EAN32 diver below you at 40-odd meters?

[flots am]

I'm receptive to those who can explain persuasively why I made the wrong choice, as well as those who can persuasively back me up. I think there's more to it than just PP02 because divers on air and EANx seem to tolerate greater PP02s than divers on trimix (in theory because the narcotic effect of N2 counteracts the neuroexcitatory effect of 02 toxicity, but helium doesn't). Any empirical data on what % of divers tend to tox at what depth, on what gas mix?

Without trying to sound too "Zen", your choice wasn't right or wrong, it just "was".

As you learned, on that particular dive, you safely descended to some particular PO2, did something, then returned and didn't die. This doesn't mean that if you try it again, you'll get the same results or that you won't be hit by a bus while walking to your car.

You took a risk and it worked out OK, but nobody can really second-guess you on whether or not you were "right".

P.S. As I learned later, he's a scuba instructor qualified to teach nitrox courses. :depressed:

Don't put too much stock in that. Instructors screw up as much as anybody else.

flots.

 

[hypertech]

I'm glad it worked OK, but I'm not sure I would go after them. An older diver I've dove with had a story from 20 or so years ago - true if you believe him and I have no reason not too.

On a warm water trip, there were 2 pairs that descended well below the plan and were still descending. Likely didn't realize it or couldn't control their buoyancy. The DM from the dive op tried to get their attention and failed. He went down, got to the first pair, and sent them up. Then, he went deeper to get the second pair. None of them came back up.

Who knows what happened, but people depend on me making it back to the surface. I'm not sure that I would put myself at a significant risk to go after someone who either isn't paying attention or doesn't care enough to do so.

 

[F106A]

OK, so:
snip> I'm receptive to those who can explain persuasively why I made the wrong choice.... <snip

1. Why?
2. You made your choice.
3. What was your family's take on your choice?

 

[ktomlinson]

If you download the pdf you can find here: Rubicon Research Repository: Item 123456789/4855
and go to pages 92-93 (95-96 on pdf) you will find a discussion in which they go around the table asking if they are knew of any single exposure CNS hits. This was the DAN nitrox workshop, and they would have brought up this case...

Was the case that you remember a tech dive?

I didnt remember that much about the case, I just noted that at least one person has had an oxtox event at a ppo2 of 1.3. I looked up the same article you quoted for me and found on page 60 that "The lowest PO2 at
which a CNS oxygen toxicity event was noted was at 1.3 atm. We explored the viability of using a maximum PO2 of 1.2 atm and 90 fsw as the maximum depth."

Page 94 says "There was one documented incidence of an O2 convulsion after 75 minutes at 25 feet"

I understand that it is time x ppo2 that really matters, and that the Navy may have chose 1.3 more for an operational reason than because of a physiological reason, Im just saying that there has been at least one case of a ppo2 of 1.3 causing oxtox. I dive 1.4 because that is what I was taught and that is the risk I am willing to take.

 

[Graeme Tolton]

Ok, after some searching, I found it... In the January/February Issue of Alert Diver, There is a 3 page article about an incident, suspected to be ox tox at 1.4ppo2. It was a tech cave dive. However, I personally believe that there is a much stronger possibility that I will get into a car crash on the way to the dive site, than Toxing at 1.4ppo2... or perhaps i will fall on the rocks on my way into the water.

 

[clifftondiver]

This is the kind of flame-free discussion SB should have more often. It started asking for opinions, but has cited several articles. After reading the OP, I was against going down for the diver. But after reading the research articles posted, I'm firmly on the fence with a solid "I don't know". But I surely don't think going after them was wrong, like stated before, "it just was".

Good topic. Thanks.

 

[NAM001]

Just read slamfires post #27

best post read i have had in a long time. made me think about cause and effect. zero risk, 1.2ppo, no computer's. it seems to put some value to using computers when diving contrary to some groups founding principles. not that ratio deco is bad, i think it is a neet thing so long as it isnot used as an excuse to get rid of USLESS baggage. I think that 1.2 may be a very reasonable figure for some tech stuff. just not the golden rule for recreational. it is amazing how the motives when cuopled with the variouus ppo levels recommended say volumns about what is probably the actual safe levels. one rule for zero risk is also non realistic. i wonder if there is some simple guidance or tables to use to match ones type of diving. ie single dive as opposed to say 5-10 dives a day on a boat verses or in the recreational world <50 ft and >50 feet. certainly 1.2 has its use somewhere in the realistic rec world. the tecs should have thier own limits perhaps the non computer croud can just take off .2 or .3 of the realisitic ppo.

also how do you know what ppo's are used in various tables?

i am copying post 27 and putting it in my log book. thanks

 

[Slamfire]

I looked up the same article you quoted for me and found on page 60 that "The lowest PO2 at which a CNS oxygen toxicity event was noted was at 1.3 atm. We explored the viability of using a maximum PO2 of 1.2 atm and 90 fsw as the maximum depth."

The criteria they were using at the DAN workshop was to only count recreational CNS hits, no tech hits, and no commercial hits. Brett Bjorkmann, from EnviroDive Services, wrote the text you are quoting. He is referring to commercial diving. Because it was a commercial dive, it wouldn't have made it to the count. The thinking behind this is that commercial and technical divers are often subjected to multilevel exposures, which "are a whole new ballgame."

That said the type of commercial diving he describes, fish farms, is shallow. So they are probably not being getting multilevel exposures, but they could be having more CO2 buildup because they stay down for long periods of time, potentially doing vigorous work all that time.

Page 94 says "There was one documented incidence of an O2 convulsion after 75 minutes at 25 feet...

Page 94 is part of the same conversation I quoted to you in page 95-96. It basically started with, something like, 'I know of this case and that case.' But when they got to the details of said cases, it turns out they were either tech dives with multi level exposures and an advil overdose. So they all ended up agreeing that there were no cases of single exposure at 1.6 atm or below.

Ok, after some searching, I found it... In the January/February Issue of Alert Diver, There is a 3 page article about an incident, suspected to be ox tox at 1.4ppo2. It was a tech cave dive.

DAN nitrox workshop said tech dives don't count. We also have to keep in mind that this is NOT scientific data, therefore it can hardly be considered scientific proof. Scientific data is obtained in controlled environments that try to eliminate other variables that could potentially influence the outcome. With this type of anecdotal "evidence" there is no control whatsoever over any variable. If somebody toxed at 1.4, there is no way of knowing if it was epileptic episode unrelated to diving. Conversely, because there is no control, diving incidents that could have included a CNS hit may have gone undetected and unreported. Also keep in mind that 1.6 is the upper limit. In a typical recreational scuba profile you will not spend a lot of time at the max ppO2 and not all of the dives will take it to the upper limit. So in reality maybe only a fraction of those quarter million dives actually went to 1.6 ppO2. Personally, I think 10 yrs and a quarter of a million dives is plenty chance to detect something while operating at typical parameters.

Here's another opinion:

Dan Kerem (2000) of the Israeli Navy Medical Institute, "I'll stress again that with pure oxygen diving, as long as your gear is okay and there is no CO2 buildup in the system, divers routinely dive for hours at 1.6 atm with no incidence of oxygen convulsion."

Just read slamfires post #27

best post read i have had in a long time.

I'm just regurgitating statements from people that are better informed than I am, and learning a couple of things in the process. I try to present different sides of the issue without bias and then present my own personal opinion. Thanks for the comment.

 

[ZenDiver.3D]

You'd think right? But (and don't ask me how it happened) one night you're walking down the street and you try to help some poor disabled guy load a sofa into his van, and before you know it, you friggin' wake up at the bottom of Temple of Doom and he's standing over the edge with a basket and it's "It rubs the lotion on its skin and then it puts the regulator in" all over again.

Giving up diving is no guarantee against toxing.

My OW instructor refused to use EAN on wall dives for that very reason. Said it limited her from safely grabbing runaway students/customers, and that she had a bit more wiggle-room with air to make the plunge and bring them back to safety.

Yup. I do that for the just in case scenario too.

OP. Quickly-
You did the right thing. You said the guy was narked, and apparently his buddies didn't notice or care. He was very fortunate you were there and willing to put yourself out there to help.
As for rescues- the rescuer always puts themselves at risk when affecting a rescue. It is the level of risk that you are willing to go to, that is your hard decision in a rescue. I'm glad everything worked out, and be proud of yourself.

 

[jhelmuth]

i have read a lot of guff about this in many threads. perhaps i am wrong but i read limits as the "in normal conditions" situations. this is not a normal sitiation. this is an emergency
the short duration at the higher ppo's should not be considered in a save a life situation as a lind drawn in the stand and written in stone because of blind trust and lack of understanding. one day the gospel will be 1.2 and there will be those who will say we will all die if we hit 1.3 .....
teh physics doesnt change only the inbread fear of the unknown.

when i took my first class the levels were ppo 3.0 death, 2.0 onset of ox tox or anoxia as used. dont push 1.8 because you may be one of those who is more sensitive to o2.
ppo of 1.8 went to 1.6 went to 1.4.

at what level will divers completely ignore levels all together.
how long will it be untill a realistic level in some other area be ignored as being assumed to be over conservitive as is the ever lowering ppo's and then hurt someone.

ie so my puter says deco, no biggy it surely has been programmed to be over precautions so i probably really have an extra 10 minutes.

30 ft ascent rate heck use to be 60 so surely 90 is safe.

I watched a friend, a highly experienced Red Sea dive guide who was using EANx 36, drop to around 50 mtr to recover two idiots who had chosen to ignore the dive briefing about a down current. She got away with it (the two idiots had just had their last dive of their holiday).

I've dived to a pO2 of 2.7 in warm water without incident. A friend has several times dived to 109 mtr on air in bitterly cold water (Dorothea Quarry in North Wales) and lived to tell the tale. Oxtox truly is unpredictable.

The point is pretty simple. Humans can tolerate high PPO2s for brief periods. You were at considerably less risk than the other diver if he was just going to stay there.

That said, you didn't know the guy. I wouldn't fault you either for not chasing after him. Clearly there is SOME depth at which chasing strangers around isn't going to be worth my effort / the risk. I hardly see a brief, calm swim down to 1.7, though, as threatening. I've worked much harder at 1.6 (decoing in currents) several times.

Thing is that you're assuming that the convulsions at 1.4 were primarily caused by O2 tox.

Once you hit a convulsion at 0.21 ppO2 then you're quite certain that the convulsion had nothing to do with O2 tox and was just an underlying undiagnosed seizure disorder.

At 0.22 you can be pretty damn certain O2 tox wasn't the culprit, same with 0.23, 0.24, etc. At some point it starts to fuzzily become more likely that O2 tox either was the cause or a contributing factor, but there's always going to be a non-zero chance at any ppO2 of seeing the symptoms of a convulsion. At what point does the incidence of convulsions become low enough that its like worrying about a billion other low-risk things that we do every day that might kill us? Absolute zero risk isn't possible.

NOTE: Before reading the following, please note that I am not advocating anything here. These are just SOME facts and you (as a certified Nitrox diver) should follow your training...

> 1965 Tom Mount and Frank Martz dive to a depth of 360 feet (110 m) on air

> 1967 Hal Watts and AJ Muns dive to a depth of 390 feet (120 m) on air

> 1968 Neil Watson and John Gruener dived to 437 feet (133 m) on air in the Bahamas. Watson reported that he had no recollection at all of what transpired at the bottom of the descent due to narcosis.

> 1990 Bret Gilliam dives to a depth of 452 feet (138 m) on air. Unusually, Gilliam remains largely functional at depth and is able to complete basic maths problems and answer simple questions written on a slate by his crew beforehand.

> 1993 Bret Gilliam extends his own world record to 475 feet (145 m), again reporting no ill effects from narcosis or oxygen toxicity.

> 1994 Dan Manion sets current record for a deep dive on air at 509 feet (155 m). Manion reports he was almost completely incapacitated by narcosis and has no recollection of time at depth.


... these are all obviously way beyond any limits (and that is very much at the core of why these fellas did this). So I think we can conclude that current training is designed to look at some very conservative and safe practices in setting limits around O2 toxicity (and that makes good sense to me). Maybe one thing we lack in some of the training today is the need to do additional research/reading and to make a greater effort to fully understand the subject with a higher degree of competancy.

Given the circumstances (the OP posed), I have no problem in going below my MOD to help avoid a potentially tragic event. I would do so consciously and knowingly that I do not have any guarantee that I too might tox - but I would/will weigh those issues at the given time and circumstance.

My initial recreational Nitrox (EAN) training allowed a contingancy of 2.0 and 1.6 was considered the "norm" (at that time). I've since planned my dives between 1.4 and 1.2 (other than my deepest and longer technical dives) for the most part.


Just my 2 cents....

Jim