How did old-school deep air divers avoid ox tox hits?

[ADeadlierSnake]

DISCLAIMER: This is not the monthly "deep air" thread. I am not attempting to promote deep air diving, nor am I considering it. Onto the question...

I recently read Shadow Divers and it got me wondering how in the hell these guys were avoiding dropping dead left and right from ox tox hits. I know people DID die, but with dives such as the Andrea Doria where the depth could reach well over 200ft (at parts), it baffles me that oxygen toxicity wasnt more common. So were they all just incredibly lucky? Are the 1.4 and 1.6 limits just reeeeaaaally conservative? (if you dont want to answer that last one publicly, send me a PM. I wont break the limits. Promise! )
Im sure the question has been asked, but its sort of a tough Google search... I couldnt come up with any phrasing that would work. And if any deep air divers on the board want to chime in, that would be welcome. And if this topic needs to be moved, thats cool. I had no clue where to put this.

Lastly, I will reiterate that this is not information that I am seeking to apply.

 

[spectrum]

Consider that the recreational PPO limits are designed to be safely used my the marginally trained masses. That alone implies some amount of headroom. Deep air time at depth would be limited and O2 tox is not usually an instantaneous phenomenon. Everyone has different tolerances and most probably worked their way progressively deeper, testing their typical tolerance. Lastly as you noted, some die.

Pete

 

[rongoodman]

I have seen conjecture that the increased nitrogen present in deep air dives, as opposed to trimix, has a protective effect against oxygen toxicity too.

 

[Dive-aholic]

Read Bret Gilliam's book Deep Diving. Great book that helps explain what they did.

 

[danvolker]

No, the nitrogen just made you more narced as you got deeper You could say it made some people calmer and more relaxed, though essentially losing half of their functional IQ.

When George Irvine, Bill Mee and I were doing our deep air dives between 93 and 1996, prior to George bringing Trimix to us, we did many hundreds of dives to as deep as 290 feet, on air.
The belief we had at the time, is that each individual had their own unique tolerance for high PO2's. Some divers could not really handle much deeper than 200, others could go considerably deeper. The entire enzyme and reaction cascade that would create the seizures, would sometimes be preceeded by a distinct malaise. Some divers believed they could feel good down to a certain depth, and then they felt this was as deep as they could go....George, Bill and I all felt comfortable to 280 or 290, though the narcosis was so intense that you had to be careful not to add too many thoughts into your head beyond checking time and remaining tank psi....I could handle three basic concurrent thoughts at 290...hunt( look for fish to spear), check time, check air.....If I shot a fish, stringing it meant I had added a 4th, and this would mean losing track of time or psi or both.....fortunately, we had a strong buddy system, and I was the only spearfisherman--so if I lost concentration on duration, Bill or George would swim up and tap on computer.

I had one incident where I shot an 80 pound grouper on a 250 foot deep wreck off of Fort Pierce, where the fish fought me as I tried to hold it at the spear, and use the knife to finish him off...the exertion level became so high that after 20 seconds of this, I felt a sudden massive shutdown coming on, in myself, so I hit my inflator and rocketed to 100 feet, where I dumped the bc, and then began feeling better quickly...this would have been ox tox, just before it became critical. Not something you would expect would always provide such a warning, but in my case, this was the only time I had not been careful enough to AVOID significant exertion at depths over 140 feet deep.

And this avoidance of exertion was our primary technique to avoid ox tox. Never swim fast, don't get excited, keep heart rate low, etc...I was always taking huge amounts of Alacer Supergram II vitamin C every 3 hours back then, along with 1000 IU's of high gamma Vitamin E, and several other antioxidants... i believed that this was protection for Ox tox, and the enzyme issues created by deeper than 200 foot dives on air.

The more streamlined and horizontally trimmed the diver was( as DIR pioneers, we were always maximally streamlined) , the less work they did moving around, and the less exertion was there to make Ox tox occur.
The less gear you carried, the less drag and less work in water....Some divers would drag 4 big tanks, huge bellowing BC,s and tons of junk with them...they would exert far too much, and were at much greater risk over 200 feet deep ( in our way of thinking) ... We would use double al 80's or double steel 72's, and then have one 20 or 30 cu ft Oxygen pony slung stage style on the left. It was negligible drag in this position and size, so did not effect our swimming underwater. This was for the final 20 foot stop.

Out of about 30 people we dived with back then, there were about 12 of us that were comfortable at 290, and the rest never felt good below 200. There was some talk about ability to get rid of Co2 being quite different from person to person, and that this may have been a key difference in depth potential...George and Bill and I were all doing competitive level aerobic sports, so by definition, we were good at getting rid of CO2. As CO2 levels climb, obviously Oxtox becomes far more likely.

Some blamed their regulators on not getting rid of CO2 well, but I never really bought into that one. I did most of my deep dives with a scubapro mark2 first stage, and R190 second

 

[AfterDark]

Danvolker is right on the money in post 5.

The Navy and commerical divers were given O2 tolerance tests which gave an idea of general tolerance to higher P02. It was risky because what they were really getting was their tolerance on that day. When these guys left the service/job some continued to dive and knew their "limits" others learned from those guys and found their own limits such as Danvolker posted " and the rest never felt good below 200." I'm going back further than the 90's here, my perspective startes back in the 70's, before Nitrox and trimix was common to sport divers.

 

[Bombay High]

In my transition from Air to Sat diver in 1989, we were put in a chamber and exposed to increasingly higher PPO2 to determine what our individual tolerance was. This was done so that our employers could put us on very accelerated deco schedules coming out of saturation.
As Dan Volker has mentioned, we all took high doses of vitamin C. Divers who went into tox early were sidelined from doing Sat. It was an incredibly unethical practice, and one that was fought by divers organisations. Accelerated deco with high O2 levels is responsible for more damage to commercial divers than most people are aware of. It is thought to be responsible for the thinning of the protective sheath surrounding nerves, amongst other things, which could explain a lot of phantom pain that veteran divers endure. Phantom because often there appears to be no cause for the pain.

 

[HowardE]

I recently read Shadow Divers and it got me wondering how in the hell these guys were avoiding dropping dead left and right from ox tox hits. I know people DID die, but with dives such as the Andrea Doria where the depth could reach well over 200ft (at parts), it baffles me that oxygen toxicity wasnt more common. So were they all just incredibly lucky? Are the 1.4 and 1.6 limits just reeeeaaaally conservative? (if you dont want to answer that last one publicly, send me a PM. I wont break the limits. Promise! )

Yes. Very conservative, and another KEY point I'm not seeing above is this:

OxTox is NOT just a function of PPO2, but TIME at exposure. It's not like spending 2 minutes at 1.8 is going to cause OxTox, or even 10 minutes at 2.0 is unlikely to cause Tox. These key points are left out of basic Nitrox, and even Advanced Nitrox, and cause many people turmoil, when they feel like they must "Violate" the MOD to either make a rescue, or recover something which might put them at a very high PO2 (1.8 or 2.0 even)

My associate John Chatterton tells me that when he was becoming a commercial diver, he was put in a chamber, and dropped to a 2.0 PPO2 for 30 minutes to see if they toxed. He says, "If you toxed, you couldn't be a commercial diver. If you didn't, you were good." Obviously John didn't tox, since he was a commercial diver in NY for many years prior to the Shadow Divers days. Also, 1.6 PPO2 for Air is about 218 feet.

So... Remember this the CNS Clock for 1.6 PPO2 is 45 minutes on a single dive and for a 24 hour period. For most people, 10-15 minutes won't cause tox. Most of John's dives on the Uboat were less than 25 minutes of bottom time, at depths above 215. Brett Gilliam's record breaking dives were bounces.

If you ask me... The reason 1.6 is the MOD is because your clock ticks off very quickly at that PO2, which could greatly effect your subsequent dives, or an extended dive with longer decompression times.

For more information on CNS Ox Tox... read Steve Lewis' (Doppler) article here on SB. http://www.scubaboard.com/forums/content/357-daily-limits-cns-oxygen-toxicity.html

 

[beaverdivers]

Ditto on HowardE's post. CNS O2 tox is a function of depth and time.

In the 80's, we were doing warm water dives using the EDGE that were similar to the cold water dives of Shadow Divers.

We were alot younger ( & Smarter or thought we were smarter ) then, and didn't think about living this long.

 

[captain]

Ditto on HowardE's post. CNS O2 tox is a function of depth and time.

We were alot younger ( & Smarter or thought we were smarter ) then, and didn't think about living this long.

Ain't that the truth.