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.