MOD Stickers

[boulderjohn]

I’m told the reason GUE uses 1.2 is because people have drowned from CNS oxygen toxicity at 1.3 and above.

I would like to see details of this.

In every case of CNS toxicity I know of, the diver made a serious error by breathing out of a wrong gas at a seriously wrong depth for quite some time. For example, I talked to the buddy of a diver who thought he had air in his doubles, but he had EANx 36 instead. The two of them were diving together on the Hydro Atlantic, a wreck that sits at 170 feet to sand, with the deck at 150. They were on the wreck for about 20 minutes when he must have realized he was about to tox and sprinted toward the surface. I can think of about 4 other cases that were in that ballpark. I can't think of one that was in the 1.3 range.

 

[Colliam7]

I’m told the reason GUE uses 1.2 is because people have drowned from CNS oxygen toxicity at 1.3 and above.

I would also like to see details, as I am not aware of any such incidents (that does not mean they haven't occurred, only that I am not aware of any cases).

I AM aware of a case, mentioned by Petar Denoble in an article in the Winter 2013 issue of DAN Alert Diver (Alert Diver | Understanding Oxygen Toxicity), which he described as: 'DAN was contacted by a diver who experienced symptoms of oxygen toxicity after using EAN at an oxygen partial pressure of 1.3 ATA.' The diver was also taking several medications which, it was believed, probably contributed to his symptoms.

 

[tbone1004]

@boulderjohn and @Colliam7 I don't know if anyone has drowned from it, but the biggest thing is the duration that you may be at those elevated PP's especially while working. Obviously we can't abide by the NOAA CNS table on cave dives, but there is a pretty substantial difference in exposure limits with 1.2 vs 1.4 and when you have to deal with quite a bit of deco at the end, it may not hit you at the bottom, but may put you at higher risk of getting hit on decompression.

Best person to ask on that would be Dawn Kernagis who did oxtox studies but was also the surface mgr for the WKPP during the 90's

 

[Akimbo]

I would also like to see details, as I am not aware of any such incidents (that does not mean they haven't occurred, only that I am not aware of any cases).

I haven't found the origin of these limits either but the US Navy Diving Manual includes this:

3‑9.2.2 Central Nervous System (CNS) Oxygen Toxicity. Central nervous system (CNS) oxygen toxicity, sometimes called high pressure oxygen poisoning, can occur whenever the oxygen partial pressure exceeds 1.3 ata in a wet diver or 2.4 ata in a dry diver... ​

This is interesting because the Navy sets operational limits at 1.4/1.6 wet and 2.8 dry (in a chamber). There is some discussion in this thread: Oxygen Toxicity Limits & Symptoms

 

[KevinNM]

I would like to see details of this.

In every case of CNS toxicity I know of, the diver made a serious error by breathing out of a wrong gas at a seriously wrong depth for quite some time. For example, I talked to the buddy of a diver who thought he had air in his doubles, but he had EANx 36 instead. The two of them were diving together on the Hydro Atlantic, a wreck that sits at 170 feet to sand, with the deck at 150. They were on the wreck for about 20 minutes when he must have realized he was about to tox and sprinted toward the surface. I can think of about 4 other cases that were in that ballpark. I can't think of one that was in the 1.3 range.

Oxygen Toxicity Limits & Symptoms

 

[boulderjohn]

Oxygen Toxicity Limits & Symptoms

The discussion that follows is interesting. See especially posts 31 and 33.

The general sense I get from this is that if this diver did tox at 1.3, it is a surprise because it would be such a very rare event.

 

[JohnnyC]

I get funny looks when I tell people I dive a 0.8 in the cave. When you're 4-6+ hours on the loop, you've gotta make a concession somewhere. And much more comfortable to deco out at higher PO2's when your lungs aren't already feeling a little toasted.

Some people forget that there are other considerations at play beyond preventing a seizure.

 

[PfcAJ]

I get funny looks when I tell people I dive a 0.8 in the cave. When you're 4-6+ hours on the loop, you've gotta make a concession somewhere. And much more comfortable to deco out at higher PO2's when your lungs are already feeling a little toasted.

Some people forget that there are other considerations at play beyond preventing a seizure.

Yes.

Most of my longer dives are 1.0 or less on the bottom.

 

[Michael Guerrero]

all that is sensible. even better if you have a habitat to deco in for the shallow spots.