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

[dumpsterDiver]

yes and they are presumably resting relatively comfortably at 20 feet.

 

[Riger]

Surely most responses in this thread are technically out of context in terms of the OP's Question.

It is not fair to bundle the risks associated with diving outside published limits (whichever they are and however they are interpreted) with the negative side (if any) of diving Nitrox.

In order to keep it real;

Assuming that a diver remained within prescribed depth/time limits and was not unusually susceptible to oxygen toxicity and assuming that his equipment was working properly and that the tank was filled correctly and that the Air was analysed by the diver and that there were no freak natural events etc.....

...is there any physiological disadvantage to diving on oxygen enriched air?

Best Regards

Richard (Riger)

 

[ianr33]

No.

Actually an advantage. Safety stops will be more efficient (effectively a weak deco mix)

 

[scubadobadoo]

In order to keep it real;

Assuming that a diver remained within prescribed depth/time limits and was not unusually susceptible to oxygen toxicity and assuming that his equipment was working properly and that the tank was filled correctly and that the Air was analysed by the diver and that there were no freak natural events etc.....

...is there any physiological disadvantage to diving on oxygen enriched air?

Best Regards

Richard (Riger)

No.

 

[tschmitt]

No.

Actually an advantage. Safety stops will be more efficient (effectively a weak deco mix)

And you are exposed from 1% to 19% less inert Nitrogen gas (EANx22 - EANx40) while diving under all those assumptions and conditions you listed, which is a physiological advantage.

 

[Catt99]

I tried to resist responding to this thread again.

Diving to 130 fsw on EAN 32 is no sweat. This would give you a ppO2 of 1.6 ATAs for which the safe oxygen exposure time is 45 minutes. At that depth, your NDL limit is going to be a whole lot less than 45 mins.

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).

Diving with EAN 36 should be limited to 95 fsw, as I said originally, and which you apparently misunderstood.

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.

Novice divers are recommened to limit their ppO2 exposure to 1.4 ATAs, and if you are a novice, that is what you should also do.

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.

 

[ianr33]

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).

If everything goes perfectly (no current,no exertion,perfect buoyancy.high performance reg) then 36% at 110 feet would be fine.
But,start working hard kicking into a current,producing lots of CO2 and retaining more of it (due to gas density at 4ATM),maybe drop down to 120 without noticing and things could start to go bad. High PO2 and high CO2 is a REALLY bad combination.
Its all about risk management and where you choose to draw the line. In the past some divers would routinely use a PO2 of 2.0 Most of them did not die from it.

Another point is that when using a PO2 of 1.6 for deco most divers will not breathe this for longer than 12-15 minutes without taking a break to lower PO2's. High PO2's for any length of time will cause lung irritation/coughs.

 

[String]

Lets just keep this simple.

Provided you know your maximum depth and are sure of your ability not to violate that the best mix for that dive is whatever would give you a ppO2 of 1.4 at max depth. Simple as that.

 

[String]

W
For tech-deco diving, the oxygen exposure limit is an overall factor for the entire dive, and in that case, you would normally be limiting your ppO2 to 1.2 ATAs during the bottom phase,

Why? When every agency i can think of says 1.4. Where are your sources for this?

And you would normally need V-Planner software to determine the overall limit,

No you don't. Every single Adv Ean course ive seen by any agency covers manually calculating CNS% (and OTUs).
V-planner is nothing more than a VPM-B/E planner. There are many others around using many different models and not one of them is essential to calculating CNS.

and it is common to create a margin of error with 80% of the CNS Ox Tox total. But that is a different topic.

"Create a margin of error" ?! What type of crap is this. NOAA and others recommend 80% max exposure. Nothing to do with an error margin.

Some of the things you've posted here and other threads lead me to believe you've never received any formal technical training or if you have you didnt listen to it or the instructor wasnt qualified.

 

[Blackwood]

Why? When every agency i can think of says 1.4. Where are your sources for this?

GUE recommends (or demands, depending on how you look at it) 1.3 for bottom mixes. Though the texts list the same 'industry standard' 1.4, the standard gases reflect 1.3 for backgas (and 1.6 for deco gas excepting the 190 bottle which is a 1.4).