EaNX and PPO2 of 1.6

[jviehe]

Ill admit Im wrong in that the table is tracking pulmonary toxicity. PADI seems to simply be ignoring pulmonary tox for recreational limits, and using the CNS table as a more conservative 24 hour clock to avoid any tox. There is no mention of time based CNS tox, only depth based. The eanx manual has much more limited info, but the encyclopedia expands on that and mentions OTUs and mentiones 850 as the limit for single days, and 300 per day if multiple. This is more inline with advanced nitrox material.

 

[HowardE]

The thing is - that to reach an OTU level high enough to be of concern... you'd have to exceed the CNS clock by more than 200% the daily limit.

Time based CNS tox is definitely a reality. My tech instructor (who was at one time commercial diver) told me that when he was in commercial diving academy.... They (at the time) put the would be divers in a chamber and exposed them to 2.0 ATA PPO2 for 30 minutes. If they convulsed... they couldn't be commercial divers. If not... they could be. The point is... CNS Ox Tox is a function of both PPO2 and TIME. It's not an instant hit if you go to 2.0 or beyond. CNS Ox Tox is the MAIN thing to worry about as both tech and rec divers.

 

[Charlie99]

Although this is apparently what you believe, and unfortunately what you are apparently teaching your students, the DSAT/PADI Oxygen Exposure Table has NOTHING to do with pulmonary toxicity. The PADI Oxygen Exposure Table is based upon CNS oxtox experimental data and is used to track CNS toxicity.<I assume that this is the section you are responding to>

Then it appears that you think PADI is wrong. Is this your belief?

My belief is that PADI is correct, but that you have misunderstood what PADI is teaching. It appears that you are not alone in the misunderstanding, so it seems like PADI should alter or add to the training materials a bit.

 

[Charlie99]

For the next iteration of PADI training materials, I would also recommend PADI use an appropriate halftime calculation for oxtox decay. Right now, they use the NOAA tables where previous exposures are treated as if they have full effect for 24 hour hours and then instantaneously go to zero effect after 24 hours.

Many dive computers assume a 90 minute halftime for CNS oxtox clock decay calculations -- in other words, if a dive pushes you to 60 percent of the allowable O2 clock, then after 90 minutes the computer assumes that you are only at 30% of the clock. (For comparison, the NOAA/PADI table would keep you at 60% from that dive for 24 hours, and then drop instantly to 0 after 24 hours).

Strangely, one computer manufacturer that doesn't use an assumed 90 minute halftime for CNS O2 clock is Suunto. They use a more agressive 60 minute halftime -- not at all what one would expect considering their conservative decompression calculations.

 

[ianr33]

As an aside does anybody know of a case where a diver has suffered pulmonary oxygen issues diving open circuit? It would seem to be pretty much impossible so its not something I worry about.

 

[jviehe]

My belief is that PADI is correct, but that you have misunderstood what PADI is teaching. It appears that you are not alone in the misunderstanding, so it seems like PADI should alter or add to the training materials a bit.

I can agree with that, but after rereading the material a few times, I think its also that its not detail enough for advanced thinkers, and so I made the jump with connecting pulminary to the exposure table. The reason being that CNS tox is not mentioned in regards to time, only depth. Essentialy the how is correct, the why is not expanded upon. This works for recreational diving. Consider me corrected.

 

[nereas]

As an aside does anybody know of a case where a diver has suffered pulmonary oxygen issues diving open circuit? It would seem to be pretty much impossible so its not something I worry about.

Exactly!

I have no idea why the pulmonary chart is even taught.

CNS problems will catch up to and haunt you long before anything else, and even that is primarily a tech-deco issue.

Neither is a realistic issue for NDL as long as depth is controlled so as not to wander too far into forbidden territory.

 

[nereas]

The thing is - that to reach an OTU level high enough to be of concern... you'd have to exceed the CNS clock by more than 200% the daily limit.

Time based CNS tox is definitely a reality. My tech instructor (who was at one time commercial diver) told me that when he was in commercial diving academy.... They (at the time) put the would be divers in a chamber and exposed them to 2.0 ATA PPO2 for 30 minutes. If they convulsed... they couldn't be commercial divers. If not... they could be. The point is... CNS Ox Tox is a function of both PPO2 and TIME. It's not an instant hit if you go to 2.0 or beyond. CNS Ox Tox is the MAIN thing to worry about as both tech and rec divers.

I am sure you would agree that there is lots of beach (sand) in Colorado, just no ocean!

[We joke about that whenever we are in Las Vegas, too!]

I have noticed that people who live on the seashore vacation in the mountains, and vice versa. I guess that is what a change of pace is all about.

I have friends in Key West Florida who run a dive boat business, and every year the whole extended family meets for a vacation at Lake Tahoe California!

 

[Tienuts]

Exactly!

I have no idea why the pulmonary chart is even taught.

CNS problems will catch up to and haunt you long before anything else, and even that is primarily a tech-deco issue.

Neither is a realistic issue for NDL as long as depth is controlled so as not to wander too far into forbidden territory.

I was taught OTU's come in to play over multiple days. 2 deco dives a day over 7 days kind of thing....

 

[Shawn@IReallyloveScub]

I am an ICU nurse, whole body tox or pulmonary oxygen tox is not ever going to happen to a tech diver in the real world. Now the WKPP divers who are in caves 24+hours do. But with the right gas mix's even then they dont have worries other than to be aware of it.
Pulmonary tox is possible in some pts on vents in ICU or babys in O2 tents for days at a time on high % of O2.