The Truth About Nitrox

[TexasMike]

Rodale's just posted a good article about diving with Nitrox (also known as EAN or Enriched Air Nitrox) on their website. Click the link to read: http://www.scubadiving.com/gear/truthnitrox/

Thought it was kinda timely since my Nitrox class is tonight (Tues, 6/12/01)

 

[bluebanded goby]

Mike, thanks for posting this link.

One statement in the article caught my eye. One of the disadvantages of nitrox is cited as being:

"Impracticality of the most common nitrox mixtures in water less than 50 feet and greater than 130 feet deep."

Now, I realize that you can't use a given nitrox mix below its maximum operating depth, but what's the impracticality of using nitrox at depths less than 50 feet? I suppose one might argue that (a) since the no-deco time at shallow depths is already relatively long, it isn't necessary to extend it with nitrox; and (b) if you're diving nitrox using air tables as a hedge against DCS, you're unlikely to get hit at shallow depths anyway. But if you get to liking nitrox just to play it safe on DCS, is there any real reason not to use it on a shallow dive? (Speaking as one who is not yet nitrox-certified but who plans to be within the next few weeks.)

 

[Warhammer]

Statistically, there is no meaningfull safety improvement from diving nitrox on air tables at any depth. Course that's statistically, and you can draw your own conclusions. The reasoning behind this is that the rate of DCI hits is already so low that it would only improve safety a fraction of a percent. And like you said, above 50ft one would generally run out of air long before they ran out of no decompression time. There are some exceptions however, divers with deco obligations use nitrox at high 02 levels in depths less than 50' to speed up deco and shorten their obligations.

And there are nitrox mixes with safe oxygen partial pressures below 130', so that's not much of a factor. The big enemy at depths greater than 130' is narcosis, and that's why trimix is generally recommended for those depths and beyond.

You'll learn all this in your upcoming nitrox class. It's a good class with alot good material, at least mine was. Have fun.

 

[TexasMike]

Goby....Your welcome for the link.

I just returned from my TDI Nitrox class, and Warhammer is correct, from the safety standpoint, there is not that much statistical difference for DCI between air and Nitrox for 50 feet or less.

Looking at my PADI Recreational Dive Planner, the no deco limit (NDL) for 50 feet on air is 63 minutes. And from what I have observed, heard, and studied, 1 hour is typically how long an "average" diver can make an aluminum 80 tank last at that depth (considering a square profile, and average or less exercion).

If you were to replace air with Nitrox for 50' (or less), it would, in theory, provide more no deco time, but your limiting factor is the quantity of air in your tank. You would run out before you could appreciate the bottom time extension afforded by the increased 02.

Nitrox is mostly used to extend your NDL (no deco limit) for deeper dives. For the new divers following along, you remember that standard air is 21% O2 and 79% nitrogen. And if you were to consult your dive tables, you would see that at a depth of say, 80' you can stay down 25 minutes with no deco.

With EAN36 (Enriched Air Nitrox with 36% oxygen), your gas mix is 36% O2 and 64% nitrogen. In other words, the gas you are breathing has 15% less nitrogen. An immediate benefit is that since you are inhaling less nitrogen, there is less being forced into your bloodstream. Thus the reduced chance of DCS. And your no deco bottom time is nearly doubled.

(Warhammer, check me on this please. I think I explained this right, but I've only had one class and no nitrox dives, yet.)


Finally, if I can sway your choice of agencies to obtain your nitrox cert, please consider TDI (Technical Diving Institute). With their sister agency (Scuba Diving International, or SDI http://www.tdisdi.com) they are rapidly becoming one of the more "realistic" training agencies out there. By realistic I mean they are not so rigid in what and how they teach. They acknowledge the current trends and technologies in diving and include that in their information and methods. Plus, if you have a desire to be certified in some of the advanced diving areas (wreck, nav, cavern/cave, etc), then TDI/SDI will do an excelent job of training.

Good luck in your upcoming class, and be sure to keep us informed of the fun you are having.

--TM

 

[Rick Murchison]

As usual, the Rocket Scientists at Rodale's have sacrificed the "whole truth" on the altar of the "headline."
Let's say, for example, you want to make two dives to 49' (that's "less than 50'," yes?) for a nice, leasurely 50 minutes.
Using the Navy or SSI tables for this example, on air, a surface interval of four hours, twenty-six minutes minimum would be required between the two, while on EAN32, the second dive could be commenced as soon as you can change tanks.
Sure sounds like a pretty good reason to use Nitrox to me!
And, tangentially, to learn that anything you read in Rodale's should be taken with a grain of salt.
Rick

 

[greg somers]

Who is diving with EAN36 at 130 ft? 6 atms?
With oxygen toxicity coming into effect at 1.4 - 1.6 atms
partial pressure that would place the start of that threshhold at 30m,not 43m.I am not a nitrox diver but we did the maths during dive leadership training.It seems to me that it is cutting the line a little close.Those of you who dive nitrox,how about you explain this for me please?
Cheers,
Gasman

 

[devjr]

Rick, Rodales provided an excellent summary of their factual findings. Your repetitive observation that cookoff or dive intervals are lessened simply repeats and elaborates on their original statement on this matter. Yours is a cheap shot.

 

[Natasha]

Good post Mike.
I'd like to hear more about your clases as you take them.
I'm not Nitrox ceritified. But I have been considering it.
I've talked to instructors that say they are, and they don't even use it.
:sunny:

 

[Rick Murchison]

How so? Did they or did they not make the statement that using Nitrox at less than 50' is "impractical?" And is a significant reduction in required surface intervals for multiple dives in the 40-50' range of no practical value? It is to me. And while this particular headline is far from their most egregious, it is illustrative of a pattern of sensationalism in their headlines that I find at least misleading if not often downright dishonest. Nevertheless, I read the magazine cover to cover - sometimes there's great information there, even if it ain't what the headline promised.
Rick

 

[kubefish]

the advantage of nitrox is that you can stay down longer.
if your 80 tank does not allow you to stay down longer than 60 minutes you need to bring more air down with you.
maybe a 100 or a 120 of even double 80's