Hypothetical question about decompression

[rongoodman]

It's not exactly what the OP was asking about, but there is the concept of "ceilings", as opposed to discreet deco stops. V-Planner Live running on the Liquivision X1 computer has the option of continuously calculating the exact required deco depth required, according to its model, in real time, so the the diver can continuously ascend holding the specified depth, rather than spending time at evenly spaced stops. Although the displayed ceiling changes continuously, I doubt very much that it's a linear progression.

 

[daniel1948]

The OP specifically asked if you could take the same amount of time ascending at a constant rate as you would take if you used the standard tables. The answers above confirm my original answer: ascent must be faster at first, slowing greatly as you get shallower.

I presume it would be possible for a computer to calculate a safe continual ascent profile, without stops, but the ascent rate would slow greatly as you neared the surface. And I suspect that such a profile would be extremely difficult to adhere to unless you were sitting on a platform that was being raised under control of the computer doing the calculations.

So the answer remains a categorical no.

 

[nereas]

Nereas - You did not answer the original question.

I am starting to worry that I/Qs have tanked in Redondo Beach. Let's study why ...

This is a hypothetical question, as I've been doing some reading on decompression theory lately.

Lets say you do a dive to 150ft that reqired at total accent time of 60 min. where you would do a staged acent stopping at the reqired stops for the reqired time.

...I hope that makes sense.

It did not make sense, therefore I showed him a typical deco profile for a typical dive that does make sense.

...

Would this be, in theory, and assuming it were possible to even physically do this, the same as making a direct controled acent of 2.5ft/min without stopping from 150ft???

...I hope that makes sense.

It did not make sense. Therefore I pointed out that he should stop at his stops.

This is a hypothetical question, as I've been doing some reading on decompression theory lately...

In other words is a direct acent totaling 60min the same as a staged acent totalling 60min from the same depth?

I hope that makes sense.

It did not make sense, therefore I gave him the potential injuries that result from violating a deco program. These injuries are all findings of fact, not theory.

NWGrateful's pretty pictures which illustrate the idea of what might be happening when you subject your body to hydrostatic ambient pressures in excess of 14.7 psi are lots of fun, but like Santa Claus and Tooth Faeries they are just ideas. Scuba 101 covers all this for the basic NDL certification.

I gave the O/P something that he can dive with. And I told him what he needs to do to go diving, for the kind of dives he asked about specifically. Whereas NWGrateful told him bedtime stories.

I have no doubt that I/Qs in Seattle are higher than at Redondo Beach, at the moment, if this is a good sampling of only 2 people.

However I doubt the value of bedtime stores about little bubbles in multicolored boxes.

Because if you are going to dive deco profiles, then you need a deco plan. And you need to follow the plan. And you dare not vary from the plan. Your woody and your continence depend on it. That is covered in Deco Diving 201.

And low I/Qs go onto my ignor list, with the others.

 

[Charlie99]

Jaycanwk, your question is one that was asked in the very early days of decompression science, back in early 1900's. At that time, "caisson disease" was a big problem for construction crews (aka "sandhogs") working in a pressurized caissons beneath rivers, doing things like building the foundations for large bridges. Caisson disease is what is now called the bends or DCS.

One researcher, Hill, proposed a linear ascent, such as you mentioned in the opening post. J.S. Haldane proposed a staged decompression approach, which spends more time shallow than deep. Haldane's approach proved to be much better.
https://diversalertnetwork.com/membership/alert-diver/article.asp?ArticleID=573

While there is some difference between various models in the exact shape of the ascent depth vs. time curve, all models spend more time shallow than deep.

One could efficiently offgas using a constant ascent, but the speed of ascent would be faster when deep; slower when shallow. On a practical basis, experience has shown that a stepped approximation of this ideal NON-linear ascent by a series of stops 10' apart is close enough that going to a continous (but varying with depth) ascent doesn't improve the decompression enough to make it worth the extra effort as compared to 10'/3m stops.

-------------------------

Decompression is a balancing act. One wants to get shallow in order to stop further ongassing and to promote offgassing. OTOH, one wants to stay deep in order to prevent bubble formation. These are conflicting goals, and the "faster when deep, slower when shallow" type of ascent has been found to be the best balance between these conflicting goals.

Bubble models such as RGBM and VPM differ slightly from neo-Haldanian models in that the bubble models spend a bit more time deep than does the Haldane model, but the basic ascent curve for both is weighted with more time shallow.

 

[DwayneJ]

I gave the O/P something that he can dive with. And I told him what he needs to do to go diving, for the kind of dives he asked about specifically. Whereas NWGrateful told him bedtime stories.

...and are you suggesting someone could actually use what you published while you continue to throw flippant comments at some of the smartest people on this list? Amazing.

The added irony here is that only a few posts ago, you were stating not to follow tables, only follow computers. Which is it today - Tables or Computers?

 

[ianr33]

And low I/Qs go onto my ignor list, with the others.

Thats funny

 

[nereas]

This message is hidden because DwayneJ is on your ignore list.

 

[wve]

No question that deco is theory, but please consider the following, from the DAN website (citation below):

British physiologist Sir Leonard Hill theorized that decompression should be by linear ascent to the surface; he strongly disagreed with Haldane's approach. However, in the end Haldane was able to prove, using goats, that a slow linear ascent was not only ineffective, but unsafe; too much nitrogen remained on surfacing resulting in frequent DCS.​

Full article is available at DAN.

-Bryan

Thanks. I'll check that out.

 

[nereas]

Thats funny

Where are you from, Ian?

 

[Tassie_Rohan]

The question Neras was -

In other words is a direct acent totaling 60min the same as a staged acent totalling 60min from the same depth?
.

Not only were you unable to provide what the answer is, you were unable to provide a why, and now it's back to your usual response of personal attacks.

Unfortunately a lot of people nowadays seem to rely on their computers without understanding the fundamental physics and physiological responses behind the various algorithms used.

I thing bobs, daves, byrans and charlies posts hit the nail on the head. The ascents are treated differently because of the different rates of off-gassing from various tissue compartments. I don't have to resort to cutting and pasting from Vplanner to know that.

Cheers,
Rohan.