Basic decompression questions

[HBO MD]

That's bubble pumping, more akin to AGE (which only takes 3 to 4 feet) than to DCS. I know of no cases of actual DCS shallower than 20 feet.

Actually published these incidents in SPUMS journal around '91, '92.
They are not in isolation and are in the literature.

 

[kgault]

Actually published these incidents in SPUMS journal around '91, '92.
They are not in isolation and are in the literature.

Any references, or even partial titles?

Keith

 

[lefemme36]

I am a little surprised by some of the statements to this OP's question.

How can anyone say there is NO RISK?

Dive tables are not LAW. Dive tables are theory.

T H E O R Y

If you consider that there is enough pressure to make you equalize while diving at the bottom of a 10 foot pool, than who's to say you aren't going to absorb ANY nitrogen at 18 feet for 2.5 hours?

And for those of you who mention you are "off gassing" at -20', think again. You are off gassing until ambient and even after. If you want to say it is relative to the depth you were previously diving to, that's a different story.

The question is clear, IS THERE ANY RISK. The answer is NOT CLEAR. But for those of you who think the answer is clear, why would there be a 20' reading on any charts if there were no absorption?

I think some of you are misinterpreting the question. OP is not comparing depths.

 

[eponym]

Whoa, Nellie.

I am a little surprised by some of the statements to this OP's question. How can anyone say there is NO RISK?

I can see how you got this impression. Please note that my post above stated the outcome of a detailed discussion with a doctor on my situation (many particulars discussed but not posted). I added that I did not want anyone to construe what I said as advice, and I meant that. Returning to one atmosphere (or less) entails some risk and we all make risk/reward calculations. I think I shall edit that post to make the point stronger, so thanks for the feedback.

who's to say you aren't going to absorb ANY nitrogen at 18 feet for 2.5 hours?

No one actually said that, did they. I think we all know that breathing air at more than one atmosphere leads to an increase in the nitrogen dissolved in your tissues, over and above the base load we carry around on the surface. I think we're debating whether or not you can absorb enough to make the difference between the nitrogen pressure in your tissues and the ambient nitrogen pressure on the surface so great that it leads to DCS (see "M-Value" here or elsewhere online).

And for those of you who mention you are "off gassing" at -20" [20 feet?] think again. You are off gassing until ambient and even after. If you want to say it is relative to the depth you were previously diving to, that's a different story.

Could you explain this? I'm not sure what you mean by "offgassing until ambient" and "it is relative to the depth etc."

Cheers,
Bryan

PS. 20" means twenty inches. 20' (single apostrophe) means twenty feet.

 

[captain]

Fairly common chamber practice here (and recommended as a first aid measure by some groups).

As with any medical issue that could lead to a blood clot, aspirin is a common medication to limit the possibility.

 

[eponym]

I am a little surprised by some of the statements to this OP's question. How can anyone say there is NO RISK? Dive tables are not LAW. Dive tables are theory. T H E O R Y

A correct and commendable attitude. On the other hand . . .

There is an article abstracted on the Rubicon website. It dealt with experimental data (not theory). Its title is:

DIRECT ASCENT FROM SATURATION DIVES: DCS INCIDENCE IS ZERO FOR DEPTHS SHALLOWER THAN A THRESHOLD DEPTH

Abstract includes the following sentence: "The DCS cases that result from deeper exposures lie on a sloping line that intersects the zero-DCS axis abruptly at 21 fswg, suggesting that there is a threshold for development of clinical DCS symptoms."

Full abstract is on Rubicon here.

Thanks, Gene, once again,
Bryan

 

[Blackwood]

e).

Could you explain this? I'm not sure what you mean by "offgassing until ambient" and "it is relative to the depth etc."

My best guess is he's saying that with a change in depth, you'll off- or on gas until the pressures in your tissues reach ambient (i.e. are saturated), and that said ambient pressure is depth-dependent.

 

[lefemme36]

My best guess is he's saying that with a change in depth, you'll off- or on gas until the pressures in your tissues reach ambient (i.e. are saturated), and that said ambient pressure is depth-dependent.

Thanks. That is exactly what I am saying. I'm not trying to say diving above 20' is dangerous or not. I just don't feel the replies are focused on sticking to the questions posed. That's all. But I do believe tons of risk is eliminated with proper education, training, and practice. But since all of our bodies differ, so do the results.

 

[Thalassamania]

Actually published these incidents in SPUMS journal around '91, '92.
They are not in isolation and are in the literature.

But they are not "true" DCS cases, they are cases were someone bubbled venus side (quite normal) and then as a result of a subsequent descent pushed gas through the alveolar bed into the arterial side and suffered what are essentially the effects of an AGE. Without the rather uncontrolled yo-yo ascent/descent profile nothing would have happened.

I am a little surprised by some of the statements to this OP's question.

How can anyone say there is NO RISK?

Dive tables are not LAW. Dive tables are theory.

T H E O R Y

If you consider that there is enough pressure to make you equalize while diving at the bottom of a 10 foot pool, than who's to say you aren't going to absorb ANY nitrogen at 18 feet for 2.5 hours?

And for those of you who mention you are "off gassing" at -20', think again. You are off gassing until ambient and even after. If you want to say it is relative to the depth you were previously diving to, that's a different story.

The question is clear, IS THERE ANY RISK. The answer is NOT CLEAR. But for those of you who think the answer is clear, why would there be a 20' reading on any charts if there were no absorption?

I think some of you are misinterpreting the question. OP is not comparing depths.

There is nitrogen absorption with any increase in pressure; there is nitrogen offgassing with an any decrease in pressure; even as little as a change in barometric pressure due to a weather front passing by. The point is that there is some level of supersaturation that the anyone's body can deal with without any problem and there is some level of supersaturation that will cause problems for the most susceptible of people. There was a time when we thought that level was saturation at 33 FSW, then 30 FSW, then 24 FSW, now 20 FSW. As more work has been done the "correct" answer has been refined. But we need to be careful not to compare apples and oranges, saturation followed by direct ascent to the surface at a controlled rate is very different from prolonged shallow dives with profiles that feature uncontrolled and repeated yo-yos.

 

[Gene_Hobbs]

Any references, or even partial titles?

Keith

Sorry Keith, I only have 1994 - 1999 of the 90's entered so far. I'll pick up at 1990 for you next or if I can find these later tonight, I'll get them in individually.

Talked to Rob Perkins yesterday, he says hi and he likes our abstract...