Nitrox and Photography

[DeepScuba]

Sounds good James, but my thoughts will probably still be that all things being equal, there's no possible way that diving Nitrox "as air" is a safer bet, hands down. It's just too obvious. Anythign else would turn the Nitrox tables and chemistry upside-down.

Which is, of course wrong.

So there has to be other reasons why people are taking similar numbers of hits doing the same "profile" of Air vs Nitrox.

(I personally DON'T believe what you're saying, but at least I'll wait to be proven incorrect, it's no problem with me).

ALIKAT:

Don't worry, if you're not diving Nitrox much, you'll probably not remember what you SHOULD be remembering

I've found most students (It totally amazes me, by the way) how much they still don't "Get It".

I've talked to a lot of students 3 months after a Nitrox course, and when discussing an upcoing dive, they can't "plan" a damn thing as it pertains to Nitrox mixes etc......

They seem to have no clue as to the Po2, times, ox-tox limits for a particular dive.......nothing. I'm blown away.

Learn it well, it's the (mathematic) base for all future Adv Nitrox/Trimix courses.

Regards

 

[Genesis]

Reality is that DCS incidents, IF you truly stay within the tables, AND you make controlled, safe ascents, are extremely unlikely.

So much so that discerning a difference between air and nitrox is going to be difficult.

When something is far enough down the statistical curve, finding real differences that you can actually attribute to a causative factor is difficult - or impossible.

That's what's likely going on here.

 

[DeepScuba]

Fully agreed, Genesis. I think Jepuskar got some bad info.

Now just to be sure, I'm talking about diving Nitrox AS air (For Nitrogen loading).

 

[Genesis]

I suspect that MOST recreational hits fall into one of two categories;

1. You do something stupid (e.g. Polaris, etc) and odds are you'd have gotten the hit irrespective of whether you were breathing air or Nitrox.

2. You have some unknown succeptability to a hit (e.g. an open PFO, or one that is sometimes open, and is this day, etc) that nails you, and again, probably would have irrespective of what you were breathing.

Let's assume that 90% of the DCS cases in recreational diving fall into one of these two categories.

If this is the case, then diving Nitrox as air doesn't really provide any safety margin in fact (as opposed to theoretically), since the cases of incidence of a hit where it could be a factor are so rare in the first place that statistically-speaking you can't measure the statistical impact of using Nitrox as air.

Given that, the "best practice" seems to be to use Nitrox to extend your bottom time, since the actual "protection" from backing off that far on your dive profiles is statistically insignificant.

 

[AliKat]

DeepScuba,

I think I remember knowing it all pretty well when I went through the class. But what I remember most now, is sitting at the instructors kitchen table at 11PM on a Friday night doing all this MATH!

 

[ScubaRon]

According to DAN/PADI, the chance of getting DCS by air diving is approx. 0.004%. When diving nitrox the chance is 0.003% (Undersea Journal 3-97).

Thus nitrox seems to lower the chance of getting bent somewhat. However nitrox also introduces other risks that are not/less present with air:
- oxygen toxicity
- increased risk of narcosis
- errors in gas mixing
- combustion due to hydrocarbon contamination

Taking this into account it seems hardly likely that nitrox is safer than air diving. So unless you need the extra bottom time, why bother with the extra effort and expense.
ScubaRon

 

[Genesis]

is likely not statistically significant. It might be, but single-count differences, even when percentage-wise they are large (this is - 25%!) - are likely not to be.

As for the other risks, whether they are present or not depends on the situation. Oxtox is possible, but if you dive Nitrox where there is a hard floor above the MOD, its a non-issue.

Combustion is possible with AIR. There is no statistically-significant increased risk using Nitrox up to 40% (there may be MIXING it, but usually that's the shop/filler's problem, not the diver's!)

As for narcosis, there is no statistically-valid evidence that Nitrox is any more or less narcotic than air. Some people claim Nitrox is less narcotic, but agan, there is no science to back that up.

 

[cornfed]

Genesis once bubbled...
Some people claim Nitrox is less narcotic, but agan, there is no science to back that up.

These claims are based on faulty logic. They neglect the fact that oxygen is also narcotic.

 

[Genesis]

There is little science on this that actually counts.

For example, we know that Argon is EXTREMELY narcotic. What we don't know is if narcotic properties are strictly additive - that is, if you have a PPN2 that would produce a given level of narcosis, if you add a very small amount of Argon would you get the amount of narcosis that would be suggested by the Argon, the Nitrogen, some blend, or a pure additive function?

There's no straight answer to that question. To the best of my knowledge there has been no formal, controlled study in an attempt to find out.

In my personal experience there is no difference in narcosis between Nitrox and Air. That would support the idea that O2 and N2 are roughly equivalent in narcosis, and they are additive, But those are two gasses very close on the periodic table in terms of their molecular weight - and lipid solubility.

The lipid solubility index, often cited as the "indicator" of narcosis, is a theory. It seems to work for 1.0 ATM pressures, but whether its really all that accurate of an indicator - or whether that's the mechanism by which narcosis happens, or just happens to be a correlation that stands up (most of the time) is not known.

 

[AliKat]

The main benifit I found from nitrox is I had more energy after a day of diving nitrox than with air. I also wasn't left with the headaches I used to get after diving. However, I worked on my breathing and now no longer get those with air.

The main disadvantage I saw to nitrox was the cost...about $12 compare to $1 to fill my air tanks. Plus all the nitrox tanks were 80's and I dive 63's.