Shallow then deep dive.

[Brewingfisherman]

Yes I know I should plan deep dives then shallow dives.

My plan is to do 2 shallow dives 30 ft.

Then possibly use ean32 on my 2nd dives which are to 90 ft.

Scheduling and the people I want to dive with this would have to be the plan.

I will be diving with a computer and programming it as I need to.

My first 2 dives will be with a newbie and chances are bottom times will be fairly shortly.

 

[tursiops]

Yes I know I should plan deep dives then shallow dives.

My plan is to do 2 shallow dives 30 ft.

Then possibly use ean32 on my 2nd dives which are to 90 ft.

Scheduling and the people I want to dive with this would have to be the plan.

I will be diving with a computer and programming it as I need to.

My first 2 dives will be with a newbie and chances are bottom times will be fairly shortly.

What is your question?
If it is, "Is this OK?" the answer is yes. There was an entire DAN workshop on this issue, called "reverse profiles," with a report.
http://archive.rubicon-foundation.o...6789/4244/AAUS_ReverseProfiles.pdf?sequence=1

So long as you manage your nitrogen loading, you will be fine. Shallow-then-Deep does not manage nitrogen as well as Deep-then-Shallow; the later dives of the reverse profile give you more on-gassing rather than helping with off-gassing.

 

[Addicted2H2O]

Reverse profile diving is fine as long as you stay within NDLs. Like Tursiops said, deeper first is better, but it won't hurt you to do a reverse profile. I did one a couple weeks ago in the cenotes with my first dive bottoming out around 20ft and my second one at 107 ft, followed by a third dive to a maximum of around 30 ft. No issues noticed. Did normal profile dives the day before to 80 ft and 25 ft respectively. So you should be fine, especially diving EAN32. EAN36 would be even better if you can find it, but either will be better than air.

 

[Brewingfisherman]

Turiops, I should have proof read and thought about my post more before posting.

Shallow then deep is ok I understand. But mainly I wanted to get an opinion on using regular air before using an ean32 mix.

Shorbus.

I figured that using an ean mix would be beneficial to help reduce my nitrogen intake. I wanted an honest opinion about it. I'm going to use ean32 since my 90 foot dives I will not be on the seafloor. I am going use the more conservative mix so I can account for anything that may arise. It's a dive I have done before and haven't had any issues.

To both of you I owe you a bee . Thank you for a quick and informative answers.

 

[tursiops]

No problem using air-then-nitrox or vice versa, reverse profiles or not.
Just manage your nitrogen, and be conservative.
The way you have less nitrogen uptake is to stay far away from your NDL....if you dive right up to your NDL you are taking on the same amount of nitrogen with air or nitrox.

 

[lermontov]

No problem using air-then-nitrox or vice versa, reverse profiles or not.
Just manage your nitrogen, and be conservative.
The way you have less nitrogen uptake is to stay far away from your NDL....if you dive right up to your NDL you are taking on the same amount of nitrogen with air or nitrox.

vaguely recall an issue with some DC (oceanic pro plus ) not liking Nitrox then air - might be wrong ?

 

[Searcaigh]

There shouldn't be an issue with this, it's all down to managing the NDLs which your computer should display.

Some computers once used on "AIR" mode don't allow you to switch to Nitrox until after 24 hours, in which case use Nitrox mode at 21% and change later to 32% for your 90' dive.

 

[tursiops]

vaguely recall an issue with some DC (oceanic pro plus ) not liking Nitrox then air - might be wrong ?

Right. So you set it on 21% nitrox. Should be close enough! But not relevant here, he is diving air then nitrox.

 

[Outbound]

I might be incorrect, but I believe it is generally better to use nitrox first and then switch to air for subsequent dives rather than the other way around (if you have to switch at all; I would just use nitrox for all dives if possible). I recall seeing a video where an instructor worked through this using tables and the calculations resulted in nitrox being better for the first dive than the other way around. But in any event, so long as you manage your NDLs and your MOD for the nitrox dive, it shouldn't be an issue.

 

[Rooster59]

US Navy’s Thalmann algorithm has you ongassing exponentially but offgassing linearly for some compartment(s). That would make it more of an advantage to do your deeper dive first compared with the algorithms programmed in recreational dive computers. If I’m doing the numbers rightly, which is not a given.