Can anybody dive a rebreather (subtitle can anybody do everything?)

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fsardone

Solo Diver
Messages
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Location
Rome, Italy
# of dives
I just don't log dives
I was in the process of responding to a thread:
O2 Cell Replacement Time....
but then what it came out (this post) probably would sit best in a different thread, and here we are.

In the thread @Superlyte27 states that being unable to do something needed to dive a rebreather disqualify you from doing so safely. My point being: you can do it but then do not be surprised by winning a Darwin award.

My reply in that thread to @doctormike would have read as follows:

OK, you convinced me! Will flush at the start of the dive from now on.

(...)

When you said that there was a bad argument for not doing an O2 flush, you meant for not doing one on descent, right?

The way I do (and it is not exactly as I was tought but in aviation we have procedures and techniques: procedures are mandated and need to be adhered too, techniques are best practices and you improve share validate and adopt them while you operate) I felt it was a technique.

So, before diving and on a new filter do a cell checker run (is a device that APD build allowing you to pressurize the loop at 1.35 exactly) at high setpoint (it takes a while to reeach 1.3 butit eventually does and then setpoint 1.4 it will never reach 1.35. This checks the whole system for functionality and the cell.
The next step (and usually he next day too) is at dive site. I prebreath at 100%, adv closed (need to add O2 manually and do a couple of full nose dumps).
Then I jump in the water and descent to 6mt rotate my hypoxic bailout into position (if it is at least 10%) check all cells for about 1.45-1.5 (you never get 1.6 ...) open ADV breath out from nose inspire and start descent.
If you are running min volume loop and you have fully inspired (to the stop) before opening adv, as soon as you open d
the adv you will hear a brief burst (ensuring it works) then dumping gas from nose actually dumps most of the oxygen from the loop.

Then when you inspire you get straight diluent from (at least in my case) inspire counterlung. This could present some issues in case you are runnng a low O2 mix. But considered you have your residual ventilatory volume, all the loop exchept the counterlung full of O2, is less problematic than expected atl least down to 10%.

This means I am checking the loop at 1.6 bar ambient with almost 100% oxygen with some moisture in the loop (prebreath) making efficient use of time.

What is is dangerous and need to be taken good care is that I am doing stage rotation with an O2 loop at or near 1.6 .... by having a good rdepth reference. In non permissive condition: bad viz, no anchor line I forgo rotation until 20 meters and after the loop has been set for descent.

----<break>-------

At this point I realised I was describing complex operation, requiring sound decision making prioritization of attention and understanding of involved risk.

Doing complex operations (flying, diving, operating a particle accelerator ...) require a different mind set from "everybody can do this at any time". These activities require understanding consequences of mistakes and failure modes in order to recover from them and clear prioritization of attention/task. Above all, an understanding of human fallacy and training in recognising wrong mental attitude. If you do not grow those aspects, risk is higher than it should be.

When we approach training we need to fully understand not everybody can do everything so failure is a component of trying.

A few years ago I wrote a small article for an online magazine based on our best practices in aviation. It is about decision making. How we approach decision making (the decision to go diving in the first place) seals the outcome. The amount of risk we accept in diving, how current we are how well maintained is our equipment and how benign (or not) are the environmental conditions are all factors.

I thought the dive industry was trying to develop and encourage a 'Just Culture', whereby divers can feel free to talk about the mistakes they made in the dive community without fear of being called derogatory terms such as 'stupid'.

I live in an environment of just culture: it took years and a lot of effort by men much better than me, to develop it and is based on many mistakes and a lot of lives lost. What a squadron pilot say when he stands up in front of more and also less experienced crew members, he/she start by saying I did something stupid today. The just culture is based on the fact that we do something stupid sooner or later, we learn why to teach others not to make the same mistakes. Not by not saying it was not stupid what you did. Your are not an (insert your best derogatory word here) because you did something stupid, unless you did it on purpose. The idea that anybody can do everything is the source of many thread in the A&I forum (example, do 3 deco dives, not change scrubber and fill tanks before being qualified to even do the first of the three, go in overhead before knowing the risks, fly a faster than you can handle aircraft in weather conditions you are not qualified ...)

I attach to this post the article, it might be a good read if you have no familiarity with risk based activity and risk based decision making. My hope is people start realising that not everybody can do everything and stay away from things cannot do (may be for lack of training understanding or immature decision making) and seek mentoring and training and accepting their limits.

Fabio
 

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Fabio, nice write-up. As a former pilot I appreciate your insight. Acceptable risk is an individual concept and learning from the bonehead moves of myself and others in any endeavor (flying, diving, ...) is the hallmark of experience (and modifying your approach, technique, situational response... appropriately from the knowledge gained).

I think rebreathers are fascinating. A number of years ago I started (as is my custom with any new interest) by reading every book, manual, article and training guide I could get my hands on. I spoke at length with rebreather divers, I researched the mechanics, physics, chemistry and human biology/physiology involved. Full disclosure, I never took a training course, and never used a rebreather. I came to the conclusion for myself, and myself only, that whatever the risk (great, small, whatever), it was not a risk I personally was willing to take. Could I do it? Sure. Do I want to do it? Yes. Will I do it? No.

A good friend who is a long time rebreather diver and has made some (to me anyway) horrifically deep dives using them, chided me the other day about my "irrational fear" when it comes to rebreathers. I sat down my Mai Tai, moved the little umbrella to the other side of the glass, looked him in the eye (he only has one - long story but it involves our respective difference in risk tolerance) and said, "look, too much O2 and you are dead, too little O2 and you are dead." He seemed nonplussed and replied, "oh, there's a lot more that will kill you using a rebreather than just that," Considering I had proven my point we ordered another round (keeping my little drink umbrella to use as a toothpick of course).

I applaud you rebreather divers out there. Good luck and safe dives. I'll be happy to watch your GoPro videos and live your dives vicariously. Others opinions may differ and you are welcome to them. My 2psi.

Mai Tai Mark
 
Passenger in a submarine, I think just about anyone can do that. No different then a passenger in an airplane. Technically they will be diving and a rebreather is keeping them alive.

Now to get into the pilot's seat is another story.
 

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