You look and find the loop hypoxic....

[Garth]

On another thread we have been discussing cell health and wellness but while conversing about cells another topic came up.. That of hypoxic loop. Quote below....

I believe there have been quite a few people who have demonstrated the extended period of time where PPO2 will drop. My biggest concern and the number one reason I'm turned off from that MAV inhale position is that if a problem with the MAV occurs it's seconds from a disaster where as if the O2 MAV stuck open on exhale it has to go through the entire rebreather giving you more time.

As you know the response to Hypoxic isn't oxygen flush but actually Diluent flush.... Known PPO2.

During the training for this rebreather if the diver all of the sudden notices the PPO2 of 0.18 would you add oxygen or do a diluent flush? Real question.

Thanks
Garth


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Genuine question, which training was this?

I certainly didnt get taught that and even if i had, I'd be questioning the logic behind this one.

If you looked down to find your cells reading a PPO2 nearing hypoxic what would you do and why would you do it?

Also please state the rebreather you dive for training trending.

Thanks,
Garth


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[Mr fish]

Ybod

Dill flush
Why , to up the ppo2 and see what the cell,s are going to read from my known dill,

Training mod1

 

[Igor P]

Ybod

Dill flush
Why , to up the ppo2 and see what the cell,s are going to read from my known dill,

Training mod1

No dil mav on my CCR, but making dil flush by ADV. Same reason as above

Igor P
TR300c

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[Mike Ferguson]

It all depends on circumstances and my response would very much depend on what my diluent was and what depth I was at. I once experienced a hypoxic loop incident on a surface swim and experienced narrowing of vision and felt I was starting to pass out. my response was to blow the wing and take the mouthpiece out.

at depth dil flush to fill loop with known breathable gas. then check ppO2 is where it should be.

YBOD / deep pursuit ish

 

[Mr fish]

It all depends on circumstances and my response would very much depend on what my diluent was and what depth I was at. I once experienced a hypoxic loop incident on a surface swim and experienced narrowing of vision and felt I was starting to pass out. my response was to blow the wing and take the mouthpiece out.

at depth dil flush to fill loop with known breathable gas. then check ppO2 is where it should be.

YBOD / deep pursuit ish

Good point , depends on where you are in the dive ,

If I'm in 6m or less I'd be on the O2 button asap

 

[Captain Starfish]

AP Classic. Happened to me late last year. 14m dive leading a couple of n00b open waters, distracted by them and by the time we had all reached the bottom and settled my PPO2 had dropped low enough that I was tunnelling out. Nothing on HUD, had bumped the switch. Handsets were asking to calibrate, guessing battery bounce on entry. Knew straight away my O2 would be low. Good squirt on O2 MAV, not a flush, got everything up and running and here to tell the story.

In hindsight I should have flipped the BOV, got the loop stable and back to a known state then gone back.

Thanks for the reminder, Garth, time for some drills tomorrow!

 

[Garth]

So with the response in an emergency to a hypoxic loop is to diluents flush why would you want the oxygen on the inhale counter lung? Furthermore if the diluent manual add valve is in the exhale counter lung the response to resolving an issue is delayed if following proper procedure given the diluent takes longer to resolve the issue.

I'm failing to see the benefit to having an oxygen manual add valve in the inhale counter lung at all.

Theoretically if the diver needs to manually operate his rebreather to exit a dive the difference of the actual inspired PPO2 and what you handsets are reading can be quantified by the metabolic oxygen consumption of the diver. And scientifically what does that do to your decompression algorithm? How do you take that into account?

So what I'm trying to attain from this thread is whether there is variation in training standards for hypoxic loop as well as determine why anyone would consider oxygen manual addition would 'ever' be a good thing in the inhale counterlung...
Given that "ebt" the diver in the other cell husbandry thread post who stated that a diluent flush was not how he was trained to react to a hypoxic loop I considered the fact that maybe some people in different units are trained differently. EBT is a ton more experienced than me diving since 1992 and Rebreathers since 2001 so I am curious as to whether others would treat realizing a hypoxic PPO2 and a clearly non-functioning rebreather with a simple addition of oxygen.

Not to add another discussion point to my already long post but I see a BOV as more important than a remedy to a CO2 hit because diagnosing problems in the loop become quicker and in my opinion more safe as long as you ensure a breathable gas is plugged ( preplanning a dive will solve of course).

Thoughts?

Garth


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[Garth]

I think somebody in the dive industry who is well respected (obviously not me.. ;-) ) should put together a failure mode effects analysis youtube presentation discussing rebreather hazard control and unit specific weakness advantages. Edit:... Every unit has them.
Independent and unbiased perspectives are few and far between but imagine ..


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[trimixdiver]

So with the response in an emergency to a hypoxic loop is to diluents flush why would you want the oxygen on the inhale counter lung? Furthermore if the diluent manual add valve is in the exhale counter lung the response to resolving an issue is delayed if following proper procedure given the diluent takes longer to resolve the issue.

I'm failing to see the benefit to having an oxygen manual add valve in the inhale counter lung at all.

Theoretically if the diver needs to manually operate his rebreather to exit a dive the difference of the actual inspired PPO2 and what you handsets are reading can be quantified by the metabolic oxygen consumption of the diver. And scientifically what does that do to your decompression algorithm? How do you take that into account?

So what I'm trying to attain from this thread is whether there is variation in training standards for hypoxic loop as well as determine why anyone would consider oxygen manual addition would 'ever' be a good thing in the inhale counterlung...
Given that "ebt" the diver in the other cell husbandry thread post who stated that a diluent flush was not how he was trained to react to a hypoxic loop I considered the fact that maybe some people in different units are trained differently. EBT is a ton more experienced than me diving since 1992 and Rebreathers since 2001 so I am curious as to whether others would treat realizing a hypoxic PPO2 and a clearly non-functioning rebreather with a simple addition of oxygen.

Not to add another discussion point to my already long post but I see a BOV as more important than a remedy to a CO2 hit because diagnosing problems in the loop become quicker and in my opinion more safe as long as you ensure a breathable gas is plugged ( preplanning a dive will solve of course).

Thoughts?

Garth


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Garth I wouldn't normally express my opinion , I dive a meg as you are aware the 02 Mav is in the inhale lung, when I did my Mod1 I do remember asking my Instructor why the 02 is on the inhale side...
His answer was that in the case of a hypoxic situation you have very fast a breathable gas.....

 

[Mr fish]

So with the response in an emergency to a hypoxic loop is to diluents flush why would you want the oxygen on the inhale counter lung? Furthermore if the diluent manual add valve is in the exhale counter lung the response to resolving an issue is delayed if following proper procedure given the diluent takes longer to resolve the issue.

I'm failing to see the benefit to having an oxygen manual add valve in the inhale counter lung at all.

Theoretically if the diver needs to manually operate his rebreather to exit a dive the difference of the actual inspired PPO2 and what you handsets are reading can be quantified by the metabolic oxygen consumption of the diver. And scientifically what does that do to your decompression algorithm? How do you take that into account?

So what I'm trying to attain from this thread is whether there is variation in training standards for hypoxic loop as well as determine why anyone would consider oxygen manual addition would 'ever' be a good thing in the inhale counterlung...
Given that "ebt" the diver in the other cell husbandry thread post who stated that a diluent flush was not how he was trained to react to a hypoxic loop I considered the fact that maybe some people in different units are trained differently. EBT is a ton more experienced than me diving since 1992 and Rebreathers since 2001 so I am curious as to whether others would treat realizing a hypoxic PPO2 and a clearly non-functioning rebreather with a simple addition of oxygen.

Not to add another discussion point to my already long post but I see a BOV as more important than a remedy to a CO2 hit because diagnosing problems in the loop become quicker and in my opinion more safe as long as you ensure a breathable gas is plugged ( preplanning a dive will solve of course).

Thoughts?

Garth


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Eccr and mccr
If I'm diving a eccr and I see low ppo2 I know it's a problem with the unit ,
Mccr chances are Iv not keeped the ppo2 up near my set point , and Id have a better feed back on whan I last pressed the O2 add button , so maybe I'd hit the O2 first then be looking at cell,s next ,

 

[Garth]

Garth I wouldn't normally express my opinion , I dive a meg as you are aware the 02 Mav is in the inhale lung, when I did my Mod1 I do remember asking my Instructor why the 02 is on the inhale side...
His answer was that in the case of a hypoxic situation you have very fast a breathable gas.....

I've heard that a lot which I think is a dangerous suggestion but who the hell am I, because I don't have that much experience and I am not an instructor but I will say I think about failure and response all the time. It fascinates me.

Was the skill of dealing with low oxygen taught as in they made you perform an oxygen flushing to solve a low hypoxic oxygen reading?


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[Garth]

Eccr and mccr
If I'm diving a eccr and I see low ppo2 I know it's a problem with the unit ,
Mccr chances are Iv not keeper the ppo2 up near my set point , and Id have a better feed back on whan I last pressed the O2 add button , so maybe I'd hit the O2 first then be looking at cell,s next ,

That's reasonable but would you be able to verify what you were seeing on the PpO2 display?

I see your point about mCCR but I don't have experience with a CMF valve.

Edit: I guess I should have asked, when you were trained on an mCCR, what was your training response to an abnormally low PPO2 in expectantly?


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[Jeff Pack]

Meg, Mod 1 class, hypoxic, O2 Flush via O2 MAV, OPV Open

 

[Captain Starfish]

Garth: bear in mind that the meg inhale lung ain't empty, so you won't be getting smashed with pure O2 because it will be mixed with whatever (hypoxic) shite is in the lung before it gets to you. Still, I kinda prefer the inspo approach where you have the whole loop for mixy mixy and dilution before the O2 slug reaches your gob.

 

[ebt]

Good call to split this one out To be accurate, I should probably have said "I dont recall being taught that". The problem is so much time passes and the student notes are almost as appalling as my memory.

My Default response to low PO2 would be:

<6m, hit the O2. Any time Im less than 6m, the loop is 100% O2.
>6m, it should be 'dil flush'. but if Im being honest, in reality it'd be "is it lkely to be inattention, in which case I'd squirt o2", or "is it critical/unexplainable, in which case dil flush".

The original training question is an interesting one, it kind of plays into the whole "how do you ensure a <insert agency name> trained diver still has access to current information".

ps. my answers are based on a KISS.

 

[Captain Starfish]

The more I think about this the more I go back to "stop dicking around, trying to make decisions. Bail out first, then sort your shit, then get back on the loop if and only if it's safe to do so".

Which leads me to another disturbing thought. Dunno about the rest of you, but my MOD1/MOD2 skills drills basically went on the line of "Bailing out is always an option but let's sort the problem out instead during the course" or similar. I get it. Limited number of contact hours, need to get through the extended thing. But maybe the emphasis should be more on the lines of:
1. Something's wrong. Don't care what. Get off the loop.
2. Now you have a little time to diagnose and correct without worrying about making it worse or lethal.
3. When you've got it back together, get back on the loop.

Particularly on MOD1 with an air diluent, switching to a BOV costs nothing - so maybe it's worth drilling home as always the first step?

Just a drunken musing...

 

[Mr fish]

Can't say my noddy1 was about fixing problems , it was bailout

 

[Garth]

Good call to split this one out To be accurate, I should probably have said "I dont recall being taught that". The problem is so much time passes and the student notes are almost as appalling as my memory.

My Default response to low PO2 would be:

<6m, hit the O2. Any time Im less than 6m, the loop is 100% O2.
>6m, it should be 'dil flush'. but if Im being honest, in reality it'd be "is it lkely to be inattention, in which case I'd squirt o2", or "is it critical/unexplainable, in which case dil flush".

The original training question is an interesting one, it kind of plays into the whole "how do you ensure a <insert agency name> trained diver still has access to current information".

ps. my answers are based on a KISS.

First off, thank you for inspiring me to think critically about design, training and procedure.
Secondly, thank you for not getting pissed at me for taking our conversation on one thread and making another one. I was hoping you wouldn't get upset but I thought this discussion is worthwhile to have.

I have my ADV off below 20ft and only use oxygen manual at such a shallow depth but the situation in my mind had to do with the working part of the dive which I probably could have specified better however I'm glad I didn't because the idea of only using oxygen above 20 feet i support.

I know that reality and hypothetical situations can sometime be different due to the additional information a diver has but I'm not so sure even if you think the gas is breathable by simply adding a little oxygen to the inhale counterlung it seems as though we are forgetting that that assumption also assumes the cells are not damaged or incorrect. As the saying goings assuming makes an ass out of u and me but what happens when you make a double assumption..? Does it make an ass out of everyone? bahah.. er.. jk.

So i'll continue to watch this thread as time goes on because i am fascinated by all this but for the divers who have a rebreather designed, on purpose, to have oxygen manually added to the inhale counter-lung please understand I know that this topic has been discussed "ad-nauseum" as one diver stated. My point is WTF have we actually come up with as far as real actual benefits to having this design. I mean if this design was created in the 90's and considered worthy of keeping there has to be some other reason other than the Navy chooses to dive it. Seriously? Are we thinking divers?

Call me an ass all you want but there is so much innovation going on right now with electronics, Shearwater, the Meg 15 head, sidemount systems being perfected, scooter/battery technology excelling, and we can't even come up with a standard or best practice for placement of something as simple as a MAV.

Innovation is important for humans otherwise we would never try something new, never have been to the moon, and would never have been able to explore a cave. Standards are also important because as we learn there are bits of info that are better than others. Thinking brings innovation and standards to a whole other level. So as I enjoy reading on the forums I find myself constantly thinking and I'd like that thank all of you for that.

Cheers to all those who have responded thus far. Where the hell are all the supporters of the Inhale O2 MAV? I figured that someone would have thrown some dung by now...

 

[matt]

I cannot imagine how I get to hypoxic levels without noticing. If I did I'd also be deaf not to have heard the O2 alarm. Perhaps the entire unit is switched off?

If I had 0.18 0.18 0.18 I'd add a squirt of O2 and see what happens.

If I had odd readings, like 0.18 1.22 0.75 then I'd do a dil flush and see what happens.

Matt.

 

[Captain Starfish]

I cannot imagine how I get to hypoxic levels without noticing. If I did I'd also be deaf not to have heard the O2 alarm. Perhaps the entire unit is switched off?

That would have been my response until it happened. Combination of battery bounce effectively turning the unit off with insane task loading from the moment of backward roll into the water onwards.