Info Some History of the NOAA Oxygen Limits

[PfcAJ]

@PfcAJ

Yup. I don’t find these guidelines to be worth much. Their predictive value is just about 0.

“Well we had to come up with SOMETHING” is now gospel for so many. Not for me. In my mind, it’s analogous to overfilling LP steels. After so many years of people doing it, eventually you have to call into question if the “limit” is even somewhat close to reflecting reality. If it’s not, I tend to discard it.

Reality is all I’m interested in.

This is not to say that I feel that you can just do whatever the **** you want and expect to be risk-free, but managed properly and with the right combo of techniques and procedures (low bottom po2, resting deco, 1.6max, gas breaks…..hydro, VIP, slow fills), it’s clear that exceeding the limit (NOAA limits, fill pressure) isn’t some super high risk activity.

 

[boulderjohn]

The latest issue of DAN's Alert Diver has an article on the early history of experimentation on oxygen limits. It frankly is not all that informative, and its last paragraph sums it up, saying until we get better information, every dive that exceeds established standards is a risk. The problem I see is that nothing is going on formally to give us that better information, so we have to rely on the informal experiences of people going out on their own. I think there is an obvious reason for it.

When I got my basic nitrox certification in 2002, the PADI test was challenging, with lots of math. The thing I remember most was what they had to do on that test to create a dive situation in which pulmonary oxygen toxicity was a factor that had to be considered. I told my instructor that it looked like it was pretty darn unlikely for that to become an issue, and he agreed. I'm pretty sure that is why all of that disappeared from the course soon after that. As I went through technical diving and instructor training, I saw the same thing. In order to create a situation where we had to be concerned about this, they had to create dive profiles that few people would ever consider doing.

I think that is part of the problem, and you can see it in the conclusion of the NOAA statement in the first post:

These investigations have shown...that substantially longer times appear to be possible for pure oxygen working dives than those given in Table 16.5, without the occurrence of oxygen convulsions ...; however, NOAA finds that the conservative limits established in this table are satisfactory for NOAA diving operations.​

In other words, for the dives they're doing, it doesn't matter if the table is too conservative, so they aren't going to worry about it.

The problem is that a tiny portion of the diving community is doing those dives, the current level of research is giving them no guidance, and there do not appear to be any studies planned in the immediate future. Those divers will therefore continue to test those boundaries. There are no studies planned because so few people are doing it, and those few people do not include the people who would be doing such tests (like NOAA).

Another subset of the diving community is also affected, even if they have no intention of doing those dives--technical diving instructors. When students ask their technical diving instructors about the people wo are famously violating these standards by a country mile and suffering no ill effects, the instructor has to be careful. Telling students they can ignore the limits creates a potential for liability should a student violate those limits and suffer a toxic event.

 

[rddvet]

Not sure what the arguing is about with all of this. All the tables prove is long exposure to high O2 levels can lead to toxicity. As far as actual limits, I think the tables are pretty useless. There is so much variability from person to person it's ridiculous. Many people are regularly diving way past oxygen limits with no consequence. I think the tables are great academically, but are pretty useles in real world use. They're what I'd call an OK "starting point".
Let's focus on more important stuff, like don't be the jag off that dies in Ginnie at 60 feet because you're too lazy or full of yourself to analzye your tank before diving it. Or properly doing a gas switch at depth. Those are the things that are killing people.

 

[scubadada]

There are distinctly 2 groups of divers that may exceed NOAA oxygen exposure limits.

One group is like me, doing enough dives at a high enough pO2 in 24 hours to exceed the 24 hour limit. All my dives are no stop or light deco. As mentioned, I would never exceed the NOAA 24 hour limit if the 90 minute half life of oxygen elimination is used.

The other group are technical divers who exceed the single exposure and the 24 hour exposure in a single dive.

I have always assumed that I am pretty safe. I'm not sure what to say about technical divers. Oxygen toxicity appears to be very unusual outside of breathing gas errors.

 

[atdotde]

In my blog, I wrote more about the poor empirical state of oxygen limits here: Oxygen – The Theoretical Diver

 

[Kendall Raine]

don't be the jag off that dies in Ginnie at 60 feet because you're too lazy or full of yourself to analzye your tank before diving it.

So true.

 

[sea_ledford]

I think that is part of the problem, and you can see it in the conclusion of the NOAA statement in the first post:

These investigations have shown...that substantially longer times appear to be possible for pure oxygen working dives than those given in Table 16.5, without the occurrence of oxygen convulsions ...; however, NOAA finds that the conservative limits established in this table are satisfactory for NOAA diving operations.​

In other words, for the dives they're doing, it doesn't matter if the table is too conservative, so they aren't going to worry about it.

The problem is that a tiny portion of the diving community is doing those dives, the current level of research is giving them no guidance, and there do not appear to be any studies planned in the immediate future. Those divers will therefore continue to test those boundaries. There are no studies planned because so few people are doing it, and those few people do not include the people who would be doing such tests (like NOAA).

As NOAA moves more into the CCR world, I wonder if this will change. We now have 2 NOAA divers at the Flower Garden Banks that are on CCR. No deco yet, we'll see if that happens in the future. But a couple 2 hour dives at 60' will get you into the 100%+ CNS range without any deco.

There is also a Oxygen Toxicity Workshop at this years AAUS Symposium that is being hosted by NOAA and Simon Mitchell. Maybe there will be so guidance coming out of that.

From the Symposium registration page:
NOAA will host a workshop to focus on a review of oxygen toxicity for a variety of applications (saturation diving, repetitive diving, etc...) and propose potential changes to community standards. For example, OTU tables for repetitive diving and diving for multiple consecutive days have not been reassessed in many years and the community now has decades of practical experience operationally across a number of partners. The goal of this workshop is to re-evaluate existing thresholds based on practical experience and seek consensus standards to align exposure limits to the best available data. Prior to the workshop, participants will be provided read ahead materials from the organizers that will frame the discussion for the in-person workshop. The in-person session will be coordinated by the organizers to facilitate discussion amongst the expertise of participating OMs/attendees. Workshop organizers intend to publish the proceedings from this session. Hosted at NOAA Diving Center. Organizers: NOAA Diving Program (Host), DEEP, Simon Mitchell.

 

[boulderjohn]

As NOAA moves more into the CCR world, I wonder if this will change. We now have 2 NOAA divers at the Flower Garden Banks that are on CCR. No deco yet, we'll see if that happens in the future. But a couple 2 hour dives at 60' will get you into the 100%+ CNS range without any deco.

There is also a Oxygen Toxicity Workshop at this years AAUS Symposium that is being hosted by NOAA and Simon Mitchell. Maybe there will be so guidance coming out of that.

From the Symposium registration page:
NOAA will host a workshop to focus on a review of oxygen toxicity for a variety of applications (saturation diving, repetitive diving, etc...) and propose potential changes to community standards. For example, OTU tables for repetitive diving and diving for multiple consecutive days have not been reassessed in many years and the community now has decades of practical experience operationally across a number of partners. The goal of this workshop is to re-evaluate existing thresholds based on practical experience and seek consensus standards to align exposure limits to the best available data. Prior to the workshop, participants will be provided read ahead materials from the organizers that will frame the discussion for the in-person workshop. The in-person session will be coordinated by the organizers to facilitate discussion amongst the expertise of participating OMs/attendees. Workshop organizers intend to publish the proceedings from this session. Hosted at NOAA Diving Center. Organizers: NOAA Diving Program (Host), DEEP, Simon Mitchell.

That sounds very interesting--and promising.

 

[tursiops]

There is also a Oxygen Toxicity Workshop at this years AAUS Symposium that is being hosted by NOAA and Simon Mitchell. Maybe there will be so guidance coming out of that.

From the Symposium registration page:
NOAA will host a workshop to focus on a review of oxygen toxicity for a variety of applications (saturation diving, repetitive diving, etc...) and propose potential changes to community standards. For example, OTU tables for repetitive diving and diving for multiple consecutive days have not been reassessed in many years and the community now has decades of practical experience operationally across a number of partners. The goal of this workshop is to re-evaluate existing thresholds based on practical experience and seek consensus standards to align exposure limits to the best available data. Prior to the workshop, participants will be provided read ahead materials from the organizers that will frame the discussion for the in-person workshop. The in-person session will be coordinated by the organizers to facilitate discussion amongst the expertise of participating OMs/attendees. Workshop organizers intend to publish the proceedings from this session. Hosted at NOAA Diving Center. Organizers: NOAA Diving Program (Host), DEEP, Simon Mitchell.

Excellent! That is how things should be done, and it is certainly timely. I'm sure the discussion will be fascinating. Let's hope there is consensus on some good recommendations.

 

[scubadada]

Thanks @sea_ledford

I hope the proceedings of the oxygen toxicity workshop are available publicly soon after the March meeting.

I assume you are attending, perhaps you could share top line results on SB