Nitrox Question

[maranda1389]

So my fiance and I were talking about nitrox today and got into a little debate. I said that if nitrox wasn't so expensive to fill I would dive it because I always feel like crap after my dives and I have heard many times that nitrox makes you feel alot better than air after dives (YES I know this is debatable but this isn't this issue). Then I said, oh nevermind, I don't like to dive more than like 30-40' so it would be kind of pointless to dive nitrox anyways. He said "Well why would it matter what depth your at?" and I told him I thought that nitrox was intended and best utilized at deeper depths and he said it doesn't matter what depth your at for nitrox. So which theory is right? Can you dive nitrox safely at ANY depth or is it really just meant for deep diving (deep as in like 80+ feet)?

 

[gcbryan]

It safe at shallower depths it's just that your nitrogen loading is so minimal at 30-40 fsw that it's overkill. It's not really doing anything for you. There is no problem using it however.

 

[doctormike]

I'll assume that neither of you are nitrox certified, as this is the basic content of that course... but it is certainly a good question!

There is no hard evidence that nitrox really makes a difference in how one feels after diving, although many people swear that this is true. Of course, to really be sure, you would need to do a double blinded study with people being evaluated post-dive by some reproducible test of "well being", which has not been done as far as I know.

In a nutshell, the main advantage of nitrox is that it increases your non-decompression limits, that is, the amount of time you can stay at a given depth before acquiring a decompression obligation. This is because it contains less nitrogen per unit volume of gas, so tissue nitrogen loading is less (all other things being a constant). Furthermore, offgassing is more rapid the less nitrogen that there is in your breathing gas, this is why divers with a decompression obligation will often breathe from richer mixes (up to 100% O2) to reduce the time that you need to safely decompress.

Now here is the downside of nitrogen - oxygen is toxic above a certain "concentration" (partial pressure), so for every mix, there is a maximum operating depth (MOD). If you go below this, the partial pressure of oxygen will rise above a certain point (let's use 1.4 atmospheres to simplify things), putting a diver at risk of seizures. The abovementioned 100% O2 can't be used below about 20 feet for this reason. Also, there is a cumulative toxicity of oxygen that can cause other problems, but I'll leave that out for now to make the answer to your question a bit simpler.

So to settle the discussion between you and your fiance… there isn't much point in using nitrox at very shallow depths since you wouldn't see much of an extension of your NDL - in fact, I believe that the NDL on air at shallow enough depths is essentially infinite (that is, you are offgassing as fast as your are ongassing). As a practical matter, you would run out of air from a single tank even at slightly deeper depths before you would run up against your NDL.

Nitrox is most useful at depths closer to the MOD, where nitrogen loading is more of an issue, and especially as you get better at gas consumption so that you are more likely to be NDL limited as opposed to gas limited. For the common mix of EAN 32%, the MOD is around 110 feet, and for EAN 36%, it is about 90 feet.

 

[Notso_Ken]

So my fiance and I were talking about nitrox today and got into a little debate. I said that if nitrox wasn't so expensive to fill I would dive it because I always feel like crap after my dives and I have heard many times that nitrox makes you feel alot better than air after dives (YES I know this is debatable but this isn't this issue). Then I said, oh nevermind, I don't like to dive more than like 30-40' so it would be kind of pointless to dive nitrox anyways. He said "Well why would it matter what depth your at?" and I told him I thought that nitrox was intended and best utilized at deeper depths and he said it doesn't matter what depth your at for nitrox. So which theory is right? Can you dive nitrox safely at ANY depth or is it really just meant for deep diving (deep as in like 80+ feet)?

When you learn about diving with nitrox, you will learn about the maximum operating depths for the various mixes. With higher O2 and lower N2, you are constrained to shallower depths. When I dove 30% on the Oriskany, I was limited to 121', and could not even reach the flight deck. Richer mixes (higher O2), limit you even shallower than that. Max benefit for nitrox is around 60-100 feet.


Ken

 

[sardiverdan]

It all depends on what % of O2 you plan on using in your mix. Lets say 60 feet on air will give you 60 min NDL. Now 60 feet on 32% may give you 100 min NDL (IANTD Charts). Basic EAN will be 32% or 36% for the most part. Other mixes are used for DECO mixes or deeper dives to lower your PPO2. Now 100 feet on air will give you a NDL of about 25 min while EAN 32 will give you a NDL of 30 min while 36% will give you 40 minutes. I know sounds difficult but if you take a class you will have it all figured out.

 

[EZ Scuba]

There is no hard evidence that nitrox really makes a difference in how one feels after diving, although many people swear that this is true. Of course, to really be sure, you would need to do a double blinded study with people being evaluated post-dive by some reproducible test of "well being", which has not been done as far as I know.

it's just hyberbaric o2, the people who feel better after hi po2 were run down before or during the dive, this is no different from what football players do when they get back to the bench after a long stretch on the field (except they aren't at depth). So people who get a good rest, are properly hydrated, maybe even carb'd up a bit----AND---didn't spend that night before partying, shouldn't feel any difference between nitrox and air.

It has been said that a bottle of O2 at the bottom of the pool for half an hour after a hard night helps.

 

[kombiguy]

Although, Undercurrents magazine reports that the results of a self-directed, anecdotal study indicate that couples who both dive nitrox while on a dive vacation have more sex than couples diving air. Enough reason to use nitrox? Depends on how much you like your wife, I suppose.

 

[Crush]

So my fiance and I were talking about nitrox today and got into a little debate. I said that if nitrox wasn't so expensive to fill I would dive it because I always feel like crap after my dives and I have heard many times that nitrox makes you feel alot better than air after dives (YES I know this is debatable but this isn't this issue).

Why do you feel like crap after diving? I am not a physician, but there are a few of them on the board and you should consider chatting with one of them in case your body is giving your warnings.

 

[EZ Scuba]

Although, Undercurrents magazine reports that the results of a self-directed, anecdotal study indicate that couples who both dive nitrox while on a dive vacation have more sex than couples diving air. Enough reason to use nitrox? Depends on how much you like your wife, I suppose.

in the water?

 

[Thalassamania]

Feeling poorly post dive is usually considered to be a symptom of incomplete or improper decompression. The original DIR folks were even willing to readjust their decompression procedures and schedules based on how they felt after a dive. There are a few things that you can do. First is to decrease your nitrogen uptake by staying shallower or by breathing EAN, second is to wash out the nitrogen by going to pure oxygen on a 20 and then 10 foot stop, and third is to slow you ascent either by reducing the rate or adding or lengthening stops. Combinations of these three approaches also work.