Use a gag strap?

[stuartv]

A better solution is to just stay in the ocean, where divers belong...

 

[JohnnyC]

A better solution is to just stay in the ocean, where divers belong...

Gross stingy eye water? Do you have any idea what fish do in the ocean?! EVERYTHING.

 

[doctormike]

Gross stingy eye water? Do you have any idea what fish do in the ocean?! EVERYTHING.

Yeah, better stay away from fish... stick to caves and swimming pools. You can tell the difference because the cave is the one with the duckweed!

 

[silent running]

Why yes he was!

This is not the first time I’ve heard of this and an engineer friend of mine told me that by his calculations they are fundamentally unsafe under very high workloads.

Cartridge scrubbers are just like everything else in CCR diving, a compromise: You trade ease of use and lower WOB than granular media for the possibility of CO2 bypass during high workloads.

I would never use one. Diving in the South Pacific I regularly found myself swimming hard in high currents, because that’s where the fish are. I once got caught in a tidal down current and had to maximally exert myself off/on for over 30 minutes. My in to out flow radial scrubber was in its last hour of my typical usage and had no problem at all handling the increased ventilation. If I had a cartridge scrubber loop, I would’ve almost certainly had a CO2 hit, panicked, switched to BO (if I even could while panicking and struggling to hold onto a piece of coral with one hand to keep myself from being blown even further down) and breathed through all my gas in few minutes and drowned.

In the real world people do find themselves working hard underwater, whether they want to or not. I wonder how many other CO2 hits happened on cartridge scrubbers from over breathing and no one thought to ask if the divers were using granular sorb or a cartridge...

 

[Dsix36]

This is not the first time I’ve heard of this and an engineer friend of mine told me that by his calculations they are fundamentally unsafe under very high workloads.

Cartridge scrubbers are just like everything else in CCR diving, a compromise: You trade ease of use and lower WOB than granular media for the possibility of CO2 bypass during high workloads.

I would never use one. Diving in the South Pacific I regularly found myself swimming hard in high currents, because that’s where the fish are. I once got caught in a tidal down current and had to maximally exert myself off/on for over 30 minutes. My in to out flow radial scrubber was in its last hour of my typical usage and had no problem at all handling the increased ventilation. If I had a cartridge scrubber loop, I would’ve almost certainly had a CO2 hit, panicked, switched to BO (if I even could while panicking and struggling to hold onto a piece of coral with one hand to keep myself from being blown even further down) and breathed through all my gas in few minutes and drowned.

In the real world people do find themselves working hard underwater, whether they want to or not. I wonder how many other CO2 hits happened on cartridge scrubbers from over breathing and no one thought to ask if the divers were using granular sorb or a cartridge...

CO2 incidents were extremely common when I was using an extendaire in my Optima. Stopping to relax, and/or short periods of BO to catch my breath almost every time that I worked too hard. Just something that I had to learn to live with until I changed units. Needless to say, I am no longer a fan of extendaires.

 

[KenGordon]

It seems even more like having a BOV that someone can flip to get you on a breathable gas is the best way to go. Of course, there is still the issue of possibly having a hypoxic mix connected to the BOV and what happens if someone flips your BOV switch and then tries to surface you. I reckon if I'm going to be diving with hypoxic mixes (sometime, way down the road), I'd probably want to stick to only diving with a buddy that is also a CCR diver and has been thoroughly versed in my rig, as I would need to be for my buddy's rig.

If you have hypoxic bailout you ought to be doing a serious enough dive that your buddy understands it. Don’t take 10/70 on a 30m dive with an AOW level diver.

 

[Brad_Horn]

This is not the first time I’ve heard of this and an engineer friend of mine told me that by his calculations they are fundamentally unsafe under very high workloads.

Cartridge scrubbers are just like everything else in CCR diving, a compromise: You trade ease of use and lower WOB than granular media for the possibility of CO2 bypass during high workloads.

I would never use one. Diving in the South Pacific I regularly found myself swimming hard in high currents, because that’s where the fish are. I once got caught in a tidal down current and had to maximally exert myself off/on for over 30 minutes. My in to out flow radial scrubber was in its last hour of my typical usage and had no problem at all handling the increased ventilation. If I had a cartridge scrubber loop, I would’ve almost certainly had a CO2 hit, panicked, switched to BO (if I even could while panicking and struggling to hold onto a piece of coral with one hand to keep myself from being blown even further down) and breathed through all my gas in few minutes and drowned.

In the real world people do find themselves working hard underwater, whether they want to or not. I wonder how many other CO2 hits happened on cartridge scrubbers from over breathing and no one thought to ask if the divers were using granular sorb or a cartridge...

CO2 incidents were extremely common when I was using an extendaire in my Optima. Stopping to relax, and/or short periods of BO to catch my breath almost every time that I worked too hard. Just something that I had to learn to live with until I changed units. Needless to say, I am no longer a fan of extendaires.

Gents, you may have reached the wrong conclusion with regards the root cause of the incidents you have looked at or experienced. While all scrubbers can be over breathed given sufficient workload. The Micropore ExtendAir Cartridge in isolation is likely not the culprit behind the issue reported.

In isolation, when tested the 2.2kg Micropore EAC is more efficient that the same weight of granular absorbent, by quite some margin. To get comparable scrubber duration results you need to have at least 2.6kg of good diving grade absorbent. Put that same EAC in a poorly designed rebreather and you will considerably reduce your scrubber duration. The EACs performance remains a fixed constant, but you just don't get the most out of it.

In a high performing, low WOB rebreather you get exceptionally good scrubber duration results from a 2.2kg EAC, as shown http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf This is independent of the safety benefits of a truly flood recoverable system, with minimal caustic cocktail risk and ease of scientifically repetitive packing etc etc. You also have a considerably extended breakthrough period from 0.5 to 2% SEV on an EAC than granular sorb; which is a small and very unappreciated design quirk.

Noting those results published by Deeplife are ‘at the mouth’ as required by the fine print in EN14143 and therefore account for the deadspace of the ultra-low WOB BOV, that those units are fitted with. This probably gives the ‘best case’ scrubber duration available from the Micropore EAC and it takes into account what the diver is actually breathing. But, as numerous manufacturers have identified, inclusive of VR and ISC, if you don’t design the rebreather to work with the attributes of the EAC, inclusive of their unique linear gas flow requirements, you get less than optimal performance out of the EAC.

So if you therefore put that known high performing low WOB EAC in a poorly designed rebreather. You will a) have a still high WOB unit, which causes the diver to work excessively hard on high flow dives but also b) a less than optimum scrubber duration. Which I would argue is the true root cause for your reported incident. I’d therefore take a stab and guess that the rebreather in question was almost certainly untested for WOB and the diver likely had no idea what their actual scrubber duration would be under any high workload conditions at the respective water temp and depth of the cave in question? And by extension they had no idea of the safe design envelope of the rebreather in question for any manned dives outside a controlled environment. Which makes it look as if it was a simple failure to plan the dive and not the fault of the EAC itself.

Sure you can still over breath an EAC, just not if you dive within the design envelope of any rebreather, purpose designed for its use. And not without exceeding the units recommended scrubber duration, as tested, under the same or more extreme conditions than as dived.

While OSEL don’t publish granular scrubber performance figures for direct side by side comparison with the performance of an EAC in their rebreathers, Hollis’s PRISM II very conveniently takes 2.6kg of granular absorbent and while we need to consider that the testing they paid for at QinetiQ doesn’t take into account the deadspace of the DSV/BOV or significantly increased WOB of the BOV. The comparable scrubber durations of a considerably higher WOB unit such as the PRISM II, are quite reasonable https://www.hollisrebreathers.com/wp-content/uploads/2019/08/QQ-1900385-HollisPrism-v1-1.pdf And I’d hazard a guess that if Hollis submit it for CE certification down the track, the resultant scrubber durations when measured ‘at the mouth’ of the PRISM II, will be less than that offered by an EAC in OSELs units under identical test criteria, due to the higher WOB and less optimised gas flow dynamics. Even worse if Hollis do the testing with their BOV to give a truly identical comparison. Though it will be nice to see both their DSV and BOV come with a gag strap as a default if ever CE’d.

Not considering the overall unmanned performance of the specific rebreather, when looking at the implications of one just component is risky.

In this case the units WOB, workload implications and scrubber duration all need to be factored in. Simply substituting 2.2kg of granular sorb for the EAC would have led to CO2 breakthrough even sooner. Substituting a lower WOB rebreather with 2.6kg of granular sorb, than the one dived in the above example, might not have led to CO2 break through quite as soon as was experienced. Though if it’s a PRISM 2 you will have an issue sooner if it has a BOV as opposed to DSV, due to higher WOB. But the issue likely isn’t the EAC, as in a truly low WOB rebreather, the divers workload would have been significantly less in the first place and the resultant scrubber duration higher under the same dive conditions; so the chance of exceeding the rebreather performance envelope, would be significantly less.

 

[Dsix36]

Gents, you may have reached the wrong conclusion with regards the root cause of the incidents you have looked at or experienced. While all scrubbers can be over breathed given sufficient workload. The Micropore ExtendAir Cartridge in isolation is likely not the culprit behind the issue reported.

In isolation, when tested the 2.2kg Micropore EAC is more efficient that the same weight of granular absorbent, by quite some margin. To get comparable scrubber duration results you need to have at least 2.6kg of good diving grade absorbent. Put that same EAC in a poorly designed rebreather and you will considerably reduce your scrubber duration. The EACs performance remains a fixed constant, but you just don't get the most out of it.

In a high performing, low WOB rebreather you get exceptionally good scrubber duration results from a 2.2kg EAC, as shown http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf This is independent of the safety benefits of a truly flood recoverable system, with minimal caustic cocktail risk and ease of scientifically repetitive packing etc etc. You also have a considerably extended breakthrough period from 0.5 to 2% SEV on an EAC than granular sorb; which is a small and very unappreciated design quirk.

Noting those results published by Deeplife are ‘at the mouth’ as required by the fine print in EN14143 and therefore account for the deadspace of the ultra-low WOB BOV, that those units are fitted with. This probably gives the ‘best case’ scrubber duration available from the Micropore EAC and it takes into account what the diver is actually breathing. But, as numerous manufacturers have identified, inclusive of VR and ISC, if you don’t design the rebreather to work with the attributes of the EAC, inclusive of their unique linear gas flow requirements, you get less than optimal performance out of the EAC.

So if you therefore put that known high performing low WOB EAC in a poorly designed rebreather. You will a) have a still high WOB unit, which causes the diver to work excessively hard on high flow dives but also b) a less than optimum scrubber duration. Which I would argue is the true root cause for your reported incident. I’d therefore take a stab and guess that the rebreather in question was almost certainly untested for WOB and the diver likely had no idea what their actual scrubber duration would be under any high workload conditions at the respective water temp and depth of the cave in question? And by extension they had no idea of the safe design envelope of the rebreather in question for any manned dives outside a controlled environment. Which makes it look as if it was a simple failure to plan the dive and not the fault of the EAC itself.

Sure you can still over breath an EAC, just not if you dive within the design envelope of any rebreather, purpose designed for its use. And not without exceeding the units recommended scrubber duration, as tested, under the same or more extreme conditions than as dived.

While OSEL don’t publish granular scrubber performance figures for direct side by side comparison with the performance of an EAC in their rebreathers, Hollis’s PRISM II very conveniently takes 2.6kg of granular absorbent and while we need to consider that the testing they paid for at QinetiQ doesn’t take into account the deadspace of the DSV/BOV or significantly increased WOB of the BOV. The comparable scrubber durations of a considerably higher WOB unit such as the PRISM II, are quite reasonable https://www.hollisrebreathers.com/wp-content/uploads/2019/08/QQ-1900385-HollisPrism-v1-1.pdf And I’d hazard a guess that if Hollis submit it for CE certification down the track, the resultant scrubber durations when measured ‘at the mouth’ of the PRISM II, will be less than that offered by an EAC in OSELs units under identical test criteria, due to the higher WOB and less optimised gas flow dynamics. Even worse if Hollis do the testing with their BOV to give a truly identical comparison. Though it will be nice to see both their DSV and BOV come with a gag strap as a default if ever CE’d.

Not considering the overall unmanned performance of the specific rebreather, when looking at the implications of one just component is risky.

In this case the units WOB, workload implications and scrubber duration all need to be factored in. Simply substituting 2.2kg of granular sorb for the EAC would have led to CO2 breakthrough even sooner. Substituting a lower WOB rebreather with 2.6kg of granular sorb, than the one dived in the above example, might not have led to CO2 break through quite as soon as was experienced. Though if it’s a PRISM 2 you will have an issue sooner if it has a BOV as opposed to DSV, due to higher WOB. But the issue likely isn’t the EAC, as in a truly low WOB rebreather, the divers workload would have been significantly less in the first place and the resultant scrubber duration higher under the same dive conditions; so the chance of exceeding the rebreather performance envelope, would be significantly less.

I gotta call total ******** on this one Brad. My rebreather at the time was an Optima and it was tested for WOB. This would often happen on a brand new scrubber during the descent from having to work hard to pull down the line. Many times, sanity breaths were required on the line. this was noit just my experience but almost all of the local Optima divers had the same issue. I can still work a damn lot harder on my rEvo with sorb than I ever could on the Optima. You and your pdf's will never change my dive history or my mind on this matter.

 

[JohnnyC]

I gotta call total ******** on this one Brad. My rebreather at the time was an Optima and it was tested for WOB. This would often happen on a brand new scrubber during the descent from having to work hard to pull down the line. Many times, sanity breaths were required on the line. this was noit just my experience but almost all of the local Optima divers had the same issue. I can still work a damn lot harder on my rEvo with sorb than I ever could on the Optima. You and your pdf's will never change my dive history or my mind on this matter.

Total ******** on just that one? Dude is a dumpster fire that should be banned like Ross.

 

[silent running]

Gents, you may have reached the wrong conclusion with regards the root cause of the incidents you have looked at or experienced. While all scrubbers can be over breathed given sufficient workload. The Micropore ExtendAir Cartridge in isolation is likely not the culprit behind the issue reported.

In isolation, when tested the 2.2kg Micropore EAC is more efficient that the same weight of granular absorbent, by quite some margin. To get comparable scrubber duration results you need to have at least 2.6kg of good diving grade absorbent. Put that same EAC in a poorly designed rebreather and you will considerably reduce your scrubber duration. The EACs performance remains a fixed constant, but you just don't get the most out of it.

In a high performing, low WOB rebreather you get exceptionally good scrubber duration results from a 2.2kg EAC, as shown http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf This is independent of the safety benefits of a truly flood recoverable system, with minimal caustic cocktail risk and ease of scientifically repetitive packing etc etc. You also have a considerably extended breakthrough period from 0.5 to 2% SEV on an EAC than granular sorb; which is a small and very unappreciated design quirk.

Noting those results published by Deeplife are ‘at the mouth’ as required by the fine print in EN14143 and therefore account for the deadspace of the ultra-low WOB BOV, that those units are fitted with. This probably gives the ‘best case’ scrubber duration available from the Micropore EAC and it takes into account what the diver is actually breathing. But, as numerous manufacturers have identified, inclusive of VR and ISC, if you don’t design the rebreather to work with the attributes of the EAC, inclusive of their unique linear gas flow requirements, you get less than optimal performance out of the EAC.

So if you therefore put that known high performing low WOB EAC in a poorly designed rebreather. You will a) have a still high WOB unit, which causes the diver to work excessively hard on high flow dives but also b) a less than optimum scrubber duration. Which I would argue is the true root cause for your reported incident. I’d therefore take a stab and guess that the rebreather in question was almost certainly untested for WOB and the diver likely had no idea what their actual scrubber duration would be under any high workload conditions at the respective water temp and depth of the cave in question? And by extension they had no idea of the safe design envelope of the rebreather in question for any manned dives outside a controlled environment. Which makes it look as if it was a simple failure to plan the dive and not the fault of the EAC itself.

Sure you can still over breath an EAC, just not if you dive within the design envelope of any rebreather, purpose designed for its use. And not without exceeding the units recommended scrubber duration, as tested, under the same or more extreme conditions than as dived.

While OSEL don’t publish granular scrubber performance figures for direct side by side comparison with the performance of an EAC in their rebreathers, Hollis’s PRISM II very conveniently takes 2.6kg of granular absorbent and while we need to consider that the testing they paid for at QinetiQ doesn’t take into account the deadspace of the DSV/BOV or significantly increased WOB of the BOV. The comparable scrubber durations of a considerably higher WOB unit such as the PRISM II, are quite reasonable https://www.hollisrebreathers.com/wp-content/uploads/2019/08/QQ-1900385-HollisPrism-v1-1.pdf And I’d hazard a guess that if Hollis submit it for CE certification down the track, the resultant scrubber durations when measured ‘at the mouth’ of the PRISM II, will be less than that offered by an EAC in OSELs units under identical test criteria, due to the higher WOB and less optimised gas flow dynamics. Even worse if Hollis do the testing with their BOV to give a truly identical comparison. Though it will be nice to see both their DSV and BOV come with a gag strap as a default if ever CE’d.

Not considering the overall unmanned performance of the specific rebreather, when looking at the implications of one just component is risky.

In this case the units WOB, workload implications and scrubber duration all need to be factored in. Simply substituting 2.2kg of granular sorb for the EAC would have led to CO2 breakthrough even sooner. Substituting a lower WOB rebreather with 2.6kg of granular sorb, than the one dived in the above example, might not have led to CO2 break through quite as soon as was experienced. Though if it’s a PRISM 2 you will have an issue sooner if it has a BOV as opposed to DSV, due to higher WOB. But the issue likely isn’t the EAC, as in a truly low WOB rebreather, the divers workload would have been significantly less in the first place and the resultant scrubber duration higher under the same dive conditions; so the chance of exceeding the rebreather performance envelope, would be significantly less.

Hi Brad, while I appreciate that you provide so much information, I’m not sure it’s helping to clarify things in this instance. Isn’t what you are describing actually 2 different CO2 issues? The difference between retained CO2 from high WOB, and the other kind of bypass/breakthrough CO2?