Info Some History of the NOAA Oxygen Limits

[sea_ledford]

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

I'm going to the symposium, and currently planning on attending the O2 workshop. But I'm also doing another "design by committee" thing there so my brain might be full by then.

Symposium proceedings generally take a few months to come out, but it sounds like NOAA might publish the results independently.

 

[sea_ledford]

I did end up attending the workshop. I certainly can't definitively report what will be in the consensus statement, but I'll relay my understanding of it.

The primary emphasis was on long duration moderately high po2 levels below 1.4. The data set that established the NOAA O2 limit tables was from military combat swimmers using pure O2 units and the current limits in the 1.6 and above range, the panelists all agreed, were appropriate as they are.

The problem with all the lower limits were they were just a "well, that seems about right" seat of the pants interpolation of the higher limits, and all of the panelists agreed that they were so far off they were useless. An additional problem is that on the tables the higher PO2 limits are based on CNS toxicity, while the lower PO2 limits are based on pulmonary toxicity. So the table (below) was always a bit of a mess.

What seems to have been ultimately agreed upon (again, my interpretation and understanding) is for a po2 of 1.3, the recommended limit would be 4 hours (240 min) of working dive time, with an additional 4 hours of resting/deco time. There are caveats that conducting 8 hour dives at 1.3, particularly over multiple days, will have increased pulmonary and ocular toxicity issues. Because those are transient and not life threatening in water, the recommended limits don't address it, so be an adult and manage your own exposure.

When I asked what "work" meant in this situation, anything under 22.5 lpm RMV or nothing to raise your heart rate was considered at rest.

Extrapolating that from 1.3 will require some number crunching and modeling, so it was not addressed beyond that it would require number crunching and modeling. The panelist also didn't feel that exceeding the 8 hours would necessarily lead to horrible things, but they have no data to support anything beyond that, and will likely never get the data. In this situation, anecdotal evidence of "I know a guy that does way more than that, and no problems" is not data, even if that guy was on the panel.

This is also not intended to modify nitrox MOD limits, so you can still plan for 1.4 working/1.6 deco limits for max depth.

Panelists were:
Joe Hoyt - NOAA dive program
Dr. Greg Murphy - US Navy (experimental dive unit, I think)
Dr. Simon Mitchell - Anesthesiologist and diving physiology charismatic megafauna
Dr. Neal Pollock - Laval University Quebec, formerly at DAN/Duke University
Michael Menduno - In Depth Magazine
And a sixth person that I am embarrassed to say I didn't write down his name or information.

 

[scubadada]

I did end up attending the workshop. I certainly can't definitively report what will be in the consensus statement, but I'll relay my understanding of it.

The primary emphasis was on long duration moderately high po2 levels below 1.4. The data set that established the NOAA O2 limit tables was from military combat swimmers using pure O2 units and the current limits in the 1.6 and above range, the panelists all agreed, were appropriate as they are.

The problem with all the lower limits were they were just a "well, that seems about right" seat of the pants interpolation of the higher limits, and all of the panelists agreed that they were so far off they were useless. An additional problem is that on the tables the higher PO2 limits are based on CNS toxicity, while the lower PO2 limits are based on pulmonary toxicity. So the table (below) was always a bit of a mess.

View attachment 891187
What seems to have been ultimately agreed upon (again, my interpretation and understanding) is for a po2 of 1.3, the recommended limit would be 4 hours (240 min) of working dive time, with an additional 4 hours of resting/deco time. There are caveats that conducting 8 hour dives at 1.3, particularly over multiple days, will have increased pulmonary and ocular toxicity issues. Because those are transient and not life threatening in water, the recommended limits don't address it, so be an adult and manage your own exposure.

When I asked what "work" meant in this situation, anything under 22.5 lpm RMV or nothing to raise your heart rate was considered at rest.

Extrapolating that from 1.3 will require some number crunching and modeling, so it was not addressed beyond that it would require number crunching and modeling. The panelist also didn't feel that exceeding the 8 hours would necessarily lead to horrible things, but they have no data to support anything beyond that, and will likely never get the data. In this situation, anecdotal evidence of "I know a guy that does way more than that, and no problems" is not data, even if that guy was on the panel.

This is also not intended to modify nitrox MOD limits, so you can still plan for 1.4 working/1.6 deco limits for max depth.

Panelists were:
Joe Hoyt - NOAA dive program
Dr. Greg Murphy - US Navy (experimental dive unit, I think)
Dr. Simon Mitchell - Anesthesiologist and diving physiology charismatic megafauna
Dr. Neal Pollock - Laval University Quebec, formerly at DAN/Duke University
Michael Menduno - In Depth Magazine
And a sixth person that I am embarrassed to say I didn't write down his name or information.

What about the 90 min half-life for oxygen elimination vs. the cliff vesting of the NOAA table?

 

[boulderjohn]

I did end up attending the workshop. I certainly can't definitively report what will be in the consensus statement, but I'll relay my understanding of it.

The primary emphasis was on long duration moderately high po2 levels below 1.4. The data set that established the NOAA O2 limit tables was from military combat swimmers using pure O2 units and the current limits in the 1.6 and above range, the panelists all agreed, were appropriate as they are.

The problem with all the lower limits were they were just a "well, that seems about right" seat of the pants interpolation of the higher limits, and all of the panelists agreed that they were so far off they were useless. An additional problem is that on the tables the higher PO2 limits are based on CNS toxicity, while the lower PO2 limits are based on pulmonary toxicity. So the table (below) was always a bit of a mess.

View attachment 891187
What seems to have been ultimately agreed upon (again, my interpretation and understanding) is for a po2 of 1.3, the recommended limit would be 4 hours (240 min) of working dive time, with an additional 4 hours of resting/deco time. There are caveats that conducting 8 hour dives at 1.3, particularly over multiple days, will have increased pulmonary and ocular toxicity issues. Because those are transient and not life threatening in water, the recommended limits don't address it, so be an adult and manage your own exposure.

When I asked what "work" meant in this situation, anything under 22.5 lpm RMV or nothing to raise your heart rate was considered at rest.

Extrapolating that from 1.3 will require some number crunching and modeling, so it was not addressed beyond that it would require number crunching and modeling. The panelist also didn't feel that exceeding the 8 hours would necessarily lead to horrible things, but they have no data to support anything beyond that, and will likely never get the data. In this situation, anecdotal evidence of "I know a guy that does way more than that, and no problems" is not data, even if that guy was on the panel.

This is also not intended to modify nitrox MOD limits, so you can still plan for 1.4 working/1.6 deco limits for max depth.

Panelists were:
Joe Hoyt - NOAA dive program
Dr. Greg Murphy - US Navy (experimental dive unit, I think)
Dr. Simon Mitchell - Anesthesiologist and diving physiology charismatic megafauna
Dr. Neal Pollock - Laval University Quebec, formerly at DAN/Duke University
Michael Menduno - In Depth Magazine
And a sixth person that I am embarrassed to say I didn't write down his name or information.

Thank you very much for this. I believe a full description (without the preceding context of this thread) should be a new and separate thread rather than come at the end of page 3 of a 4-month old thread.

 

[Deep Wreck Diver]

I did end up attending the workshop. I certainly can't definitively report what will be in the consensus statement, but I'll relay my understanding of it.

The primary emphasis was on long duration moderately high po2 levels below 1.4. The data set that established the NOAA O2 limit tables was from military combat swimmers using pure O2 units and the current limits in the 1.6 and above range, the panelists all agreed, were appropriate as they are.

The problem with all the lower limits were they were just a "well, that seems about right" seat of the pants interpolation of the higher limits, and all of the panelists agreed that they were so far off they were useless. An additional problem is that on the tables the higher PO2 limits are based on CNS toxicity, while the lower PO2 limits are based on pulmonary toxicity. So the table (below) was always a bit of a mess.

View attachment 891187
What seems to have been ultimately agreed upon (again, my interpretation and understanding) is for a po2 of 1.3, the recommended limit would be 4 hours (240 min) of working dive time, with an additional 4 hours of resting/deco time. There are caveats that conducting 8 hour dives at 1.3, particularly over multiple days, will have increased pulmonary and ocular toxicity issues. Because those are transient and not life threatening in water, the recommended limits don't address it, so be an adult and manage your own exposure.

When I asked what "work" meant in this situation, anything under 22.5 lpm RMV or nothing to raise your heart rate was considered at rest.

Extrapolating that from 1.3 will require some number crunching and modeling, so it was not addressed beyond that it would require number crunching and modeling. The panelist also didn't feel that exceeding the 8 hours would necessarily lead to horrible things, but they have no data to support anything beyond that, and will likely never get the data. In this situation, anecdotal evidence of "I know a guy that does way more than that, and no problems" is not data, even if that guy was on the panel.

This is also not intended to modify nitrox MOD limits, so you can still plan for 1.4 working/1.6 deco limits for max depth.

Panelists were:
Joe Hoyt - NOAA dive program
Dr. Greg Murphy - US Navy (experimental dive unit, I think)
Dr. Simon Mitchell - Anesthesiologist and diving physiology charismatic megafauna
Dr. Neal Pollock - Laval University Quebec, formerly at DAN/Duke University
Michael Menduno - In Depth Magazine
And a sixth person that I am embarrassed to say I didn't write down his name or information.

Thanks very much for this information which I think provides validation for what deeper/longer divers are already doing!

 

[sea_ledford]

What about the 90 min half-life for oxygen elimination vs. the cliff vesting of the NOAA table?

Didn't come up.

 

[sea_ledford]

Thank you very much for this. I believe a full description (without the preceding context of this thread) should be a new and separate thread rather than come at the end of page 3 of a 4-month old thread.

That's probably a good idea, but I think waiting for the actual statement would be more useful for a new post.

 

[Nick_Radov]

As a practical matter one issue that comes up is how various dive computer manufacturers have extrapolated CNS% O2 limits beyond 1.6 atm. Most of them appear to have done some sort of curve fitting based on the NOAA table between 0.6 - 1.6 atm, so the results in that range tend to be pretty consistent between manufacturers. But since the NOAA table doesn't go any higher, the dive computer manufacturers have extrapolated the shape of the curve with significantly different results.

I'm not advocating exceeding the 1.6 atm deco limit. But if you're sitting at a 20 ft stop on 100% O2 and accidentally drift down to 22 ft for a few seconds then you'll briefly be over 1.6. I doubt this really has much effect physiologically but the CNS% number on the computer might jump up. Garmin seems to be particularly bad in this regard: I've received alerts on regular tech dives (nothing really extreme) stating something like "CNS toxicity at 105%. End your dive now." even when I still had a lot of deco to finish.

 

[boulderjohn]

I'm not advocating exceeding the 1.6 atm deco limit. But if you're sitting at a 20 ft stop on 100% O2 and accidentally drift down to 22 ft for a few seconds then you'll briefly be over 1.6. I doubt this really has much effect physiologically but the CNS% number on the computer might jump up.

Even with a Shearwater it is something of a pain. You make that brief drift down a foot or so and you get a high PPO2 warning, and you then have to press the button confirming that you are aware of it on both your computers.

That is a reason I don't understand the people who leave 20 foot as their final stop while using oxygen. If you instead select 10 feet, after the 20 foot stop you then get a 10 foot range in which your depth doesn't matter. Many people, including me, take advantage of that to do light exercise during the final stop to improve perfusion and assist off-gassing.

 

[Nick_Radov]

That is a reason I don't understand the people who leave 20 foot as their final stop while using oxygen. If you instead select 10 feet, after the 20 foot stop you then get a 10 foot range in which your depth doesn't matter.

Sure, I do that when practical. As has been discussed here before, buoyancy control can be challenging when trying to hold a 10 ft stop during a drifting deco in the open ocean with large swells passing through. I mean I can do it if I have to but it requires constant attention and fine adjustments.

Maybe as a compromise we should move up to 15 ft after clearing the 20 ft stop?