Thread split: CNS toxicity limits

[Kay Dee]

It was explicitly part of my crossover in May 2018, including adding the shutoff to the stock MAV and "breathing down" a higher ppO2 (e.g like 1.35 down to 1.2).

No disrespect meant to yourself @rjack321, but I am simply stunned that folks would think (or now think / are taught) that 1.35 is a 'relatively high' po2, CCR or otherwise, unless one was doing very extensive long duration dives.

 

[rjack321]

No disrespect meant to yourself @rjack321, but I am simply stunned that folks would think (or now think / are taught) that 1.35 is a 'relatively high' po2, CCR or otherwise, unless one was doing very extensive long duration dives.

1.35 is high for a planned 4+ hour dive. Recheck you pulmonary limits, at 1.2 you are already slightly over for a 4 hour dive. So yes, you need to breath that down or add some dil to drive it down.

 

[Kay Dee]

1.35 is high for a planned 4+ hour dive. Recheck you pulmonary limits, at 1.2 you are already slightly over for a 4 hour dive. So yes, you need to breath that down or add some dil to drive it down.

Not every one dives caves. And as I said "except on longer duration dives". And I wasn't discussing the pros and cons of breathe it down, or dil it down. However, while folks do much longer dives than four hours, I'd certainly say that was long enough to drop the Po2 (say from 1.4 or thereabouts), but IMO / experience, not for pulmonary reasons. It may help with HIM though.

 

[Manatee Diver]

Not every one dives caves. And as I said "except on longer duration dives".

We are discussing two different deaths of cave divers. The main audience is going to be cave divers talking about cave procedures.

 

[Kay Dee]

We are discussing two different deaths of cave divers. The main audience is going to be cave divers talking about cave procedures.

If IIRC, this is an "accident and Incidents' forum, not a cave diving (deaths) only forum, so a variety of readers for all the threads (trying to learn something that may carry over into their sphere of diving, be it cave or not). So lets hope you dont make those kind of general mis-assumptions when cave diving. Besides, I was commenting on the Po2 part, which along with long duration dives is not confined to cave diving, nor are the myths opinions about it.

 

[Manatee Diver]

If IIRC, this is an "accident and Incidents' forum, not a cave diving (deaths) only forum, so a variety of readers for all the threads (trying to learn something that may carry over into their sphere of diving, be it cave or not). So lets hope you dont make those kind of general mis-assumptions when cave diving. Besides, I was commenting on the Po2 part, which along with long duration dives is not confined to cave diving, nor are the myths opinions about it.

We simply have different procedures based on different normal dive profiles. How common are OW tech dives that have three to four hour bottom time? At least in Florida not very common, OTOH they are very common in cave circles. I have a friend that did them three times a week when he was living in High Springs (he moved a couple hours away).

Our profiles and risks are different and so our procedures are different. It is the same reason why the max END and gas density standards are followed more strictly in the cave community than outside of it.

And when we discuss accidents that are from our community we are going to use the standards of our community. To impose other standards would be like applying strict cave diving rules on people doing 30ft reef bumbles in the Keys.

 

[billgraham]

There's an entire culture, in the mCCR universe especially, of "breathing down" a modestly high ppO2.

Oy. Again?

 

[billgraham]

Not every one dives caves. And as I said "except on longer duration dives". And I wasn't discussing the pros and cons of breathe it down, or dil it down. However, while folks do much longer dives than four hours, I'd certainly say that was long enough to drop the Po2 (say from 1.4 or thereabouts), but IMO / experience, not for pulmonary reasons. It may help with HIM though.

It's been a long time since I did my CCR class but I think I learned the answer to this in Nitrox, the max exposure time at 1.4 is 2 1/2 hours, but maybe I'm missing some new information? At four hours, you'd be way over 100%

 

[Manatee Diver]

It's been a long time since I did my CCR class but I think I learned the answer to this in Nitrox, the max exposure time at 1.4 is 2 1/2 hours, but maybe I'm missing some new information? At four hours, you'd be way over 100%

NOAA's CNS Limits

1.4 150 minutes
1.3 180 minutes

 

[PfcAJ]

NOAA's CNS Limits

1.4 150 minutes
1.3 180 minutes

Which aren’t reflective of any real “limit”.