What is the deepest you have been on pure O2?

[100days-a-year]

30ish but have seen people IWR @ 60' about a dozen times.I try to avoid getting bent to avoid having to do that.Nobody I know has toxed doing deco even doing ridiculously stupid things.

 

[Kevrumbo]

Kevin, just for my understanding, as I'm not a tec diver, and I'm trying to follow you, but it is kind of confusing to me, as well I have other questions.

If you start with deeper than normal stops to avoid rapid expansion of the bubbles in your fast tissues, and you start your dive with less conservative profiles but then you switch to conservatives at 6m plus you extend your Deco time, why you just don't go conservative for the complete profile of the dive ? have you experienced type 1 events doing so or worse by following VPM or Buhlmann or RGBM profiles without changing them ?

What about your daily O2 CNS limits, and your OTU for multiple deco dives during the week, are you not getting to close to the limits or exceeding them ?

Is part of your dive planing to change the Deco stops profiles or you just change them at your convenience ?

If you plan on doing only a single tech deco dive in one day, or one per day over a three-day weekend, then straight forward do your profile per your Deco Software or Dive Computer schedule, and follow your CNS tox limits as trained.

However Multiple Deco Dives Over Several Days. . .

My point is from my own anecdotal experience: two or more deep deco dives per day over a week or more, especially on non-Helium high FN2 bottom mixes like Nitrox or Air -you will start to N2 load your slow tissues over the course of several days such that they will not clear or perhaps even accumulate if you use the exact same Deco Profile from Day 1 consecutively thru Day 7 (or more).

The Shearwater Petrel computer helps by keeping a continuous record of your tissues' loading/saturation/off-gassing/residual tensions and provides info data you might have to use to start padding your shallow O2 deco stop times after Day 4 or 5 of consecutive dive days (i.e. Petrel computer's real time GF adjustments & tissue loading graph features etc, and CNS Ox-tox tracking) in order to keep slow tissue tensions reasonably below surfacing M-value levels on ascent. But most of all, it primarily depends on how you feel upon surfacing & post-dive several hours before deciding how much extra O2 deco time you should do on subsequent dives on the next days to come. . . (And also figure in a previous history of DCS injury if you had one.)

Just a general Rule-of-Thumb recommendation for those doing these types of deco dives (should be no more than two deep deco dives a day with minimum SIT 3hrs between them) over several consecutive diving days --even if using Standard Helium Gases for bottom mix-- by Day 4 start adding more O2 time at 20'/6m with a very slow ascent (0.5 m/min or a foot per minute) to the surface, monitoring for signs & symptoms of slow tissue DCS --"niggles" to obvious acute joint & limb pain and have an IWR contingency profile ready in your Wetnotes (or immediate access to a Recompression Chamber if you are in some remote part of the world).

Better yet, allow your slow tissue more time to off-gas residual N2 and to reset your CNS exposure time to zero, take a mandatory day-off from diving after Day 3 or 4. . .
​

---------- Post added November 25th, 2015 at 02:33 PM ----------

30ish but have seen people IWR @ 60' about a dozen times.I try to avoid getting bent to avoid having to do that. Nobody I know has toxed doing deco even doing ridiculously stupid things.

An infamous tragic accident, as told by Dan Volker:

Then, there was the Jane Orenstein death... In it, tech instructor Derrick McNulty, had his buddy and student with him on ascent from a 280 foot dive. He did not watch her switch gas from bottom mix to travel gas at 100 feet, and missed that she went to her O2 bottle. Jane breathed the O2 from 100 feet, through the 50 foot, 40 foot, and 30 foot stops....at the 30 foot stop, she signalled she was low on gas, and McNulty waved her up to the 20 foot stop direction--she ascended by herself, and then McNulty watched her stop ascending, and begin a plunge downward.....He just watched as she began falling, and the 2 tech students below saw her dropping at their 50 foot stop, and one tried to chase after her, but could not equlalize, and had to stop....The instructor later said that he could not follow her, because he did not have enough gas to go after her and to rescue her.

Jane's boyfriend was a freediver I knew well, and he called me to find her body. George and Carmichael located her 24 minutes into the first dive, at 280 by the Coryn chriss....But they had to surface because she was too negative to lift.

I went down with George and brought Jane up on the second dive, and used less than a third of the gas that McNulty had remaining in his back gas, on his return to the boat. That is with George and I pulling a body so negative that ultimately it took 6 people to pull it up on the boat.

So this is another Pariah. He chose not to assist, it was every man for himself. Jane paid the price of diving with a person like this. If Jane had been my girlfriend, I would be in Jail right now because there would have been no force on heaven or earth that would have prevented my killing McNulty.

Point is -besides obviously always check & buddy double check the MOD of the gas cylinder you're switching to- you may or may not tox immediately if you inadvertently breath Oxygen at 4 ATA (although if the victim was physically exerting & breathing harder with indications of CO2 retention, she might have gone into OxTox seizures within minutes of breathing O2 at 100').

 

[100days-a-year]

I know of a couple people personally who died breathing the wrong mix.In one case the tank wasn't analyzed,it contained 50% and in one the diver put a 100% reg in his mouth in 3' seas after his primary came out just before he rolled,both tragically preventable in hindsight but inevitable given the situation at the time.

I always have my own personal analyzer now...in case and don't wear a lame ass bracket mounted deco bottle but stage them under my arm and in sight when needed.

 

[Kevrumbo]

And even the best trained cave dive explorers can make fatal gas switch mistakes:

I'm very sorry to report to you that our friend and fellow explorer Jim Miller died today during a dive in the WKP.

It's too early for us to report on the dive in great detail, but what I can tell you is that he seized and drowned in the cave after breathing a 70ft deco bottle for an extended period of time on his way into the cave. The bottle was marked and analyzed correctly. The depth was approximately 200ft and the incident occurred soon after the team turned and began their exit. He was brought back to the basin by his buddies following an unsuccessful attempt to revive him at depth, and then to the surface by other team members.

http://www.scubaboard.com/forums/accidents-and-incidents/385666-fatality-wkp-8.html

Interesting too, that the victim OxTox-seizured not immediately, but after nearly an hour on a RB80 Rebreather inadvertently gas switched to a 21m MOD tank (50% or 50/25 mix) at approx 7 ATA. . .

 

[Divetech99]

Kevin, what is your emergency IWR procedure in remote locations with no recompression chamber? What if you only had Nitrox36?

 

[Kevrumbo]

Kevin, what is your emergency IWR procedure in remote locations with no recompression chamber? What if you only had Nitrox36?

Best protocol for expedition technical deco diving in remote locations without Recompression Chamber support along with enough Oxygen gas supply--is not to go diving there at all. . .

 

[Germie]

The problem with oxtox that you can never say this time it happens. That is the tricky part. Yes, there are divers that have breathed pure oxygen on 30m depth without problems, and there are divers with an oxtox with PO2 below 1.6
I few weeks ago in a German mine a diver toxed because he took the wrong cylinder at depth (was labelled, analysed, was smaller than the cylinder he had to take, but even his buddy did not see he took the wrong one I heard).

The best thing you can do or you have to do as diver: Always analyse yourself (yes I had 1 time a 50% in a cylinder where I asked for a 15/50 trimix, or I got ean32 when I needed air or I got air when I asked for ean32). Label your cylinders on the right way. Check where you hang your cylinders on your harnass, when dropping in a cave, check if you drop the right one. And when diving with a buddy, let them check switches and drops too when possible.
And as buddy: really check. My favorite 'you have killed me switch' as instructor has an 8 out of 10 that divers do not see I make the wrong switch. After this, a second try from my site it is always seen. oh no, by writing this, potentially students are reading this and will now know some instructors test them with wrong switches

 

[Remy B.]

Thanks Kevin for the Clarification

 

[Akimbo]

The problem with oxtox that you can never say this time it happens. That is the tricky part. Yes, there are divers that have breathed pure oxygen on 30m depth without problems, and there are divers with an oxtox with PO2 below 1.6...

Yep, it's a crap shoot. Here's a quote from the US Navy Diving Manual:

3-9.2.2 Central Nervous System (CNS) Oxygen Toxicity. Central nervous system (CNS) oxygen toxicity, sometimes called high pressure oxygen poisoning, can occur whenever the oxygen partial pressure exceeds 1.3 ATA in a wet diver or 2.4 ATA in a dry diver. The reason for the marked increase in susceptibility in a wet diver is not completely understood. At partial pressures above the respective 1.3 ATA wet and 2.4 ATA dry thresholds, the risk of CNS toxicity is dependent on the oxygen partial pressure and the exposure time. The higher the partial pressure and the longer the exposure time, the more likely CNS symptoms will occur. This gives rise to partial pressure of oxygen-exposure time limits for various types of diving.

Want to guarantee never getting an OxTox hit? Stay on deck. Why do divers risk it at all?

http://www.scubaboard.com/forums/diving-medicine/440726-oxygen-toxicity-limits-symptoms.html

 

[Kevrumbo]

. . .
Want to guarantee never getting an OxTox hit? Stay on deck. Why do divers risk it at all?

http://www.scubaboard.com/forums/diving-medicine/440726-oxygen-toxicity-limits-symptoms.html

If you gotta do an extended O2 Deco at 1.6 ATA, or an IWR at 2.0 ATA, and you are relaxed, warm & breathing nominally with no indications of physical exertion CO2 retention/Hypercapnia under physical exertion --the OxTox seizure risk "might " be minimal (see: End tidal CO2 in recreational rebreather divers on surfacing after decompression dives. - PubMed - NCBI )

However, if you unluckily & catastrophically lose all your backgas at operational depth (and your buddy), and all you got is your 100% O2 Deco bottle -well you got no choice: switch to your deco bottle and immediately ascend "without physical exertion under heavy work of breathing" to a depth of 2 ATA, and do whatever deco time you can and/or ascend slowly to surface. There's a chance you may not OxTox seizure immediately (see Post #34 and especially #32 above).