hearing the reasoning on this. Are you saying that breathing Nitrox causes lower CO2 retention in your body? I would suspect shallow breathing to be the more likely possiblility.

 

[perpet1]

Grier, trust me, do the nitrox last...If you don't you're going to end up with a greater amount of CO2 in your system and a splitting headache to go along with it.

It happened to me about 2 1/2 yrs ago when I did two dives to 40'. Why do you think I dive nitrox 100% of the time now???

Could you please explain your rational for this post. I am NOT saying nor am I implying that you are wrong just asking for an explaination.

 

[Rick Inman]

Depths are so shallow that, if you are one of those people (like I sometimes am) that feel better and more aleart after a Nitrox dive, you might use the Nitrox first so you are up for the 2nd. Just a thought...