How Deep Is Air Safe As A SCUBA Breathing Gas?

[bm9]

my answer would be choice 5-none of the above. My switching to nitrox is not dependent on depth necessarily, but more dependent upon whether the dive will push no decompression limits or be planned as a deco dive.
I hardly ever use nitrox for a recreational dive unless it is a bottom time where I would have a deco obligation with air that I want to avoid. Dives completely within recreational limits I can usually accomplish just fine with air.

 

[DeepTechScuba]

Offhand, BM9, it looks like 97% of the respondents agree with you, so far.

We are still in the 1970s then, when it comes to breathing mix. Maybe even still in the 1960s, what the heck?

 

[CD_in_Chitown]

DeepTechScuba once bubbled...
looks like 97% of the respondents agree with you

Where do you draw that conclusion, looks like at least 13% say air shouldn't be used below 50fw or less

 

[DeepTechScuba]

One of the things about these poll results that has surprised me is that 88%, currently, do not use nitrox for scuba. Or possible they do not feel that it is necessary.

 

[cornfed]

DeepTechScuba once bubbled...
One of the things about these poll results that has surprised me is that 88%, currently, do not use nitrox for scuba. Or possible they do not feel that it is necessary.

How did you come to that conclusion? 88% of who don't use nitrox? You can't draw any useful information from this poll.

 

[sulaiman]

AT 100 MSW the partial pressure of the oxygen will kill your nerve system even the air you breath will test different


Since you know now the limit of the pure air scuba tank we can talk about the safty

Go by the diving table don’t push it

 

[RichLockyer]

DeepTechScuba once bubbled...
Choice #4 embraces the 130', 150', 170' etc answers BECAUSE you cannot dive on nitrox at those depths. (I am not considering EAN25 as "nitrox" although technically it is I suppose.)

I want to know at what SHALLOW depth divers here will use nitrox instead of air.

This is not a deep air discussion.

Okay, then I think the poll results are completely invalid IF that was your intention.

I answered 100ft, but I ALWAYS dive nitrox (when available)... air when it's not available.
My logic in selecting 100ft is because of narcotic issues, not because of N2 loading issues. I suspect that most responses used the same logic, and even the wording of the poll implies this, IE: "How deep is air safe"...

N2 loading is not a good thing, but it comes with the territory.
There is no difference in N2 loading between breathing EAN40 at 70ft and breathing air at 45ft. This can hardly be approached as a SAFETY issue as the poll indicates.

From a safety aspect, the narcotic differences between air and EAN are debatable, and at best, even if O2 is not narcotic, the benefit of nitrox WRT narcosis decreases as you approach depths where narcosis can create a safety issue simply because the amount of O2 must be reduced. At 150ft, where few would argue that narcosis is not an issue, you can't safely use nitrox.

Another interesting thing about the results.... At first glance, it appears that we have an even split between the traditional rec limit of 130ft and the more conservative END limit of 100ft... but add up the responses indicating deeper than 130.... 45% of responses indicate that air is safe below 130ft.

Ignoring the issues of narcosis, I'm with the 6% on the first answer, and would have answered that way had the poll not been titled in a way that made it appear to be a safety issue.


Perhaps the poll should have been worded as follows:

1) you always dive on nitrox
2) you dive on nitrox when available
3) you never dive on nitrox
4) you always dive on trimix/heliox
5) you dive on trimix/heliox when available
6) you never dive on trimix/heliox
7) you dive on nitrox deeper than 20 ft
8) you dive on air deeper than 20 ft
9) you dive on trimix/heliox deeper than 20 ft
10) you dive on nitrox deeper than 50 ft
11) you dive on air deeper than 50 ft
12) you dive on trimix/heliox deeper than 50 ft
13) you dive on nitrox deeper than 80 ft
14) you dive on air deeper than 80 ft
15) you dive on trimix/heliox deeper than 80 ft
16) you dive on nitrox deeper than 100 ft
17) you dive on air deeper than 100 ft
18) you dive on trimix/heliox deeper than 100 ft
19) you dive on air deeper than 130 ft
20) you dive on trimix/heliox deeper than 130 ft
21) you dive on air deeper than 150 ft
22) you dive on trimix/heliox deeper than 150 ft
23) you dive on air deeper than 170 ft
24) you dive on trimix/heliox deeper than 170 ft
25) you dive on air deeper than 200 ft
26) you dive on trimix/heliox deeper than 200 ft

.... and allow for multiple selections.

The problem is, in a simple poll like this, even the above results would be meaningless without some crunching.

 

[Ender]

sulaiman once bubbled...
AT 100 MSW the partial pressure of the oxygen will kill your nerve system even the air you breath will test different


Since you know now the limit of the pure air scuba tank we can talk about the safty

Go by the diving table don’t push it

Uh.. Wrong. PP02 2.3 is very likely to cause convulsions in most people. But it may not.
A (relatively) large number of people dived to more than 100m on air and came back to tell the tale.
Last century salvage hardhat divers dived - and worked hard! - to more than 100msw and _most_ of them survived - and most of those that died died because of DCI.
For the matter, to my knowledge diving protocols for some navies call for starting to decompress on pure oxygen in 20msw (that's PPO2 3ATA!) - but it's usually on a platform and using full face mask (and support divers around).
Both US Navy treatment tables 5 and 6 start with this.

So it's not "can't be done on air" it's "can be done more safely with a different gas".
Vlad