Nitrox for shallow water artifact diving??

[BRT]

So what mix would be good @ 25FSW 70% maybe 100% O2? How high is up?

You do you. If I was doing multi-hour dives to 30 feet I'd use nitrox if it were available.

 

[AfterDark]

You do you. If I was doing multi-hour dives to 30 feet I'd use nitrox if it were available.

Must be nice to have money to burn.
Then there's O2 toxicity to consider.

 

[AfterDark]

I am really baffled by this exchange. This is all standard nitrox training.

Start with the basic equation PG = FG * P, with P expressed in ATA. If you have two of the variables, you can find the value of the other one. If we want to find the nitrox percentage (FG = Fraction of gas), we divide PG by P.

With oxygen levels, our primary concern is not exceeding a safe gas pressure (PO2), which is usually considered to be 1.4 for active diving or 1.6 for decompression stops, so let's use 1.4 for PG. For P, we have to convert 25 feet of sea water to ATA. (It will be slightly different for fresh water.) 25/33 + 1 = 1.76. Now that we have two of the variables, we can find the third. FG = PG/P, or in this case, FG = 1.4/1.76 = 79.5.

So a diver can safely use 80% nitrox at 25 feet on the 1.4 standard.

Gee thanks John! I never could have figured that out!
It was a rhetorical question. One by the way the poster I quoted answer correctly.

So here's a problem: A diver on air makes 5 1 hour dives to 25FSW with 3 20min SI and 1 60min SI inside of a 12 hour period. How are the repetitive dives calculated?

Is the answer different if the same dives are done on nitrox?

Bonus ? Can that diver fly afterward?

 

[ginti]

I am really baffled by this exchange. This is all standard nitrox training.

Start with the basic equation PG = FG * P, with P expressed in ATA. If you have two of the variables, you can find the value of the other one. If we want to find the nitrox percentage (FG = Fraction of gas), we divide PG by P.

With oxygen levels, our primary concern is not exceeding a safe gas pressure (PO2), which is usually considered to be 1.4 for active diving or 1.6 for decompression stops, so let's use 1.4 for PG. For P, we have to convert 25 feet of sea water to ATA. (It will be slightly different for fresh water.) 25/33 + 1 = 1.76. Now that we have two of the variables, we can find the third. FG = PG/P, or in this case, FG = 1.4/1.76 = 79.5.

So a diver can safely use 80% nitrox at 25 feet on the 1.4 standard.

1.4 is a PP that shouldn't be kept for more than 2.5hrs; I know you know it, but here's a reference for the ones who don't, figure 2:
https://www.shearwater.com/wp-content/uploads/2012/08/Oxygen_Toxicity_Calculations.pdf
NOTE: I used to find online the original NOAA manual from 1991, but I can't anymore. I will be immensely grateful to anyone who can share the link.

I haven't understood yet how long are OP's dives, but at these depths, for artefacts diving, maybe he is diving even more than 150minutes, so the 1.4 standard might be a bit risky... don't you think?

 

[AfterDark]

From the Merriam-Webster dictiionary:

However, there are two senses of theory which are sometimes troublesome. These are the senses which are defined as “a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena” and “an unproven assumption; conjecture.” The second of these is occasionally misapplied in cases where the former is meant, as when a particular scientific theory is derided as "just a theory," implying that it is no more than speculation or conjecture. One may certainly disagree with scientists regarding their theories, but it is an inaccurate interpretation of language to regard their use of the word as implying a tentative hypothesis; the scientific use of theory is quite different than the speculative use of the word.
​

@AfterDark I fear you are using theory in the speculative sense, which is NOT appropriate for how it is used in the scientific context, as in "decompression theory," as @boulderjohn is using it.

I'm sure you do. However when I see the word theory I read, we have some facts, but we don't know what we don't know, however here is what we think is going on.

We do have the fact that nitrox was developed to extend NDL/BT.
The fact that there is no NDL above 30FSW.
So what tangible benefit does a diver receive from using nitrox above 33FSW?
My answer is I can't name any based on the known facts.

And I'm still trying to find a case of DCS using air diving above 33FSW. Can you help me with that?

 

[Storker]

when I see the word theory I read, we have some facts, but we don't know what we don't know, however here is what we think is going on.

As in "theory of relativity", "theory of gravity" or "theory of evolution"?

What you are describing is a hypothesis. A theory is a hypothesis which science has not been able to falsify despite several attempts to do so, and which can safely be used for prediction. IOW, we have some facts (the apple fell to the ground), here is what we think is going on (gravity), and we can quite safely predict that also that rock will fall to the ground if we drop it.

 

[AfterDark]

As in "theory of relativity", "theory of gravity" or "theory of evolution"?

What you are describing is a hypothesis. A theory is a hypothesis which science has not been able to falsify despite several attempts to do so, and which can safely be used for prediction. IOW, we have some facts (the apple fell to the ground), here is what we think is going on (gravity), and we can quite safely predict that also that rock will fall to the ground if we drop it.

Precisely like that, the rock falls if dropped fact, we think we know why theory. thank you.

 

[Centrals]

We do have the fact that nitrox was developed to extend NDL/BT.
The fact that there is no NDL above 30FSW.
So what tangible benefit does a diver receive from using nitrox above 33FSW?
My answer is I can't name any based on the known facts.

And I'm still trying to find a case of DCS cause by diving on air above 33FSW. Can you help me with that?

My personal opinion ONLY:
1. I really do not see the point to use Nitrox for such a shallow dive.
2. There is such a thing as "earned" or "unearned" DCS. We are all individual so anything is possible.

Science cannot explain everything.

P9 already!!!! Incredible. We must be bored.

 

[calabash digger]

90 to 120 minutes on a 10 to 25 ft dive. I was taught at these depths there was really no risk of DCS on a two tank dive. ???? I would say 80% of my dives have been in the 20 to 25 ft range and that depth changes up and down a lot sometimes. I climb up and down the wall looking for artifacts so I might be at 25 feet one minute and in five feet of water few minutes later.
I can get Nitrox fills very easily about a mile from my house...couple dollars more I think for each tank...

 

[ginti]

90 to 120 minutes on a 10 to 25 ft dive.

Do you do repetitive dives? If yes, how long are, usually, the surface intervals?