Crazy question from the family table

[rjack321]

Rjack, we appreciate the 45 minutes, but honestly man, people have been doing as much as 3+ hours at 20' on pure oxygen OC for the last 10 years. I strictly dive CCR now for fun dives, but I still have OC friends doing 2-3 hours at 1.6

that's why I put max in quotes. The OC plan here had 233 mins of O2 time. 95 of that was at 20ft which could be done with some backgas breaks - at least CNS wise.
It's still hard on the lungs OTU wise which for me is the bigger "ugh" - along with boredom.

 

[Superlyte27]

When I was diving OC, I did air breaks every 20 minutes. It got me through the dive. The next day my lungs would hurt. I love CCR

 

[JohnnyC]

Lung stuff is OTU related, totally separate idea from CNS%.

Only in that you're using a different metric for calculation.They're still physiological components related to high PO2 exposures. I simply grabbed the 45 minute CNS number as the NOAA table is the most widely accepted guidelines.

 

[PfcAJ]

Only in that you're using a different metric for calculation.They're still physiological components related to high PO2 exposures. I simply grabbed the 45 minute CNS number as the NOAA table is the most widely accepted guidelines.

They’re attempting to track two totally separate things.

CNS toxicity is not the same thing as pulmonary toxicity.

CNS% does not attempt to track pulmonary toxicity at all. Not even a little.

 

[JohnnyC]

They’re attempting to track two totally separate things.

CNS toxicity is not the same thing as pulmonary toxicity.

CNS% does not attempt to track pulmonary toxicity at all. Not even a little.

I understand that. I’m simply pointing out that there are metrics that we use to judge high PO2 exposure and they have physiological affects on the body. They have different mechanisms, but high exposures are the root cause of those mechanisms. As that pertains to CCR diving as was mentioned in the original post I quoted, once can significantly increase their exposure when compared to OC diving.

 

[Superlyte27]

I think what he’s trying to say is lung burn and oxtox are two different concerns, tracked with OTU and CNS respectively.

 

[JohnnyC]

I think what he’s trying to say is lung burn and oxtox are two different concerns, tracked with OTU and CNS respectively.

I know, my point is that both are caused by exposure to high PO2. I simply grabbed a convenient metric (the NOAA exposure table) to demonstrate that there are recommendations for limiting high PO2 exposure.

The original post I quoted was asking about running a rebreather as a pure O2 rebreather at 6m. I then pointed out that rebreathers afford the opportunity to run significantly higher PO2’s throughout the ascent, increasing exposure to high PO2 gas that doesn’t exist in OC diving until shallow. This has the potential to cause issues.

I’m not sure what’s up for debate here? High PO2 exposure can cause several issues. Personal physiology plays a part. This has all been demonstrated reliably over the years. Not everyone is affected in the same manner, and whether you choose to follow those guidelines is a purely personal choice.

 

[Superlyte27]

That's exactly the point. It hasn't been demonstrated reliably. Sure, we all agree that 1.6 is the absolute max. But MANY of us have exceeded 1000 CNS without issue. We've soared past our OTU's without issue. Pfcaj is right. It's a terrible metric. So many people cling to that 45 minutes at 1.6. But what's the max at 1.0? And then is that any more or less safe when we do 10 hours at 1.0 instead of two hours at 1.6?

And its done so often without issue that maybe the math is wrong, like what pfcaj alluded to several posts above.