Nitrox discussion (Split from "Reasons not to use Enriched air" thread in Basic)

[Thalassamania]

It's just a common sense rule that a buddy pair of divers either dive the same mix (preferable) or follow the more conservative decompression schedule (e.g., you dive air and I dive EAN, we follow your deco schedule). You'd have to check the more aggressive nitrogen exposure's deco schedule against the less trying dive.

 

[Blackwood]

It's just a common sense rule that a buddy pair of divers either dive the same mix (preferable) or follow the more conservative decompression schedule (e.g., you dive air and I dive EAN, we follow your deco schedule). You'd have to check the more aggressive nitrogen exposure's deco schedule against the less trying dive.

And you'd have to account for the additional oxygen exposure of the EAN deco diver as well, adding backgas breaks where applicable.

 

[nereas]

Here is how ppO2 exposure limitations work:

for ppO2 of 1.6 ATAs the exposure limit is 45 mins

for ppO2 of 1.5 ATAs the exposure limit is 120 mins

for ppO2 of 1.4 ATAs the exposure limit is 150 mins

for ppO2 of 1.2 ATAs the exposure limit is 210 mins

And regarding repetitive dives, a surface interval of 60 mins reduces an 80% exposure from the first dive to 50%.

A surface interval of 90 mins reduces an 80% exposure from the first dive to 40%.

Since tech-deco diving involves long dives of an hour or more, it is normal to limit your own ppO2 to 1.2 ATAs, until the deco time begins.

However in the case of NDL diving, with nitrox of EAN 32 or EAN 36, due to the relative shortness of the dives, controlled by NDL limits (which are much shorter than the ppO2 exposure limits shown above), you can freely use 1.6 ATAs or 1.4 ATAs as your maximum limit.

We teach novice divers to use 1.4 because this gives them a much greater margin for error.

It is not a margin for safety, it is a margin for error.

 

[nereas]

I think the stock answer will be that you two will agree beforehand on the gases/deco schedule. In other words: you'll be diving the same profile...

The nice thing about the advanced helium dive computers is that they are very flexible, and you can change your profile as needed, and they will take all this into account. Of course, your backup slate won't take anything into account, but then it is only a backup.

Normally what is agreed upon is the MOD and the bottom time. This means you then all head back to the anchor line together. From that point on, if some divers take longer to decompress for safety reasons, I do not see the need to do everything exactly the same, once you are back at the anchor line.

And yes, Blackwood, if you cannot agree, then we would normally not want you in our group.

But this has nothing to do with the O/P's question. He asked is there any reason not to use nitrox?

The answer is that nitrox is good for sea level diving in the range of 50 to 130 fsw, and for all high altitude (mountain) diving.

 

[Bismark]

Here is how ppO2 exposure limitations work:

Since tech-deco diving involves long dives of an hour or more, it is normal to limit your own ppO2 to 1.2 ATAs, until the deco time begins.

However in the case of NDL diving, with nitrox of EAN 32 or EAN 36, due to the relative shortness of the dives, controlled by NDL limits (which are much shorter than the ppO2 exposure limits shown above), you can freely use 1.6 ATAs or 1.4 ATAs as your maximum limit.

We teach novice divers to use 1.4 because this gives them a much greater margin for error.

It is not a margin for safety, it is a margin for error.

In order to help educate member of SB,

1) Please provide us with the appropriate reference material supporting these statements.
2) Please differentiate between your opinion and what is not your opinion.
3) Please support your statement in regarding to "freely use 1.6 ATA's or 1.4 ATA's as your maximum limit.
4) Who is the "We" in "we teach novice divers to use 1.4 because........."

 

[nereas]

The whole _ppO₂ thing has changed over time. It used to be a _ppO₂ of 2.0 ATA, after a test to not quite 3.0 ATA was standard. Then it got cut back to a _ppO₂ of 1.8 ATA, then 1.6, then 1.4, then just to do one better GUE went to a _ppO₂ of 1.3.

Everyone needs to grasp a few realities:

1. Diving an elevated ppO2 has hazards associated with it.
2. The higher the elevation the greater the potential hazard.
3. The longer the exposure the greater the potential hazard.
4. The higher the work load the greater the potential hazard.

So the question is, why are you using an mix with an elevated _ppO₂ and does its use offset the increased level of potential hazard?

For me it does, and from past experience (which is not a perfect guide) I am willing to accept (for myself only) a _ppO₂ of almost 2.0 for decompression, 1.8 for resting and 1.6 for "normal" diving. But I'd not recommend those exposures to others ... its just that I'd allready done that for years before the agencies got into the topic with recommendations that they had to run through their docs and their lawyers and the accountants

DWayne, hopefully Thal's explanations help you to understand better what is "safe."

As I said, 1.6 ATAs on EAN 32 to 130 ft is no sweat for NDL diving. Hopefully you are starting to agree.

As I have also tried to explain, there is nothing magical about 1.4 ATAs, since sometimes a dive plan must be constructed with a 1.2 ATA limit, when it involves tech-deco. It all depends on the overall ppO2 exposure time.

If you stick with 1.4 ATAs for your own NDL diving, you should be fine, because it gives you a large margin for error. Errors like dropping down deeper than you thought, or cutting surface intervals too short, etc.

 

[nereas]

I tried to resist responding to this thread again.

If 1.6 ATAs is safe oxygen exposure for 45 mins (and I am not disputing that it is otherwise because I simply don't know whether it is "safe"), then why wouldn't EANx36 be the ideal gas to 110 ft instead of 90 ft? You're not going to get 45 mins of NDL time at 110 ft (nor at 90 ft though getting close).

Why, exactly? EANx36 at a ppO2 of 1.6 should give you a max depth of ~113 feet and you've already said that 1.6 ATAs is fine for up to 45 mins.

Also, you're being disingenuous by saying " . . . as I said originally, and which you apparently misunderstood." You originally said EANx36 should be limited to 90 ft (see my quote of your post from yesterday) and you edited your post today, almost 24 hours later, without noting the reason you had edited your post (I haven't read closely to see if you made other changes). No biggee if you meant 95 ft and originally typed 90 ft -- but editing your post and then saying "as I said originally" leaves a pretty bad taste for readers paying attention.

You're responding to a thread titled "Reasons NOT to use Enriched Air" in a forum titled "Basic Scuba Discussions" and throwing around phrases like " . . . the general rule is that EANx is ideal and better than air for any depth between 50 ft and 150 ft" and "for dives in the range of XX to XX EANxXX is the best mix." And now you want to make the point that "oh, by the way, novice divers should do something ENTIRELY DIFFERENT than I originally suggested" and "it normally requires a tech-deco course to fully explain oxygen exposure time limits" so you won't provide more detail on your basis for the statements in this thread?

I'm really not trying to flame you personally (though my disapproval of your approach to posting is clearly evident) -- whatever motivates / causes your approach, I'd urge you to be more sensitive to the scope of readership on these boards and be cautious about making declarations regarding what is appropriate and safe for the general readership on something as critical as breathing gases.

The myth of the magical properties of 1.4 ATAs as a limit is the main cause for my concern. Hopefully you have now got a better picture of that from some of the technical replies, such as Thal.

 

[Bismark]

The nice thing about the advanced helium dive computers is that they are very flexible, and you can change your profile as needed, and they will take all this into account. Of course, your backup slate won't take anything into account, but then it is only a backup.

Normally what is agreed upon is the MOD and the bottom time. This means you then all head back to the anchor line together. From that point on, if some divers take longer to decompress for safety reasons, I do not see the need to do everything exactly the same, once you are back at the anchor line.

And yes, Blackwood, if you cannot agree, then we would normally not want you in our group.

But this has nothing to do with the O/P's question. He asked is there any reason not to use nitrox?

The answer is that nitrox is good for sea level diving in the range of 50 to 130 fsw, and for all high altitude (mountain) diving.

1) What do you do when your computer breaks down?
2) Do all members of your "group" wear exactly the same computer, operating the same decompression algorthims, and operating at exactly the same levels of conservatism?
3) Am I correct in reading that a common mix and common deco mix are not necessary in your view because an "advanced helium dive computer" will do this for you?
4) How does your "advanced helium dive computer" work when one or more of your group are a) blown of the line in current and/or bad viz; b) suffer a catastrophic lose of one or more deco gases; c) are unable to help each other when at different depths and stages of decompression.
5)Does your "group" actually not agree on the other, I guess what I can only assume are less important, phases of the dive, (because you didn't mention them)such as....decompression?

And finally, if your bottom time and MOD are agreed upon before the dive as per your post above, what exactly do you mean by stating that "The nice thing about the advanced helium dive computers is that they are very flexible, and you can change your profile as needed"? I thought we had just agreed on the MOD and bottom time (as he sits here scratching his head) So unless the group all operates the same computers, set at the same conservatism levels, and has "programmed" into said computers all the various bottom mixes and deco mixes, things could get a bit...........interesting........

 

[nereas]

A working dive at a PP02 of 1.6 is risky in many peoples opinion. Typically a PP02 of 1.4 is the accepted working limit, with 1.6 reserved for resting deco.

You should not be working during a scuba dive. That is for commercial divers to do. You should be resting, drifting, and enjoying.

If you are working, then you should be wearing a hard-hat and be commercially certified.

This is because a whole bunch of really bad things can happen, physiologically and biochemically, which you don't even know about, if you are exerting yourself at depth. And then, an FFM would be your minimal safety need, with a hard-hat being preferred.

Always stay within your recreational limits.

 

[String]

Here is how ppO2 exposure limitations work:

for ppO2 of 1.6 ATAs the exposure limit is 45 mins

...Snip...

No it isn't. You're completely ignoring the increased risk of an immediate acute reaction and only using the oxygen clock.

Since tech-deco diving involves long dives of an hour or more, it is normal to limit your own ppO2 to 1.2 ATAs, until the deco time begins.

According to who ?! Lets see your sources. Certainly not TDI,IANTD,BSAC,DSAT.

ers to use 1.4 because this gives them a much greater margin for error.

It is not a margin for safety, it is a margin for error.

Wrong. It also places them further to the safe side of the curve for immediate acute O2 hits. Something you dont seem to realise even exists.


You repeatedly make sweeping statements without providing any reference or source for these. You word it to try and pass it off as common protocol when it is nothing of the sort. You then repeatedly fail to provide any reference to anyone that has asked you.

Some of the comments you make here yet again are ridiculous, incorrect and at best completely without references. Some of the other comments such as clipping the long hose to the necklace are bordering on the insane.