Deep Bailout Gas Choice for ~70M / 230FT

As a non-CCR diver, I can't see the need for a gas you can breathe from 70m to the surface if you have bailed out.

You are not going to be on that gas at the end of the ascent. If you are, you are going to be fizzing like anything, so being hypoxic may not be your major concern when coming up from 6m where you can breathe it...

Regards
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Not necessarily breath it to the surface, but could breath it from the surface down and back up. Why carry a gas that could kill you on the surface if you don't absolutely have to? I believe this has been a factor in some mishaps when it is plumbed into the ADV which then leaks in shallow water. Also having more O2 in the mix gives you more options--say you loose your O2...Having more in your Dil gives you more options.

Again WHY CARRY A MIX THAT COULD KILL YOU WHEN YOU DONT HAVE TO?
Lazy, cheap haven't thought it through?

Back to the CO2 stuff. My personal experience indicates that if you are fit and mentally tough you can get through it. As soon as I realized it was happening, it was already bad. You have to bailout and stabilize your situation (buoyancy etc) focus on what you must do to survive the next minute. I think a reasonable minimum is three minutes at a very high sac rate that are just "lost" trying not to panic/die. Then enough to travel to your rich mix without ascending overly fast.
Then you have to take a little time and do all you can to lower your heat rate and respirations, all those relaxation games:Smile, breath deeply, but with a passive exhale, Think happy thoughts, envision your heart slowing down etc. If the hit didn't come from a complete loop failure, flush and try gingerly to get back on the loop. It took me a few trys to get back on the loop. Try--bail out etc. You have been slowly ascending during this time if possible, if you haven't time to go. At this point one would asses ones decompression obligation and gas available. Tell yourself you are going to be just fine, think of any alternative solutions--Your buddy, sending a bag up for more gas, doing as much deco as you can, surface grab some more gas and do some more deco. Fix your loop and get back on it. Even if its badly compromised, perhaps you can do two breath SCR and extend your gas that way once you have settled down a bit.

While the Shaw video is stark, I think the lesson there has more to do with
equipment failure (not assembled right) and failure to recognize something was wrong until it was too late. In his case my opinion is that the dive was not survivable with the rebreather miss assembled, in that once the problem started the depth etc made it instantly mentally disabling --he was so impaired he didn't have the tools to help himself.
 
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Fireman said:
Again WHY CARRY A MIX THAT COULD KILL YOU WHEN YOU DONT HAVE TO?
Lazy, cheap haven't thought it through?
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Did a course, learnt to dive, practised, at least bothered to read the thread before being rude.

While the Shaw video is stark, I think the lesson there has more to do with
equipment failure (not assembled right) and failure to recognize something was wrong until it was too late. In his case my opinion is that the dive was not survivable with the rebreather miss assembled, in that once the problem started the depth etc made it instantly mentally disabling --he was so impaired he didn't have the tools to help himself.
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And nothing at all to do with his lack of experience and the dive being 275m....
 
matthewoutram said:
What I see in this thread is that plenty of eCCR divers have not moved on from OC thinking.
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matthewoutram said:
I'm totally unclear, Mark, why you so strongly believe you are correct and everyone else with whatever experience or research they offer is wrong. You're fast to dismiss everything to the contrary yet only offer anecdotal hearsay evidence to support your claims. It just doesn't make sense?
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matthewoutram said:
Did a course, learnt to dive, practised, at least bothered to read the thread before being rude.
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At least we agree on one thing.
 
Fireman said:
Not necessarily breath it to the surface, but could breath it from the surface down and back up. Why carry a gas that could kill you on the surface if you don't absolutely have to? I believe this has been a factor in some mishaps when it is plumbed into the ADV which then leaks in shallow water. Also having more O2 in the mix gives you more options--say you loose your O2...Having more in your Dil gives you more options.

Again WHY CARRY A MIX THAT COULD KILL YOU WHEN YOU DONT HAVE TO?
Lazy, cheap haven't thought it through?

Back to the CO2 stuff. My personal experience indicates that if you are fit and mentally tough you can get through it. As soon as I realized it was happening, it was already bad. You have to bailout and stabilize your situation (buoyancy etc) focus on what you must do to survive the next minute. I think a reasonable minimum is three minutes at a very high sac rate that are just "lost" trying not to panic/die. Then enough to travel to your rich mix without ascending overly fast.
Then you have to take a little time and do all you can to lower your heat rate and respirations, all those relaxation games:Smile, breath deeply, but with a passive exhale, Think happy thoughts, envision your heart slowing down etc. If the hit didn't come from a complete loop failure, flush and try gingerly to get back on the loop. It took me a few trys to get back on the loop. Try--bail out etc. You have been slowly ascending during this time if possible, if you haven't time to go. At this point one would asses ones decompression obligation and gas available. Tell yourself you are going to be just fine, think of any alternative solutions--Your buddy, sending a bag up for more gas, doing as much deco as you can, surface grab some more gas and do some more deco. Fix your loop and get back on it. Even if its badly compromised, perhaps you can do two breath SCR and extend your gas that way once you have settled down a bit.

While the Shaw video is stark, I think the lesson there has more to do with
equipment failure (not assembled right) and failure to recognize something was wrong until it was too late. In his case my opinion is that the dive was not survivable with the rebreather miss assembled, in that once the problem started the depth etc made it instantly mentally disabling --he was so impaired he didn't have the tools to help himself.
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You realise Dave Shaw had done the same dive before and survived? Its likley he made the same mistakes he did on the dive that killed him. Only the work load was diferent.


A few questions spring to mind.

You see diving a hypoxic mix as being unessarily dangerous but dont apear to see the diving of a CCR in the normoxic range to be equaly unessarily dangerous?

Personaly i used to see shalow OC diving as safe and deep oc diving as dangerous. With a CCR i see shalow diving the CCR more dangrous than OC but deep diving the CCR safer than OC.

I negate the risk by using the same safety protocols on a shalow dive that I would employ on a deep dive.

Same with Hypoxic mix. Keep standard protacols and the risk remains the same. As i said before on a 100m dive you will probably spend more time in the shalow danger zone than you would on a 30m dive.

I dont dive Hypoxic shalow because i own a compresser and a booster pump. If i didnt i would switch to 10/50 using air tops at my LDS without a second thaught.


I both admire and aspire to your methods of deeling with C02. I have only had one C02 hit and that was at 80m on OC. I fixed that by hugging a rock till I calmed down enough to control an ascent. I dont think i was conciously planning anything i was just unsure which way was up so I staid still till that passed.

Which highlites my problem with your thaught process. Sorry if you mentioned it befroe but how deep were you when you had a C02 hit?

My great concern is the narcosis and can i handle it with so little experiance in the last 8 years. Sitting at my desk here i know what I'd do but i just worry about being capabul of doing it.

Before every dive i have a happy hippy visulisation moment where i mentaly plan for an event. I used to plan all sorts of events but now i only plan for bailout from elevated SAC.

By testing the BOV at the bottom of the shot I build up confidance in the bailout routeen and if at any time i feel odd on the dive I stop and think about my breathing. This hapens a lot with me. i get dizzy moments with early depth changes usualy going up say 5m on the wreck early in the dive. I put this down to ear imbalance as i never get this on ascent at the end of the dive sop i asume things have sorted them selves by then.

Reguardless every time it happens I am hand on BOV and assesing my breathng to see if its odd,


I passed 1500 hours on CCR last year and I have expelled any fear of diving the unit long ago. In the early days of CCR diving my primary feers were low PPo2 High PP02 and flooding. Over the years i have had all of thease symptoms many times and they dont represent any sort of drama for me. My single remaining concern is C02 because i have never suffered it on CCR and i have no idea how id deel with it if i did.

ATB

Mark
 
I did a bit of googling on this and found interesting research.

First I found that the basic time unit for Maximum Voluntary Ventilation (MVV) is 15 seconds and other tests tend to be compared to this. The main other test is the 4 minute test for which there is a fair amount of data, mostly for air, at various depths (one as deep as 1500ft!). It's also pretty clear that gas density plays a big part and that's something else to look at when I have more time. (We're lucky that 15/50 at 75m has the equivalent air density of about 39m, so we can press on for now).

I found that the 15 Second MVV averaged 192 L/min BTPS (sea-level Body Temperature & Pressure, Saturated) and that this reduced to 120 L/min BTPS at 40m using air (Fagraeus & Linnarsson, Maximum Voluntary and Exercise Ventilation at High Ambient Air Pressures, 1973).

The last thing I found was by Freedman. He suggest that it is impossible to maintain 100% of the 15 second MVV for any length of time due to fatigue. However he notes that it is possible to sustain, indefinitely, 50% of the 15 second MVV (S.Freedman, Sustained Maximum Ventilation, 1969).

There's probably more info on this which I'll look for when I have more time.

Matt.
 
matthewoutram said:
I did a bit of googling on this and found interesting research.

First I found that the basic time unit for Maximum Voluntary Ventilation (MVV) is 15 seconds and other tests tend to be compared to this. The main other test is the 4 minute test for which there is a fair amount of data, mostly for air, at various depths (one as deep as 1500ft!). It's also pretty clear that gas density plays a big part and that's something else to look at when I have more time. (We're lucky that 15/50 at 75m has the equivalent air density of about 39m, so we can press on for now).

I found that the 15 Second MVV averaged 192 L/min BTPS (sea-level Body Temperature & Pressure, Saturated) and that this reduced to 120 L/min BTPS at 40m using air (Fagraeus & Linnarsson, Maximum Voluntary and Exercise Ventilation at High Ambient Air Pressures, 1973).

The last thing I found was by Freedman. He suggest that it is impossible to maintain 100% of the 15 second MVV for any length of time due to fatigue. However he notes that it is possible to sustain, indefinitely, 50% of the 15 second MVV (S.Freedman, Sustained Maximum Ventilation, 1969).

There's probably more info on this which I'll look for when I have more time.

Matt.
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Great reserch, well done


ATB

Mark
 
I've just seen this thread.

I think it was a mild CO2 hit caused by scootering (neither of us had much experience on scooters at that point), possibly the BOV (although I didn't know about that at the time) causing poor breathing and so possibly CO2 retention.

As for comments about buddy skills, I had my bailout reg in my hand and was trying to give it to Howard. Short of removing the loop from his mouth I'm not sure what more I could have done. When he went up I went up with him until I couldn't ascend any quicker while remaining in control of my own ascent. When I hit my first stop depth I couldn't see him so decided to stop at 30-odd meters as I thought he'd hit the surface by that point.

As Mark says I don't think we've changed any procedures since then. I still have the Team Chaos procedures ppt that I wrote ahead of that trip.

Fortunately it all turned out well and Howard and I continued with the trip and had a great week of diving. The wrecks there are spectacular.

Janos
 
One more, from Anesthesia, 5th Edition, Churchill Livingstone, 2000:

3.A.24 said:
Dynamic lung function is also routinely evaluated in many pulmonary function laboratories by measuring the maximum breathing capacity or, more specifically, the maximal voluntary ventilation (MVV). This is the largest volume that can be breathed per minute by voluntary effort and reflects an estimate of the peak ventilation available to meet physiologic demands. The patient is instructed to breathe as hard and fast as possible for 12 seconds. The measured volume is extrapolated to 1 minute and is expressed as liters per minute. Because high rates of air flow are required for MVV, the measurement is significantly affected by changes in airway resistance. MVV is usually reduced in patients with obstructive airway disease and correlates reasonably well with FEV1 measured in liters (FEV1 × 35 approximates MVV). Discrepancies between the measured MVV and that predicted by FEV1 often indicate inconsistent or submaximal inspiratory effort. 7 The MVV as a comprehensive test of ventilatory function is altered by factors other than airway obstruction. These include the elastic properties of the lung and chest wall, respiratory muscle strength, learning, coordination, and motivation. In healthy male adults, MVV averages 150 to 175 L/min. This extremely high level of ventilatory effort cannot be maintained for much longer than 1 minute. However, approximately 80 percent of the MVV can be maintained by healthy subjects for as long as 15 minutes, and up to 60 percent of MVV can be sustained for even longer periods. Abnormally low values (<80 percent of those predicted) do not identify specific defects but do indicate gross impairment in respiratory function. The unique value of the test in the surgical candidate may lie in its dependence on intangible variables, such as cooperation, motivation, and stamina.
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Matt.
 
Bobjr said:
Cor ... 80% of 150-175 is 120+L per min for 15min thats alot of gas
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Yes but surely the more important fugue is the one in the previous post where it drops to 120lpm max at 40m on air. This is i assume because of the gas friction of the 5 ATM compressed gas.

Add to this he breathing resistance of a CCR loop. lets assume the panicked diver is not holding horizontal trim which minimized static lung load but is in fact in he worst possible position IE head up vertical.




Now lets ignore all of the above;


Doing breathing exercises on a bicycle to increase RMV will result in typical exercise breathing. IE big deep breaths using maximum lung volume. When i used to run long distance id do an in breath lasting four strides and an out breath lasting four strides. Id employ this breathing pattern throughout the run (usually 5m but 10 mile twice a week). Breathing in this way reduced fatigue. Breathing patterns wouldn't alter. If i wanted to speed up my breathing I had to run faster to maintain the pattern.

In this way id ensure full lung ventilation and maximum benefit from the breathing cycle.

A typical pace for me was a two second in breath and two second out. So 5ltrs every 4 seconds X 15 = 75lpm which I could keep up for hours.


So could i do this underwater in an emergency situation?


No

Because in an emergency situation you rapid breath off the top of your lungs. You'd be lucky to have a 1ltr breathing cycle so you'd have to breath 5 times harder to maintain the same gas transfer volume as i did running.


Its the short sharp breaths that make you black out not the gas volume transfered.


Also mouth opening is critical. The over sized bite piece on a Inspo improves he overall WOB significantly on the unit. When running you could have a wide open mouth reducing the effort of inhalation. When diving you just cant.


SO for the reasons of:

  • Compressed gas density
  • Restricted air flow due to the mouthpiece
  • Work of breathing of diving a CCR
  • Poor in water positioning maximizing lung load
  • and top of the lung breathing


I find the figures for maximum possible RMV to be a bit of a red herring

ATB

Mark






What
 
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Bobjr said:
Cor ... 80% of 150-175 is 120+L per min for 15min thats alot of gas
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And even if we say that the actual average rate is only half of that the figure is still pretty high at ~60LPM.

Perhaps this is why we hear vastly different anecdotal stories about consumption - the ranges are much bigger than I first though.

There's a recent post about someone making an ascent on a 7L cylinders (~1400L) and still running out from 20m (average ~140lpm, assuming 5 minutes).

Matt.
 
Mark Chase said:
Yes but surely the more important fugue is the one in the previous post where it drops to 120lpm max at 40m on air. This is i assume because of the gas friction of the 5 ATM compressed gas.

Add to this he breathing resistance of a CCR loop. lets assume the panicked diver is not holding horizontal trim which minimized static lung load but is in fact in he worst possible position IE head up vertical.




Now lets ignore all of the above;


Doing breathing exercises on a bicycle to increase RMV will result in typical exercise breathing. IE big deep breaths using maximum lung volume. When i used to run long distance id do an in breath lasting four strides and an out breath lasting four strides. Id employ this breathing pattern throughout the run (usually 5m but 10 mile twice a week). Breathing in this way reduced fatigue. Breathing patterns wouldn't alter. If i wanted to speed up my breathing I had to run faster to maintain the pattern.

In this way id ensure full lung ventilation and maximum benefit from the breathing cycle.

A typical pace for me was a two second in breath and two second out. So 5ltrs every 4 seconds X 15 = 75lpm which I could keep up for hours.


So could i do this underwater in an emergency situation?


No

Because in an emergency situation you rapid breath off the top of your lungs. You'd be lucky to have a 1ltr breathing cycle so you'd have to breath 5 times harder to maintain the same gas transfer volume as i did running.


Its the short sharp breaths that make you black out not the gas volume transfered.


Also mouth opening is critical. The over sized bite piece on a Inspo improves he overall WOB significantly on the unit. When running you could have a wide open mouth reducing the effort of inhalation. When diving you just cant.


SO for the reasons of:

  • Compressed gas density
  • Restricted air flow due to the mouthpiece
  • Work of breathing of diving a CCR
  • Poor in water positioning maximizing lung load
  • and top of the lung breathing


I find the figures for maximum possible RMV to be a bit of a red herring

ATB

Mark






What
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Don't disagree with you Mark - but it does highlight what is possible.

Your example of 1 breath every 4sec leading to 75L per min how often are you breathing with co2 even if its just shallow breathing.

I have had CO2 twice and its not pleasant - I would think a proper hit with significant deco without surface support is going to be hard to survive
 
Not too many divers giving comments to this issue.

It seems CO2 hit is a big question mark. It is quite rare to calculate gas for survival from a big hit. I feel I have usually quite a lot of gas with me but now I consider should I really double it or not?

How common is it to get a hit when you need really big amount of gas? I feel I have quite a good sense of how much I work and how much I need to breath. I feel quite uncomfortable if I have to work too hard. Usually I plan and focus to a special task beforehand and try to do it with as low effort as possible. If it gets too difficult I slow down or quit the hole task. Is it possible that in some cases one tries too hard to accomplish the job? I always plan to make just very easy dives. Easy means that all the planned tasks can be done without big effort. I can work hard when not in the water but do not like to use my muscles when diving.

I have experience that hard work is extremely hard underwater but it is very difficult for me to believe that CO2 hit could just hit me without warning and time to react and slow down in time. Would be good to get more stories how a hit develops. Why symptoms are not recognised?

Jukka
 
JukkaO said:
Not too many divers giving comments to this issue.

It seems CO2 hit is a big question mark. It is quite rare to calculate gas for survival from a big hit. I feel I have usually quite a lot of gas with me but now I consider should I really double it or not?

How common is it to get a hit when you need really big amount of gas? I feel I have quite a good sense of how much I work and how much I need to breath. I feel quite uncomfortable if I have to work too hard. Usually I plan and focus to a special task beforehand and try to do it with as low effort as possible. If it gets too difficult I slow down or quit the hole task. Is it possible that in some cases one tries too hard to accomplish the job? I always plan to make just very easy dives. Easy means that all the planned tasks can be done without big effort. I can work hard when not in the water but do not like to use my muscles when diving.

I have experience that hard work is extremely hard underwater but it is very difficult for me to believe that CO2 hit could just hit me without warning and time to react and slow down in time. Would be good to get more stories how a hit develops. Why symptoms are not recognised?

Jukka
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There are a few stories over here and on another thread that I started.
It takes a while to know and the longer it takes and the bigger the hit the slower your coming out of it. A breakthrough or retained hits are going to be the worst to recover from as you will have the highest blood CO2 levels before being able to take actions.

http://www.ccrexplorers.com/showthread.php?t=14094

I have been mulling this for some time and have changed my approach to bail out and fitness because of it. I want to know that I have the right mindset and enough confidence to go stationary for 3 minutes and just focus on recovery without being panicked into a rush ascent due to fear of not having the gas to get to surface. This way when I start it I will have more control and hopefully will be on the way out of the hit rather than doing something stupid and loosing the ascent control.
 
JukkaO said:
I feel I have usually quite a lot of gas with me but now I consider should I really double it or not?
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I think it depends if you are intending to dive solo or supported. Supported it's possible, but solo it is not.

Matt.
 
matthewoutram said:
What depth?
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Deep...... :crossfing

I will be running 3600L for deep, 2000 for intermediate and shallow deco.
My current thinking is something akin to 10/60, 35/35 & 80 for bang for buck, ICD, range flexibility and least duration hanging round shallow....
 
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