CNS Clock

[fpsndiver]

During my initial nitrox training, and then through my IANTD advanced Nitrox training, I was informed that when tracking oxygen exposures, that your exposures (CNS&OTU) should be kept under recommended levels within any 24 hour period.

So....here is the meat. If I am doing back to back decompression dives on consecutive days, using advanced Nitrox (greater than 40%) for decompression. My second day of diving becomes limited more so by my CNS clock than my absorption of inert gas. Has there been any research as to the validity of the 24 hour exposure rule? Is there any new software out there that will take this into account? DecoPlanner gives you no credit (putting in a 24 hour SI)within 24 hours on your CNS Clock. The CNS exposures and OTU's never drop? Does anyone have any idea what is current here?

Tom

 

[Diver0001]

During my initial nitrox training, and then through my IANTD advanced Nitrox training, I was informed that when tracking oxygen exposures, that your exposures (CNS&OTU) should be kept under recommended levels within any 24 hour period.

So....here is the meat. If I am doing back to back decompression dives on consecutive days, using advanced Nitrox (greater than 40%) for decompression. My second day of diving becomes limited more so by my CNS clock than my absorption of inert gas. Has there been any research as to the validity of the 24 hour exposure rule? Is there any new software out there that will take this into account? DecoPlanner gives you no credit (putting in a 24 hour SI)within 24 hours on your CNS Clock. The CNS exposures and OTU's never drop? Does anyone have any idea what is current here?

Tom

Decay of your CNS loading is covered in your Adv EAN text.

R..

 

[fpsndiver]

Decay of your CNS loading is covered in your Adv EAN text.

R..

My book, "Advanced Nitrox Diver" by Lee Somers, Ph.D. (IANTD) does not cover cns clock decay. It merely talks about OTU(UPTD) and CNS exposures within any 24 hour period. In unit 3, "Physiology of EANX Diving".

Oh, hang on, I have it here, found something in a little side bar. "Every 90 mins, while the diver is on the surface breathing normoxic air further reduces CNS load by 50%. If the entire 90 minutes has not been reached, then no reduction is assumed."


But that is the only bit? Anyone else know of any texts that have something different?

Tom

 

[Diver0001]

But that is the only bit? Anyone else know of any texts that have something different?

That's the only bit you need.

The 90 minutes is a 1/2 time.

R..

 

[fpsndiver]

Yes, but what about OTU decay, I haven't checked the OTU levels for our planned dives (CNS clock was what was limiting), but OTU's will become limiting, as you have to leave enough OTU's clear for USN Schedule VI.......does the OTU decay have the same 90 minute half-time decay?

 

[Diver0001]

Oh. And there is something about minimal SIT's in the case that you're over 80%

IIRC something like 4 hours if one dive and 12 if multiple dives. you need to take that into consideration with your CNS clock too.

R..

 

[Diver0001]

Yes, but what about OTU decay, I haven't checked the OTU levels for our planned dives (CNS clock was what was limiting), but OTU's will become limiting, as you have to leave enough OTU's clear for USN Schedule VI.......does the OTU decay have the sam e 90 minute half-time decay?

Well....that I don't recall. I think you'd have trouble getting up to your max OTU's without going over the 80% mark.

R..

 

[Diver0001]

OK, I just checked the book. OTU's don't decay and you're limited to 300 every 24 hours.

R..

 

[Rick Murchison]

Yes, but what about OTU decay, I haven't checked the OTU levels for our planned dives (CNS clock was what was limiting), but OTU's will become limiting, as you have to leave enough OTU's clear for USN Schedule VI.......does the OTU decay have the same 90 minute half-time decay?

See table 3.6, page 3-25 of the NOAA diving manual for the REPEX Oxygen Exposure Chart for Tolerable Multiple Day Exposures.
---
The problem with oxygen is that unlike an inert gas, it does damage. So the daily exposure that's allowed drops over time to allow healing. You have to take a break every now and then.
On the other hand, the CNS clock and its sliding 24 hour window likely needs some review and revision to allow much longer repetitive exposures for a day or two, so long as that's followed by a several-days-long break. Some folks are doing some deco that totally ignores the "clock" with good success.
Personally, I limit my exposure to both the REPEX table and the sliding 24 hour scale, whichever is less.
Rick

 

[Diver0001]

See table 3.6, page 3-25 of the NOAA diving manual for the REPEX Oxygen Exposure Chart for Tolerable Multiple Day Exposures.
---
The problem with oxygen is that unlike an inert gas, it does damage. So the daily exposure that's allowed drops over time to allow healing. You have to take a break every now and then.
On the other hand, the CNS clock and its sliding 24 hour window likely needs some review and revision to allow much longer repetitive exposures for a day or two, so long as that's followed by a several-days-long break. Some folks are doing some deco that totally ignores the "clock" with good success.
Personally, I limit my exposure to both the REPEX table and the sliding 24 hour scale, whichever is less.
Rick

Rick, I don't have access to that book. Would you mind reproducing the table here?

R..