CCR Trimix Simplified by Mel Clark question

***ScubaDadMiami*** · 21st December 2007, 16:54

My personal parameters (which may not be yours):

SCR is something that you perform when your handsets die and you want to extend your gas while having a good, working scrubber. If you are a long way back in a cave and want to give yourself a good margin for the already adequate gas quantity you are carrying (not in order to make the inadequate amount of gas barely get you out alive), you can extend that gas by going SCR, use OC for steep ascents to reduce the chances of hypoxia, and then go on the loop for an O2 flush at 20 feet. In such a situation, I'd do extra deco to make up for possible miscalculation from the SCR time and how this affected your deco obligation. Sure, you could have just gone OC for the entire exit, and there is nothing wrong with this per se. However, going SCR will make sure that any unexpected delays don't bring you down to a critical gas margin, which adds further stress to an already stressful situation.

Now, if you had both breakthrough and were running low on gas at the same time, SCR is something you can resort to because you don't have many other choices. Hopefully, by slowing your workload, your scrubber can still be effective enough to get you back alive. Howevever, SCR in this situation should be a last resort because you could black out and die from CO2 at any point. SCR is not something you do when you have plenty of gas and a dead scrubber.

If I were to have any kind of strange feeling during a dive, I would activate my BOV for a few sanity breaths and would stop all activity. (If necessary, I would then go OC until my breathing rate would back down.) If I had been working hard up to that point, I would suspect (assuming my PO2 were within range) a CO2 issue, and then I would go back on the loop, flush and test while remaining stopped and without work load. If I felt at all out of the ordinary again (and believe me, I would be with all radar in motion to detect this), I would go OC and I would stay off of the loop from that point on (unless my life depended on going SCR to try to extend my gas).

Always carry adequate bail out. The choice is easy and safe in such a case.

***jradomski*** · 22nd December 2007, 05:09

Quote: (Originally Posted by silentscuba)

So, what some of you are saying is that you use to much gas on OC bailout and you don't carry enough so you need to stay on the loop inorder to make things work out OK.

What happens if you can't stay on the loop!!! that can happen also. You now have a second problem to solve if you don't have enough bailout with you.

I still don't understand why someone would try and figure out a problem by staying on the loop risking their life and then on top of that not have enough bailout in case they can't.

We still need to plan for the worst case (carry enough bailout) and hope for the best (maybe staying on the loop) if you can work out the problem.

In any case, you should still have enough bailout, and should not take a risk staying on a loop if it is not very clear what is wrong.

Just my own opinion

.

Sounds like a Bail Out CCR would be a good thing!!!

First the problem is YOU can't always carry enough OC bailout, on big dives even diving with team planing its can still be quite hard to carry enough gas.. You try and plan for enough gas but it cant always be done thats called taking a risk and has to be done in some cases.. its a personal choice..

secondly What RMV are you planning for..even if you plan for an RMV above what you used to use on OC its still probably short of what you actually need.. Thats why extending supplies is important.. Its gives you another opinion.. The first thing that raises consumption is that you are in an emergency situation and will natually be breathing harder, secondly as a Rebreather diver your breathing technique is all screwed up.. Unless you regularly dive bot oc and CC then it would take several DIVES to get you rmv back to what its supposed to be.. So a few minutes deep on SCR can make the difference of being safe or having to skip some deco.. or worse

WIth the right technique, taking 2 or 3 breaths off a loop then flushing keeps all the questionalbe gases low with little risk.. You ARE doing a nearly 100% gas exchange every few breaths-- co2 levels dont rise that fast nor do po2 leves fall very fast (unless you are ascending quickly)..
Just doing a 2x to 1 you cut your gas consumption in half for those few minutes.. Just because a scrubber had "breathrought" doesnt mean its not still usable.. All it means is that for some reason the level of co2 you were producing is above what the scrubber can remove.. lowering excertion levels will reduce the amount of co2 and that may be enough to help the scrubber along.. doing routine gas flash effectively does the same.. I am not advocating use of a DEAD scrubber, but with carefule monitoring a marginal scrubber can be safely used..
Its no a coincidence that a small scrubber like a drager dolphin is rated for much longer than the same size on a CCR.. because co2 is routinely being dumped out of the loop and the scrubber bed ha less to scrub..

let use an imaginary dive to 125m with about 15mins at depth... that means its about a 20minute ascent to 60m.. for simplicity in gas calcs we can use an average depth.. of about 90m (10 atm) -- so of you used 1cuft per minute at surface (in this case imperial is easier) then you need about 10 cuft per min at depth or 200 cuft! Thats alot of gas and your rate will most likely be HIGHER than that.. so just even running a 2x to one could bring you into a reasonable situation.. remember you still have to make an ascent from 60m... if you decide to skip all your deep stops you are still talking about a 7 minute ascent to 60m.. you gas situation is now doable but you have increased other risks like dcs..

Even if its a 2 man team each carrying an al 80 each it would not be enough without some gas extension (a 3 man team might work)... Total loop failures are extremely unlikely (but they do happen) so most people are willing to take the risk that they will have some limited use of the Rebreather at leas for a small portion of the time..

Your other choice is to just head for shallower water and hope for the best that you dont get bent.. Personally I rather take the SCR risk because I could still do the latter if necessary..

silentscuba · 22nd December 2007, 12:49

This has been a great discussion

and maybe we have all taken something away from the table here in a positive manner.

Different view points are always needed so people can come to their own conclusions.

Solitude Diver · 22nd December 2007, 13:56

Quote: (Originally Posted by silentscuba)

Different view points are always needed so people can come to their own conclusions.

Exactly right. Especially for new ccr divers (like myself) who are trying to learn. I'd rather learn from a consensus environment of experienced divers rather than just one person's opinion. It has been great reading the different scenarios. Good food for thought.

Carl Wern · 26th December 2007, 22:31

Good reading & comments!

18 months ago I had an incident that almost killed me. I dove on a wreck 132 feet down with an air dil. in the Baltic sea (I don´t normally go beyond 110 feet with an air dil. in cold water but this was an exception). On my way down I fellt awkward and on the bottom I really felt strange but I thought it was nitrogen narcosis. It kept getting worse during the dive and after a couple of dil. flushes I decided to bail out. After a while I felt better and we started our journey up through the short deco stops for this dive. I was analyzing what had gone wrong and I finally ruled out CO2 hit since my scrubber only had 50 minutes of diving time a week ago.... so I decided to go back on to the loop for the last deco stop at 18 feet. I flushed the CCR with pure O2 twice and got back on. I ran it on minimal loop and it fellt ok. We finished the dive and I could barely climb up the ladder. I felt very "weak" after the dive. When we got back home I asked a friend of mine to analyse the scrubber for me in his lab. The result was a totally depleted scrubber, it was dead, it did not scrub a dammed thing. (why it was totally depleted is another story...)

My point with this personal CCR experience is that I will never go back on a loop that has a suspected problem. Problem solving a CCR while diving and after co2 hit is not a good solution...the brain is not in perfect state.... I will, after this, if I leave the loop for any reason mentioned above, always stay off the loop and finish the dive on a backup CCR or bailout OC. My 2 cents.....

Calvin · 27th December 2007, 02:57

Quote: (Originally Posted by silentscuba)

Just my own feeling here-- I think Mel's position is that you don't always know what has gone wrong and maybe by trying to figure it out, it would be to late. A person should always carry enough bail out and the proper mix to go off the loop at any time during the dive.

When something bad starts to happen, I just want to be programed to do one thing- BAIL OUT!!!!!.

Based on the fact that your bailout should be a good mix for any depth and you should be carrying enough of it, bailing out to OC is the safest thing to do. And that is what she is talking about.

A person can always take a few sanity breaths and then go back and try and sort out the loop if they so desire. At least you will survive the immediate problem if you can go to OC.

Seems like sound advice to me.

**Dave Sutton** · 27th December 2007, 18:32

Quote: (Originally Posted by jradomski)

WIth the right technique, taking 2 or 3 breaths off a loop then flushing keeps all the questionalbe gases low with little risk.. You ARE doing a nearly 100% gas exchange every few breaths-- co2 levels dont rise that fast nor do po2 leves fall very fast (unless you are ascending quickly)..

Just doing a 2x to 1 you cut your gas consumption in half for those few minutes.. Just because a scrubber had "breathrought" doesnt mean its not still usable.. All it means is that for some reason the level of co2 you were producing is above what the scrubber can remove.. lowering excertion levels will reduce the amount of co2 and that may be enough to help the scrubber along.. doing routine gas flash effectively does the same.. I am not advocating use of a DEAD scrubber, but with carefule monitoring a marginal scrubber can be safely used..

Its no a coincidence that a small scrubber like a drager dolphin is rated for much longer than the same size on a CCR.. because co2 is routinely being dumped out of the loop and the scrubber bed ha less to scrub....

Read what Joe wrote here and then REALLY think about it... especially trhe last paragraph which I put in bold. It's dead-on. Bail off a flooded loop. Bail off if you are in an escalating C02 hit situation... but if the loop is not flooded, "consider" going back on later if deco gas volume is an issue. I am not saying "Go back on the loop", I'm saying "don't rule it out". Always keep an ace in the hole.

Dave

Nad · 27th December 2007, 22:43

Quote: (Originally Posted by Dave Sutton)

Read what Joe wrote here and then REALLY think about it... especially trhe last paragraph which I put in bold. It's dead-on. Bail off a flooded loop. Bail off if you are in an escalating C02 hit situation... but if the loop is not flooded, "consider" going back on later if deco gas volume is an issue. I am not saying "Go back on the loop", I'm saying "don't rule it out". Always keep an ace in the hole.

Dave

This is a perfect summary.

Cheers

Nad

diverklondike · 27th December 2007, 23:07

Gang,

Training... Practice... Training... Practice... Practice... Practice... Practice... Plan... Plan... Plan...

My one concern about Mel's book is that someone may think it's a substitute for good training and practice regardless of the position you may be taking on any specific point...

Sorry for the hijack but reading threads like this can get kinda scary...

M

***jradomski*** · 28th December 2007, 05:24

Due to lots of PMs, here is a simplified analysis/example of what can happen in a loop when running SCR

Lets use the following parameters

1.5l tidal volume, 3l "dead space" = 4.5 l
1 lpm o2 production therefor .9lpm of co2
depth 90m - 10ata
4.5l * 10ata = 45.0l of gas in loop
after 1 min, loop is 44.9l of gas
no CO2 scrubbing, 1 liter of o2 metabolized (no addition)
%co2 = 2%, if o2 addition still working 1.96% (loop is 45.9l)
These are worse case numbers... assuming you went a full minute before refilling the loop.. (not very likely) and swimming at a reasonable pace..

now lets look at reality, assuming a person who has a rmv at the surface of about 14lpm (~.5cuft per min)
thats going to be at least 10 breaths per minute, probably 15....
lets assume that you are doing a 3 to 1 extension, that means at worse case you have
less than .67% co2 in the loop (.67 is 9 breaths per minute for ease if calculations)... and that is on a TOTALLY dead scrubber, which is unlikely...
Now lets look at the loop volume, 4.5 is quite low, most people are going to be at least 50% greater..
with the increased volume te co2 percentage would drop.. now we are in the range .4% co2 in the loop..
at 10atas this is below what we define as scrubber breakthrough..
You can see on the above even a totally DEAD scrubber could be used for a short period if time (but not advocating use)...
With controlled breathing, Deep breaths adn a partially working scrubber.. things are even better..

21st December 2007, 16:54	#41 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,132	Re: CCR Trimix Simplified by Mel Clark question My personal parameters (which may not be yours): SCR is something that you perform when your handsets die and you want to extend your gas while having a good, working scrubber. If you are a long way back in a cave and want to give yourself a good margin for the already adequate gas quantity you are carrying (not in order to make the inadequate amount of gas barely get you out alive), you can extend that gas by going SCR, use OC for steep ascents to reduce the chances of hypoxia, and then go on the loop for an O2 flush at 20 feet. In such a situation, I'd do extra deco to make up for possible miscalculation from the SCR time and how this affected your deco obligation. Sure, you could have just gone OC for the entire exit, and there is nothing wrong with this per se. However, going SCR will make sure that any unexpected delays don't bring you down to a critical gas margin, which adds further stress to an already stressful situation. Now, if you had both breakthrough and were running low on gas at the same time, SCR is something you can resort to because you don't have many other choices. Hopefully, by slowing your workload, your scrubber can still be effective enough to get you back alive. Howevever, SCR in this situation should be a last resort because you could black out and die from CO2 at any point. SCR is not something you do when you have plenty of gas and a dead scrubber. If I were to have any kind of strange feeling during a dive, I would activate my BOV for a few sanity breaths and would stop all activity. (If necessary, I would then go OC until my breathing rate would back down.) If I had been working hard up to that point, I would suspect (assuming my PO2 were within range) a CO2 issue, and then I would go back on the loop, flush and test while remaining stopped and without work load. If I felt at all out of the ordinary again (and believe me, I would be with all radar in motion to detect this), I would go OC and I would stay off of the loop from that point on (unless my life depended on going SCR to try to extend my gas). Always carry adequate bail out. The choice is easy and safe in such a case. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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22nd December 2007, 05:09	#42 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 3,008	Re: CCR Trimix Simplified by Mel Clark question Quote: (Originally Posted by silentscuba) So, what some of you are saying is that you use to much gas on OC bailout and you don't carry enough so you need to stay on the loop inorder to make things work out OK. What happens if you can't stay on the loop!!! that can happen also. You now have a second problem to solve if you don't have enough bailout with you. I still don't understand why someone would try and figure out a problem by staying on the loop risking their life and then on top of that not have enough bailout in case they can't. We still need to plan for the worst case (carry enough bailout) and hope for the best (maybe staying on the loop) if you can work out the problem. In any case, you should still have enough bailout, and should not take a risk staying on a loop if it is not very clear what is wrong. Just my own opinion . Sounds like a Bail Out CCR would be a good thing!!! First the problem is YOU can't always carry enough OC bailout, on big dives even diving with team planing its can still be quite hard to carry enough gas.. You try and plan for enough gas but it cant always be done thats called taking a risk and has to be done in some cases.. its a personal choice.. secondly What RMV are you planning for..even if you plan for an RMV above what you used to use on OC its still probably short of what you actually need.. Thats why extending supplies is important.. Its gives you another opinion.. The first thing that raises consumption is that you are in an emergency situation and will natually be breathing harder, secondly as a Rebreather diver your breathing technique is all screwed up.. Unless you regularly dive bot oc and CC then it would take several DIVES to get you rmv back to what its supposed to be.. So a few minutes deep on SCR can make the difference of being safe or having to skip some deco.. or worse WIth the right technique, taking 2 or 3 breaths off a loop then flushing keeps all the questionalbe gases low with little risk.. You ARE doing a nearly 100% gas exchange every few breaths-- co2 levels dont rise that fast nor do po2 leves fall very fast (unless you are ascending quickly).. Just doing a 2x to 1 you cut your gas consumption in half for those few minutes.. Just because a scrubber had "breathrought" doesnt mean its not still usable.. All it means is that for some reason the level of co2 you were producing is above what the scrubber can remove.. lowering excertion levels will reduce the amount of co2 and that may be enough to help the scrubber along.. doing routine gas flash effectively does the same.. I am not advocating use of a DEAD scrubber, but with carefule monitoring a marginal scrubber can be safely used.. Its no a coincidence that a small scrubber like a drager dolphin is rated for much longer than the same size on a CCR.. because co2 is routinely being dumped out of the loop and the scrubber bed ha less to scrub.. let use an imaginary dive to 125m with about 15mins at depth... that means its about a 20minute ascent to 60m.. for simplicity in gas calcs we can use an average depth.. of about 90m (10 atm) -- so of you used 1cuft per minute at surface (in this case imperial is easier) then you need about 10 cuft per min at depth or 200 cuft! Thats alot of gas and your rate will most likely be HIGHER than that.. so just even running a 2x to one could bring you into a reasonable situation.. remember you still have to make an ascent from 60m... if you decide to skip all your deep stops you are still talking about a 7 minute ascent to 60m.. you gas situation is now doable but you have increased other risks like dcs.. Even if its a 2 man team each carrying an al 80 each it would not be enough without some gas extension (a 3 man team might work)... Total loop failures are extremely unlikely (but they do happen) so most people are willing to take the risk that they will have some limited use of the Rebreather at leas for a small portion of the time.. Your other choice is to just head for shallower water and hope for the best that you dont get bent.. Personally I rather take the SCR risk because I could still do the latter if necessary.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated. Last edited by jradomski : 22nd December 2007 at 13:55.
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22nd December 2007, 12:49	#43 (permalink)
silentscuba rEvo CCR Driver Current Rebreather/s: Classic Kiss rEvo Other Rebreather/s: Inspiration Classic rEvo Join Date: Jun 2005 Location: Mill Creek, WA USA Posts: 587	Re: CCR Trimix Simplified by Mel Clark question This has been a great discussion and maybe we have all taken something away from the table here in a positive manner. Different view points are always needed so people can come to their own conclusions. __________________ Curt McNamee rEvo CCR Diver KISS CCR Diver www.silentscuba.com
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22nd December 2007, 13:56	#44 (permalink)
Solitude Diver New Member Current Rebreather/s: Evolution Other Rebreather/s: Evolution Join Date: Nov 2007 Location: Seattle, WA Posts: 36	Re: CCR Trimix Simplified by Mel Clark question Quote: (Originally Posted by silentscuba) Different view points are always needed so people can come to their own conclusions. Exactly right. Especially for new ccr divers (like myself) who are trying to learn. I'd rather learn from a consensus environment of experienced divers rather than just one person's opinion. It has been great reading the different scenarios. Good food for thought.
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26th December 2007, 22:31	#45 (permalink)
Carl Wern No bubbles no troubles Current Rebreather/s: Inspiration Classic Other CCR Home Build Other Rebreather/s: Not Bought Yet Sport Kiss Other CCR Home Build Join Date: Apr 2005 Location: Sweden Posts: 44	Re: CCR Trimix Simplified by Mel Clark question Good reading & comments! 18 months ago I had an incident that almost killed me. I dove on a wreck 132 feet down with an air dil. in the Baltic sea (I don´t normally go beyond 110 feet with an air dil. in cold water but this was an exception). On my way down I fellt awkward and on the bottom I really felt strange but I thought it was nitrogen narcosis. It kept getting worse during the dive and after a couple of dil. flushes I decided to bail out. After a while I felt better and we started our journey up through the short deco stops for this dive. I was analyzing what had gone wrong and I finally ruled out CO2 hit since my scrubber only had 50 minutes of diving time a week ago.... so I decided to go back on to the loop for the last deco stop at 18 feet. I flushed the CCR with pure O2 twice and got back on. I ran it on minimal loop and it fellt ok. We finished the dive and I could barely climb up the ladder. I felt very "weak" after the dive. When we got back home I asked a friend of mine to analyse the scrubber for me in his lab. The result was a totally depleted scrubber, it was dead, it did not scrub a dammed thing. (why it was totally depleted is another story...) My point with this personal CCR experience is that I will never go back on a loop that has a suspected problem. Problem solving a CCR while diving and after co2 hit is not a good solution...the brain is not in perfect state.... I will, after this, if I leave the loop for any reason mentioned above, always stay off the loop and finish the dive on a backup CCR or bailout OC. My 2 cents..... __________________ When you realize that you have so much more to learn, thats when the real learning begins! ........................................... ............... Last edited by Carl Wern : 26th December 2007 at 22:39.
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27th December 2007, 02:57	#46 (permalink)
Calvin New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jun 2007 Location: Seattle Posts: 11	Re: CCR Trimix Simplified by Mel Clark question Quote: (Originally Posted by silentscuba) Just my own feeling here-- I think Mel's position is that you don't always know what has gone wrong and maybe by trying to figure it out, it would be to late. A person should always carry enough bail out and the proper mix to go off the loop at any time during the dive. When something bad starts to happen, I just want to be programed to do one thing- BAIL OUT!!!!!. Based on the fact that your bailout should be a good mix for any depth and you should be carrying enough of it, bailing out to OC is the safest thing to do. And that is what she is talking about. A person can always take a few sanity breaths and then go back and try and sort out the loop if they so desire. At least you will survive the immediate problem if you can go to OC. Seems like sound advice to me. __________________ My Divesite *** Northwest Dive Club
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27th December 2007, 18:32	#47 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,672	Re: CCR Trimix Simplified by Mel Clark question Quote: (Originally Posted by jradomski) WIth the right technique, taking 2 or 3 breaths off a loop then flushing keeps all the questionalbe gases low with little risk.. You ARE doing a nearly 100% gas exchange every few breaths-- co2 levels dont rise that fast nor do po2 leves fall very fast (unless you are ascending quickly).. Just doing a 2x to 1 you cut your gas consumption in half for those few minutes.. Just because a scrubber had "breathrought" doesnt mean its not still usable.. All it means is that for some reason the level of co2 you were producing is above what the scrubber can remove.. lowering excertion levels will reduce the amount of co2 and that may be enough to help the scrubber along.. doing routine gas flash effectively does the same.. I am not advocating use of a DEAD scrubber, but with carefule monitoring a marginal scrubber can be safely used.. Its no a coincidence that a small scrubber like a drager dolphin is rated for much longer than the same size on a CCR.. because co2 is routinely being dumped out of the loop and the scrubber bed ha less to scrub.... Read what Joe wrote here and then REALLY think about it... especially trhe last paragraph which I put in bold. It's dead-on. Bail off a flooded loop. Bail off if you are in an escalating C02 hit situation... but if the loop is not flooded, "consider" going back on later if deco gas volume is an issue. I am not saying "Go back on the loop", I'm saying "don't rule it out". Always keep an ace in the hole. Dave __________________ "Changes in Lattitudes, Changes in Attitudes, Nothing remains quite the same".... www.nobubblediving.com
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27th December 2007, 22:43	#48 (permalink)
Nad Rebel to the Bone Current Rebreather/s: Ouroboros Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Join Date: Mar 2005 Location: Europe Posts: 976	Re: CCR Trimix Simplified by Mel Clark question Quote: (Originally Posted by Dave Sutton) Read what Joe wrote here and then REALLY think about it... especially trhe last paragraph which I put in bold. It's dead-on. Bail off a flooded loop. Bail off if you are in an escalating C02 hit situation... but if the loop is not flooded, "consider" going back on later if deco gas volume is an issue. I am not saying "Go back on the loop", I'm saying "don't rule it out". Always keep an ace in the hole. Dave This is a perfect summary. Cheers Nad __________________ The Impossible is often the Untried
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27th December 2007, 23:07	#49 (permalink)
diverklondike Just one of the Peasants Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Oct 2005 Location: Delaware, USA Posts: 1,613	Re: CCR Trimix Simplified by Mel Clark question Gang, Training... Practice... Training... Practice... Practice... Practice... Practice... Plan... Plan... Plan... My one concern about Mel's book is that someone may think it's a substitute for good training and practice regardless of the position you may be taking on any specific point... Sorry for the hijack but reading threads like this can get kinda scary... M
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28th December 2007, 05:24	#50 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 3,008	Re: CCR Trimix Simplified by Mel Clark question Due to lots of PMs, here is a simplified analysis/example of what can happen in a loop when running SCR Lets use the following parameters 1.5l tidal volume, 3l "dead space" = 4.5 l 1 lpm o2 production therefor .9lpm of co2 depth 90m - 10ata 4.5l * 10ata = 45.0l of gas in loop after 1 min, loop is 44.9l of gas no CO2 scrubbing, 1 liter of o2 metabolized (no addition) %co2 = 2%, if o2 addition still working 1.96% (loop is 45.9l) These are worse case numbers... assuming you went a full minute before refilling the loop.. (not very likely) and swimming at a reasonable pace.. now lets look at reality, assuming a person who has a rmv at the surface of about 14lpm (~.5cuft per min) thats going to be at least 10 breaths per minute, probably 15.... lets assume that you are doing a 3 to 1 extension, that means at worse case you have less than .67% co2 in the loop (.67 is 9 breaths per minute for ease if calculations)... and that is on a TOTALLY dead scrubber, which is unlikely... Now lets look at the loop volume, 4.5 is quite low, most people are going to be at least 50% greater.. with the increased volume te co2 percentage would drop.. now we are in the range .4% co2 in the loop.. at 10atas this is below what we define as scrubber breakthrough.. You can see on the above even a totally DEAD scrubber could be used for a short period if time (but not advocating use)... With controlled breathing, Deep breaths adn a partially working scrubber.. things are even better.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
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