mCCR Training Regarding Total Electronic Failures

[dspe]

Garth, perhaps you are referring to monitoring your PO2 by paying to attention to your loop volume. If you were to maintain a constant depth and lost all electronics, and could not bailout for one reason or another, it is possible to somewhat estimate when to add O2 by monitoring your loop volume. As your counter lungs start to decrease in volume, you know that you have metabolized O2 and it is time to add O2. It takes quite a bit of practice to get the hang of it and really only works at a constant depth for obvious reasons. I don't teach this skill until the more advanced courses because most newbie CCR divers don't have the fundamental skills down good enough to recognize when to add the O2. If you are running your unit manually, most people will naturally start to do it anyway after a few hours on your unit. Of course, I am not suggesting that this is something for people to do in lieu of using electronics. Its simply another do or die skill that could be used as a last resort if bailout is not available and SCR is not appropriate for whatever reason. If your unit is an mCCR, it becomes a little trickier due to the constant flow valve, but ultimately, the same principal works, its just a matter of learning how much to add based upon loss of loop volume due to metabolism. Again, this is an advanced skill and should be practiced initially with your instructor and while monitoring your electronics.

Yes it does work i did it on corses minimum loop volume ,just one breath then just add one press of o2 works well if you stay the same depth

 

[mike]

SCR is nice to have in reserve but why would you need it if you planned adiquate bailout?

Because there is no such thing as too much gas?

I'm not a fan of SCR - my nose gets blocked and it becomes hard work. But if I was at max distance from the shotline and wanted to return to it, I'd go SCR for the swim back to the shot at constant depth. I'd be really nervous doing any sort of ascent on SCR.
I calculate bailout gas for a 90/90 profile from the worst point of the dive - so going SCR on the bottom means I have lots more gas left for the OC ascent and deeper deco stops.
Then, if possible, back onto the loop for O2 deco.
Meaning that for an electronics failure, my bailout supply is oodles for a normal ascent - I'd only need to pull the 90/90 profile if I had a complete flood at maximum distance and depth... and only then if I wasn't able to find a friend.

(I also don't include any onboard gas in my bailout calcs, when in reality I can access everything if required, and if I'd done a 90/90 ascent I'd be padding it by draining my onboard O2 at 3m.)

Mike

 

[Chris Brown]

Are people getting trained to deal with a total electronic failure with an mCCR with the possibility of staying on the loop?

This sounds rather hard core for me but I heard it still goes on and wonder what others thought about this. I'm not trying to be controversial here by bringing this up but I do admit there will probably will be strong opinions potentially on both sides.

I don't want to just know eCCR or just mCCR so whenever I meet someone diving rebreathers I always try to ask them what type of training they got on their unit? I think this could lead to healthy discussion with the intent to learn more. I want to be a thinking diver and right now I just don't know enough about everything.

Oh, lastly the environment in which the training occurred was in a cave.

Thanks,
Garth

This is an easy one Garth.

The training between the two is virtually the same, especially at mixed gas level where we try and get people to think about their options a bit more.

A solenoid is just an efficient finger. It doesn't replace the need for thinking and monitoring like you would do on mCCR. That's why I don't agree with those that feel there's an advantage/disadvantage in mental awareness or capacity between the two.

The only difference on mCCR is that there's a leaky valve that may need isolating by turning the valve off. No biggie.




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[Mark Chase]

Just to be clear the environment or the type of unit I used would make no diferance at all.

Adiquat bailout meens exactly what it says on the tin.

My bailout is now on a 50/90GF and is planned on a 25 SAC at max limit of the tank size.

My working SAC average is 12-15 and my deco is 10-12

QED unless thers some issue with my gas AND I loose my buddy, I have no reasion to breath gas blind and risk hypoxia

Lots of things in diving i feel confident to deel with, but I have no answer for passing out.

ATB

Mark

 

[Chris Brown]

Agreed.

I view semi closed as an option for mod1 level ascents. After that, its only a return to the shot line or to help out with gas volumes in a cave egress.

Even then, not sure Id put it anywhere near the top of the list of options in a real scenario

 

[Dave1w]

I had a bit of a think about this ages ago. It was along the lines of verifying the orifice is still working and adding O2 by turning off the O2 and observing the needle dropping, then go SCR, which brings you down to near dil PO2, but with more than 3 breaths, as the O2 is still being added at near metabolic, flushing out your nose gets you back close to dil PO2, it shouldn't ( fingers crossed) peak, and as you ascend, add some O2, or flush and sort of reset the PO2 level.

At the same time, having a good understanding I how much your PO2 goes up with say 2 seconds on the MAV would also help.

I haven't tried it, but could be a good experiment to try out under supervision?

 

[divingabe]

I think that the individual you spoke with may have had his facts somewhat confused. Especially in a cave environment with the saw tooth profile there is no training or possible way of knowing accurately your loop ppo without a readout from your gauge. Total loss of monitors means using scr or bail out. Proper planning as Mark mentioned means having sufficient oc bail gas available for the planned dive. Scr is a good back up to oc but is a real pita for an extended period on a ccr having to vent out your nose or mouth every so many breathing cycle can be confusing and difficult.

 

[Mr fish]

Running up a shot blind and trying to work out my ppo2 needs would be something id only try at deaths door , it would scare the shite out of me .

Scr ok iv got a know starting ppo2 and some numbers to work with , you could teach me loop volume ppo2 drop all day and i still not want to give it a bash coming up the shot ,

Sometime,s in life you just need to say to your self , fook that im just not that good a ccr diver , i need to find a better way to get my self out of this mess ,
And im going to say running blind up the shot and popping some o2 in as and when i think its needed is way past my pay grade,

i have a few bits tacked on to my breather to help me stay on the loop , but i have a line in the sand , and when i hit it , then its time to bail out , no Mickey Mouse bullshit im gone .

id like to know at what depth this loop volume ppo2 stuff is passed on to a student at ,

even doing a Expedition mod 3 , bail out test maybe from 100m or less would be scr to say 60m then bail out cylinders to 6m, back on to breather and 02 blind , ( no matter as you know what ppo2 is in the loop and if you want to slow down the cns clock you move to 5m or 4m 3m , ) you may get a few other stocking fillers tossed in as well ,

even that play test is far far a way from popping some o2 in your unit as and when you THINK you may pass out ,,


CMF i dont dive , but i can see some numbers to work with , and im sure you would have a better chance with your guess work,
put thats all it is guess work ,

 

[Philippe GERIN]

I'm simply asking if anyone was trained on their mCCR to control PPO2 without the readings to simulate the worst failure possible....?

Absolutly not. In all of the agencies I know, no PO2 reading means BO to a known gaz source.

Do people know how to maintain PPO2 on their mCCR without actually having to look at their gauges...

If you stay at your depth, you don't do anything, the orifice is doing it for you. If you ascend I don't see how you could maintain a constant PO2, pressing the MAV, without watching your PO2 gauges. Same when descending.
Well, after a few hudred hours of experience you could guess it. Actually I can, but I'm still validating it reading my gauges. In case of more than 1 gauge failure, see above. No SCR for me, even with 1 good gauge/cell, but I'm not a caver, and BO is planned accordingly.

Philippe

 

[SlowDiver]

For most agencies it is a required skill to learn.


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Garth this has been a good topic to start a debate on. First I'm am NOT a rebreather instructor so what I'm thinking may be way off base. And yes I had the SCR drill in MOD 1, and thought there goes my bail out gas I'll never get back.
Since the training is done per unit specific this is where I have a problem. I can see having the training on a unit if it has only one display, has two displays but are connected to the three cells at a common point.
The one display is a no brainier, if it failed your pp02 information is gone. Now the units that have two displays stand a better chance of maintaining a correct pp02 if one display fails, but it is possible for one display to kill the other display. Since all three cells are fed into each handset a short across the leads will render the cell useless for the other handset. A cut are crushed cable wiring can cause this problem.
Just look at the way the manufactures have changed the design and you can see that they have thought about this problem. Kevin of Jurgenson Marine made the HH where it would take a fourth cell without having to drill or modify the head. Paul with his rEvo has made some great improvements on cell isolation.
What I'm getting at it is now possible to have one handset completely destroyed and it not completely effect the other. The unit I know best is my own. I have two wired computers to the head, one displays cell 1,2 & 3 which I also have my HUD tied into. Now the other computer is wired in cells 2,3 & 4. Notice that cell 1 & 4 are NOT connected to both computers.
The equipment is getting better so maybe in the future SCR training will go the way buddy breathing did in OC. Just my 2 cents worth.

Fred Summerlin



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[Garth]

Garth this has been a good topic to start a debate on. First I'm am NOT a rebreather instructor so what I'm thinking may be way off base. And yes I had the SCR drill in MOD 1, and thought there goes my bail out gas I'll never get back.
Since the training is done per unit specific this is where I have a problem. I can see having the training on a unit if it has only one display, has two displays but are connected to the three cells at a common point.
The one display is a no brainier, if it failed your pp02 information is gone. Now the units that have two displays stand a better chance of maintaining a correct pp02 if one display fails, but it is possible for one display to kill the other display. Since all three cells are fed into each handset a short across the leads will render the cell useless for the other handset. A cut are crushed cable wiring can cause this problem.
Just look at the way the manufactures have changed the design and you can see that they have thought about this problem. Kevin of Jurgenson Marine made the HH where it would take a fourth cell without having to drill or modify the head. Paul with his rEvo has made some great improvements on cell isolation.
What I'm getting at it is now possible to have one handset completely destroyed and it not completely effect the other. The unit I know best is my own. I have two wired computers to the head, one displays cell 1,2 & 3 which I also have my HUD tied into. Now the other computer is wired in cells 2,3 & 4. Notice that cell 1 & 4 are NOT connected to both computers.
The equipment is getting better so maybe in the future SCR training will go the way buddy breathing did in OC. Just my 2 cents worth.

Fred Summerlin



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Can you post a picture or two of your head with attention to how you manage to incorporate the CMF valve and the solenoid?

Thanks
Garth


Garth

 

[Mr fish]

Can you post a picture or two of your head with attention to how you manage to incorporate the CMF valve and the solenoid?

Thanks
Garth


Garth

i think he has posted some photos in some other thread , he has a nice set up ,

 

[Garth]

I was looking for them and only found the h valve pictures. I wanted to see how the head looks.

I'll look under his posts again.


Garth

 

[Garth]

Okay. Found the photos of the leaky valve head.

There are a lot of pictures of the setup on Rebreatherworld but figure I would just post one of them in case someone else was interested in viewing.

Interesting setup. I think I'll let the need for this setup define my action and at this point there is no need for me to have this level of reduction. I'll continue to practice SCR and bailout procedures and look forward to CCR cave.

After all, my machine has had no in water failures to date, and only one battery issue was me leaving them out in the cold garage one time.

I have a few mCCR buddies that I will pick their brains to learn more about the operation and safety procedures aside from the obvious "turn O2 off when getting off the loop."

Thanks all for the discussion thus far. It's always a nice to hear different points of view.




Garth

 

[SlowDiver]

Garth glad you found the photos. Here are some I just took. Getting ready for a dive. These pictures show how the inline orifice connects to the head.


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[Aquanomad]

WIth no PP02 display id bailout to OC and go home

That would be a zero stress situation so no elevated SAC so id have a big safety margin in my OC gas.

Only hapened once to me. Flooded a rEvo and it trashed all three cells. No amount of redundent displays was going to help.

As above i bailed and ended the dive OC

SCR is nice to have in reserve but why would you need it if you planned adiquate bailout?

ATB

Mark

Hey Mark,
How did you flood your rEvo?

Bull Shit Filter

 

[Mark Chase]

Hey Mark,
How did you flood your rEvo?

Bull Shit Filter

My rEvo had a dump on the counterlung at the base of the unit for flood recovery. Ironicly it jamed open on giant stride entry and totaly flooded the unit

Aparently a common problem and they removed the lower dump. Sadly thus removing any chance of flood recovery on a rEvo

But that aside you can flood a rEvo in many ways. Spit mouthpiece? failed P Port? cut loop hose?

ATB

Mark

 

[Garth]

So DSix36 (The Don) stated on another thread that this topic is put to bed and so I replied below. I figured I would copy it here in case others are not members of CaveDiver.net. Do we do math underwater?

Are we monitoring PPO2? Do we go beyond and figure FO2 in the loop? Do we notice changes and expect results with changes in depth? Could we be so good to know what your PPO2 is given the FO2 in the loop and a known change in atmospheric pressure and a known oxygen consumption while a constant mass flow is bleeding oxygen at a known rate? Could we Don?

(Quote):
The reason the thread keeps going is because deep down there is more to the story than simply SCR. mCCR has the benefit of a mechanical device that will continue to bleed oxygen into the system at a known rate and unlike eCCR's it doesn't require the electronics to do so... would you agree?

First, So if there is an electronic failure there is oxygen being bled into the system on an mCCR and there isn't with an eCCR.
Second, Divers that use mCCR's can use this to their advantage.

For a diver that is at 100' (4 ATA) at a PPO2 of 1.2 will be breathing an FO2 of 30%. This is true for eCCR and mCCR. If all the electronics fail at this moment for both divers the eCCR diver will have a PPO2 which will drop significantly faster than the mCCR diver. The mCCR diver if trained and practices this could determine average consumption of oxygen and how many minutes/breaths go by for PPO2 to drop by 0.1. The eCCR diver has no Oxygen being bled into the loop and therefore should perform SCR to exit.

The mCCR diver if at 100' at a PPO2 could ascend to 66' (3 ATA) and know what his PPO2 would be even after considerable time. Starting from 1.2PPO2 or 30% FO2 you would calculate using FO2=PO2/ATA. So at 66' the diver is at 3 ATA or ... 0.30*3=0.9 PPO2.


When the mCCR diver is ascending to 33' he is then at 0.6PPO2 (in incriments of 0.3). This is because you are maintaining 30% FO2 in the loop instead of maintaining the PPO2 in the loop.

When the mCCR diver is at 20 feet he could flush with oxygen to pad any decompression or consider no decompression he could ascend to the surface and be at a ppo2 of 0.3.

I have no idea how to operate an mCCR but I do know that people out there are doing calculations in their head to plan for catastrophic events with their CCR's that go well beyond SCR operation.

Judging by the responses thus far I don't expect the calculations to go very far in the hearts and minds of the forum and presume massive flogging and skepticism with attacks at the lack of sawtooth profile listing. So flog away my friends, flog away.


What I also know is that... Don.... This conversation is not over. ;-)
(End Quote)


Garth

 

[Igor P]

Are people getting trained to deal with a total electronic failure with an mCCR with the possibility of staying on the loop?

How would you know your PPO2 with total electronics failure on mCCR? The only electronics is PPO2 monitors? Even being math guru I belive you can not good enought calculate the PPO2 in the loop. The factors you can not know and control change ppo2 too much to rely only on math.

Igor P
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[Captain Starfish]

Even on an eCCR you could work out (ahead of time) how many full cheek mouthfulls are contained in minimum loop volume. Maintaining depth and re-topping with O2 via MAV as it gets hard to breathe you're maintaining your PPO2 reasonably. Ascending? Well, work out the drop in PPO2 from the pressure drop. Work out what proportion of the loop you've dumped on the way up, mouthful by mouthful. Then work out how much more you have to dump and replace with O2 to get your PPO2 back.

Hah.

Maybe, if you utterly had your act together and practised these calculations as a way of getting to sleep on a regular basis.

My maths get fuzzy even at 15m on a good day. Now my loop's flooded at depth, I'm stressed, I'm trying to juggle shot and my bailout deco schedule sheet plus torch and god knows what else, and now I'm trying to do long division in my head? For me that's going straight in the same bin as ratio decompression: too damned hard to calculate in those circumstances, too damned easy to get wrong, and too savage the consequences if I don't get it right. Bail if you can, SCR if you can't.