50 feet for 3.5 hours

[Charlie99]

jbd once bubbled...
responses. I noticed that most of you used little or no conservatism. I think V-planner had set on 2 for conservatism had longer stops.

Second question for this scenario--The diver made an ascent directly to the surface in probably a little less than a minute. The diver made no mention of any symptoms of DCS at all. Any explanation for this?

Decompression is not an exact science by any means, and the limits are set well within the point where DCS is probable.

More specifically, after a 50' 210 minute dive, the comparment furthest past the limit in the Buhlmann model is #7, 54.3 minute halftime and it is only 14% over the limit -- i.e. gradient factor of 114% rather than 100% or my typical 85%. There is high likelyhood that there was some bubbling and sub-clinical DCS, but fatigue after a 210 minute dive probably wasn't considered significant by the diver

The faster compartments (halftimes of 20 minutes or less), the ones I believe are most often related to the nervous system hits are all below their M values. Even if the diver did get DCS, there is a good chance that it would be joint and pain, not nervous system.

 

[jbd]

to ask the diver more specifically if there was any fatigue or unexplained aches or pains. Wish I hadn't missed that opprotunity when I was talking to him. He has commented that he has done this kind of profile several times without any apparent ill effect.

I think Charlie99 is spot on with, "the limits are set well within the point where DCS is probable."

The supply was air from a hookah type system so no nitrox. The diver may very well not have been aware that fatigue and any other symptoms were due to DCS if he had any syptoms at all.

 

[Dr Deco]

Dear Readers:

DCS Probability

That this diver did not get any symptoms of DCS is not really remarkable. There is not a real “DCS limit” in any physical or physiological sense. That idea is based on the old Haldane concept of the “metastable state.” Today it is strongly suspected that microbubbles exist prior to decompression and the supersaturation simply causes some of them to grow.

Individuals differ in their response to decompression. The reason might be partly physical and partly physiological. You certainly can get DCS if you are within the table and it is possible that you will not get DCS even if you are outside of them. Increasing the gas load is analogous to increasing speed on a twisting highway. Up to a point you might be able to exceed the speed limit, but the faster you go, the more probably that a mishap will occur.

Dr Deco :doctor:

Please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[blacknet]

Hello,

As others have stated it's a role of the dice, as is O2 Cleaning. The reverse can also apply, see "undeserved dcs". Tho I hate that term as no one deserves dcs, I don't care how stupid they have been or what they did.

Ed

 

[fins wake]

The reverse can also apply, see "undeserved dcs". Tho I hate that term as no one deserves dcs

Hence the increasing usage of the term "unexpected DCS".

 

[Dr Deco]

Dear Readers:

Undeserved DCS

This business of “deserved” and “undeserved” DCS must be viewed in light of decompression theory. I personally believe that there are problems with this and have indicated some of them on this FORUM over the past several years. I suspect that some day these will be adapted, in principle, by all groups. They will also probably say that none of this was true and that it was already known [partially correct]. These concepts fall into two groups: halftimes and micronuclei concentrations.

Halftime

The concept of JS Haldane in designing his algorithm was [1 ] that the halftimes were associated with actual tissues, and [2 ] that they were unchanging. My analysis while at NASA of washout during oxygen prebreathe has lead me to the conclusion that halftimes can and do change. Nitrogen washout can be increased considerably (ten fold) by exercise depending on the intensity. Haldane himself recognized the possibility and commented on it.

There is not any algorithm today that will modify the halftimes [shorter and longer] commensurate with exercise intensities. [I understand that some adaptation exits in the Uwatec computers, but I am unfamiliar with specific beyond what is in their literature.] Thus it is possible that gas uptake and elimination could be vastly different from what was predicted by the algorithm. Some groups might acknowledge this but only in a very general, nonspecific way. Since tables can be tested only under certain conditions [all combinations are not financially possible], it is incumbent on the diver to use the decompression system under the conditions in which it was tested. Since the vast majority are not laboratory tested, those conditions are not mentioned.

Micro Nuclei Concentration

Micronuclei never entered into the model of Haldane. EN Harvey introduced it in the 1940s, and it forms part of contemporary decompression thought. However, the nuclei are in a fixed number in the tissues in all decompression algorithms outside of NASAs. That means activity greater than that proposed by the algorithm designer will not be reflected in the change of DCS risk. Most current concepts do not incorporate any idea of stress-assisted nucleation at all, and they do not have a time dependence for their resolution.

The question of “undeserved” or “unexpected” will not get resolved until divers are on the alert for the causative factors of DCS in addition to nitrogen loading. :book2:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Big Blue One]

I don't really use luck as a way to identify whether I will get DCS. Quite happy with the theoretical tables and various software available.

Does this guy also have experience of crossing eight lane highways during peak hour against the lights without getting hit.

Methinks he/she probably does so will continue to do it.