Diving "Conservative" vs Nitrox

[boulderjohn]

It's been proven time and time again people move too fast, especially in the last 20'.

How has this been proven? I am not familiar with the studies that have proven this. Could you provide links?

 

[GreggS]

Maybe I should have stated it more clearly. We were on a 15' dive on Sat, buddy said his buddy always dives nitrox, no matter what the depth / dive is. He said he always felt tired on air. To me this says something else is going on. My argument was that if you change the way you dive on air I bet you would feel much better.

I agree nitrox is a better gas (that was never my argument). Understanding why you get tired on air is just a better place to start.

My question is...do you think he's diving differently on nitrox than he is on air? If he is, then why would he? Divers generally dive the same way all the time. If he's moving "too fast" in the last 20 feet on air, he's almost certainly doing the same thing on nitrox. So for me, that negates your argument.

Personally, I am one of those that say I am less tired on nitrox than I am air. I generally use air when diving locally in quarries or do a 2 dive charter at the coast on a single day. For these types of dives I feel that nitrox is an unnecessary additional expense. But on a week long dive trip, I prefer nitrox for several reasons, one of which is I just don't feel as tired towards the end of the week as opposed to diving air. My wife says the same thing.

Most divers want to make their dives as long as possible. Why would anyone want to increase the conservatism of their DC and shorten their dives?

 

[lexvil]

I always feel worse post dive after using nitrox! Unless it was included in the price.

 

[inquis]

Can you get the same results from setting a computer to be more conservative vs just switching over to nitrox?

No, because "result" includes tissue loading AND dive time. For the same bottom time (e.g, you're gas-limited), nitrox absolutely reduces tissue loading and the likelihood of subclinical DCS. That choice is inherently a cost-benefit evaluation. OTOH, for a similar (tissue) benefit on air, the "cost" is a shorter dive. Still a personal cost-benefit decision.

I can't see how making such an evaluation is a "band-aid" in one case but acceptable in the other.

 

[inquis]

Most divers want to make their dives as long as possible.

Some would append, "... while remaining within their personally acceptable level of risk".

Why would anyone want to increase the conservatism of their DC and shorten their dives?

See above!

 

[Angelo Farina]

This topic has been discussed nearly an infinite number of times on SB. All else being equal, your risk of DCS is related to your nitrogen exposure and accumulation. Reduce your nitrogen exposure with decreased dive times and/or use of nitrox and you reduce your risk. Dive nitrox to the same limits that you dive air and the risk is equalized.

Not PERFECTLY equalised. If you dive Nitrox at 30m to the NDL, your exposure profile is a bit WORST than diving air up to the NDL limit at 30m.
In fact, diving Ntrox is like diving "less deep" in air, for a longer time.
And it is well known that long shallow dives up to the NDL limit result in a distribution of nitrogen which favours tissues with a longer emisaturation time, which then needs more time to release it, and more often can be cause of DCS.
Instead a short, deep dive only loads the "fast" tissues, resulting in a much easier release of Nitrogen.

 

[boulderjohn]

Air, Nitrox and Fatigue

Is there any solid evidence to support the observation that nitrox reduces fatigue? The experts weigh in on the intersection of air, nitrox and fatigue.

dan.org

From the DAN article:

Harris: No. Three articles in the peer-reviewed literature (see the first three in the references sidebar) contribute evidence to the nitrox and fatigue question, but I am not convinced that the size and power of any of them have addressed the problem comprehensively.​

​

He's being very polite. The studies I've looked at were, IMHO, worthless. With some admitted exaggeration, they're like "Let's have 3 people do a 30 minute dive to 60 feet on air and 3 people do a 30 minute dive to 60 feet on nitrox and compare how they say they feel afterwards." To test an issue like this, you have to be able to push the envelope.

For me personally, I think of how I felt at the end of my first liveaboard trip (wiped out after 3 days on air) to the way I felt after every full week trip since (feeling great after 6 days on nitrox). It would be very difficult to make a test of that duration.

 

[Bob DBF]

He's being very polite. The studies I've looked at were, IMHO, worthless. With some admitted exaggeration, they're like "Let's have 3 people do a 30 minute dive to 60 feet on air and 3 people do a 30 minute dive to 60 feet on nitrox and compare how they say they feel afterwards." To test an issue like this, you have to be able to push the envelope.

...and do it in a chamber, not the water.

The big issue is that recreational scuba is it a niche market and its highly unlikely that funds will be spent on that research.

Any real underwater research is being done by the US Navy's NEDU, and they already did most of their research making diving safe in the recreational range before I was born, and I'm not a spring chicken.

 

[Bigbella]

This topic comes around time and time again, in one form or another, and you could do any number of things -- dive more conservatively; more slowly as others have already mentioned (in a big hurry, are you?), along with a longer safety stop; and / or set those increasingly complex computers accordingly.

I have used nitrox, well before it was ever approved by any of the money-grubbing agencies (one of whom even offers -- damn -- "mermaid" training), when none of them green-lit EAN use at all; and dismissed it, as Vance Harlow described, as "voodoo gas" -- never mind that it had been around since the nineteenth century.

In that entire time, I have never noticed a whit of difference, in terms of some great "lack of fatigue" or "increased energy," whatever subjective description, over an enormous number of dives, of nitrox use over air -- though an old college friend debated that topic with me, over the years.

That was, until he got away from his daily Macintosh workout and unceremoniously dropped thirty pounds along with the absurd ponytail and aging hipster beard-o combo; ended his three martini lunches; and most important of all, jettisoned his harridan of a wife -- who could truly suck the air (or EAN, if you will) out of a room.

He now dives -- eh, primarily on air, once again -- and enjoys it, especially minus that additional Oz two-hundred dollar, plus, live-aboard nitrox fee <º)))>< . . .

 

[The Chairman]

He made the comment that his buddy dives nitrox all the time even on dives where it wasn't needed because it makes him feel better.

The older you get, the less elastic your cells are through aging. The less N₂ you absorb, the less you have to deal with, so sure. I dive NitrOx even in the pool.

However, I really started feeling better when I made my minimum safety stop at least five minutes long, and not just three. If I'm on a boat, I'll sit at 20 FSW and watch for the last butt to approach the ladder before I gently ascend and pull myself in. That might give me a 20-minute safety stop. If I'm in a spring, I'll not only do the five at 15 or so, but I'll do another 5 on the surface. No need to shake the soda before you open it, right?

Of course, this is entirely dependent on gas supply and other conditions. Otherwise, you simply can't overstay your safety stop.