Average depth finder

[tbone1004]

or just use a computer with an algorithm you believe in that tracks it in real time...

 

[scubadada]

Take the average of the particular bottom depth segment (in this instance 90' and 130'), and then weight that average larger if you spent time deeper (example: 120'), or lesser if time spent shallower (100') over that bottom segment.

This is simply not practical or accurate. You don't spend specific times at specific depths. I have better things to do when I'm diving that track these numbers and doing the math...

 

[Kevrumbo]

@Kevrumbo so you wrote a novel about ratio deco theory, in response to a bolded fragment from me about why half depth is dumb. However, nothing in there said anything about why they think depth is better than pressure. In contrast, you are arguing about tissue loading and bubble formation, which is caused by pressure, not depth, so if you actually believe in that, you would adjust those stop profiles to account for half pressure instead of half depth and you wouldn't be loading the slow tissues. You would also realize that you can adjust the buhlmann gf-lo in order to force ascent profiles for deep stops which has been studied since that article was written and there were more DCS incidents with deep stops than with shallow stops, and there have been a lot more reports of DCS from guys diving VPM than Buhlmann lately

Again the motivation is to not approach the actual theoretical Buhlmann M-value (in either pressure or depth units), and to prevent bubble formation by inert gas diffusing into micro nuclei/bubble seeds in the leading tissue compartment controlling the ascent from bottom depth. Therefore the RD paradigm has staged deep stops starting at 75% depth for bottom times of 25min over NDL, or 50% depth within NDL. (Again with regard to the NEDU Deep Stop Study, the practical applied solution for us non-military/non-commercial "sport" tech divers to account for the resultant slow tissue supersaturation within RD or any other Dual Phase/Bubble Model is to extend out the shallow O2 profile stops as needed, especially after consecutive days of staged decompression diving.). For UTD Table NDL repetitive dives after minimum 60 minutes to 90 minutes SIT, they also double the stops to 2 minutes each at 30'/9m, 20'/6m and 10'/3m for conservatism.

 

[Kevrumbo]

This is simply not practical or accurate. You don't spend specific times at specific depths. I have better things to do when I'm diving that track these numbers and doing the math...

That's fine.

But it's not all that hard to do depth averaging unless you like performing extreme saw-tooth profiles (which aren't recommended anyway). Through experience and rote repetition of dive profiles (and "wrote" dive log entries), it becomes habit figuring out an average depth -even on a NDL/NoStop multi-level ascent- just as long as I'm not "yo-yoing" up & down all over the place +/- 6meters or more in a saw tooth pattern.

 

[tbone1004]

@Kevrumbo and what does depth have anything to do with it? It is pressure not depth that determines the bubble size. Call up DAN and talk to Dr. Pollock about why half depth makes no sense. If you guys said we do stops at half pressure because that makes the bubbles all double in size and that makes it not dependent on depth then I think we would have a different discussion, and no, it doesn't really matter all that much when you're super deep because the first atmosphere gets rounded out pretty quickly, but when you're in non-trimix depths? It makes no sense at all, and you have still yet to give an argument on why you use half depth instead of half pressure.

of further importance, what do you do when diving at altitude when the depth starts lying to you? You can't just ignore the surface atmospheric pressure...

 

[CAPTAIN SINBAD]

So here is what Mark Powelll writes about Deep Stops.

"Deep stops were initially developed by technical divers but the advantages may be relevant for all divers."

This is exactly what UTD/GUE has been saying all along but recreational dive computers do not seem to think that way. I am sure you guys remember that never ending scubaboard thread in which the credibility of deep-stops was questioned in the light of US Navy studies. That thread left a lot of people convinced that deep stops is a thing of the past and we need to move away from that thinking. Mark Powell disagrees:

"There has been a recent study by the US Navy which appeared to show the opposite conclusion to DAN study in terms of benefits of deep stops. This received a lot of publicity and was seen by many as evidence that deep stops were not such a good thing. However if you look at the US Navy study, you can see that they are testing something very different to what we have been calling deep stops so their conclusions do not apply to this discussion."

The DAN study that Mark Powell mentions above is actually very supportive of deep stops. In this study a series of dives were done to 25 meters with a deep stop at 15 meters + another at 6 meters. These were compared against another set of dives that skipped the deep stop at 15 meters and just did a conventional stop that recreational computers generate at 6 meter depth. The test divers who incorporating deep stops at 15 meters surfaced with very low Bubble Score Index (BSI). In the light of this particular study Powell writes:

"This seems to confirm that incorporation of deep stops has a positive effect on bubble formation even on recreational dives in 25 m range."

This goes totally in line with what UTD has been saying all along and is totally against the computer generated recreational profiles that I have been diving all my life. Mark Powell writes the following:

"A number of most popular manufacturers of dive computers have recently introduced models that include some form of deep stop or micro-bubble suppression algorithm and the Sub Aqua Association International has recently introduced a set of deep stops tables designed for recreational diving."

He seems to be convinced that as time goes by recreational dive computers and tables will modify their present stops and ascent rates and future of recreational diving would look more like what UTD seems to be doing now. In my earlier post, I mentioned that a lot of people are abandoning computers and diving with deep stops and they are no longer experiencing the post dive lethargy that they always did while chasing the computer. Here is what Mark Powell writes:

"The inclusion of additional safety stops on recreational dives is likely to be more widely adopted in the future in an attempt to provide an additional safety margin and as a way of reducing post dive fatigue."

 

[Kevrumbo]

So here is what Mark Powelll writes about Deep Stops.

"Deep stops were initially developed by technical divers but the advantages may be relevant for all divers."

This is exactly what UTD/GUE has been saying all along but recreational dive computers do not seem to think that way. I am sure you guys remember that never ending scubaboard thread in which the credibility of deep-stops was questioned in the light of US Navy studies. That thread left a lot of people convinced that deep stops is a thing of the past and we need to move away from that thinking. Mark Powell disagrees:

"There has been a recent study by the US Navy which appeared to show the opposite conclusion to DAN study in terms of benefits of deep stops. This received a lot of publicity and was seen by many as evidence that deep stops were not such a good thing. However if you look at the US Navy study, you can see that they are testing something very different to what we have been calling deep stops so their conclusions do not apply to this discussion."

The DAN study that Mark Powell mentions above is actually very supportive of deep stops. In this study a series of dives were done to 25 meters with a deep stop at 15 meters + another at 6 meters. These were compared against another set of dives that skipped the deep stop at 15 meters and just did a conventional stop that recreational computers generate at 6 meter depth. The test divers who incorporating deep stops at 15 meters surfaced with very low Bubble Score Index (BSI). In the light of this particular study Powell writes:

"This seems to confirm that incorporation of deep stops has a positive effect on bubble formation even on recreational dives in 25 m range."

This goes totally in line with what UTD has been saying all along and is totally against the computer generated recreational profiles that I have been diving all my life. Mark Powell writes the following:

"A number of most popular manufacturers of dive computers have recently introduced models that include some form of deep stop or micro-bubble suppression algorithm and the Sub Aqua Association International has recently introduced a set of deep stops tables designed for recreational diving."

He seems to be convinced that as time goes by recreational dive computers and tables will modify their present stops and ascent rates and future of recreational diving would look more like what UTD seems to be doing now. In my earlier post, I mentioned that a lot of people are abandoning computers and diving with deep stops and they are no longer experiencing the post dive lethargy that they always did while chasing the computer. Here is what Mark Powell writes:

"The inclusion of additional safety stops on recreational dives is likely to be more widely adopted in the future in an attempt to provide an additional safety margin and as a way of reducing post dive fatigue."

I believe that may be fine for NoStop/NDL Recreational Diving. Where Deep Stops have to be carefully considered is in deep staged decompression diving in which the slow tissues become supersaturated as you come shallow, requiring more O2 profile stop time for effective inert washout before surfacing.

 

[dumpsterDiver]

so.. dive a recreational computer, add in some deep stop(s) where you want and follow the computer - to the surface.. Still seems to make more sense then guessing on average depth?

I feel no difference between air and nitrox when I push to the limits of the computer, but the introduction of a deep stop on aggressive no deco (or slightly into deco) dives in recreational depths, helped me to eliminate pain in my elbow joint..

 

[Kevrumbo]

@Kevrumbo and what does depth have anything to do with it? It is pressure not depth that determines the bubble size.

First of all you don't want to get any pathological bubbles at all. . . We're not talking about simple Boyle's Law mechanics here. This is about applied decompression theory and tissue modeling.

There are levels of "safe" inert gas supersaturation that can be represented in several ways.
For example, the surfacing M-Value of the 80min tissue compartment can be represented by:

Equivalent Saturation Depth to Ambient Pressure Ratio = 2ATA / 1ATA = 2:1
or;
Nitrogen Pressure:Ambient Pressure Ratio = (2ATA x 0.79) / 1ATA = 1.58:1
or;
Total Allowable Nitrogen Pressure = 2ATA x 0.79 = 1.58ATA N2 = 52fsw N2
or;
Total Pressure Differential = 2ATA - 1ATA = 1ATA = 33fsw
or;
Nitrogen Pressure Differential = (2ATA x 0.79) - 1 = 0.58ATA N2 = 19fsw N2.

The point is you don't want to surface exceeding any of these representative M-values -whether in pressure or equivalent depth units- if this 80min tissue happens to be the leading inert loaded compartment.

Call up DAN and talk to Dr. Pollock about why half depth makes no sense. If you guys said we do stops at half pressure because that makes the bubbles all double in size and that makes it not dependent on depth then I think we would have a different discussion, and no, it doesn't really matter all that much when you're super deep because the first atmosphere gets rounded out pretty quickly, but when you're in non-trimix depths? It makes no sense at all, and you have still yet to give an argument on why you use half depth instead of half pressure.

(Again this is not about Boyle's Law mechanics: pressure and volume inversely proportional relationship, and bubble size proportional to the cube root of its volume).

This is just a simple consistent and controllable ascent strategy for the recreational diver within NoStop/NDL limits, ascending 30 fpm/10mpm to half of max or average depth, and then a slowing ascent at 10fpm/3mpm to the surface, instead of doing an ascent 30fpm all the way to 15fsw and then "jam on the brakes" for a 3 to 5min Safety Stop.

Within general Ratio Deco methodology, 100fsw/30msw is the reference set point for the NoStop Table with a 20min NDL and the 10min half-time Tissue Compartment controlling the ascent. Once again, the motivation in RD methodology is to prevent surfacing supersaturation of this leading tissue caused by approaching its M-value (such as going all the way to the surface after a Safety Stop as most conventional tables would allow with a 20min NDL @100fsw), which is why the stop at half-depth 50fsw/15msw just as the compartment begins to desaturate/unload. So in this example from 100fsw for any bottom time up to 20min NDL, the stops are at every 10' up starting at 50fsw, with a 30second hold & 30second move for a 10fpm ascent rate to the surface.

...of further importance, what do you do when diving at altitude when the depth starts lying to you? You can't just ignore the surface atmospheric pressure...

As for diving at altitude, it makes sense that attempting to surface with the same sea level saturation value at a diminished atmospheric pressure can only be possible with a much lower inert gas load for a particular leading compartment; in-other-words decompression profiles have to be compensated with either longer shallow stop times and/or more conservative stop depths than the allowable Buhlmann M-values.

Other than that, @boulderjohn can comment more on the specifics of decompression diving at altitude, and the RD profiles of the divers that suffered the unfortunate dive accident.

 

[tbone1004]

@CAPTAIN SINBAD when did he write that and which studies from when was he citing? also, 25m/75ft recreational dives with safety stops are not something you can use to argue with when you are comparing them to mandatory decompression diving. Especially one where you will have mandatory "deep" stops. I.e. even diving with a GF lo of 45, in most of the cave dives that I do in the 90-100ft range, we have a mandatory 30ft stop. Isn't for very long, but it is still there. That is half pressure, and is not a stop I'm going to want to skip.