Air divers and nitrox divers, acceptable buddies?

[JoeFL]

tigerdiver once bubbled...
Well, one of the reasons I decided to get Nitrox certified was to have it available as an option on types of diving. Just because I can dive Nitrox doesn't mean I always do. It depends on the dive. So I would at least consider getting Nitrox certified.

As far as your question is concerned it is not advisable to dive with a Nitrox buddy while you are on air IMO. There are numerous differences and considerations with Nitrox vs Air that could cause difficulties.

If you plan to dive with a Nitrox buddy you will have to plan the dive conservatively (not that anyone plans a non-conservative dive.) Your Nitrox buddy has depth limitations that you do not and you have time limitations that he will not. So you will have to use your max bottom time as a parameter and his max depth as another when planning your dive.

With all of that said, I think in an emergent situation switching air to nitrox or vice versa to complete a 3-5 min safety stop at 15 fsw or an out of air situation may be acceptable. I am not an instructor and have only been recently certified in Nitrox. At the minimum I would not dive again after that situation for 12-24 hours to allow for a "re-set" of your off gassing.

Just my $.02.

We would dive a "conservative" plan in that we would stay within both our limits regarding his depth and my air time constraints. The emergency gas sharing was my main concern... for either of us. Chances are after whatever problem that would cause us to have to share a tank, we'd be ready to call it a day... I like to play it safe for the most part.

And as far as getting a nitrox certification, I am pretty much on the same page as you. It wouldn't be for exclusive use (probably)... just to have it as an option for certain dives. On most dives I usually run low on air before I run out of no-deco time anyway. Plus I just got two new AL80's for air... I want to get my moneys worth : )

-Joe

 

[Scubaroo]

tigerdiver once bubbled...
As far as your question is concerned it is not advisable to dive with a Nitrox buddy while you are on air IMO. There are numerous differences and considerations with Nitrox vs Air that could cause difficulties.

I think this is too conservative.

Generally you pick a dive site and dive the appropriate gas, not pick a gas and dive an appropriate dive site. If you're buddy's not diving a standard Nitrox like EAN32 all of the time, which sets his MOD around 111' with a PPO2 of 1.4 anyway, he's probably picking a "best mix" for the particular dive (one of the benefits of diving a standard nitrox blend all of the time - if you're always diving ENA32, you can do any dive between 0 and 111'). So if you're the air diver on this dive, your nitrox buddy should be diving an acceptable gas for this dive. You shouldn't be limited because your buddy says "I only have a tank of EAN40, so we can only go to 82' this dive". If that's the case, find a buddy who understands nitrox (or get nitrox certified yourself). Plan the dive.

The MINIMAL gas onloading/offloading effects of switching between air and a recreational (<40%) nitrox blend in the case of an emergency air share in a recreational setting should not prevent you from doing another dive that same day. However, whatever failure (be it equipment or training issues) caused the airshare to occur in the first place should be addressed before diving again :tease:

reefraff and daylight had it nailed. In an ideal world, you would both be nitrox certified. It doesn't cost much, you have the choice of courses that do and don't require training dives, and it should give you a much better understanding of things like MOD, PPO2, PPN and oxygen toxicity than you may have received in your open water class - so go and get certified anyway!

disclaimer - the figures of 111' and 82' were not taken from any tables, rather a quick calculation - do not use them for dive planning.

 

[Atomic]

JoeFL once bubbled...
The emergency gas sharing was my main concern... for either of us

Lets look at both situations. The first situation is you sharing your buddy's nitrox on your ascent/stops. Since he's within his O2 clock limits then you will be within those limits on your ascent, since your clock ticks slower on air than his on nitrox. By sharing the nitrox, you're actually better off than ascending with air. This is because you will be offgassing faster with a lower nitrogen gradient than with air. Planning your next dive with air tables puts you in front of the game because you did your offgassing with nitrox.

The second situation is if you share air with your buddy. Since you both were diving an air plan, and you are still within recreational limits, then he will be even more within the limits because he was ongassing slower than you due to breathing a lower nitrogen gradient than air. So doing his ascent on air isn't as efficient as on nitrox, but when the sharing started he had less nitrogen in his system then you did.

However, if he had a previous dive that you didn't do it gets more complecated. If he plans his second dive, your first dive, as if he was doing the dive on air, and his NDL times are lower than yours, there is no guarantee that his offgassing on air is enough. If he has previous dives to consider, then the easiest thing to do is dive the bottom time for if his dive was on air. In other words, the most conservative of the three.

If I'm diving nitrox and using the extended bottom times nitrox will give me, my plan is to double my safety stops if I have to switch to air on the ascent. If that happens I will treat the first dive as if it was air for planning subsequent dives. If the dive didn't fit into a plan that was all air, then I end my day.

 

[herman]

Some would have you think that diving Nitrox is some big deal, it's not. Follow RR and O-rings advise and both of you will be fine. Don't get me wrong, you do need training to use it safely but its not rocket science either. Atomic has a good point as well, but the same problems arise if you both were on air or nitrox for that matter.

Here is a link for you to check out and get a better understanding of what Nitrox diving is all about. IN NO WAY DO I SUGGEST THAT THIS SITE IS AN ACCEPTABLE SUBSTITUTE FOR NITROX TRAINING, but it does give you a pretty good overview of the subject. Get your nitrox cert, but in the mean time have fun diving.

http://www.americandivecenter.com/nitrox/n2o2_m00.htm

 

[gazza]

Hi Joe,

I dive on nitrox most of the time, but my buddies normally dive on air - it's my loss.

You should have no problems whatsoever, espeically as you're current an OW diver, which means none of your dives should be over 18mtr - which is not an issue for nitrox.

The one thing you will need to remember is that a nitrox mix at those depths will normally give you a much longer ndl time than air will, so you an your buddy will need to plan and dive on the most conservative plan / computer, which will be yours.

if you end up in any situations where you need to use eachother's gas, obviously we're talking about a freeflow or something rather than running out of air, again there should be no issues.

For example (in padi),

if you and your buddy were going to go on an 18mtr dive, the rdp tells me that you can do 56mins maximum on air, with a 3 min safety stop.
As a nitrox diver, you can dive on a mix of 40% which is an equivilent air depth (or nitrogen loading) of 11.6mtr. According to the rdp again, 12mtrs gives ndl of 147mins plus the safety stop.

At this point, the plan you are both going to do is the first one, it's more conservative and is the only plan that both of you can safely undertake.

let's say after 50mins, your buddy has a problem with his gas and uses yours to do the ascent and safety stop. at the end of the dive, you buddy is within the ndl for the air rdp - so everything's fine.

let's say you run out fo air after 50 mins and you go onto your buddy's nirtox. again, you come up within the air ndl and again everything's fine.

where it starts to get dangerous is if you let your buddy control the dive and he's using a nitrox dive computer. you could be diving for 90mins before he calls the dive and does the 3 min safety stop. obviously, at this point you are well of the end of your air table and bad things could happen.

i hope that makes some sense.

 

[raviepoo]

tigerdiver once bubbled...

With all of that said, I think in an emergent situation switching air to nitrox or vice versa to complete a 3-5 min safety stop at 15 fsw or an out of air situation may be acceptable. I am not an instructor and have only been recently certified in Nitrox. At the minimum I would not dive again after that situation for 12-24 hours to allow for a "re-set" of your off gassing.

Why would you need to do that? If both divers are diving air tables and the MOD dictated by the Nitrox divers mix there is no reason to treat the dive as anything other than a regular dive.

Think about it. The Nitrox diver is diving his mix on air tables. No big whoop. He may as well be diving air as long as he doesn't violate his MOD. If he ends up breathing air at the safety stop, it makes absolutely no difference. He is only diving the gas that goes with the tables (or computer) he is using.

If the air guy breathes Nitrox at the safety stop he actually taking in less Nitrogen than his tables expect. There is no earthly reason for him to wait 12 - 24 hours for his off gassing to "reset." He is actually offgassing a tiny bit faster than anticipated.

The ONLY thing the divers in this scenario have to worry about is being arrested by the Nitrox cops when they get back to the dock. I hear they take away your scuba license, confiscate your house and lock you up for 10 - 20 for this kind of crime against society.

=-)

 

[cornfed]

raviepoo is right. Just enjoy your surface interval (I normally have lunch during mine) then get back in. If you switched to nitrox, then you're better off then your tables suggest. If you switched to air, you're a little worse off, but this doesn't matter because you're not using more then 3/4 of your NDL time anyway, right?

Cornfed

 

[JoeFL]

raviepoo once bubbled...


The ONLY thing the divers in this scenario have to worry about is being arrested by the Nitrox cops when they get back to the dock. I hear they take away your scuba license, confiscate your house and lock you up for 10 - 20 for this kind of crime against society.

=-)

...but I was afraid to ask. People always tell me there are no scuba police down there, but I've seen em. Out at the absolute limit of my vis with that great white shark that's always following me on my dives. And now I find out there's Nitrox cops too. What's this world coming to???

The truth is out there.

Thanks
-Joe