Thread split: CNS toxicity limits

[Manatee Diver]

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

Maybe, but I rarely see anyone suggest pushing PPO2 limits on the active phase of the dive. Doesn't the GUE suggest a maximum PPO2 of 1.2 even for OC?

 

[PfcAJ]

Maybe, but I rarely see anyone suggest pushing PPO2 limits on the active phase of the dive. Doesn't the GUE suggest a maximum PPO2 of 1.2 even for OC?

It’s the times associated with it that aren’t good measures of anything.

 

[rjack321]

NOAA's CNS Limits

1.4 150 minutes
1.3 180 minutes

Its not the CNS that is so bad (cause its based on fantasy). Pulmonary limits are a real thing

 

[boulderjohn]

I have no idea what kind of scientific validity the numbers associated with long term oxygen exposure have. I don't know how they were derived. I do know that many of the really long cave dives we hear about (and which I have never done) blow well past them.

 

[steinbil]

Its not the CNS that is so bad (cause its based on fantasy). Pulmonary limits are a real thing

What kind of pulmonary limits are you referring to? What are the guidelines for exposure concerning pulmonary toxicity?

I might be confused by the terminology here, so please bear with me if this is a silly question.

If I'm not mistaken, CNS is the toxicity we worry about underwater, because it can lead to seizures. The three oxygen toxicity precautions I know of are (1) maximum PPO2, (2) CNS clock and (3) oxygen breaks. Am I right that these all relate to seizures, in other words CNS toxicity?

I have heard of pulmonary issues with long term oxygen exposure, but I don't think I have heard of any recommendations for limiting exposure...

Edit:
And I'm pretty sure you are referring to the CNS clock as being based on fantasy, not the PPO2 limits

 

[rjack321]

What kind of pulmonary limits are you referring to? What are the guidelines for exposure concerning pulmonary toxicity?

I might be confused by the terminology here, so please bear with me if this is a silly question.

If I'm not mistaken, CNS is the toxicity we worry about underwater, because it can lead to seizures. The three oxygen toxicity precautions I know of are (1) maximum PPO2, (2) CNS clock and (3) oxygen breaks. Am I right that these all relate to seizures, in other words CNS toxicity?

I have heard of pulmonary issues with long term oxygen exposure, but I don't think I have heard of any recommendations for limiting exposure...

Edit:
And I'm pretty sure you are referring to the CNS clock as being based on fantasy, not the PPO2 limits

Does nobody teach OTUs anymore? This is covered or SHOULD have been covered in every nitrox class. On OC it's not particularly relevant, on CCR and for long cave dives it absolutely is relevant. And its right there on the tables.

https://www.shearwater.com/wp-content/uploads/2012/08/Oxygen_Toxicity_Calculations.pdf

Oxygen Exposure Tracking Table

The International Association of Nitrox and Technical Divers (IANTD) prepared these dive schedules in a standard structure that is familiar to divers trained in the use of traditional dive tables.

www.divegearexpress.com

 

[steinbil]

Does nobody teach OTUs anymore? This is covered or SHOULD have been covered in every nitrox class. On OC it's not particularly relevant, on CCR and for long cave dives it absolutely is relevant. And its right there on the tables.

https://www.shearwater.com/wp-content/uploads/2012/08/Oxygen_Toxicity_Calculations.pdf

Oxygen Exposure Tracking Table

The International Association of Nitrox and Technical Divers (IANTD) prepared these dive schedules in a standard structure that is familiar to divers trained in the use of traditional dive tables.

www.divegearexpress.com

Thanks! Now that you mention it, OTUs might have been mentioned briefly as part of my OW+Nitrox class, but as it doesn't really apply to my OC rec diving, I must have forgotten about it. I'm not tech, CCR or cave trained, and I managed to miss this while browsing google/diving literature.

EDIT:
Also found it in my GUE books now. Total brain fart on my end. I must have conflated them with the CNS clock, and as they weren't that relevant for my diving I put it in the "learn about that later" box. Just goes to show, what you learn but don't apply is quickly lost...

 

[Capt Jim Wyatt]

Does nobody teach OTUs anymore?

Yes. OC & CCR.
Not only because it is required by standards but also because it is relevant, in spite of what others may think.

 

[billgraham]

It’s the times associated with it that aren’t good measures of anything.

Yes, correct me if I'm wrong but I think these were created based on data collected from navy divers (poor guys!)

 

[PfcAJ]

Yes, correct me if I'm wrong but I think these were created based on data collected from navy divers (poor guys!)

Regardless of where the data came from, it’s not a useful tool.

“100%” of the limit doesn’t really mean anything. Also, being below the limit doesn’t mean anything either. Passing 100% doesn’t mean anything. It doesn’t give you and information of value as to your risk of experiencing a CNS toxicity episode.