Accidental DECO and mild panic in a non tech certified diver.

[YZed426]

To the best of my knowledge- there has never, ever been a single documented case of a recreational single tank diver breathing <40% EAN getting an 02 hit at any depth. Not one.

Possible central nervous system oxygen toxicity seizures among US recreational air or enriched air nitrox open circuit diving fatalities 2004-2013. - PubMed - NCBI

This is US only, and fatalities only. I imagine there would be reports of symptoms that did not result in death, and unreported symptoms. I couldn't read the actual report, so not sure which of the 3 ppo2's were the "likely" nitrox death, or what the circmustances were, but even the 1.9 could still be within within your requirements (40% @ 37.5m)

Just as a disclaimer, I have no dog in this fight. I am nitrox certified, but have less than 30 dives. While I am interested in ppls opinions on the subject, I have no experience/knowledge to provide my own...this was purely a response to a challenge.

 

[Dan]

Yeah, and people survived air dives to 250’ as well. But that doesn’t mean it was safe.

I have been to 2.2 during an incident, but wouldnt suggest for a second that its ok. We dealt with it and got sorted and went back to back gas. All good on THAT occassion. It shows no one figure is right or wrong, just a guideline on what we think is ok.

I try and maintain 1.6 or less always during deco and 1.4 or less on the bottom.

I have no intention to dive beyond MOD of PO2 1.4. That was one of special situation. We (a group of 16 divers with 2 DMs) were in Palau. Head DM asked me what I haven’t seen, I said Zebra shark. He said he knew where some like to hang out. We were cruising at around 100’ depth. At one point, he looked down pointed to a ledge. He turned, looked at me and gave me a shark sign (open high 5 hand on his forehead). I looked to where he pointed object about a couple inches long from where we were, couldn’t tell what it was unless I descent closer to it. I pointed to my camera & to it. He replied with 2 fingers and pointed to his dive computer, which I interpreted as I got 2 minutes to get down take the dang picture & ascend back to save level.

So I did under the watchful of 17 divers. I descent to the ledge at 144’ depth. It turned out to be a 5’ Zebra shark. I took this picture.

after 2 minutes I could hear the DM banged his tank to tell me to get the heck back up. I did.

The 2nd deepest dive I did was in Bali, Indonesia. I went to 143’ with 27% Nitrox (PO2 of 1.44) for 5 minutes to take a picture of Mola Mola being cleaned by Emperor Angelfish (see my Avatar).

 

[caruso]

Possible central nervous system oxygen toxicity seizures among US recreational air or enriched air nitrox open circuit diving fatalities 2004-2013. - PubMed - NCBI.

I have cited this study before. It strongly supports my contention that it is highly unlikely that a recreational single tank diver breathing less than or equal to EAN 40 will have an issue with 02 toxicity.

 

[Soloist]

This wasn't a diving skills issue it was a procedural one.

I’m glad your sister is okay, but I respectfully disagree with the contention you can have one without the other. A diver may have “spectacular diving skills” with regards to buoyancy, trim, air management, negotiating currents and spatial awareness, but if they disregard NDL, residual nitrogen, MOD, dive planning, assent rates or any other “procedural” element they are a danger to themselves and others around them.

Case in point: Insta-buddy DECO Diver: What’s NDL?
.

 

[caruso]

A diver may have “spectacular diving skills” with regards to buoyancy, trim, air management, negotiating currents and spatial awareness, but if they disregard NDL, residual nitrogen, MOD, dive planning, assent rates or any other “procedural” element they are a danger to themselves and others around them.
.

This post summarizes things rather well.

 

[NAUI Wowie]

I almost completely agree with you., however, if I would dive with a buddy on air, while I had Nx (rec diving, no deco planned) I would switch the computer to air, so that I would be closer to him concerning NDL (The issue about different computers/ deco models has been mentioned, so I usually try to synchronize it as best as I can).
The reason for me is, that I think it is easier to keep in mind the different MOD and stick to the Nx MOD, then it is to guess/ estimate, where my buddy would be concerning NDL. Especially if the dive is a multi-level dive. So the main reason would not be added conservatism/ safety margin, but rather to have a "harmonized" remaining bottom time.
Of course, if you have a buddy that is thinking while you are diving and the communication is, as it should be, this wont be necessary.

why would you switch to air just because dive partner is on air? Can they not monitor their own NDL time? I mean thats pretty scary if they cant. Also what if you are at about 100 ft and you both see something crazy spectacular and your partner goes down to 130 ft and you are on 32 nitrox? you may forget as you put your computer on air and when you look at it everything looks okey dokey..... you could easily end up putting around at 130 for a few minutes on 32 and maybe nothing happens but i wont do it

 

[johndiver999]

130 ft on 32 % for a few minutes.... is not that big of a deal, In reality, having your computer set for air or nitrox is not going to affect your propensity for toxing out. A touch of reality is needed here.

 

[stretchthepenn]

Someone on here posted "If your dive computer is showing a screen that you've never seen before you are probably in deco." But that can be solved by RTFM.

True...but there are two problems with the "RTFM, dude" answer. First, hands-on practice trumps book learning. Second, manuals are often pieces of crap. (I'm an educator by profession, and I teach technical writing, so I speak from a position of expertise on both issues.)

 

[Storker]

having your computer set for air or nitrox is not going to affect your propensity for toxing out.

If you're properly nitrox qualified, you should know the MOD of your mix. "Setting the computer on air" while diving nitrox is a certain indication that you don't know what you're doing and that you should review your nitrox cert theory.

 

[W W Meixner]

Yesterday afternoon my sister and I dived the Rebel wreck in Fort Lauderdale. The wreck is 128' long in about 110' to the sand. It's largely broken up but the bow and stern still have large open areas that can be penetrated. Because of her schedule my sister could not join me this past week of diving in South Florida but due to a last minute change she was able to join me for 4 dives on Sunday.

American Dream Charters has no "store", their shop is basically the back of a box truck approximately 20' long that sits on the parking lot next to the boat. Which is rather convenient by the way, as long as you don't need to purchase any dive gear. All their rental equipment is inside the big box including a compressor and dozens of tanks, and the boat is right there, they check you in at the boat and you can park nearby.

Probably because of their rather limited facilities, they don't have Nitrox available. Knowing this in advance, I had rented 2 steel 100 tanks from Gold Coast Scuba, with EAN 35 for this dive. I use a P02 setting of 1.6 for all dives but I'm getting off topic. Point being, since my sister joined me last minute, she was unable to get Nitrox so she was diving an AL80 on air. She's got an extremely low SAC rate, always surfacing with more than a half a tank while the rest of us are at our reserve. My sister is an intelligent woman but when it comes to diving, although she's smooth in the water and has over 700 dives, it's scary what she doesn't know about decompression.

We're about a half hour into this deep wreck dive and I've still got about 10 minutes left. I signal to her "is it ok" if I go and check out this forward hold one more time, she glances at her gauges, shrugs an "ok" so in I go, she follows and here I am pointing out 4 huge lionfish when she suddenly bolts for the line and starts ascending like she was about to miss a train.

I catch up to her on the line at 15' and she's totally freaked out- very unlike her. Gesturing, eyes wide, looking all around and pointing to her computer which says DECO, with an up arrow and "10''" and "1 minute". She's stopped at about 15' and has no clue. I calm her down with reassuring signals and gesture she follow me up to 10' but of course that's the last thing she wants to do. Luckily she trusts me when it comes to all things diving and gear related (although possibly not so much after this dive). We get to 10' and the DECO obligation is gone almost immediately.

We did a nice long 5 minute (or longer) safety stop until those dots got to the bottom of the yellow and the whites of her eyes looked normal again, and slowly ascended to the surface, with no issues.

Interestingly- and I messaged @scubadada about this- her Veo200 did not provide safety stop information. Once the DECO obligation was satisfied it simply reverted back to normal dive mode.

A few take-aways:

1- Know your dive computer! Especially what the alternate "DECO" screens mean. She had NO clue.
2- Watch your bottom time- She said "I just watch the dots go up the side and suddenly it went from yellow to DECO!" [nitrogen bar loading graph]. She didn't even monitor the "dive time remaining" numbers!
3- I suppose I bear some responsibility for going back into that hold, knowing I was on EAN35 and she was on air- but again- she's supposed to know her computer and after 700 dives you'd think she'd know if there was sufficient dive time remaining.
4- If she had panicked and surfaced rapidly things could have gone from "mildly bad" to much worse.

She's fine by the way and now she gets to tell everyone who wants to listen that she "went into DECO!".

And yes we sat down with the computer manual and went through all the different DECO screens and I showed her how you need to watch those big "DIVE TIME REMAINING" numbers right there on the face of the computer.

C...

Your computer should have been set at 1.4...your mix should have been 30%/121 ft as opposed to 35%/99 ft...

If you went over your NDL...you should have made a deep stop at 60 ft until your computer signalled you to ascend to 20 ft...

Your sister's computer should have been set at 1.4...her 21% is good for 186 ft and again...if she stayed beyond her NDL which would have been shorter than yours...she should have made a deep stop at 60 ft until her computer signalled her to ascend to 20 ft...

You should both have been slinging bailout at that depth...single AL 80's with no bailout at 110' is insufficient quantity...and 21% will require her deco obligation at 60' to be considerably longer than yours...which will likely lead her into an ''out of air situation''...

Learn your tables...do not dive outside your training limits...suggest you thoroughly re-read your Basic NITROX...and make sure your computer is preset for the mix you are diving with...

Don't accrue a deco obligation if not trained...there is no risk versus reward...

W...