Nitrox 32 first dive, air second dive?

[DandyDon]

It sounds like you are diving those pretentious computers that penalize you 10% of safe diving standards so they can claim to be safer - a smoke & mirrors show that has sold many.

If you want to dive nitrox on the first, go with 32% as there are some deeper dives there that I do enjoy. I might incur a couple of minutes of deco even on my "liberal" computers that are actually no more liberal than accepted safe standards approved by all agencies, but I clear those easily on ascent and safety stop, which are more important factors in avoiding hits. I don't remember the bottom for 32% tho so you may need to watch that closely, a bigger risk than nitrogen loading. I don't mind a short drip to 150 feet on rare occasion, but you can watch me from above. I think Cathedral can be done on 32% without hitting your nitrox bottom.

After a 60 minute SI, there is just no need in doing nitrox again for the shallow dive. Your computer includes planning mode doesn't it? Check it.

$70 over 7 days is money well spent on an additional factor of safety.

DAN studies do not support that myth. Nitrox gives longer NDLs which is great on square bottom wreck diving, but really does not add value or safety on multilevel reef dives. Your ascents, safety stops, floating stops, and minimum activities after the dive are more important.

I'm assuming that the next morning we're all cleared and ready to start loading from scratch again.

Theoretically, you're virtually clean after 90 minutes according to tables, but your computer will show time to fly which is more realistic. There is still some buildup left, but too small to calculate.

 

[tomhooper]

I notice a fairly substantial difference. Diving on air, I'm usually in bed asleep by 10 or earlier. On Nitrox I can go get wild.
Of course I'm an old.

 

[deepsea21]

We've been diving for 15 years now and Coz has been an annual destination most of those years. We've always been on air as we've never had a reason to get Nitrox certified. The last three years we've been diving with Tres Pelicanos in Coz after switching from our prior dive op that was sold to new management. On 3P's boats there is always a mix of divers... Some dive Nitrox on one dive, others on both dives but the majority dive air. If you were running up against your NDL on air simply adjust your dive profile. Do you really need to be at 80-90ft for that long where all of the color is gone and everything looks blah anyways? As we enjoy UW photography and max bottom time we almost always hang about 15-20 feet above the majority of the group as do other UW photography divers where there's more light, the color is far better, and quite frankly we can see and find far more sea life and critters. In my opinion, deeper just means shorter, darker, and less to see... NOT better! If you aren't an air hog which I am guessing you are not because you ran up against NDL limits before running low on air, just hang shallower. Hanging 15-20 feet above the group that may be diving air or NItrox will result in you being the last to surface. Even the Nitrox divers will have surfaced before you as they chose deeper. The only site I've been diving in Coz where we could have benefited from Nitrox (as I think Devils Throat is a waste of a dive and can view that dive on youtube for free) is Chun-Chacaab where a multi-level dive isn't an option as your looking at an average of 80' all the time with no option to ascend a reef where more can be seen and add bottom time.

 

[tursiops]

Theoretically, you're virtually clean after 90 minutes according to tables

No, you are virtually clean after your slowest tissue has had 6 half-times to offgas. 90 minutes would only clear the 15-minute compartment, which is one of the fastest. PADI uses the 60-minute compartment to track satus; the US Navy uses the 120-minute compartment. So, 6h (PADI) would be a safe wash-out time, not 90 minutes. Either way, of course, you are in pretty good shape by the next day's diving.

 

[doctormike]

If you were running up against your NDL on air simply adjust your dive profile. Do you really need to be at 80-90ft for that long where all of the color is gone and everything looks blah anyways?

So, if someone is feeling limited by NDLs, they should change their dives? As opposed to just switching to a richer mix? Maybe snorkeling would be a good option - lots more light, and you can't get bent!

 

[keesmon]

Thanks everyone. Some interesting responses. There are many ways to get it done, and it's very informative to see the different approaches people take to get the most out of their dives. In hearing back from Jeanie, it seems like we are best set up with a first dive EAN32 second dive EAN36 so that is what we will do. We'll be there diving March 4-11. Hope to see some of you on the Skinny Shark!

 

[ChrisM]

I just dive 32 for both dives, analyzer on the boat and analyze every tank (I'd never dive a tank I didn't see analyzed).

Rarely below 80, will go to 90 or 100 maybe 2-3 times over a week, and always over an hour.

AFAIK there isn't any real solid statistically significant evidence that EANx is "safer", but it's just what we do, and there are anecdotal beneifts.

 

[deepsea21]

So, if someone is feeling limited by NDLs, they should change their dives? As opposed to just switching to a richer mix? Maybe snorkeling would be a good option - lots more light, and you can't get bent!

Yes, snorkeling would be a great option for unlimited wet time. Obviously it all depends on the individual... If someone wants to stay deeper longer Nitrox is certainly the way to go. I personally find going deeper detracts from my experience as the color is washed out, it's darker and there is less to see in my opinion. Everyone needs to decide what they want to make of their dive experiences and if deeper means better to them then that's what they should do and utilize Nitrox. For me deeper isn't better and, in fact, it detracts from my experience and makes it that much shorter. I have yet to see someone 15-20' deeper than I am find something that is so spectacular I feel I missed it as if they do find something great I just drop down to check it out and then head right back up again without delivering a significant blow to my bottom time.

I also prefer to dive more conservative and that's just me as I'm not in my 20's or 30's anymore. I know many push it to their absolute NDL over and over again and have no problem going beyond and then hanging for a deco stop but at the end of the day it is a crap shoot. There is no shortage of divers who got bent who never came close to their NDL so that should factor into one's desire to go deeper and whether there is really more to see that's worth pushing it. Furthermore, in an emergency the trip to the surface from 60' is 20' less than the trip from 80'!

 

[gopbroek]

I dive somewhat aggressively while looking for lions and run an Oceanic on DSATand rarely do I not cross 100', the length of time below 100' is based upon the gas in my tank. If I am planning two dives I will run EAN 36 for the first and air on the second provided I am not planning on working the wall below 100' for any reasonable length of time (primarily to control costs). If it looks like I will be going to spend any length of time below 100' I run either 32 or air for the first dive and planning running the highest percentage EAN available for the second. If I run 32 first and air second I am banging hard against NDL about 30 minutes into the second dive. If I do four dives a day I try to run three of them on EAN (32, 36, 36, 21). If I run 4 tanks of nitrox on subsequent days my computer gets cranky.

 

[doctormike]

Everyone needs to decide what they want to make of their dive experiences and if deeper means better to them then that's what they should do and utilize Nitrox. For me deeper isn't better and, in fact, it detracts from my experience and makes it that much shorter. I have yet to see someone 15-20' deeper than I am find something that is so spectacular I feel I missed it as if they do find something great I just drop down to check it out and then head right back up again without delivering a significant blow to my bottom time.

I guess my point is that it's sort of arbitrary to say ahead of time that this or that depth is good enough, and that anything lower than the random depth that I am currently at isn't worth the descent. There is all sorts of stuff to see everywhere. All nitrox does is give you less N2 loading above the MOD. Unless you know that your target depth is below the MOD of your available mix, what's the downside? $70 extra? If you are flying to the Caribbean for a dive vacation, I just can't imagine that being the thing that makes the decision.

Unless you are diving very shallow, you will either have a safer dive or a longer dive. Why wouldn't you want the option of staying longer?