You look and find the loop hypoxic....

[Captain Starfish]

Just what are the things that could cause a .18 READING? ... (paraphrasing) if a loop with functioning monitor drops to 0.18 the diver is an idiot blah blah blah"

Yes, you can preach this as much as you like. We all know that's what we should be doing. Fact is, though, we're human. We get complacent, we get distracted, and occasionally we make an oopsie. Sometimes all this happens at the same time and all the mantras of "know your PPO2" ain't going to help you when you finally do know your PPO2 - and it's wrong.

So the question is what happens then?

This thread's been great for me personally, a few things have been highlighted for me that I need to tighten up in my dive style. Even started practicing some bailouts last dive (chuckled when I saw your next post!) for the first time in too long. Realised that, much as I love the streamlining and red hot air delivery of the AP OCB, the switch from CC to OC is a dog of a thing and work is coming up to make it a simpler affair.

 

[uwxplorer]

First stage fail shut , is that something that happen s often , Iv never had it happen to me in 30 years of diving , but if so it could just as well be the dill fail , bail out fail all 6 regs I have on my unit and side cans
Fail .

I know shit happens but come on

Recently, a guy found out that the pO2 in his loop was getting low at ~250 ft (manual rEvo). Pressed the MAV, nothing happened. Checked the valve, everything looked fine. Pressed the MAV again: Nada. Bailed out and canned the dive.
Turns out, the first stage's IP had drifted down and there was no gas flow below a given depth (~200 ft? I don't recall the exact figure). In fact he was able to return to the loop once shallow enough.
Not strictly speaking a "failure", but close enough?

Edit: the loop did not get hypoxic because the guy was on top of it, but it took him time to work on checking the source of the problem because he was busy tying a line.

 

[snarkcon5]

The ADV on a KISS was behind my head on the top of the scrubber I had about as much chance of reaching it as I did of flying to the moon

leaning left or right made sod all diferance.

On my JJ I can get to my ADV but its not "to hand"

Droping my left sholder to get dill to inject does absolutly nothing on my unit as I have a harder ADV spring fitted after complaining I strugled to find minimum loop on tyhe protatype JJ i dived.

Our discussion started because you stated the JJ didn't have a dil MAV, but you've evolved it into something both unrelated (KISS) and specific to you (unit mods). The only reason I made a comment was to clarify that the JJ does, in fact, have a dil MAV. If you have trouble reaching it, that doesn't mean it isn't there. Also, the CE unit comes stock with a MAV at the chest. Not trying to argue; just trying to clarify facts in case a potential JJ buyer stumbles across this.

My bailout is on a tight necklace just below my chin. I breathe it uncharged while loading gear and charged in the water to ensure the flappers work and gas is being delivered. A few times during the dive I put my hand on it to make sure it's where I think it is. If I need to bail, there won't be any fumbling around for the reg, as would likely be the case if it were stowed on the bottle. It's as close to BOV response time as you can get, but provides a reg that breathes great for CO2 events. If I am alerted to a hypoxic PO2 by looking at the handset (and not because I'm starting to black out), I'm going to bail because I know exactly what I'm going to get. Given this scenario is most likely caused by an O2 supply or delivery problem (for my eCCR), hitting the O2 seems like the worst thing to do.

 

[divingabe]

Recently, a guy found out that the pO2 in his loop was getting low at ~250 ft (manual rEvo). Pressed the MAV, nothing happened. Checked the valve, everything looked fine. Pressed the MAV again: Nada. Bailed out and canned the dive.
Turns out, the first stage's IP had drifted down and there was no gas flow below a given depth (~200 ft? I don't recall the exact figure). In fact it was able to return to the loop once shallow enough.
Not strictly speaking a "failure", but close enough?

Edit: the loop did not get hypoxic because the guy was on top of it, but it took him time to work on checking the source of the problem because he was busy tying a line.

Just to make you aware, on an mccr with a fixed orifice (non needle valve) the first stage in not depth compensated. The ip remains constant regardless of depth. The difference between the ip and water pressure decreases with depth to the point that delivery of gas is nonexistent. So when the ambient water pressure is app 130psi about even to the ip in the first stage there cannot be any flow through the needle valve or mav.

Gabe

 

[matt]

Recently, a guy found out that the pO2 in his loop was getting low at ~250 ft (manual rEvo). Pressed the MAV, nothing happened. Checked the valve, everything looked fine. Pressed the MAV again: Nada. Bailed out and canned the dive.
Turns out, the first stage's IP had drifted down and there was no gas flow below a given depth (~200 ft? I don't recall the exact figure). In fact it was able to return to the loop once shallow enough.
Not strictly speaking a "failure", but close enough?

Edit: the loop did not get hypoxic because the guy was on top of it, but it took him time to work on checking the source of the problem because he was busy tying a line.

mCCR? Had the guy done a course?

Matt.

 

[uwxplorer]

mCCR? Had the guy done a course?

Of course. What can be faulted in his reaction?

 

[matt]

Of course. What can be faulted in his reaction?

mCCR utilising CMF would always behave like that, so surprised it was classed as close to a failure by your friend, that was all.

Matt.

 

[uwxplorer]

mCCR utilising CMF would always behave like that, so surprised it was classed as close to a failure by your friend, that was all.

OK, except that the rEvo he had was in principle limited to 90 m (~300 ft), so having it fail shallower was in the "unexpected"category.

 

[Mr fish]

OK, except that the rEvo he had was in principle limited to 90 m (~300 ft), so having it fail shallower was in the "unexpected"category.

I'd class that as unexpected at 200f , shit happens for sure ,

My post was more about the standard regs , but it,s a good point in your post for all divers on that set up .
Test your Ip , in norm do mine if Iv not had the box in the water for some time , and all ways do it if I'm off for a week s diving ,

Just one more thing on the list that can make for a bad day

Ps. I also have a 2nd off board O2, and can buy pass the main unit feeds ,
Iv seen this used on units set up like the one in your posts , but most use it to get past the 300f cut off , but still makes for a good back at 200f

Best

 

[uwxplorer]

I'd class that as unexpected at 200f , shit happens for sure ,

My post was more about the standard regs , but it,s a good point in your post for all divers on that set up .
Test your Ip , in norm do mine if Iv not had the box in the water for some time , and all ways do it if I'm off for a week s diving ,

Just one more thing on the list that can make for a bad day

Ps. I also have a 2nd off board O2, and can buy pass the main unit feeds ,
Iv seen this used on units set up like the one in your posts , but most use it to get past the 300f cut off , but still makes for a good back at 200f

Best

The whole story is that the guy who clipped his bailout unfortunately clipped it though a loop of the hose and prevented it from extending fully, so he ended up his neck twisted to try and suck from his bailout reg. That was problem number 2 and when he decided to can the dive.
In normal circumstances, he would probably have figured out the source of the problem and indeed, connected his richest mix as an external O2 supply.
I just mentioned the story as an example of why you may expect pO2 to drop (and if you don't act on it quickly, result in a hypoxic loop).

PS: I guess S-drill are not considered cool in our neck of the woods.

 

[Randy Thornton]

The whole story is that the guy who clipped his bailout unfortunately clipped it though a loop of the hose and prevented it from extending fully, so he ended up his neck twisted to try and suck from his bailout reg. That was problem number 2 and when he decided to can the dive.
In normal circumstances, he would probably have figured out the source of the problem and indeed, connected his richest mix as an external O2 supply.
I just mentioned the story as an example of why you may expect pO2 to drop (and if you don't act on it quickly, result in a hypoxic loop).

PS: I guess S-drill are not considered cool in our neck of the woods.

I haven't read a single post here that does not magnify the fact that CCR divers are not consistently allowing themselves to either bypass protocols or are not practiced sufficiently at our existing protocols and skills to safely execute fairly simple dives. I feel strongly that as a community, it is time for us to step back and take a fresh look at our commitment to our safety protocols. For the most part, I think the protocols are there. We are just not practicing our skills and following universally accepted safety procedures on a consistent basis.

Warm regards,
Randy

 

[Wol]

I thought we were all dive gods on here ????:banana1: What happened to minimum loop volume ? If you are on MIL then you are only one breath away from hitting the ADV ?

Probably my preference too - breath out through nose and in through and adv - then check hand sets - lot less thinking in my opinion.

 

[rjack]

For those of you diving without a BOV are you putting your bailout reg on a necklace so its immediately available? Or is it stuffed away? I have mine on a necklace, but I adopted this from my OC days and it wasn't a required bit of gear for my CCR training.

 

[DSix36]

For those of you diving without a BOV are you putting your bailout reg on a necklace so its immediately available? Or is it stuffed away? I have mine on a necklace, but I adopted this from my OC days and it wasn't a required bit of gear for my CCR training.

Necklace for me and the valve is always open.

 

[Garth]

A bit of clarification needed here:

I would like to say that I apologize if any of my comments were taken negatively. My dive buddy has accused me of having some kind of vendetta against the MEG and as I re-read the posts I had over the last few days they could be considered strongly against the MEG however I would like to state that I don't have any Ill feelings for it at all except of the counterlung design. My dive buddy will be diving a Meg and for some reason my comments infuriated him. He also told me to take a physics class which I of course laughed at because just the statement alone is funny not because it isn't true just because he said it. I could stand to browse up on a few physics equations here and there i do admit. I just don't understand what the benefits are to having the oxygen in the inhale counter-lung when there appears to be multiple reasons not to.

For some reason, "Its not a problem", is not good enough for me.

The purpose of this thread was to encourage thought on failure management and periodic evaluation of disaster scenario.

And, there is so much I don't know. I don't know what its like to be in a different course, to dive a different rebreather, to react to a scenario in a different way. Much of my goals were to read how others treat and mitigate risk. I wanted to read what was important to others.

My passion for understanding comes off the wrong way commonly. I'm really not a dick head in real life, I just want to understand (my dive buddy may disagree because I am constantly trying to get information out of him and play devils advocate).

Part of my discussion with him today was why if there is a better way don't we choose it? Maybe there isn't a better way just a different way but if thats the case it would appear there should be equal supporting information that makes both ways just that, "equal."

Hard to say, i'm just a peabody looking to get back underwater.

Party on.
Garth

 

[Garth]

Probably my preference too - breath out through nose and in through and adv - then check hand sets - lot less thinking in my opinion.

I think i like thinking, at least thats what I remember the last time I thought about it.

 

[Garth]

Here are the papers I have. There is also a MSc thesis by Elizabeth Humm in the Cranfield library from 2010

http://www.hse.gov.uk/research/rrpdf/rr436.pdf - Formal risk identification in professional SCUBA (FRIPS)
- This report describes how fault tree analysis and failure modes and effects criticality analysis (FMECA) can be carried out on activities and hardware typical of a professional SCUBA diving activity. The methodologies are described and conclusions drawn from each technique. Examples are given of how the techniques can be used to assess diver risk in a quantitative way to aid assessing equipment configurations.

https://www.shearwater.com/wp-content/uploads/2012/08/Underwater_Technology_Paper.pdf - The use of fault tree analysis to visualise the importance of human factors for safe diving with closed-circuit rebreathers (CCR)
- Closed-circuit rebreathers (CCR) have been used for many years in military diving but have only recently been adopted by technical leisure divers, media and scientific divers. Rebreather divers appreciate the value of training, pre-dive checks and equipment maintenance but it is often difficult to visualise just how important these factors are and how they inter-relate for a rebreather. In this paper, the well-known tech- nique of fault tree analysis (FTA) is used to identify risk in a rebreather. Due to space constraints, only the branch of the tree for unconsciousness as a result of hyperoxia is considered in detail but, in common with the whole tree, end events are shown to be human- factor related. The importance of training to the emer- gency situation, the use of formal pre-dive checklists and the value of good design to prevent accident escalation are discussed further.

http://www.hse.gov.uk/research/rrhtm/rr871.htm - RR871 - Assessment of manual operations and emergency procedures for closed circuit rebreathers
- Closed Circuit Re-breather (CCR) diving has become increasingly popular as more sophisticated units enable diving for longer and at greater depths. CCR diving is much more complex than traditional open circuit diving in many ways and there is an increased potential for problems and diver errors to emerge. However, formal research examining CCR safety has been rare. To address this, the UK Health and Safety Executive commissioned the Department of Systems Engineering and Human Factors at Cranfield University to conduct a scoping study into the human factors issues relevant to CCR diving apparatus. The scoping study was designed to explore five principal subject areas: accident / incident analysis, unit assembly / disassembly, normal / non-normal diving operations, training needs analysis, interface and display. This scoping study has approached this with a series of studies each addressing separate issues that are relevant to the principal subject areas. These studies can be seen as potentially stand alone, each with its own objectives, method and results. These studies comprise; Accident / Incident Analysis; Human Error Potential Analysis: Assembly and Disassembly; Human Error Potential Analysis of Diving Operations; Training Needs Analysis; Interface and Display Recommendations and Human Error Potential in Non-Normal Operations.

http://www.dhmjournal.com/files/Fock-Rebreather_deaths.pdf - Analysis of recreational closed-circuit rebreather deaths 1998--2010
-There is a probability failure tree for failure modes of both OC and CCR within this paper.

Regards

Awesome post dude!!!!

I read them and gotta say that the last paper on recreational CCR deaths was interesting especially the fact that the majority of deaths that had information surrounding the death were deemed hypoxic deaths.

 

[cferrar]

A bit of clarification needed here:

I would like to say that I apologize if any of my comments were taken negatively. My dive buddy has accused me of having some kind of vendetta against the MEG and as I re-read the posts I had over the last few days they could be considered strongly against the MEG however I would like to state that I don't have any Ill feelings for it at all except of the counterlung design. My dive buddy will be diving a Meg and for some reason my comments infuriated him. He also told me to take a physics class which I of course laughed at because just the statement alone is funny not because it isn't true just because he said it. I could stand to browse up on a few physics equations here and there i do admit. I just don't understand what the benefits are to having the oxygen in the inhale counter-lung when there appears to be multiple reasons not to.

For some reason, "Its not a problem", is not good enough for me.

The purpose of this thread was to encourage thought on failure management and periodic evaluation of disaster scenario.

And, there is so much I don't know. I don't know what its like to be in a different course, to dive a different rebreather, to react to a scenario in a different way. Much of my goals were to read how others treat and mitigate risk. I wanted to read what was important to others.

My passion for understanding comes off the wrong way commonly. I'm really not a dick head in real life, I just want to understand (my dive buddy may disagree because I am constantly trying to get information out of him and play devils advocate).

Part of my discussion with him today was why if there is a better way don't we choose it? Maybe there isn't a better way just a different way but if thats the case it would appear there should be equal supporting information that makes both ways just that, "equal."

Hard to say, i'm just a peabody looking to get back underwater.

Party on.
Garth

That was an apology for bashing megs? Ok, if you say so. And no I don't dive a meg, I dive a bastardized meg like thing and an evolution. The problem is that you listen about as well of as a 3 year old when you have made up your mind. I still think you need to go back and look at your ideal gas laws.

 

[Garth]

That was an apology for bashing megs? Ok, if you say so. And no I don't dive a meg, I dive a bastardized meg like thing and an evolution. The problem is that you listen about as well of as a 3 year old when you have made up your mind. I still think you need to go back and look at your ideal gas laws.

Those tricky gas molecules are never behaving themselves...

http://youtu.be/BxUS1K7xu30

Brushing up for my reply. Baha


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[Garth]

Wait for it... Yup, I'm not sure exactly what you think I would understand better with looking at ideal gas laws...

I'm not saying the gas doesn't mix before you breath it I just don't quite understand why it was chosen for the design.

Stuck open MAV would be an immediate imminent danger without a BOV which isn't standard. Not that it's not dangerous in the exhale counterlung but oxygen directly exploding into the divers mouth sounds like a really bad day no matter how unlikely it is to occur....

Would that be less than "ideal?"


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