PpO2 time limits on deep air

[Spectre]

<disclaimer>
Deep air: Bad!
exceeding MOD: Bad!
</disclaimer>


When someone takes a Nitrox course, it's all but stated "if you exceed a PpO2 of 1.6 ATA, your ears'll ring, your face'll twitch, and you'll start ceasing".

Obviously it's not going to be immediate on exceeding your MOD.

It got me thinking about deep air, and how they do it. For example, an air dive on the Doria puts you at a PpO2 of 1.73 @ 240 fsw.

So my question is. How was this done? Is it just that they got lucky, or was there O2 exposure planning performed? Perhaps they got lucky because they were within O2 exposure limits? All the tables I've seen go up to 1.6 ATA, with a %CNS/Min of 2.22. Since I've heard the PpO2 for CNS oxtox is 2.5 ATA, I would assume that there are exposure time limits from 1.7 ATA to 2.5 ATA.

My assumption is that there was no exposure limit planning, but the luck involved was that the dive profile happened to fall within the exposure limits that assumedly exist for 1.7 and 1.8 ATA.

 

[FredT]

is an invitation to join the benthic food chain, as lunch! To say the diver'd be stoned out of his mind on N2 is a bit of an understatement!

That aside, I have seen Navy or NOAA tables showing exposure limits for O2 up to 4.0 ATA. Of course the Navy expects a certain percentage of hits in their tables. The exposure times do start to get REALLY short above 2.0 though. No time for any useful work at depth, even if breathing a non-narcotic mix.

FT

 

[AquaTec]

the concern of high PO2 is a cns O2 hit more than an OTU build up. the otu limits have built into them a reserve incase you need to do a chamber ride.

the cns o2 limit is based on statistics, at 1.6 there is a very high likelyhood that you will end up with cns o2 toxicity which isn't terrible unless you are underwater using a standard second stage regulator, if you are you will most likely drownd, if you are using a full face mask you will most deffenitly survive.

there are divers that are going to full face masks at the deco bar just for this purpose. it is usualy the 20 foot stop on 100% that your cns climbs up twords 100%

as for your statement "if you exceed a PpO2 of 1.6 ATA, your ears'll ring, your face'll twitch, and you'll start ceasing".

you might remember PADI say that if you go deeper than 130 feet you will die.

well there is more truth to your statement but it isn't writen in stone.

as for the narcosis issue, i do believe that reapeted exposer to N2 will provide you a level of comfort with it at depth.
like many will say here and i believe it is true. it is the same as learning to drive while drunk. not safe or advaised but possible.

 

[Dr Deco]

Dear Spectre:

CNS Oxygen Limits

Unlike Pulmonary Oxygen Toxicity, CNS comes on quickly and is quite variable in an individual from day to day. The attachment shows data from Donald indicating the variable time to onset of convulsions. It is clear that there can be some days when you might get lucky. There is not anyway at the current time to know what day that will be.

Adaptation

I have seen some lab evidence that CNS effects are mitigated when individuals breathe an inert gas diluent. Thus you might get a bit more time with air than with pure oxygen – but I would not count on it in the water.

Luck

Some say that it is better to be lucky than good. You might be a good diver, but, in this case, it is better to be very lucky. It is not a clever diver who pushes oxygen limits with a mouthpiece as his breathing gear. That is a pathway to a watery grave. There are not any training techniques to allow high oxygen partial pressures nor are there any reliable drugs that can reliably stave off the effects of CNS poisoning by oxygen.

Dr Deco :doctor:

 

[Spectre]

Dr Deco once bubbled...

CNS Oxygen Limits

The attachment shows data from Donald indicating the variable time to onset of convulsions.

I see the variation in time. Obviously it's based on the same O2 level, but was the study done with a specific ATA at the outset, or was it determined by the O2 level that caused immediate CNS symptoms in the subject? Also, was it 100% O2, or a different gas blend? What was the O2 ATA for the study?

Adaptation
I have seen some lab evidence that CNS effects are mitigated when individuals breathe an inert gas diluent. Thus you might get a bit more time with air than with pure oxygen – but I would not count on it in the water.

Interesting... Since there is the concept of 'air breaks' when breathing pure O2, I wondered if there was a possible difference in O2 exposure limits when using pure oxygen vs. a mix.

There are not any training techniques to allow high oxygen partial pressures nor are there any reliable drugs that can reliably stave off the effects of CNS poisoning by oxygen.

Completely understood. FYI: These questions have nothing to do with any sort of plan I have in my head... they are just the result of a long commute and curiosity in how, scientifically, these dives were performed in the past...

 

[MikeFerrara]

With all that said...What is the record depth for an air dive? I know it is below 450 ft
DON'T DO THIS. IT IS STUPID AND WILL LIKELY KILL YOU

The las time I was at 40 fathom gratto I asked just this question to Hal Watts. He has held deep air records and maybe still does. He stated that he doesn't condone divers doing it and his agencies texts use the same O2 exposure limits as the rest. He also has an explanation as to why he thinks he can do it.

 

[Spectre]

MikeFerrara once bubbled...
What is the record depth for an air dive? I know it is below 450 ft

I'm going to guess 513, Done in 1999 by Mark Andrews

He also has an explanation as to why he thinks he can do it.

Have you heard it? Is it something reasonable, or a "I'm blessed" sort of thing?

 

[Dr Deco]

Dear Spectre:

CNS Oxygen Limits

In the study by Donald, pure oxygen (100%) was breathed by mask. The pressure was 71 feet or 3.1 ATA, but I am sure why that pressure was picked. I only know that it was a day-to-day constant. He was interested in the degree of daily variation. He certainly found it.

Air Breaks

I do not know if “air breaks” for CNS toxicity are a variation of “reduction by decreased percentage.” I am inclined to believe that they are not. The reason is that breaks seem to work in all people on all occasions. Changing the oxygen percentage by dilution (but maintaining the same elevation PPO2) is not definitely demonstrated.

Tolerance

It is said that the famous diver of yesterday, Alexander Lambert, was quite resistant to oxygen toxicity and to DCS. While true most of the time, both of these did catch him on at least one occasion. In this ATTACHMENT, the exposure tolerance is given as a function of oxygen pressure. High exposure for a short time is possible.

Dr Deco :doctor:

 

[MikeFerrara]

My conversation about deep air with Hal Watts was several years ago so this is not an attempt at a word for word quote but he first pointed out the fact that they were bounce dives (very short bottom time) and he also credited the fact that he remained very relaxed (little exertion). He also pointed out that he has trained several others who have also been record holders including his daughter and all of them were still alive. I believe he said that he only experienced symptoms of O2 toxicity once and that was on a dive where he did exert himself (I think). Obviously it was not a convulsion. I don't remember what he said the symptoms were. It's not something I would ever try. ox tox is a fact not a theory and while we may not be able to predict it in certain ranges it seems fairly predictable on the high end at least enough so to keep me below 1.6 ata. I get nervous on O2 at 20 ft.

 

[MikeFerrara]

Spectre,
I checked out that link. I should have known it would be a PSA guy.