Why Nitrox?

[rambaldi]

You are missing the point. I agree, there have been no scientific studies on whether you feel better diving nitrox. But there are plenty of people who DO feel better, and the evidence is pretty compelling when they were never told about anything other than the standard longer NDL stuff. This is, in fact, physical evidence. What you should be arguing is that there are no studies....instead you are arguing that because there are no studies it is not true.

I believe there have been studies showing that Nitrox has no benefit, although one reason posited for this that I have heard that I like the sound of (so really non-scientific at all) is that they profiled general divers which include a lot of people who don't dive often so would be tired after a day of diving either way. When really a better measure would have been asking those that dive a lot, who are more in-tune with their bodies after a dive (i.e. are aware when they have pushed the profile a bit and know they should back it off next time).

 

[Max Speed]

Max;

With your now "Nitrox" mark tanks not being O2 cleaned, if a shop like mine was to do partial pressure mixing there could be some serious issues.

Why would they partial blend a tank that didn't have an oxygen clean vip sticker? Lack of training? Kind of like cleaning a loaded gun!

 

[Steve_C]

Dives get canceled. Dives suddenly pop up. Fills take a couple days of advance planning. Since I do not know 100% where the next dive is my main tanks (HP 100s) are usually filled with 30%. Just less hassle that way.

 

[Superlyte27]

Hemoglobin is already nearly 100% saturated breathing air at 1 atmosphere in healthy individuals. Higher pressure will not take you over 100% since what is limiting oxygen transport is the quantity of hemoglobin and not the quantity of oxygen.

Uh! Hmm, glad to know this. I'll throw all my materials out about hemoglobin and oxygen toxicity. LOL (FOR YOU NEW GUYS, THIS IS SARCASM!)

Two years ago a friend of mine had to do his dive master swims. The first swim was 900' in nothing but swim suit. The second swim was 1800' in Mask Fins and Snorkel. The third swim was 1800' in full scuba on the surface, and the fourth swim was 1800' in full scuba underwater. The resting period between these skills is less than 5 minutes. So, he does swim 1. 5 minutes or less after completing swim 1, he must start swim 2, 5 minutes or less after completing swim 2, he must start swim three, etc. etc. As you can imagine, this is pretty exhausting. But, what's interesting is that on Swim 4 and Swim 5, even though he had WAY more drag by being in full scuba as opposed to being in just a mask, fins and snorkel, the candidate shaved almost 8 minutes off his time. How did he do this? He had already swam almost a mile, and on his last dive, after what seemed like forever swimming, he shaved 8 minutes off his time. Well, he was diving with a bottle of pure oxygen.

I've seen people repeat this *cheat* several times over the years. It works every time.

 

[MXGratefulDiver]

This is quite true. I saw a tank with a Deadhead sticker on it. I'm sure Jerry Garcia was not inside.

One would hope not, as that would mean you'd be breathing ashes.

I used to have Deadhead stickers on my tanks, but it got expensive replacing them after each annual VIP. Now they just have green and yellow "Geezer Gas" stickers on 'em ...

... Bob (Grateful Diver)

---------- Post added February 13th, 2014 at 07:14 AM ----------

While that is true, I think a tank with a NITROX sticker on it that contains air could be a problem. I guess that's why you should analyze the gas in your tank before diving.

On a shallow dive, it would make no difference whatsoever ... particularly if it's a recreational (less than EAN40) mix.

... Bob (Grateful Diver)

---------- Post added February 13th, 2014 at 07:25 AM ----------

Nice article, but it is not about O2 under pressure.....the whole saturation thing changes then. Doing studies at sea level when you are talking about blood saturation and relevance to diving misses the point.

But my suspicion is that the primary reason so many folks say they get less tired using Nitrox is NOT because of the increased PPO2, but rather because of the decreased PPN2.

My suspicion is that the primary reason so many folks say they get less tired using Nitrox is because of what occurs at the very end of the dive ... when, after religiously doing a 3 minute safety stop, they give their dive buddy a thumbs-up signal and end up on the surface five seconds later ... violating their recommended ascent rate by a large margin at the very part of the dive where it's most important not to. Fatigue is one of the symptoms of a mild case of DCS. After your safety stop you're still going to have a lot of dissolved gas in your body coming out of solution, and because this is the part of the dive where changes in depth are going to have the most impact on relative pressure differential, it's the very place where you should least want to exceed recommended ascent rates ... and yet the vast majority of divers do just that.

Breathing nitrox will reduce the overall amount of nitrogen in your body at that point in the dive, which will have some degree of impact on how much you are affected by that common error ...

... Bob (Grateful Diver)

---------- Post added February 13th, 2014 at 07:30 AM ----------

I have 6 tanks with nitrox stickers and none of them have ever been oxygen clean. A dive shop in Florida insisted on applying the stickers after filling with banked 30%.

Prior to that shop the same tanks had a long history of banked nitrox fills with no stickers. Just duct tape with the percentage.

There is no industry requirement to mark your nitrox cylinders with anything other than mix and mod. The only sticker "required" is a VIP sticker that indicates the tank was cleaned either for recreational nitrox mixes up to EAN40 or has been O2 cleaned.

The NITROX banner is a shop requirement ... some shops insist on them, others do not.

... Bob (Grateful Diver)

---------- Post added February 13th, 2014 at 07:33 AM ----------

Max;

With your now "Nitrox" mark tanks not being O2 cleaned, if a shop like mine was to do partial pressure mixing there could be some serious issues. Most shops in cave country bank 30%-32% to ensure that there are no mistakes in fills ( liability issue) and to protect their employees from the possible explosive effects of a none properly cleaned tank.

All my tanks are O2 clean and honestly wont dive a tank that is not; Nitrox fill or not.

T.

Although partial-pressure blending is still common, it's not nearly as common as it used to be. Most shops that offer nitrox either bank it or use a blending stick ... it's just easier and safer than messing around putting pure O2 into cylinders when you don't know where they've been or what was in them last ... and despite the presence of a sticker that says the tank was O2 cleaned at some point in the past year, you have no way of knowing what people have been putting in that tank since that sticker went on ...

... Bob (Grateful Diver)

---------- Post added February 13th, 2014 at 07:36 AM ----------

It is generally between 92-99%. If the level falls below 90% hypoxemia may result. Breathing nitrox under water gives two results; longer NDLs and/or shorter required surface intervals. Many people have beliefs that are not based in fact. Belief that something will make you feel better despite a lack of physical evidence is not just for the religious.

When someone tells me that feeling better is all in my head, my response is "that's fine ... as long as my body believes what my head is telling it".

... Bob (Grateful Diver)

---------- Post added February 13th, 2014 at 07:39 AM ----------

Uh! Hmm, glad to know this. I'll throw all my materials out about hemoglobin and oxygen toxicity. LOL (FOR YOU NEW GUYS, THIS IS SARCASM!)

Two years ago a friend of mine had to do his dive master swims. The first swim was 900' in nothing but swim suit. The second swim was 1800' in Mask Fins and Snorkel. The third swim was 1800' in full scuba on the surface, and the fourth swim was 1800' in full scuba underwater. The resting period between these skills is less than 5 minutes. So, he does swim 1. 5 minutes or less after completing swim 1, he must start swim 2, 5 minutes or less after completing swim 2, he must start swim three, etc. etc. As you can imagine, this is pretty exhausting. But, what's interesting is that on Swim 4 and Swim 5, even though he had WAY more drag by being in full scuba as opposed to being in just a mask, fins and snorkel, the candidate shaved almost 8 minutes off his time. How did he do this? He had already swam almost a mile, and on his last dive, after what seemed like forever swimming, he shaved 8 minutes off his time. Well, he was diving with a bottle of pure oxygen.

I've seen people repeat this *cheat* several times over the years. It works every time.

[tongueincheek]

... or you could use nitrous oxide, in which case your body will feel like crap but you really won't care ...

[/tongueincheek]

... Bob (Grateful Diver)

 

[TMHeimer]

I've never noticed feeling any different after using nitrox, but that's an old thread. Several of our instructors use nitrox for 2 a day OW checkout dives in 20' of water. My guess is they do feel better, think they feel better, or use it because the fills are free. Well hey, I've been using only free 21% O2 nitrox......

 

[Dr. Lecter]

A Nitrox sticker on a tank only means that the tank has been O2 cleaned and the tank valve has been installed with an O2 compliant O ring and with O2 compatible grease. Thats all that it means. I can then use any variation of O2 levels in this tank safely without the fear of combustion due to the chemicals or parts used on this tank.

Remind me to keep well clear of you when you're filling/boosting rich O2 mixes, if you think an EAN tank wrap has anything to do with O2 clean.

 

[Bob DBF]

You are missing the point. I agree, there have been no scientific studies on whether you feel better diving nitrox. But there are plenty of people who DO feel better, and the evidence is pretty compelling when they were never told about anything other than the standard longer NDL stuff. This is, in fact, physical evidence. What you should be arguing is that there are no studies....instead you are arguing that because there are no studies it is not true.

There was one study on Nitrox which determined there was no difference in how tired you are after using air or Nitrox.

However, I tracked down the study and I felt it had no bearing on the discussions of the subject. I had a link to it in another discussion but have had too many Longboard's to try to find it. The study was done in a chamber using one tank, having the subjects exercise and ask them how tired they were. Since I don't notice any positive effects until after 3 or so tanks on the first day of a live aboard, I would agree with them on one tank but disagree with extending the findings past the first tank.



Bob
---------------
I may be old, but I'm not dead yet.

 

[Max Speed]

There are plenty of studies indicating that nitrox should make you feel worse. Your blood vessels become irritated, loose their elasticity and so on.

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[tursiops]

There are plenty of studies indicating that nitrox should make you feel worse. Your blood vessels become irritated, loose their elasticity and so on.

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Can you provide any citations?