Where does the 60ft/minute ascent rule come from?

[Kingpatzer]

While that's true, it's also not addressing a reasonable response.

I imagine the risk curve for DCS related to ascent rates, depth and bottom time is a fairly complex thing. Perhaps I'm wrong about that, but I bet not. Simply because one extremely slow rate, unachievable by recreational divers has a near 0 risk does not mean that the risk from there to faster ascent rates does not fluctuate, perhaps even wildly, between different rates, aepths and bottom times.

Of course, simply because I can conceive of a complex curve does not mean that is reality either. But there is pretty good evidence that it is.

 

[Thalassamania]

And your "pretty good evidence" is?

 

[rjack321]

I imagine the risk curve for DCS related to ascent rates, depth and bottom time is a fairly complex thing.

Small, smaller, smallest good luck measuring meaningful differences, Marroni had a bear of a time.

 

[Kingpatzer]

And your "pretty good evidence" is?

I'll change it to something like: what I've read on the topic strongly suggest to me that it is. If that is more agreeable for you.

 

[Thalassamania]

Not really, it may suggest it to you, but you're a minority of one.

What I think you are trying to remember, is work alluded to earlier in this thread that showed if you slowed the rate too far you actually began to take up gas in faster tissues while you waited to slower tissues to clear. This is true, which is why the question is one of "optimum" deco, usually though of as the fasted possible deco w/o significant bubbling.

 

[rjack321]

I'll change it to something like: what I've read on the topic strongly suggest to me that it is. If that is more agreeable for you.

Buhlmann has 16 compartments each with their own half-times and allowable tissue tension values - and that's just a dissolved model. Add a bubble model into the equation and sure its a complex curve - which can operationally reduced to something approximating an exponential curve or Fibonacci sequence. How long do you want to hang at 8ft, is it even practical, and does it accomplish anything measurable & meaningful on a "no deco" dive? Is your complex curve more or less useful than better fitness or hydration?

 

[Thalassamania]

But even with the most complex curve, you have a shape where you get the fastest outgassing just before you get bubble formation, in fact bubble formation slows outgassing because it reduces the gas tension(s).

 

[Kingpatzer]

But even with the most complex curve, you have a shape where you get the fastest outgassing just before you get bubble formation, in fact bubble formation slows outgassing because it reduces the gas tension(s).

You know, once I read that it's obvious, but it never occurred to me until you said it.

 

[Thalassamania]

There is a amazing lack of clarity in the way in which this sort of information is taught. It has often led me to believe that many Instructors don't really understand it themselves.

 

[Slamfire]

You're obviously going to struggle with the "art" parts of deco.

30ft/min with a 10ft/min slowing (either as one 15ft stop or sliding through the ~30ft to 0 ft zone) is pragmatic and it works. Many of us start slowing down to ~10ft/min at roughly 1/2 our depth.

Gas and conditions permitting, the more you can shape your ascent like an exponential curve the better, always remembering you <could> surface directly. This is a function of the pressure changing most rapidly the closer you get to 1 ATA to have a similar pressure change over time that you did at (e.g.) 2.5 ATA you have to slow. (among other reasons).

Art indeed. I posted this dive profile in another thread . For this particular dive plan I would have had my deco obligations fulfilled at a run time of 54 mins. But in the spirit of what Thal says about taking a week to ascend from 60', I stayed longer. There are minimal downsides with staying longer after the 54 min mark because, as rjack says, I can surface directly at any point after the 54 min mark.

You can see that before 70' I had a faster ascent rate. After 70' (gas switch) the ascent rate slows to 10ft/min and near the end it gets even slower. On this dive I remember ascending really slow following the bottom, until I saw my computer mark a depth of 4'. After that it just considered that I had surfaced and it quit showing depth. So I stood up slowly and ended the dive. It may sound dorky, but I get a kick out of looking at the shape of my profiles after a dive. It's part of that pursuit of excellence in those "art" parts of deco while trying to shape up an "ideal" curve and trying to improve my diving. It also makes me feel a little better about paying almost $100 for a stupid cable.