Another fatal record attempt in Lake Garda, Italy

[Trace Malinowski]

I used to dove 8-12 hours every single day as a commercial diver. Ever shovel horseshit 8 hours a day? Same thing, just underwater there’s no smell. And it wasn’t horseshit. It was dirt . And we didn’t use a shovel. But whatever.

Which might explain why you now are a suave jet-setting businessman instead.

 

[boulderjohn]

It's amazing how our training tells us to keep CNS/OTUs below 100/300, yet the reality is completely different.

OTUs must have been sky high on that one too. One wonders then where did the present CNS/OTU limits come from…

I think the standards for this are based upon little more than guesses.

It puts an instructor in a tough spot. You know people are regularly ignoring those limits and doing dives that far exceed them. Do you tell a student that they can ignore those limits? I am pretty sure any agency would not be happy to hear that one of their instructors is doing that.

 

[sea_ledford]

OTUs must have been sky high on that one too. One wonders then where did the present CNS/OTU limits come from…

If I remember correctly from one of my tech classes (big "if" here), they figured out what the allowable limit was (based on what I don't remember), but then pulled out what a diver would be subject to during a table 6 recompression, then took a third of that for a safety margin.

If if X= the actual allowable limit, then recreational limits would be

(X- a whole lot!)/3

Resulting in a completely meaningless number that everyone ignores. Except in class, then it's the most important thing!

 

[Hiszpan]

If I remember correctly from one of my tech classes (big "if" here), they figured out what the allowable limit was (based on what I don't remember), but then pulled out what a diver would be subject to during a table 6 recompression, then took a third of that for a safety margin.

If if X= the actual allowable limit, then recreational limits would be

(X- a whole lot!)/3

Resulting in a completely meaningless number that everyone ignores. Except in class, then it's the most important thing!

If true, we have some lead - table 6 recompression. That must have been created based on scientific evidence.

 

[Akimbo]

If true, we have some lead - table 6 recompression. That must have been created based on scientific evidence.

Recompression efficacy was a far more important driving factor than pulmonary oxygen toxicity. See section 3‑9.2.1 Pulmonary Oxygen Toxicity of the US Navy Diving Manual. Of particular note:

Return to normal pulmonary function gradually occurs after the exposure is terminated. There is no specific treatment for pulmonary oxygen toxicity.

You can recover from pulmonary OxTox without treatment, not so with a serious case of DCS that would justify such high exposures.

 

[Degenerate]

It's amazing how our training tells us to keep CNS/OTUs below 100/300, yet the reality is completely different.

Definitely not my experience.
We learned about it and then had a discussion about how some are pushing those numbers to ludicrous levels with no harm done, maybe something to keep in mind when planning dives but at the end of the day it's all pretty meh.
There's no absolute threshold like 100/300 that you have to stay below, I'm sorry to hear that your instructor explained it that way to you.

 

[Tom Winters]

I don’t get these deepest dive attempts.
Lake Garda is gorgeous, but at 20’, it’s already cold and kinda dark, and these guys still have 900’ to go. Better to just windsurf for a couple of hours, then have a nice dinner, nice bottle of wine, and a shot of grappa from the cellar.

 

[Hiszpan]

You can recover from pulmonary OxTox without treatment, not so with a serious case of DCS that would justify such high exposures.

I subscribe wholeheartedly to this premise. The question remains though how was the pulmonary toxicity qualified and quantified for the purpouses of recompression table 6’s treatment?

 

[Akimbo]

The question remains though how was the pulmonary toxicity qualified and quantified for the purpouses of recompression table 6’s treatment?

I don't think anyone is alive that can answer that from direct personal knowledge. Table 5&6 appeared in the 1970 US Navy Diving Manual. Table 4 was in use for decades before that with even higher pulmonary OxTox exposure.

---

My guess is the docs and physiologists at NEDU considered pulmonary OxTox a minor side-effect of treatment, as they do today. Navy divers would be restricted from diving for 30 days after any DCS treatment and would have to pass a diving physical before getting in the water again. No big deal, they would just work as tenders instead of taking their turn in the dive rotation.

I can only remember having pulmonary OxTox symptoms twice and it went away in an hour or two. YMMV. I doubt is is good for you but smoking or vaping is far worse in the big picture.

There was very little discussion of pulmonary OxTox when I was in Navy Second or First Class diving schools in the early 1970s. We definitely didn't calculate OTUs, but diving medical officers probably could have, if they cared.

Keep in mind that there is a huge difference between emergency DCS treatment and routine diving operations. There was no good reason for the Navy to get all that concerned with OTUs until eCCRs were approved. Surface-supplied HeO2 divers only had 3 gases available — air, bottom pre-mix, and pure O2. Outside of training, HeO2 diving itself was effectively only used in emergencies — like submarine rescue or critical salvage like a special aircraft.

There is no reason for the US Navy, and most others, to expose divers to the risks that trimix rebreather "technical" divers routinely incur. They just go to saturation if the depth and bottom time demands it, or use a ROV.

 

[beester]

A VO2 Max test could also be useful for measuring lung damage, and is relatively cheap and easy to conduct using the equipment in any sports medicine lab. Of course there are potential confounding factors that could cause a reduction in VO2 Max independent of pulmonary oxygen toxicity, like overall stress/fatigue, poor nutrition, or simultaneous infection with a respiratory disease (i.e. COVID-19). But testing several divers after similar dive profiles would probably show if there was a significant reduction.

For individual divers you if you want to check whether your deco is burning out your lungs, you can do your own informal VO2 Max testing using any modern fitness tracker like a Garmin. Those aren't as accurate as a real lab test but close enough for our purposes. You just have to do a hard running or cycling workout that gets your heart rate up near maximum.

The question is if your VO2 max results won't be impacted by spending already 3 hours in the water (being tired)?