Geezer Gas

[victorzamora]

In the last study, they found some subjects felt better but the study attributed it to less sub clinical DCS rather than fatigue. In my own case, I feel better regardless of the reason, it seems to be a distinction without a difference.

Not you, but just a general statement: I think that this difference is absolutely ridiculous. It doesn't make you less tired, it just causes less sub-clinical DCS....which makes you less tired. AWFUL differentiation. What's it matter? If subclinical DCS makes you more tired, and Nitrox causes a reduction of it, then Nitrox makes you less tired. Right?

 

[Akimbo]

Well if the studies were more realistic they might show whether it was placebo effect or not. In the last study, they found some subjects felt better but the study attributed it to less sub clinical DCS rather than fatigue…

Does it really matter enough to invest the kind of money required to prove one way or the other? Again, a question not a statement. There appears to be enough individual variation that the results are likely to be a muddled inconclusive mess since there is no reliable scale beyond asking “how do you feel”.

I never was aware of felling less fatigued even after spending several 20 minute cycles at 60' on pure O2 in the chamber. However, plenty of other divers are convinced they do and I’m sure as hell not going to call them a liar. Placebo effect, individual variation, or inability to perceive the improvement… why should any of us care? Just accept your good fortune if it works for you.

 

[NAM001]

I agree, no foul done, Its not often I am unable to keep up with a topic, but deco with all its complexxities is the main one for myself and probably also is for so many others.

KWS

I actually meant the question sincerely, meaning there may be variations in current recreation diving terminology. Keep in mind that saturation divers are surface-supplied divers long before getting in the bell and subject to the same fixation on fast tissues as recreational divers, but that doesn’t mean we use the same buzzwords.

 

[KenGordon]

In the eyes of rec divers we only are concerned with the fastest tissue. the next fastest is in the deco world that rec does not do (by design) and the slowest tissues are in the saturated diver world. That doesnt negate the significance of the slow tissues in deco but for gas loading (the rec divers concern) while submerges, and gas unloading the SI concern,, first tissue signals ndl and the dive is now over till enough SI is done. So tissue 2-16 is not in the rec world. For the majority of divers deco study ends with the coke bottle example. They are told that to avoid becoming a bottle of coke do not exceed ndl. ).

The saturation times of the compartments remains the same regardless of depth. Following this description no stop times would not vary with the depth of the dive. After 20minutes at 30m the first compartment will not be 100% saturated, come up to 10m though and it will be. By the time you get to the surface they will all be saturated (ie the tissue ppN2 will match or exceed inspired ppN2)

Whether a compartment limits the dive depends on the profile and the acceptable degree of over saturation at the ceiling (approximately the surface for a no stop dive). Multi level dives are a popular way to avoid deco and they can lead to the slower compartments being the limiting factor. If 'rec' divers are trying to avoid something it is probably good for them to have a fair model in their heads of how it works.

There is a nice diagram at the bottom of the page here - Dive-Tech: Decompression theory - Half Times Explained - which illustrates the saturation times.

 

[Storker]

Multi level dives [...] can lead to the slower compartments being the limiting factor.

This is something I've observed a lot of times. As I've said in other threads, the majority of my dives are mulitilevel.

After diving I download my profile to my PC, and the Suunto PC program gives a neat bar graph of the estimated nitrogen loading in the different compartments as I move along the timeline. On a typical rather deep dive I can see a very high, close to NDL, loading in the fastest compartments at the end of the time at the deepest level. Then, as my dive goes progressively shallower, the fastest compartments start to unload nitrogen while the slower compartments are loaded more. Sometime around mid run time, the bar graph shows a nice bell curve with the medium compartments loaded most, and towards the end of the dive it's the slowest compartments that show the highest loading.

I find it a bit interesting to see, but then I'm somewhat of a geek...


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[NAM001]

What you describe is what I would expect to see.

This is something I've observed a lot of times. As I've said in other threads, the majority of my dives are mulitilevel.

After diving I download my profile to my PC, and the Suunto PC program gives a neat bar graph of the estimated nitrogen loading in the different compartments as I move along the timeline. On a typical rather deep dive I can see a very high, close to NDL, loading in the fastest compartments at the end of the time at the deepest level. Then, as my dive goes progressively shallower, the fastest compartments start to unload nitrogen while the slower compartments are loaded more. Sometime around mid run time, the bar graph shows a nice bell curve with the medium compartments loaded most, and towards the end of the dive it's the slowest compartments that show the highest loading.

I find it a bit interesting to see, but then I'm somewhat of a geek...


--
Sent from my Android phone
Typos are a feature, not a bug

---------- Post added February 11th, 2015 at 06:40 AM ----------

Looked at the chart. It looks like nmore of a graph showing equiliberium. In the case of the 5 min tissue ,,,,staying at any depth for 5 periods for all plracticle purposes puts you at equiliberium. I think i am seeing that equilibrium and saturation as different things again. for rec depths you could be at 60 ft and the curves will still apply but you are not at saturation.
The tissues will still hold more if given a chance by going to a deper depth, so they are not saturated or fully saturated. However if you are looking at it as after 5 periods the your tissues are as full as they can get, given the driving pressures, then the level of saturation is at 100% of what it can currently be. Certainly these differences in the view of what saturation become moot when you are doing a 300 ft dive as opposed to a 50 ft dive. I dont have a better way of looking at it but I view it as a tissue at a certain PPXX is now saturated that may be say 100 ft. 5 time periods hits the NDL. At say 60 ft it would take 15 time periods to reach the same degree of saturation, (that concept seems to be supported by dive tables) which would again be NDL. Also in that case if you were much deaper then you mght reach full MaX saturation based on tissue limitatoins, in 2-3 time periods. In the case of the deep diver I would think that is the situation. Because the time is so short there is no longer much of a difference between equilibrium conditions and maximun tissue saturation. At that point when you can no longer ongass any more you are in a condition that the longer you stay down will add no additonal deco obligation. I guess we all rationalize diferent ways and perhaps it is fortunate i dont do deep diving with my less than adaquate understanding of things.

NOw i am an electronics guy my self by profession. Half lifes are second nature to me because of capacitor charging rates. We refer to it as RC time constants. every time constant a capacitor will charge a specified % for this example we will say 50% instead of 70% to make it compatable to saturation. After 5 time constants like your half lifes it is considered fully charged. Now if the cap breaks down at 100 volts. If you put a 80V charge on it after 5 time periods it will be at 80 volts. equilibrium but not fully chatrged to its rated capiblity (100v) but it is fully charged n regards to the 80v that was applied to it. if you put 150 volts on it after 2 time periods it is fully charged (>=100v) and not only can it not take no more It electrically breaks down and arcs internally. I will say that this discussion is an experience. How ever I lack the full toolset of understanding to follow any better. Perhaps one day..

The saturation times of the compartments remains the same regardless of depth. Following this description no stop times would not vary with the depth of the dive. After 20minutes at 30m the first compartment will not be 100% saturated, come up to 10m though and it will be. By the time you get to the surface they will all be saturated (ie the tissue ppN2 will match or exceed inspired ppN2)

Whether a compartment limits the dive depends on the profile and the acceptable degree of over saturation at the ceiling (approximately the surface for a no stop dive). Multi level dives are a popular way to avoid deco and they can lead to the slower compartments being the limiting factor. If 'rec' divers are trying to avoid something it is probably good for them to have a fair model in their heads of how it works.

There is a nice diagram at the bottom of the page here - Dive-Tech: Decompression theory - Half Times Explained - which illustrates the saturation times.