1/2 CNS % after 90 min. SI?

[Guy Alcala]

It was stated in my just-completed Fundies class that GUE assumes that your CNS loading % decreases by 50% after a 90 minute SI. I checked the NOAA diving manual whence the single and 24 hour CNS % dive time limits are given (that GUE and every other agency AFAIK uses), but nowhere in the chapter or anywhere else in the book is this mentioned, let alone explained. Some other sources have implied that the NOAA time limits were derived empirically rather than theoretically. Can anyone point me to the source of the GUE "1/2 reduction in CNS % after 90 minute SI"? I'm assuming this is based on something more exacting than 'TLAR'.

Guy

 

[lamont]

It was stated in my just-completed Fundies class that GUE assumes that your CNS loading % decreases by 50% after a 90 minute SI. I checked the NOAA diving manual whence the single and 24 hour CNS % dive time limits are given (that GUE and every other agency AFAIK uses), but nowhere in the chapter or anywhere else in the book is this mentioned, let alone explained. Some other sources have implied that the NOAA time limits were derived empirically rather than theoretically. Can anyone point me to the source of the GUE "1/2 reduction in CNS % after 90 minute SI"? I'm assuming this is based on something more exacting than 'TLAR'.

Guy

Run the CNS clock loading for something like a 24-hour dive in Wakulla.

They regularly run 10,000+% CNS clock and have never had an ox-tox incident.

They do use backgas breaks.

Something is clearly wrong with the NOAA limits, or else they wouldn't be able to do this for years and get away with it.

 

[limeyx]

Did you ask Rob for the reference ?

 

[rjack321]

Can anyone point me to the source of the GUE "1/2 reduction in CNS % after 90 minute SI"?

Its not just GUE, many agencies assume such a halftime in CNS loading.
E.g. Teaching Oxygen Tracking Article 95-2

NOAA does not assume a half time, they just magically make all the CNS loading disappear after 24 hrs. If you assume that 6 half lives are required to reach a practical asymtote then each one is roughly 4 hours. (24/6=4)

I'm not sure there's alot of data supporting either approach, almost certainly very little in humans. Maybe ask in the decompression subforum.

 

[ucfdiver]

I've gone over 150% a few times (with backgas breaks) and have not had any issues. I know many people are pushing it further than I am and still no issues.

 

[PfcAJ]

I believe the real issue with cns isnt single dive exposures (the way gue goes about it, anyway) but multi day repetitive diving.

Many folks wake up the next day and forget about it, but 24h hasn't passed. Think spearfishing trips on rich gasses, deep, over and over.

That being said, I think the "cns clock" is bogus and needs some reworking.

 

[lamont]

I believe the real issue with cns isnt single dive exposures (the way gue goes about it, anyway) but multi day repetitive diving.

which can work up your pulmonary clock and hammer your lungs (and i guess your retinas according to the wiki-tubes).

 

[rongoodman]

I see the 90 minute half life is mentioned in the new version of the TDI Advanced Nitrox book.

 

[Guy Alcala]

Did you ask Rob for the reference ?

Meant to, but forgot during class. I wanted to give him a rest from my questions so haven't asked him since; he had to put up with them for 3 evenings and four full days during Fundies, and everyone has their breaking point.

Guy

 

[Guy Alcala]

I originally asked this in the DIR forum but no one could answer it there, and it was suggested that I re-ask it here.
It was stated in my just-completed Fundies class that GUE assumes that your CNS loading % decreases by 50% after a 90 minute SI. I checked the NOAA diving manual whence the single and 24 hour CNS % dive time limits are given (that GUE and every other agency AFAIK uses), but nowhere in the chapter or anywhere else in the book is this mentioned, let alone explained. Some other sources have implied that the NOAA time limits were derived empirically rather than theoretically. Can anyone point me to the source of the GUE (and at least some other agencies) "1/2 reduction in CNS % after 90 minute SI"? I'm assuming this is based on something more exacting than 'TLAR'.

Thanks,

Guy