Next step for longer bottom times on deep dives?

[ChuckP]

The AN/DP class does teach you to a certain depth (150' ish range), it doesn't have to be about depth because it also teaches you planning. There are many dives here in Cozumel that would be fantastic deco dives and you never drop below 130'..... Someday soon I hope to own a boat that allows that kind of diving here...

 

[Dr Simon Mitchell]

You haven't been keeping up with medical journals involving scuba, otherwise you would know Simon Mitchell is an Assistant Professor.

I'm not sure why it needed pointing out this explicitly, but for the record, I'm not an Assistant Professor.

If we asked Dr. Simon Mitchell if it is his professional recommendation that all recreational training agencies limit all recreational diving to 100' or below due to the gas density and/or narcosis safety concerns/risk in the current 101-130' recreational range until divers are trained on and using trimix to make the dive safe? I'd be very, very surprised to hear him say that should be done as a blanket "rule" for diving. I know he doesn't endorse "deep air diving", but I don't know that he 'opposes" diving on air/nitrox at 101' for instance. It seems to be that some people are saying that's his position however, so I'd love to get clarification on his professional thoughts for that scenario.

My apologies for the very delayed response to this. I have had a very busy couple of weeks clinically, and have not been around the board.

Your summary of my position is fairly accurate. Gavin Anthony's gas density data which we published in 2016 [1] suggests a significant upward inflection in the risk of CO2 retention if gas density rises above 6g/L during mild exercise while using using underwater breathing apparatus. 6g/L corresponds to air at about 40m / 130' (the typical maximum depth for air diving recommended by most training agencies). I am not much in favour of blanket rules for anything in diving, and like most other issues, the gas density issue is nuanced. An increase in risk does not = a guaranteed calamity if the density guidelines are not followed - just an increase in risk. Intelligent divers can make choices about acceptable risk, and in the case of gas density, other factors can significantly modify related risks (like low work of breathing equipment, avoiding exercise by using DPVs, benign conditions, etc etc). For me, acceptable risk would not include air at 65m (someone else said they would do that), because not only will there be a very high risk of CO2 retention, there will also be severe nitrogen narcosis which will be exacerbated by CO2, not to mention a risk of oxygen toxicity (PO2 = 1.6 atm abs). In general, I try to stick to my own recommendations about gas density byavoiding densities greater than 6g/L when planning deep diving gases, and avoiding air below 40m).

Simon M

1. ANTHONY TG, MITCHELL SJ. Respiratory physiology of rebreather diving. In: Pollock NW, Sellers SH, Godfrey JM (Editors). Rebreathers and Scientific Diving. Proceedings of NPS/NOAA/DAN/AAUS June 16-19, 2015 Workshop. Wrigley Marine Science Center, Catalina Island, CA, 66-79, 2016. Available from:

https://www.omao.noaa.gov/sites/def...rs and Scientific Diving Proceedings 2016.pdf

 

[100days-a-year]

Dr. Mitchell, again thanks for your infinite patience and also for the valuable contributions you make gratis.

 

[Bob DBF]

[1] -Narcosis tolerance, if it exists, is a very short term tolerance.
In much the same way as consuming large amounts of alcohol regularly, allows an alcoholic to appear to function normally. It was believed/hoped, that regular deep diving allowed you to function when suffering from narcosis.
I do wonder if this was more a mental stress thing. Doing deep diving regularly, meant you where relaxed and calm at depth. Unlike those who where unused too deep complex dives

My mindset was that deep diving regularly gave me a better ability to notice how narcosis affected me, and make a better decision when to thumb the dive. For the same reason, I would do work up dives to depth if I hadn't been deep for a while. I've done a lot of deep dives because I've thumbed a lot of deep dives. A lot of my deep was solo, as one needs a very good buddy that understands how dangerous it is and when to quit.

Interesting in the UK, if you where recovering Abalone for money you would be 'at work'.

Depends on what "poaching abalone" means in Australian, here it would be thievery not work related.

 

[happy-diver]

A lot of my deep was solo, as one needs a very good buddy that understands how dangerous it is and when to quit.

More than magnificent ha ha ha ha ha, the only buddy to have!

 

[Scuba Client]

If we asked Dr. Simon Mitchell if it is his professional recommendation that all recreational training agencies limit all recreational diving to 100' or below due to the gas density and/or narcosis safety concerns/risk in the current 101-130' recreational range until divers are trained on and using trimix to make the dive safe? I'd be very, very surprised to hear him say that should be done as a blanket "rule" for diving. I know he doesn't endorse "deep air diving", but I don't know that he 'opposes" diving on air/nitrox at 101' for instance. It seems to be that some people are saying that's his position however, so I'd love to get clarification on his professional thoughts for that scenario.

I could be wrong, and I'd love to hear his answer, so maybe @Dr Simon Mitchell will answer that question.

I learn from the best and the worst.

 

[RainPilot]

Generally, Professor implies Ph.D (or M.D. or J.D.), and Professor Mitchell has a Ph.D. Saying Dr. might clarify that he's qualified in the area (medicine) if we assume it refers to being a medical doctor (someone with an M.D.). Which Professor does not by itself, as he could be an economics professor....

And thank you Professor Mitchell.

All that is true, but Simon is a medical Doctor (anaesthesiologist , totally didn't rely on spell check for that...)
Back in my Officer Training days, we were taught an order of addressing peoples titles, generally a medical Dr ranked ahead of academic titles. For a PhD doctor, Professor usually outranked just Dr.

That was all 25+ years ago and I am very confident Simon doesn't give 2 hoots, I just felt that addressing him as Assistant Professor and then snarkily reverting to professor was a little disrespectful, so I thought I'd clarify a little in case they aren't aware of Dr Mitchell's qualifications.

 

[MichaelMc]

All that is true, but Simon is a medical Doctor (anaesthesiologist , totally didn't rely on spell check for that...)
Back in my Officer Training days, we were taught an order of addressing peoples titles, generally a medical Dr ranked ahead of academic titles. For a PhD doctor, Professor usually outranked just Dr.

That was all 25+ years ago and I am very confident Simon doesn't give 2 hoots, I just felt that addressing him as Assistant Professor and then snarkily reverting to professor was a little disrespectful, so I thought I'd clarify a little in case they aren't aware of Dr Mitchell's qualifications.

Yes, assistant read as being snarky. And as it turned out wrong....

I'm not sure if he cares much between Dr. and Professor. Though he has both medical and academic/research doctorates, and is additionally, to either, a professor. Engaged in research, teaching, and post graduate supervision in "pathophysiology of decompression sickness, respiratory physiology in diving, carbon dioxide removal in diving circle circuits." And he's the head of Anaesthesiology and a deep diver. As a Professor in those areas he is likely more qualified on them than a local M.D.

So really really well qualified for scuba medical and physiology questions.

(Comparing the range of professors, from teaching and research institutions, with the range of medical doctors, might be challenging to do in a meaningful way. But you might ask Nobel laureate professors how they feel about being referred to as Ms. Smith, while a local doctor is referred to as Dr. Jones. By, for example, the NYTimes style guide for the first mention of a person.)