Scientific studies on air breaks

[PfcAJ]

Post in thread 'Air Breaks: When & How Long do You do Them?'
Air Breaks: When & How Long do You do Them?

Gene posted a good summary of the literature.

Additionally,
TA 14-31, NEDU TR 17-13 Dec 2017 “MANIPULATING FREQUENCY OR DURATION OF AIR BREAKS DURING OXYGEN DECOMPRESSION DID NOT REVEAL A DIRECT CONTRIBUTION OF OXYGEN TO DECOMPRESSION STRESS” has a lot to unpack.

 

[boulderjohn]

You said it only happens at very high O2 pp. True, if you consider 1.3 to be very high. But typically people mean above 1.6 when they talk about very high. And then there was the poster who mentioned his little issue at 20ft.

Ni, I did not say that it only happens in very high PPO2. I didn't say anything like that. Here is what I wrote and to which you are responding.

In all the reading I have done in related issues over the years, I have never heard of oxygen toxicity taking place in shallow water during a decompression stop. One could say that proves that air breaks help, or one could say that there might never have been a need for them in the first place.

Every case of oxygen toxicity that I know of has occurred at greater depths with people using incorrect mixes for the depth. It is usually a labeling error.

 

[kierentec]

Also not part of CC procedures where the average pO2 during the dive is significantly higher than in OC.

Average PO2 for technical CCR and OC dives usually comes out about the same. It’s not uncommon that the deco at 20’ is as long or longer than the BT, so the 1.6 at 20’ raises the average quite quickly. On CCR it’s most common to run a 1.2, and what we’ve seen anecdotally is that if you keep the average PO2 at or below 1.2, divers (who have gradually built up to this level of experience over many years) have been able to get away with going beyond CNS limits. On OC, I try to use air breaks often enough to keep the average PO2 at or below 1.2. Earlier this year, I actually started to experience CNS symptoms, (significant ear ringing and facial twitches) at 20’ on a 6 hour dive with about an hour of deco to go. I immediately drove my PO2 down to .5 for about 30 minutes and then raised it to finish my deco and was ok. Scary stuff.

As to the comment about no ox tox events on shallow deco stops, I know of several cases. Not sure if the accident reports were made public or not, but when I did accident analysis for a training agency, I saw them. Most under CNS limits so probably accredited to other factors like CO2, being cold, drug interactions, etc.

 

[kierentec]

Ni, I did not say that it only happens in very high PPO2. I didn't say anything like that. Here is what I wrote and to which you are responding.

Well, what you really said was that every case involves using the wrong gas at the wrong depth, implying an extreme PO2 exposure as opposed to within established limits.

 

[boulderjohn]

Well, what you really said was that every case involves using the wrong gas at the wrong depth, implying an extreme PO2 exposure as opposed to within established limits.

I didn't say that either.

 

[kierentec]

Every case of oxygen toxicity that I know of has occurred at greater depths with people using incorrect mixes for the depth. It is usually a labeling error.

So what exactly do you mean by this?

 

[boulderjohn]

So what exactly do you mean by this?

Let me try to explain it.

Here is what you claimed I said:

Well, what you really said was that every case involves using the wrong gas at the wrong depth, implying an extreme PO2 exposure as opposed to within established limits.

Here is what I write:

Every case of oxygen toxicity that I know of has occurred at greater depths with people using incorrect mixes for the depth. It is usually a labeling error.

I was describing my experience, and I was suggesting that cases other than those are rare enough the I (not a noob) don't know of them. I was suggesting that such cases are unusual--not that they did not exist. I was further implying that it is hard to draw scientific conclusions from such a small history.

 

[kierentec]

I'm confused. Is this an example of "oxygen toxicity taking place in shallow water during a decompression stop"?

I think we're arguing different points. I think the problem is that this is the post that we are really discussing. You said you don't know of it happening, you were given an example, and you said it wasn't a relevant example because they were deep. The point is that oxtox events HAVE happened within PO2 and CNS limits and are not exclusively due to using the wrong gas at the wrong depth. Sorry if there was confusion about what point was being challenged.

 

[boulderjohn]

and you said it wasn't a relevant example because they were deep.

I was asking what he was talking about. I made no such assertion that it wasn't relevant.

You just keep twisting my words. Is there a reason you are doing this?

 

[kierentec]

I was asking what he was talking about. I made no such assertion that it wasn't relevant.

You just keep twisting my words. Is there a reason you are doing this?

We are seriously derailing this thread, so I’ll leave it at this. Nobody is twisting your words, only explaining that the incident is an example of a tox outside the scope of what your knowledge and experience has led you to believe. There’s no need to argue the semantics anymore.