Deep diving accident

[limeyx]

Good to know, Rick, thanks. It makes sense. That explains the struggle to maintain his buoyancy at the stop.

That has probably happened to a lot of us. It's best to do a weighting check at the end of the dive, when your tank is less full, BUT that's pretty hard to do when you're beginning a dive with a new kind of exposure protection or a new environment, ie. salt water or fresh water. Also, many of us try not to drain our tanks, so if one day we have to do the safety stop with a nearly empty tank, our weighting might be a little light. So I guess you weigh yourself to float a foot or so lower than eye level at the beginning and then re-check your weighting at the end of the dive.

So what could be done in a situation like this? I suspect holding onto a buddy might be futile - you wouldn't want to yank them up - or is it possible at that shallow depth? Or I guess if you're using a depth-sensitive gas, disregarding the last bit of deco time instead of going deeper? But then, I guess he didn't expect the oxtox issue at that depth. Don't know...

Well, one thing that can be done is to switch to back-gas and increase the deco time if you start to descend too deep.

You can in an emergency
- hand off any positively buoyant bottom stages to a buddy
- have a properly weighted buddy go negative and hold on to you to keep you down.

At that point its about survival, not "pretty"

obviously hold onto an anchor/weighted line if possible.

If I start to get 5 or so feet below the MOD, I will already be going for the backup reg honestly.

You can also decide to blow off deco, but this is when tables/computer dont come to your rescue in deciding how much you can cut.

 

[divebri]

double posted -sorry!

 

[divebri]

were they breathing 100% O2 @15FSW? Was he breathing 100% @15 and through bouyancy issues hit some lower depth and then get oxy-toxed?


It would be interesting to have one of the participants in this sagagive us a detailed post so we really, truly knew.

I thought that maybe he bounced low enough to tox. 100% O2 requires healthy respect.
It's nice to know the true story so that we can all learn from it. Congragulations again to having a buddy and being a team. Bad things occasionally happen, but a good buddy will save your hiney.

 

[padiscubapro]

I searched Rubicon and published my results here -- nothing conclusive either way.

if it's been "known for a long time" perhaps you could point me to some papers/websites or books that cover some studies? I dont seem to have anything like that in my PADI Nitrox materials.

I dont breathe Nitrous oxide underwater generally, so I dont really see how that's going to help me.

start here

Effects of nitrogen and helium on CNS oxygen toxicity in the rat

R. Arieli, O. Ertracht, I. Oster, A. Vitenstein and Y. Adir​

Journal of Applied Physiology​

​

​

98:144-150, 2005. First published Aug 20, 2004;​

doi:10.1152/japplphysiol.00506.2004

This article references 19 other papers.


here is an excerpt

The prolongation of
latency observed in some rats at certain nitrogen pressures, mostly in
the range 100 to 500 kPa, was superimposed on the general trend for
a reduction in latency as nitrogen pressure increased. This pattern was
an individual trait. In contrast with nitrogen, no prolongation of
latency to CNS oxygen toxicity was observed with helium, where an
increase in helium pressure caused a reduction in latency. This
bimodal response and the variation in the response between rats,
together with a possible effect of ambient temperature on metabolic
rate, may explain the conflicting findings reported in the literature.
The difference between the two inert gases may be related to the
difference in the narcotic effect of nitrogen. Proof through further
research of a correlation between individual sensitivity to nitrogen
narcosis and protection by N​

​

2 against CNS oxygen toxicity in rat may
lead to a personal O2 limit in mixed-gas diving based on the diver​

sensitivity to N2 narcosis.

and anotehr quote

The reduction in
latency to CNS oxygen toxicity became more pronounced
with an increase in density of the inert gas, from helium to​

nitrogen and nitrogen to argon (10).

 

[limeyx]

start here

That is the abstract that I already posted, but I belive Rubicon does not have the entire paper ...

and I am not a rat, no matter how close-set my eyes.
I also posted a paper that states that there was *no* difference between the two (also in rats I think).

So which do I believe ? And if I do choose to believe N2 helps with CNS, do I choose narcosis or CNS? These are tough questions...

 

[wedivebc]

So which do I believe ? And if I do choose to believe N2 helps with CNS, do I choose narcosis or CNS? These are tough questions...

Like everything in diving it is not an either/or it is a balance between the two extremes

 

[limeyx]

Like everything in diving it is not an either/or it is a balance between the two extremes

So how do you decide what the balance is then supposed to be w/out any actual hard data ?

EDIT:

and if this N2 stuff is so good at helping with CNS, why dont I tox immediately when I switch to 100% O2 with a PPO2 of 1.6 which has 0% of the N2

and why dont divers with 4-7 hour bottom times (admittedly mostly on scooters) diving something like 7-9% O2 and the rest helium immediately die of CNS ?

How much N2 should I add to not get CNS, based on an average bottom PPo2 of 1.2 ? Is there a table ?

In reality, it's all guesswork and based on what has worked for others and ourselves in the past.

For me, the N2 on a bottom mix is whatever is left after I add the (least) amount of O2 and whatever helium I want.

I understand that some essentially do it the other way (add the least amount of Helium, then the most O2 they are willing to tolerate and then the rest is N2).