Northwest Dive Club

Thought I'd share this here..

The Rubicon Foundation is busy doing a survey study in collaboration with the Divers Alert Network, Duke Anesthesiology, and the Navy Experimental Diving Unit.

Its about scrubber tracking technologies in the market and I know there are a ton of NWDC folks diving RB's and there might be some good data to come from this study!

The Rubicon foundation is a non profit org that houses an absolute ton of valuable diving research data and articles..

http://rubicon-foundation.org/News/rebr ... ers-needed

I dont have a RB, but if you do, please consider this quick survey.

Interesting survey. Asked some fairly technical data about scrubber performance that I had to look up. I suspect that all of us know the scrubber duration but not necessarily the millibar of PPO2 at rated duration and depth.

skubi wrote:Interesting survey. Asked some fairly technical data about scrubber performance that I had to look up. I suspect that all of us know the scrubber duration but not necessarily the millibar of PPO2 at rated duration and depth.

unless you've spent a few days with Leon from ISC, and then you know the milli and milieu of EVERYTHING 'breather related... milli-bar, milli-volt, milli-bucks yer gonna spend buying all his newest coolest toys

Or, I can just download one of Paul's dissertations on O2 sensors or CE test data information sheet

skubi wrote:Interesting survey. Asked some fairly technical data about scrubber performance that I had to look up. I suspect that all of us know the scrubber duration but not necessarily the millibar of PPO2 at rated duration and depth.

HAHA - I knew there was a reason i didnt even bother looking at the survey content.. I played with a few of them in the pool once, but looks like it would only be applicable to those of us who actually DIVE rebreathers and not just read about them and play with them in the pool or at demo days in shallows

BTW - anyone know the details behind the shearwater scrubber sensor thing? sounds pretty cool, but I am out of my depth not knowing the units.

kdupreez wrote:

skubi wrote:Interesting survey. Asked some fairly technical data about scrubber performance that I had to look up. I suspect that all of us know the scrubber duration but not necessarily the millibar of PPO2 at rated duration and depth.

HAHA - I knew there was a reason i didnt even bother looking at the survey content.. I played with a few of them in the pool once, but looks like it would only be applicable to those of us who actually DIVE rebreathers and not just read about them and play with them in the pool or at demo days in shallows

BTW - anyone know the details behind the shearwater scrubber sensor thing? sounds pretty cool, but I am out of my depth not knowing the units.

Here is a link that explains the rEvo "RMS System" I am on the list to get one, what a great product :-)

http://www.oceanedgeoutfitters.com/rEvo ... o-r408.htm

the last question about breathing rate seemed kind of leading. I'm guessing everyone at one point or another has experienced an increased breathing rate regardless of how far down the scrubber has been burned ... that's pretty much a given if you exert yourself under water, especially working against current. I sure hope you folks do some study on Co2 retention, I'm quite positive that what a lot of people think of as breakthrough is actually co2 retention from heavy exertion and or being out of shape. My self, my wife and a friend have all experienced the spiral get out of control on a scrubber that was being used well within it's specs. It's not that hard to get toxic on a perfectly working scrubber if you get caught in an over exertion scenario and the best temp stick in the world is not going to prevent it, might even encourage it. so far, AP has the best mouth piece for keeping the teeth far enough apart to reduce work of breathing under stress, it's not so comfortable, but it does keep the airway open more than others... another good thing to study. Of all the mouth pieces I've used, the Meg's is the worst, allowing the teeth to almost come together, potentially restricting air flow under stress. ... just a few thoughts.

Good post!

Gill Envy wrote:the last question about breathing rate seemed kind of leading. I'm guessing everyone at one point or another has experienced an increased breathing rate regardless of how far down the scrubber has been burned ... that's pretty much a given if you exert yourself under water, especially working against current. I sure hope you folks do some study on Co2 retention, I'm quite positive that what a lot of people think of as breakthrough is actually co2 retention from heavy exertion and or being out of shape. My self, my wife and a friend have all experienced the spiral get out of control on a scrubber that was being used well within it's specs. It's not that hard to get toxic on a perfectly working scrubber if you get caught in an over exertion scenario and the best temp stick in the world is not going to prevent it, might even encourage it. so far, AP has the best mouth piece for keeping the teeth far enough apart to reduce work of breathing under stress, it's not so comfortable, but it does keep the airway open more than others... another good thing to study. Of all the mouth pieces I've used, the Meg's is the worst, allowing the teeth to almost come together, potentially restricting air flow under stress. ... just a few thoughts.

I'm looking forward to getting my RMS also... Curt, any word on the shipping date?

Gill Envy wrote:the last question about breathing rate seemed kind of leading. I'm guessing everyone at one point or another has experienced an increased breathing rate regardless of how far down the scrubber has been burned ... that's pretty much a given if you exert yourself under water, especially working against current. I sure hope you folks do some study on Co2 retention, I'm quite positive that what a lot of people think of as breakthrough is actually co2 retention from heavy exertion and or being out of shape. My self, my wife and a friend have all experienced the spiral get out of control on a scrubber that was being used well within it's specs. It's not that hard to get toxic on a perfectly working scrubber if you get caught in an over exertion scenario and the best temp stick in the world is not going to prevent it, might even encourage it. so far, AP has the best mouth piece for keeping the teeth far enough apart to reduce work of breathing under stress, it's not so comfortable, but it does keep the airway open more than others... another good thing to study. Of all the mouth pieces I've used, the Meg's is the worst, allowing the teeth to almost come together, potentially restricting air flow under stress. ... just a few thoughts.

Gorge are you sure you had CO2 and not heat exhaustion or a combination of blood CO2 buildup and heat exhaustion? Breathing 90 deg air and working hard with all that insulation on and knowing you have a good scrubber is most likely heat exhaustion. Most every person I have talked to that thought they took a hit on a good scrubber and good unit after thinking about it have came to the conclusion that it was heat not CO2 causing the most problems. If you go to bailout and stop thinking you have gotten hit with CO2 you are now breathing cold as hell air so your body temp drops very fast. I take my hood off when I start to feel funny when working extremely hard and the issue usually goes away and I just keep motoring on. Don't get me wrong I have at times had to stop and take a break but I do not go off the loop unless the symptoms to not clear up right away. If I did go off the loop and then I go back on a few minutes latter (after feeling better) it is not CO2 from the scrubber, heat is most likely the primary culprit. If I go back on the loop and feel funny again then I know something is wrong with the unit and it was CO2.

That being all said as a norm, you can get the same blood CO2 buildup that you can on OC if working extremely hard just as you can on the surface if you are sprinting or riding a bike up a hill. That is not the units fault that is human biology and you will get that on OC as well as a CCR. In actuality the CCR will dissipate CO2 better as the differential pressure is lower allowing for blood off-gassing faster. The pressure in the lungs is much higher on OC than on a CCR. This is a very minuet difference unless you are doing extremely long dives or sat diving.

Taking little detour here and Im by no means rb expert and I always understood hypercapnia to be worse on a rb due to work of breathing?

Also curious about the co2 differentials being less in the lungs on a rb? Both rb and oc inspired gas is at ambient with a theoretical ppco2 of 0.0? Wouldn't that make ofgassing co2 equal?

Exerting on a rb would make you work much harder for your gas and hence you produce more co2 and rb therefore makes a co2 hit recovery much harder?

Like I said, not a rb diver, just really interrested to the mechanics of how these work in real life on a rb..

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PP of CO2 on OC is not zero. Depends on the mix you are breathing as there's 400-500ppm CO2 in urban air. A few ppm in O2 used when making nitrox. Essentially zero in helium. Some CO2 is removed by 13x in compressor filters but can also be offgassed by those same filters under different conditions (increasing water content displaces CO2 adsorbed earlier in the filter's life). I have no data but its not unreasonable to consider it on average a wash.

Retained CO2 is the more the issue than inspired CO2 anyway.

yeah, I'll buy that! you inspire a little bit of CO2 in OC breathing gas vs. its all washed by the scrubber on CS? But that should be pretty negligible, right?

kdupreez wrote:yeah, I'll buy that! you inspire a little bit of CO2 in OC breathing gas vs. its all washed by the scrubber on CS? But that should be pretty negligible, right?

I honestly don't know how much CO2 might be in a loop/scrubber which is being "overbreathed" vs ambient air or OC.

But really at least on OC its not about what you are breathing in, its about the CO2 you can't blow off.

Thanks for this info!

Moving to Rebreather section...

kdupreez wrote:Taking little detour here and Im by no means rb expert and I always understood hypercapnia to be worse on a rb due to work of breathing?

Also curious about the co2 differentials being less in the lungs on a rb? Both rb and oc inspired gas is at ambient with a theoretical ppco2 of 0.0? Wouldn't that make ofgassing co2 equal?

Exerting on a rb would make you work much harder for your gas and hence you produce more co2 and rb therefore makes a co2 hit recovery much harder?

Like I said, not a rb diver, just really interrested to the mechanics of how these work in real life on a rb..

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Think of the lungs as hydrophobic membrane, gas on one side liquid on the other with tiny holes that will not let a molecule of the liquid pas but the gas can pass freely. They work on a pressure differential. The higher the liquid pressure to gas pressure the faster the gas can pass through. That is up to a point, If the PD is too high the membrane can get overwhelmed and can get plugged up not allowing gas to pass though. Now if the gas pressure is too high then the liquid will not release the gas thorough the membrane in fact it my allow gas to pass into the liquid. This a very simplified method of trying to explain how a complex system works.

On OC you are drawing from a 140psi source that is throttled with a simple diaphragm valve (not very accurate). But the main difference is that OC does not have a counter lung. If you rise a foot the pressure increases in the lungs, on OC the internal pressure differential of the lungs is always going up and down. Due to the counter-lung on a CCR as we go up and down the pressure maintains whatever the ambient water pressure is. That is why as you breath on a CCR you do not go up and down you stay stationary in the water column. Unlike on OC when you take a breath you start to rise (raising the pressure in the lungs) then when you exhale you descend (lowing the pressure in the lungs). I know for myself when I am on OC I take much bigger breaths than I do if I am just walking around. I like my regs to breath as free as possible and actually shot gas into my lungs so I do not have to suck it out of the regulator.

With the new units especially the CE'ed units the work of breathing is so low. In the case of the rEvo it is 2.0-2.5 J/liter down to 300' with a 75RMV, moving 3 liters at a time. That is working balls to the wall, more than 1 breath a second. That is almost not noticeable verses being on the surface as long as you have your loop volume correct. Now some units do have a WOB that is just horrible while others are great.

Very interesting info, it would be good to get a solid grasp on how the CC thing works, so bare with me..

Can you elaborate on how its different with CC and OC with regards to the membranes getting plugged in your lungs part and how that affects us?

As I understand respiratory and circulatory system to a certain degree (as it pertains to diving and deco) and gas eventually makes it into the alveoli (through bronchial tree), these 1 cell thick air sacs are tightly wrapped with pulmonary capillaries. And the higher the PD of the gas between the blood and the alveolus, the faster the gas will diffuse into the blood (ala Henry's law), so higher PD in my mind means faster gas exchange and it cant get plugged?.. Are these membranes the one's being "plugged" and under what conditions?

Being an OC diver, I understand balanced OC second stages to deliver air at ambient and in redirect response to the negative pressure from your inhalation effort..(yes IP is around 140 psi, but thats before its handled by the 2nd stage). Typically a standard cracking effort of around 1.1 inches of water is effortless to open up air delivery and with balanced regs the breathing effort should be as easy in the water as on land, regardless of depth.. adversely on CCR's your lungs are doing the work of circulating the air through the scrubber and breathing loop, and the deeper you go, the thicker the gas and thus proportionately harder it becomes and even more so if your CCR has an ADV that you need to "suck" open.. At least this is my understanding of why CCR WOB is typically more than OC ? And I thought the pressure in our lungs are pretty much always Ambient regardless of OC or CC? But again, I'm no CCR diver so it would be good to understand how it works.

Then, I'm also not sure I entirely understand the going up and down on OC versus CC thing and admittedly I have only played with CCR's in the pool and the reason I understood on why you go up and down with OC is simply because of variable buoyancy in your lungs that keeps being filled and emptied.... you inhale.. you add more buoyancy (like inflating your bcd) and you go up.. you exhale and you reduce buoyancy (like deflating your bcd) and you sink.. This doesnt happen with with CC because the air volume is constant, i.e. buoyancy of what you breathe out is not lost, its just in the counter lung..

kdupreez wrote:Very interesting info, it would be good to get a solid grasp on how the CC thing works, so bare with me..

Can you elaborate on how its different with CC and OC with regards to the membranes getting plugged in your lungs part and how that affects us?

As I understand respiratory and circulatory system to a certain degree (as it pertains to diving and deco) and gas eventually makes it into the alveoli (through bronchial tree), these 1 cell thick air sacs are tightly wrapped with pulmonary capillaries. And the higher the PD of the gas between the blood and the alveolus, the faster the gas will diffuse into the blood (ala Henry's law), so higher PD in my mind means faster gas exchange and it cant get plugged?.. Are these membranes the one's being "plugged" and under what conditions?

You can only get so much though a membrane at any one time no mater the PD. if the pd gets too high you will start to form bubbles that are too large to easily go though the membrane. and these will plug things up.

kdupreez wrote:Being an OC diver, I understand balanced OC second stages to deliver air at ambient and in redirect response to the negative pressure from your inhalation effort..(yes IP is around 140 psi, but thats before its handled by the 2nd stage). Typically a standard cracking effort of around 1.1 inches of water is effortless to open up air delivery and with balanced regs the breathing effort should be as easy in the water as on land, regardless of depth.. adversely on CCR's your lungs are doing the work of circulating the air through the scrubber and breathing loop, and the deeper you go, the thicker the gas and thus proportionately harder it becomes and even more so if your CCR has an ADV that you need to "suck" open.. At least this is my understanding of why CCR WOB is typically more than OC ? And I thought the pressure in our lungs are pretty much always Ambient regardless of OC or CC? But again, I'm no CCR diver so it would be good to understand how it works.

You are right the work on breathing is easier on OC, I have never said it is not. The reg is breathing for you, inflating the lungs allowing you to without any effort to take in more volume of gas, thus over pressuring more than what you would have if breathing on the surface. You do have WOB on a CCR, but if you have a good CE'ed CCR the WOB even at 300' is not even noticeable compared to being on the surface and just breathing. This keeps the DP in the range that the body works the best. Like I mentioned earlier this only really makes a huge difference if you are on extremely long dives were you are saturating. That is why we always reenforce that when doing deco you should be as relaxed as possible and not working. If you are you are not off-gassing efficiently. Then you get into the info of air breaks, ICD and a few other things to make off-gassing more efficient.

kdupreez wrote:Then, I'm also not sure I entirely understand the going up and down on OC versus CC thing and admittedly I have only played with CCR's in the pool and the reason I understood on why you go up and down with OC is simply because of variable buoyancy in your lungs that keeps being filled and emptied.... you inhale.. you add more buoyancy (like inflating your bcd) and you go up.. you exhale and you reduce buoyancy (like deflating your bcd) and you sink.. This doesnt happen with with CC because the air volume is constant, i.e. buoyancy of what you breathe out is not lost, its just in the counter lung..

You are right but to make your lungs bigger to rise you are cramming more pressurized gas into them to change your volume increasing the internal pressure.

On CCR you are using the ambient water pressure to transfer the same volume of gas in and out of the lung. Never having to over pressure the lungs, just breathing in and out as if you were walking down the road.That is the reason why a over the shoulder counter lung unit typically has less WOB than what a back mounted counter lung will have. The over the should lungs are surrounded by a slightly higher pressure (they are below your lungs center line) so when you go to inhale the water pressure actually helps to push the gas into the lungs. Were certain back mounted counter lung units if you are in cave position the lung is several inches above you. You have to work to get the gas down to your lungs, bad WOB. I have dove several that when you get into CP I cannot breath and start to gag as the gas is being pulled out of my lungs. These units cannot pass the CE test because they can have a WOB of 7J/liter or more. If i recall correctly 1.78 J/liter is what is used as a average for someone just walking down the street.

Cool - Thanks for the details, very good info.