Padi Advanced OW - Deep stops??

[boulderjohn]

Because there's a difference between simplest and the most optimum approach.

The majority of divers benefit from having the simplest safe approach.

A minority of divers seek an optimum approach, possessing a capability and understanding to apply approaches that are more complex.

How do we know that the changes to the ascent profiles that divers are doing to optimize their approach are actually making it better? How do you know they are not making it worse?

Scientists like Buhlmann, Spencer, Powell, and the whole Navy Experimental Diving Unit spent enormous amounts of time and money creating what they think works best--what are the odds that some guy will dream up a tweak that will make it better? It might be better. It might be worse. How will they know?

Let's say some one tells you that before they go out for a drive in the car, they always take a stiff shot of whiskey to calm their nerves and make them a better driver. You try it and have a good drive, so you decide that you, too, will have a big best of whiskey before you drive. You do OK--no accidents. Does that make drinking before driving the optimum approach?

 

[DevonDiver]

Scientists like Buhlmann, Spencer, Powell, and the whole Navy Experimental Diving Unit spent enormous amounts of time and money creating what they think works best

The sum total of their work was the "3-min at 5m safety stop?".

I should have specified that I was talking in the context of recreational ascents. My comment was a reply to EFX's post ( Padi Advanced OW - Deep stops?? ) in a thread about AOW.

EFX asked why some [recreational] divers choose to implement alternative [safety] stops rather than simply increasing the conservatism on their dive computers.

There are justifications for a very simplistic ascent protocol for recreational divers. The 'standard' safety stop is appropriate 'enough', given risk-versus-reward in no-stop dives. That, however, doesn't make it the optimum approach from an off-gassing efficiency perspective.

Some divers elect to optimize their off-gassing and reduce decompression stress by refining their ascent/safety-stop approach beyond the simplistic recommendations of their training agency.

I don't think you're saying that no deco deep stops are the optimum approach in this case, correct?

Yep... I'm not commenting on deep stops. I'm merely contrasting the benefit of current recreational ascent protocols versus more refined, but complex, approaches to surfacing cleanly.

 

[KenGordon]

How do we know that the changes to the ascent profiles that divers are doing to optimize their approach are actually making it better? How do you know they are not making it worse?

Scientists like Buhlmann, Spencer, Powell, and the whole Navy Experimental Diving Unit spent enormous amounts of time and money creating what they think works best--what are the odds that some guy will dream up a tweak that will make it better? It might be better. It might be worse. How will they know?

Careful, you are criticising the sacred GF with this line of reasoning.

 

[boulderjohn]

Careful, you are criticising the sacred GF with this line of reasoning.

Maybe. Maybe not.

I asked how you know if what you are doing is going to make it better or worse. You do that through research. A lot of it has been done since that earlier work. If you make a decision based on a careful reading of that research, it is one thing. If you do it on blind faith in what someone else said, it is another.

 

[KenGordon]

Maybe. Maybe not.

I asked how you know if what you are doing is going to make it better or worse. You do that through research. A lot of it has been done since that earlier work. If you make a decision based on a careful reading of that research, it is one thing. If you do it on blind faith in what someone else said, it is another.

It seems to me that GF is the epitome of made up by a random bloke deco. That is not to say any of the others are any better, but Erik Baker was (is?) not a doctor or deco scientist but an engineer. The extra special bit about gf is or course that the end user can add their own spin on the numbers.

 

[dmaziuk]

Math is math whether you're a doctor or an engineer (one could argue that engineers tend to have a better grasp of it then medical doctors). You move your pressure gradient away from the M-line, you should be safer. i'd expect a point of diminishing returns there somewhere, but without sufficient empirical studies... it's your own spin, it can be whatever you want

 

[stuartv]

Math is math whether you're a doctor or an engineer (one could argue that engineers tend to have a better grasp of it then medical doctors). You move your pressure gradient away from the M-line, you should be safer. i'd expect a point of diminishing returns there somewhere, but without sufficient empirical studies... it's your own spin, it can be whatever you want

Yep. Math is math. And it will only tell you the answer to the question you asked.

If the equation has no parameter to match something the real world dictates is important, then it may tell you you've moved further from the M-value and yet what you did still produces DCS more often.

For a made-up example just intended to be illustrative, suppose there is no parameter in the equation that describes the behavior of performing multiple multi-level reverse profiles during a dive. The "math" might tell you you're descending and thus, moving your pressure gradient further from the M-value. And yet, you might still get bent as a result - even though the math said you were being safer each time you descended again.

As deco theory is not 100% understood, who can say for sure what parameters are important to predicting DCS that are not reflected in the current math?

 

[dmaziuk]

who can say for sure what parameters are important to predicting DCS that are not reflected in the current math?

I can: all of them. That is, AFAIK the actual incidence of DCS is so low it's way below variability between individual divers and/or even individual dives for the same diver. If that's true, one could say that it's things that are not math that get you bent.

 

[scubadada]

I can: all of them. That is, AFAIK the actual incidence of DCS is so low it's way below variability between individual divers and/or even individual dives for the same diver. If that's true, one could say that it's things that are not math that get you bent.

The commercially available decompression algorithms are all reasonably conservative, for instance, compared to the US Navy.

 

[KenGordon]

I can: all of them. That is, AFAIK the actual incidence of DCS is so low it's way below variability between individual divers and/or even individual dives for the same diver. If that's true, one could say that it's things that are not math that get you bent.

Nobody knows the incidence of DCS. To know that we'd need to know how many dives are done (obviously very hard) and how many DCS incidents (not so obviously hard).