Blow a Safety Stop? Redescend ?

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BTW, DAN's latest report suggests that the average ascent from the shallow stop is OVER 200 fpm. Yoiks! ....
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What is 200 fpm? surely that doesnt mean 200 feet per minute?

200/60 = 20/6

If so that means from 20 feet, the ascent is only 6 seconds. If this is average that means some are a lot faster.

We learned 60 feet in a minute 60ft/60sec or preferably 60/30sec.

The possible ramifications are?.........
How fast will kill you?.......
 
So I ask, what is the difference between in water recompression (I think it would qualify as immediate) than a chamber, in terms of it being harmfull? Again, base it on the physics of both situations, only.


You can't drown in a chamber.
 
What is 200 fpm? surely that doesnt mean 200 feet per minute?

200/60 = 20/6

If so that means from 20 feet, the ascent is only 6 seconds. If this is average that means some are a lot faster.

We learned 60 feet in a minute 60ft/60sec or preferably 60/30sec.

The possible ramifications are?.........
How fast will kill you?.......
The ascent rate is inherent to the decompression model, you can build tables around just about any desired ascent rate, the faster the ascent the less pressure exposure permissible. Keep in mind that the ascent rate for submarine escape is in excess of 300 fpm, but the pressure exposure is minuscule, just the time in the trunk.
 
Okay, this is really interesting stuff. I am learning something usefull, which I will noodle through. But, when I am told I am not understanding something correctly, I go find out.

Sooooo..... I sent an e-mail to a respected pulmonary cardiologist, who is a pulmonary specialist/professor of medicine, and wrote a really great book some years back on the subject. I asked him the basic question orginally posed; i.e. "would you redescend if you blew a safety stop?". I further clarified my question to him in that you knew nothing about the diver, their repetitive dive history, depth, bottom time, nothing.

The responses were as follows (please note this is NOT a recommendation from a doctor, and I am answering this as a point of discussion, NOTHING MORE, and and offering this only as a point of discussion):


It is really two questions, involving in-water recompression:
1. When you miss a recommended safety stop,
2. When you have (or about to develope) the bends

1. A safety stop in recreational diving is recommended because it builds a margin of safety; by definition, in recreational diving (i.e. diving by the tables) you will not get bent without a safety stop. It is 'no-decompression' diving. So if you missed a safety stop, and are worried about it, no harm at all in going back down and recompressing. Your theory is correct; it is the same (physics-wise) as the chamber in terms of increasing the pressure.

2. If you miss a decompression stop that is built in because it is necessary to avoid the bends (i.e., by definition not
recreational diving), then you have a problem. The problem is that if you get acutely ill (pain or mental confusion or whatever) and go back down, you could drown. This is probably why the docs recommend not to go back down - if the diver is unstable in any way, it could be a disaster. Controlled recompression is theoretically much safer.

So to answer your question, going back down is a good idea if there is no threat of illness (bends) that would lead to possible drowning AND (I should add) you have enough air to stay down awhile. In the real world I imagine there might be a lot of confusion over these issues if a diver surfaces without a stop and he/she asks 'what should I do?' Best to know and be prepared ahead of time.



So, I think there is lots of discussion left on this issue, and no clear consensus in the medical field. But my original point was that the physics and gas law properties do not change, but as pointed out, the controlled enviroment of a hyperbaric chamber does.
 
: I agree with many statements in your last post...but not the quoted paragraph above. Basing your decision to re-descend (under those circumstances, i.e., omitted safety stop) on the physics of bubble growth dynamics is, at best, an aggressive interpretation of the science. It's dangerous to overstate the findings of published scientific work and, even more so, to base our real-world dive profiles on bubble studies alone. Simply put...we do not understand the relationship between intravascular bubbles (as recorded by Doppler studies) and the pathophysiology of DCS. Period.


Okay, but my original point is that the physics is the same. As pointed out by others, you can't drown in a chamber, but if you are not presenting with any symptoms, have plenty of air left to redescend, then what is the scientific basis for not doing it? Specifics, please.
 
For some more fun...there is some discussion afoot to "recommend" a deeper safety stop at around 60 feet for "deep" dives, in addition to the recommended stop at 10-20fsw. Don't know what the suggestions are (yet), but have heard them discussed in the industry. Apparently the intent is to get people to slow down their ascent rate.

Students are always amazed at how SLOW 30 feet per minute really is, and how slow it seems in the water.

I know there are some really "in-the-know" people on here, whose opinion I respect. But is there anything "definite" on the theory of "bubble pumping"? Wouldn't the same issues of "bubble pumping" occur in a chamber? If not, why? Specific input would be most appreciated.
 
that's what the PADI tables require down to 90 feet. below that, safety stops are required for all dives

PADI requires them, but the algorithmically PADI's table does not.


No-decompression limit is a misnomer. Rather, what the PADI (DSAT) table displays are no-STOP limits, assuming a maximum per-tissue pressure gradient and a maximum ascent rate.
 
https://www.shearwater.com/products/swift/

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