Nitrox vs Air

[Jaeger45]

Without trying to be personal about it, I agree with mbram.

We could probably accurately state, "Although there are theoretical and anecdotal advantages to diving Nitrox on air tables while staying within oxygen toxicity limits, there is insufficient data to support a decrease in DCS while diving nitrox."

However, if you ran a dive shop at a quarry that was not overly deep, it wouldn't be particularly difficult to do a double-blind crossover study of the effects of nitrox on post-dive fatigue. You'd need informed consent of all divers, with agreement to limit the duration of their dive to the limits of the nitrox mix for the max quarry depth, and agreement to make a second dive later in the same season (hopefully on a day with similar conditions), and agreement to accept that the tank had been analyzed by two separate individuals and found to contain the appropriate mix. All tanks would be a standard volume, and assigned a unique identification number. Study participants would be assigned, by identification number, 2 tanks, one of which contained nitrox, the other air.

Study dive would be the first dive of the day (to limit any residual nitrogen from any previous dives). Ideally, instead of air, the control tanks would be 21% nitrox from the same compressor to limit the effect of any trace contaminants. The person providing the tank to the diver would not have filled, analyzed, or assigned identification number to the tank, and thus would be blinded to the contents. At the end of the dive, the participant diver would rate their fatigue on a scale of 1 to 5, and this would data be connected to the tank identification number. The participant would come back at a later date and dive the second tank, and similarly rate it.

At the end of the study, results would be analyzed for a difference in fatigue score between the two groups, and magnitude of the difference, if present. Data from any diver actually observed to be analyzing their tank would be excluded. Any actual DCS hits (hopefully none) would also be noted; in all probablilty, these numbers would be so small as to be statistically insignificant.

Practically, as you are only asking the divers to dive air limits, not to analyze the tanks, and to come back later to dive again, you could probably even get away with charging for the gas at a price between that of an air fill and that of a nitrox fill, though if you offered to refund the price of the gas on completion of the second dive it might decrease the rate of divers dropping out.

 

[Tigerman]

Problem comparing dives done on two separate days means you cant account for variation of daily conditions, like eating, drinking, possible beginning sickness etc...

 

[String]

Do you really need a reference source for people using nitrox to increase their safety margin?

Yes because no study has failed to find a single statistically significant result showing this.

A small but theoretical benefit on paper does not always translate to a real physical benefit. It happens in medicine all the time. The body and real world mess up theory a lot.

Even if nitrox on paper could reduce DCS by 0.0000001% compared to same profile on air (and theres no evidence to suggest it does) it would be masked complete by other factors such as did the diver drink 1l or 1.5l of water that day, did they run up those steps post dive slightly faster, did they have 30 minutes more sleep and so on. Tiny but theoretical benefits get masked by the real world all the time in every aspect of science.

Again the above comment is showing you have a complete lack of understanding about how science and research actually works.

Pure hyperbole. There are 2 competing hypotheses, one saying nitrox with >21% oxygen reduces post-dive fatigue and one saying it doesn't. Neither have been proved conclusively, both are equally invalid until one has been proved. Hope that's easier for you to understand. I never said it reduces DCS risk at all, it obviously doesn't. FWIW, I feel exactly the same after diving air as I do nitrox, neither leaves me fatigued.

No. The status quo says there is no difference. You have to prove that it does. You don't have to prove the negative, its up to the person claiming a benefit to prove there is. Otherwise we'd have 10s of thousands of drugs on the market saying "these help" without any proof to back it up and it would be down to the regulatory bodies to disprove it one at a time and often proving a negative is impossible. Yet again it shows you clearly have no grasp for how research, science and review are actually performed.

More hyperbole, you're still wrong, see above. Your hypothesis that it is a placebo effect is just that, a hypothesis. Surely you can see that, right? Some people report less fatigue on EAN, some report no difference. Neither has been proved. Hope I kept that on your level.

Yes, my hypothesis is that its placebo. Ive backed that up with evidence that a placebo effect is a well known, well documented peer reviewed occurence in medicine involving humans so contend the affect will carry across to nitrox. In other words, its a claim based on established fact. You provided nothing of the same.

Ive tried to lower the explanations to your level to adjust to your clear ignorance on science. Hope that helps.


Restating my position, im going with there is NO reduction in fatigue with nitrox and no statistically significant reduction in the incidences of DCI compared to diving air. It's not that hard even for you to comprehend is it?

Nitrox (at recreational level) has a proven use for increasing no-decompression times and/or reducing required surface interval. So its useful for those situations. The other claims are not backed up by any fact and are just fanciful. May as well claim it cures cancer too - there's nothing to suggest it does that either but its no difference to you claiming a fatigue reduction.

 

[sam1]

Jax, above, mentioned Mark Powell’s 2008 book Deco for Divers. Below are three paragraphs extracted from page 124.

"The lower partial pressure of Nitrogen and the increased rate of off-gassing also results in less silent bubbles being formed during ascent. This has been suggested as one of the reasons why divers often claim that they feel less tired when driving on Nitrox rather than on air. We know that silent bubbles or micro bubbles are routinely formed after dives even if there are no signs of clinical decompression sickness. The immune system reacts to the microbubbles as they are effectively ‘foreign bodies’. See Chapter 2 for more information on the body's reaction to the formation of bubbles.

The immune system’s response results in the lymphatic system having to carry off the excess dead white cells produced to mount the attack. The immune system's response, as well as the lymphatic aftermath, both serve to create fatigue, stiffness, sore muscles, etc. By avoiding subclinical DCI, the stress on the body is avoided and there is an absence of tiredness or fatigue. Similar benefits have been reported by divers who added deep stops to their profiles.

Research by Harris, et al (2003) supports the idea that the reduction fatigue experienced when using Nitrox is solely due to the reduction in subclinical DCS rather than any inherent property of Nitrox. In their double blinded, randomized controlled study 11 divers breathed either air or EAN36 during an 18m dry chamber dive for a bottom time of 40 minutes. Two periods of exercise were performed during the dive. Divers were assessed before and after each dive using a range of performance measuring tests. Diving to 18m produced no measurable difference in fatigue, attention levels or ability to concentrate following dives using either breathing gas. As a result of this and other research the current thinking at this time is that there is no difference in terms of fatigue between diving air and Nitrox."

 

[vladimir]

Yes, my hypothesis is that its placebo. Ive backed that up with evidence that a placebo effect is a well known, well documented peer reviewed occurence in medicine involving humans so contend the affect will carry across to nitrox. In other words, its a claim based on established fact.

The placebo effect has been called into question by at least one study, published in the New England Journal of Medicine. I would not characterize it as "established fact."

 

[MauiScubaSteve]

Your posts might have more meaning if you guys would cease making up data and inventing statistics.

I worded my hypothetical statistics such that any intelligent reader could see that the statistics are made up.

AFAIK, there are no statistics for nitrox dives DCS on air tables so hypothetical is all we have, and that is why I didn't even make up a number for air table nitrox DCS.

Rather than complaining that there are no "real" data and statistics, a constructive post on these lines would point out what "real" data and statistics exist.

Or maybe you were not intending that post to be constructive?

 

[DaleC]

You guys keep saying there's no study showing the positive effects of EAN even though I linked to two in post 27. The truth is, no one really wants to think about this issue so much as argue their own position. Nobodies going to plop the perfect study into your lap to convince you because nobodies done the perfect study. You have to dig a little and employ some lateral thinking.

Saying nitrox doesn't provide an increased safety factor when diving also just shows a lack of imagination. At sea level, staying within the NDL's in a nice tropical locale there may be only a miniscule, unmeasurable DCS risk to base a comparison on true; but just bump it up to repetitive, coldwater altitude diving and see what you get.

I do these dives sometimes and try to reduce as much of the DCS risk as I can. For me (amongst other strategies) this includes using an appropriate Nitrox blend at depth and a richer mix for shallower depths/extended SS's.
Placed side by side with a strictly air diver I bet it wouldn't take to long to see a difference in actual manifested DCS risk between the two gasses.

Any volunteers?

 

[Thalassamania]

I worded my hypothetical statistics such that any intelligent reader could see that the statistics are made up.

AFAIK, there are no statistics for nitrox dives DCS on air tables so hypothetical is all we have, and that is why I didn't even make up a number for air table nitrox DCS.

Rather than complaining that there are no "real" data and statistics, a constructive post on these lines would point out what "real" data and statistics exist.

Or maybe you were not intending that post to be constructive?

Weeding the garden is always constructive.

 

[scjoe]

So far as I know, there is no documented evidence that there are less undeserved DCS hits diving EAN to air tables than there are diving air to air tables.

The same could be said for the various tables and computers out there, yet some are perceived as more "conservative" than others and people make choices accordingly. The same goes for nitrox. Conventional wisdom is "don't push the tables to the limit." Diving nitrox is simply one way of not pushing the limit of an air table.

I've never heard anyone claim less fatigue after a single nitrox dive, although I have heard people claim that a week of 3 dive days is less tiring using nitrox than a week of air dives. I can't say I have ever noticed any difference, but then I also don't notice any difference in fatigue using deep stops. That claim is also based on anecdotal stories.

 

[DaleC]

Another example of how EAN can benefit divers could be constructed from resort/destination diving.
For the visitor making one or two deep(ish) dives during their vacation, nitrox may pose no (practical) DCs risk reduction but what about the DM or instructors?
Someone doing multiple dives on a daily basis with the added physiological stressors of plain old dive fatigue, rapid ascents and/or bounce profiles (chasing clients, setting anchors etc...) might appreciate the added buffer EAN would give them.
An interesting study that could be performed quite easily would be to monitor dive professionals in this category to see the differences that air vs EAN might reveal.
I remember reading about some early Cousteau and Throckmorton archeological expeditions that ground to a halt from diver fatigue (multiple multiple dives/days). Now we just don't usually do that kind of diving but I wonder what effect EAN might have had in those cases. I certainly wouldn't bet on none.

As thinking divers we have some simple tools available to us to mitigate DCS risk and even though we might not use them, we really ought to understand them:

Adjust depth
Adjust dive time
Adjust ascent time/rate
Adjust exposure protection
Adjust health (particularily cardiovascular conditioning)
Adjust hydration levels
Adjust predive fatigue level
Adjust post dive exertion levels
Adjust smoking, drug and alcohol consumption
Adjust in water psychological stress via training and experience
Adjust equipment (functional, appropriate)
Adjust gas volume
Adjust gas composition
Adjust dive planning conservatism (rounding up/EAN as air for tables or computer settings)

How far we go down the rabbit hole depends on the dives we do and the perceived need we have for risk mitigation. On a shallow tropical reef amongst other people there may not be much (perceived risk) but we shouldn't say those factors don't exist.

I have found that sometimes pushing my limits and exploring different methods/types of diving causes me to rethink risk and how I should address it. Doing altitude dives is one such recent example. I usually do between 1-4 dives a week at sea level and most times default to air because it is cheap and I do not really need the benefits of EAN. I usually do one deep, one shallow and take appropriate SI's etc...

With altitude diving I realise a completely different risk exposure. Extended predive/postdive trips, elevation gain, time constraints, isolated locales, coldwater conditions... I had to look again at my toolbox and consider which variables I could adjust to mitigate that risk:

Learn about altitude diving
Get my brother to drive if going solo
Dive EAN as air
Stay well within the NDL's
Extended SS's with rich mix and proper SI's
Limit repetitive dives
Exercise self discipline in those other areas (hydration, rest, exercise etc...)

Stuff I would have never really considered (to that degree) if I had never perceived the need for them.