why hasnt nitrox replaced compressed air completely?

[redacted]

I can't believe that people are at the beginning of the thread were saying Nitrox isn't necessary because of their NDL's. Are you guys diving in 40ft of water?

My usual diving ranges from 95-130ft. If I didn't use various Nitrox blends, I would be sitting on the boat most of the day instead of diving.

40 ft and less quite often. No need to pay extra for EAN.

In Cozumel (and many guided dive destinations), dive profiles are mostly designed and managed around air divers so, again, not much need for EAN (except maybe the last day).

When I do repeated dives in the 80 to 100+ ft range (liveaboard), I go for the added bottom time that EAN32 provides. Worth the $$$ in that case.

 

[EFX]

it's no a question of issue, it's a question of exhaustion.

There isn't a single shred of evidence that nitrox will have any effect on that. No statistics to back it up and no theoretical mechanism of action.

There is a theoretical mechanism and some practical evidence to back it up. DuboisP claims that diving on EAN makes him less tired. We know that all divers (and non-divers) have silent bubbles. These bubbles form nucleation sites that can receive offgassed nitrogen from the tissues and could grow bigger. The reason why so-called bubble models have you make deep stops is to slow down the rate of offgassing to keep these bubbles under a thoeretical critical size. Once the amount of bubbles exceeds the critical size you are at high risk for symtomatic DCS. However, current thinking suggests that before symptomatic DCS is triggered the bubbles irritate and cause inflamation to the blood vessel walls. The immune system responds as if this were an attack and the resulting physiological effect is fatigue. For more detailed information read "Deco for Divers".

Richard Pyle, an ichthyologist, routinely did deep dives and noted that on some dives he was noticebly fatigued. He kept meticulous records and searched for a pattern that would cause this. The pattern he found surprised him. On the dives where he made a deep stop to vent air from fish bladders he was less tired at the end of those dives. He came up with a procedure for the depth and time of deep stops which has become know as Pyle stops. Richard attended a meeting of other professionals to discuss decompression. One of the scientists was D.E. Yont who developed VPM (Varying Permeability Model) a "bubble" model. His theory of decompression corroborated with the practical experimentation of Pyle.

According to this theory any mixture with reduced inert gas will reduce the amount and size of bubbles and should theoretically produce less fatigue. The higher oxygen content of EAN feeding tissues provides another benefit.

 

[boulderjohn]

I don't have the tables in front of me ... but diving standard nitrox mixes at specific depths can double your dive time compared to air, depending on which tables/algorithms you're using. RGBM comes to mind as one of the algorithms that does, at depths in the 70-90 fsw range, double or nearly so your allowable bottom time.

Some examples of NDLs using PADI tables:

60 Feet: Air = 55; EANx 32 = 90; Eanx 36 = 115
70 Feet: Air = 40; EANx 32 = 60; Eanx 36 = 75
80 Feet: Air = 30; EANx 32 = 45; Eanx 36 = 55
90 Feet: Air = 25; EANx 32 = 35; Eanx 36 = 40
100 Feet: Air = 20; EANx 32 = 30; Eanx 36 = 35

Summary: According to PADI's tables, using EANx 36 doubles (at 60 feet) or nearly doubles NDLs.

 

[String]

There is a theoretical mechanism and some practical evidence to back it up. DuboisP claims that diving on EAN makes him less tired.

Placebo effect is a very very strong and common symptom. Without randomised and double blind trials you can't accept any of those claims.

We know that all divers (and non-divers) have silent bubbles. These bubbles form nucleation sites that can receive offgassed nitrogen from the tissues and could grow bigger. The reason why so-called bubble models have you make deep stops is to slow down the rate of offgassing to keep these bubbles under a thoeretical critical size. Once the amount of bubbles exceeds the critical size you are at high risk for symtomatic DCS.

That is actually unproven.

However, current thinking suggests that before symptomatic DCS is triggered the bubbles irritate and cause inflamation to the blood vessel walls. The immune system responds as if this were an attack and the resulting physiological effect is fatigue. For more detailed information read "Deco for Divers".

Again unproven. I've read the book and have talked to Mark Powell directly. Ultimately there is no study or evidence to actually suggest a real world effect. The time factors involve as well don't fit a typical immune response.

Richard Pyle, an ichthyologist, routinely did deep dives and noted that on some dives he was noticebly fatigued. He kept meticulous records and searched for a pattern that would cause this. The pattern he found surprised him. On the dives where he made a deep stop to vent air from fish bladders he was less tired at the end of those dives. He came up with a procedure for the depth and time of deep stops which has become know as Pyle stops. Richard attended a meeting of other professionals to discuss decompression. One of the scientists was D.E. Yont who developed VPM (Varying Permeability Model) a "bubble" model. His theory of decompression corroborated with the practical experimentation of Pyle.

Fully aware of Pyle stops. Again though this has nothing to do with nitrox vs air and a fatigue or safety margin.

According to this theory any mixture with reduced inert gas will reduce the amount and size of bubbles and should theoretically produce less fatigue.

Again it says nothing about fatigue here

The higher oxygen content of EAN feeding tissues provides another benefit.

[/quote]

And no it doesn't. The standard diver is not in Oxygen deficit and neither are the tissues. The higher oxygen content (we're dealing with partial pressures here) has at best no effect, at worse can make things worse with oxidative species and free radical formation.

The only study ever done testing relative risks of DCS for nitrox and air on the same profiles found no statistically significant link or benefit. None at all. That was real world with real divers (and a largeish sample size)

 

[MXGratefulDiver]

Placebo effect is a very very strong and common symptom. Without randomised and double blind trials you can't accept any of those claims.

... but so what if it's all in my head? It is my head telling my body how it feels, after all ... no one else's.

Much of what affects our body as a result of scuba diving is ill understood ... even by those most qualified to understand it. As Richard Pyle so famously put it ...

"If you ask a random, non-diving person on the street to explain what's really going on inside a diver's body that leads to decompression sickness, the answer is likely to be "I don't know".

If you ask the same question of a typical scuba diving instructor, the answer will likely be that nitrogen is absorbed by body under pressure (a result of Henry's Law); and that if a diver ascends too quickly, the excess dissolved nitrogen in the blood will "come out of solution" in the blood to form tiny bubbles; and that these bubbles will block blood flow to certain tissues, wreaking all sorts of havoc.

Pose the question to an experienced hyperbaric medical expert, and you will probably get an explanation of how "microbubbles" already exist in our blood before we even go underwater; and that ratios of gas partial pressures within these bubbles compared with dissolved partial pressures in the surrounding blood (in conjunction with a wide variety of other factors) determine whether or not these microbubbles will grow and by how much they will grow; and that if they grow large enough, they may damage the walls of blood vessels, which in turn invokes a complex cascade of biochemical processes called the "complement system" that leads to blood clotting around the bubbles and at sites of damaged blood vessels; and that this clotting will block blood flow to certain tissues, wreaking all sorts of havoc.

You will likely be further lectured that decompression sickness is an unpredictable phenomenon; and that a "perfect model" for calculating decompression schedules will never exist; and that the best way to calculate the best decompression schedules is by examining probabilistic patterns generated from reams of diving statistics.

If, however, you seek out the world's most learned scholars on the subject of decompression and decompression sickness, the top 5 or 6 most knowledgeable and experienced individuals on the subject, the ones who really know what they are talking about; the answer to the question of what causes decompression sickness will invariably be: "I don't know". As it turns out, the random non-diving person on the street apparently had the best answer all along."

... Bob (Grateful Diver)

 

[Searcaigh]

I frequently use Nitrox for dives 20M and deeper and my fills range from 32% to 40% depending on the dive site I am diving.

On one particular dive site (Inchcape 1 off the east coast of UAE) I manage 30 mins with EAN32 and surface with 100 bar when using an AL80, NDL is my issue not the gas consumption. The great point of using Nitrox on this wreck when most of the other divers use air, is I get some peace and quiet when all the air divers ascend and a chance to take better photographs.

But I understand those who don't use Nitrox because they are gas guzzlers and never reach the NDL.

 

[EFX]

Placebo effect is a very very strong and common symptom. Without randomised and double blind trials you can't accept any of those claims. That is actually unproven. Again unproven. .......

Some people are prone to plecebos while others are not. I've done enough diving on nitrox and air to know the difference.
You keep saying not proven. I agree. However, in your response to DuboisP you said "theoretical mechanism" not proven mechanism.
Finally, absence of evidence is NOT evidence of absence.

 

[boulderjohn]

Some people are prone to plecebos while others are not. I've done enough diving on nitrox and air to know the difference.
You keep saying not proven. I agree. However, in your response to DuboisP you said "theoretical mechanism" not proven mechanism.
Finally, absence of evidence is NOT evidence of absence.

I only know of one study, and its methodology was so laughably poor that you cannot possibly draw any conclusions from it.

 

[KevinG58]

I know the rate of DCS is statistically so low to start its not been possible to deduce actual reduction of DCS through use of EAN. I believe that was covered in my recreational EAN course.

But although in my years of diving I've never seen anyone bent, and I think about my profiles as well as monitor my computers closely, "undeserved hits" come to mind. So when I'm doing 1-2 weeks (or 3-4 days in cold water) of 3-4 tank days I feel as as an old fat guy its in my best interest to reduce n2 loading, if that costs me $150-200 over the course of a big trip, that's a reasonable expense for a not statistically proven margin of "safety" but measurable reduction of n2.

Doing a 1 or 2 day cold water trip here at home, I'll start the day with a tank of EAN, then use air the remainder of the day.

Sometimes I get the EAN "feel good" effect, other times I don't. Leads me to think multiple factors are in play on that front. But placebo or not if one feels better???

 

[iamrushman]

interesting thread....great reading...keep it coming!