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Discussion Starter #1
You mentioned previously that the EACS have better endurance than loose sorb when you utilise the correct flow cones in the scrubber - did you find that the flow cones would also extend the life of loose sorb as well.

Did you consider the use of sorb with hydrophobic membranes in you tests.

What were your findings based on similar sized scrubber units based on sorb in the APOC - did you test this. I would be interested to know what level of endurance reduction was experienced and the increased levels of WOB. (also were there any variability studies done based on differnt packing techniques)
 

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You mentioned previously that the EACS have better endurance than loose sorb when you utilise the correct flow cones in the scrubber - did you find that the flow cones would also extend the life of loose sorb as well.

Did you consider the use of sorb with hydrophobic membranes in you tests.

What were your findings based on similar sized scrubber units based on sorb in the APOC - did you test this. I would be interested to know what level of endurance reduction was experienced and the increased levels of WOB. (also were there any variability studies done based on differnt packing techniques)
Answers to your questions:

1. Flow cones do not help granular scrubbers much, because the gas paths through the granules is chaotic so mixes the gas anyway. They make a difference to the first inch or two only on granules.

2. Yes, we tested many different hydrophobic membranes. We published the results of water ingress into granular scrubbers, so put effort into trying to prevent this during the R&D stage of the project.

3. Using very hard packaging of 797 we found the duration actually reduced. Normal packing of 797 gave around 25% shorter duration than the EAC for the same volume. We also studies using Draeger Divesorb, as other studies found this to have longer duration than 797, a point which we concur with. With Divesorb the EAC came out at between 17% and 20% longer duration for the breakthrough points of interest to us. For multiple dives, the EAC improves further whereas the granules reduced their duration.
 

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Discussion Starter #3
Thanks for the reply- in your view would it be feasible to make a granular refill cartridge with acceptable WOB given the current dimensions of the scrubber housing albeit with reduced duration - potentially with a hydrophobic membrane.
 

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Discussion Starter #4
Thanks for the reply- in your view would it be feasible to make a granular refill cartridge with acceptable WOB given the current dimensions of the scrubber housing albeit with reduced duration - potentially with a hydrophobic membrane.
 

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Wol,
I've been having a bit of a play with my junk pile :)
It appears you can easily build a refillable granular canister that sits where the EAC does. But it's going to kill the WOB. Hydrophobic membranes will degrade the WOB further.
I've built one to prove to myself that it can be done, but if I dive it at all, in the absence of any data I won't be taking it deeper than 21m or using it for more than 110 min in 10 degree+ water.

I have no data, but I would expect that this changes a rebreather with very low WOB into something that if you are lucky will be around the CE limit for WOB (this is without hydrophobic membranes)
HTH
Simon A
 

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Wol,
I've been having a bit of a play with my junk pile :)
It appears you can easily build a refillable granular canister that sits where the EAC does. But it's going to kill the WOB. Hydrophobic membranes will degrade the WOB further.
I've built one to prove to myself that it can be done, but if I dive it at all, in the absence of any data I won't be taking it deeper than 21m or using it for more than 110 min in 10 degree+ water.

I have no data, but I would expect that this changes a rebreather with very low WOB into something that if you are lucky will be around the CE limit for WOB (this is without hydrophobic membranes)
HTH
Simon A
The WOB of the Apoc is so low that a simple axial scrubber can be used (it will add just 0.3J/L to the overall WOB using Divesorb with pads at each end)- still far below the CE limits and below other rebreathers, but the safety benefits of the EAC are lost completely and endurance is much worse than with the EAC.

For a hydrophobic membrane, you want a radial scrubber to minimise WOB (because you want as large as possible surface area). A radial in a 125mm diameter barrel assuming a 36mm central bore, has so little scrubber material that the endurance is under 20 minutes with 797 granules.

These very short endurances with granules that the use of a granular scrubber is not supported at all by DL or OSEL, as well as the other safety issues they generate (when flooded, variances in packing etc).

Alex
 

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Discussion Starter #7
Are there any comparative tables that show the endurance for dive sorb in the APOC across the range of temperatures and test durations that were done for the micropore scrubber. On an axial scrubber was a hydrophobic membrane out of the question due to the effect on WOB or would this still be within CE limits?
 

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Are there any comparative tables that show the endurance for dive sorb in the APOC across the range of temperatures and test durations that were done for the micropore scrubber. On an axial scrubber was a hydrophobic membrane out of the question due to the effect on WOB or would this still be within CE limits?
We don't plan publishing granular data for scrubbers designed for EACs, though we have done these experiments and have the graphs for the Apoc. However, almost identical graphs are publicly available. They were published in the Bergen conference papers for example. I will dig out the exact reference when I manage to get out the OSEL factory and back to our lab, where the proceedings are sitting on the shelf in my office.

We did work with hydrophobic membranes for a long time, until finally opting for the EACs. Hydrophobic membranes are rated by what pressure of water they withstand: the pressure can be quite high in a rebreather. The higher the water pressure, usually the higher the breathing resistance through it. One needs as large a surface area as possible for the membrane: this favours radial over axial designs. With an axial scrubber, it is very hard to get a decent membrane without a large pressure drop (even with no granules in the scrubber), because the surface area is so small. The EAC is really a hydrophobic membrane integrated with the scrubber, with the largest possible surface area (many times that of even a huge radial scrubber). Micropore have spent many millions on developing that technology, and it works: a water tolerant scrubber with very low WOB, and excellent duration in scrubbers that are designed properly for the EAC.

Alex
 

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Discussion Starter #9
In your view, with the additional safety features of the iccr eg the autobailout, the CO2 sensor and breathing rate sensor (can't remember if their was flood detection), - would the apoc be safer than other rebreathers using granular sorb, if granular sorb was used? eg do the counter lungs act well as water traps, and will all the other levels of protection still function as intended even with sorb? I guess my point here is that I could see after market scrubbers being developed and it would be good to be able to access the level of risk these present.
 

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Wol,
I had a play in Wraysbury today with a nearly exhausted Extendair. The water traps in the Apoc are quite good (about 400+ml of water) but I flooded the unit far further than I would dare with a granular scrubber ( so flooded through the ALBOV, you could hear the air bubbling through the water in the inhale lung).
Once I had located the pull dumps the unit recovered to a perfectly diveable state (underwater whilst diving), and when I emptied it out afterwards had less than 75ml of water in the entire unit and didn't gurgle in any orientation.
You would lose this ability with a granular scrubber (I would have bailed and remained bailed from a granular scrubber with that much water in it. Even after emptying the loop the WOB would have been like trying to suck cream cakes through a straw). My understanding is that the factory does not endorse or support the use of granular scrubber on safety grounds, and anyone manufacturing a granular scrubber for the unit would have to perform their own testing.
Also the training requirements would be different for a granular scrubber compared to an extendair (it's very difficult to pack an extendair incorrectly).

I like the extendair carts, and in my own case if extendair carts came down to £12 each delivered I wouldn't bother looking at a rebreather that used loose 'sorb ever again (sorb costs on my other rebreather works out at approx £8 a fill).
Simon A
 

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would the apoc be safer than other rebreathers using granular sorb, if granular sorb was used? eg do the counter lungs act well as water traps, and will all the other levels of protection still function as intended even with sorb? I guess my point here is that I could see after market scrubbers being developed and it would be good to be able to access the level of risk these present.
Having been one of the guinea pigs trialling the underwater recovery features of the Apoc, you don't want to be using granular in it. Its got water traps, which make it not really any different to a selection of other units but your (re)introducing a whole world of problems that have been designed out.

Having had the onset of caustic cocktail on another unit, it was a very pleasant surprise to remove the risk almost entirely diving the Apoc. A user error or slow flood turns into a so what issue as the unit can be drained while being dived. Using the EACs is just too nice, especially combined with the ability to do underwater flood recovery which makes the unit unique* especially in a BMCL rig.

I would be looking at the hazard risk assessment of using granular as high/very high where it could get flooded noting the side effects of a caustic cocktail.
If you look in 14143 there is a section where the unit has to be inverted at the end of the scrubber duration testing and the pH measured at the mouth. It would be very interesting what granular adapters for the EAC generate pH wise in a rebreather after the scrubber testing compared to the EAC in addition to the reduction in duration if a 50% loop flood was introduced into the equation.

I note there is an EAC granular adaptor for the Titan CCR already on the market, but I don't think that unit has had any testing published otherwise that might give some good comparative data to go off.

Regards
Brad

* Yes some other units can be recovered from a partial flood, when the water is just in the CLs, however recovering the entire loop is a different kettle of fish.
 

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Discussion Starter #12
I guess the real issue is the current costs of the EACs.

With shipping and UK VAT they are currently around £28 per EAC.

Based on my current profile of diving ie either 1 deep dive per scrubber or 2 shallow 60-70 minute dives this is around 3 times the cost of granular sorb.

I think the cost could be a factor in driving adoption of aftermarket scrubbers for the apoc even with all their additional risks of caustic cocktail.

I guess the the key here is what leverage the recreational dive market has for micropore in levering the prices of EACs down. (I believe their patent has many years to run) -
 

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I guess the the key here is what leverage the recreational dive market has for micropore in levering the prices of EACs down. (I believe their patent has many years to run) -
The question you hae to ask yourself is what reason is there for micropore to reduce prices. They are a business and have set costs associated with producing these EAC's and the fact you guys have no alternative but to use them, so theres no real driver for Micropore to reduce prices at this stage.
 

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Discussion Starter #14
This is my concern too. Add to that a price reduction in the recreational dive market could impact their margins in what is probably a much bigger revenue driver in the medical and military arena. Any thoughts from OSEL or Alex on this would be welcomed - On the one hand I love the added safety/flood recovery etc - particularly on longer deeper dives - but for mid week shallower diving where I may have longer than a 2 week gap between dives - the cost will hurt much more.

Maybe there could be a marketting agreement with micropore to enable a reduced cost to the recreational market for a period of time until volumes have ramped up????
 

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...what is probably a much bigger revenue driver in the medical and military arena.
Hi Wol,

I have been confused by all the claims and counter-claims on the performance of these devices. Do you (or Brad / Alex) know of any military dive teams that use them in their rebreathers? I suppose that would suggest independent testing which has been interpreted favourably.

Thanks,

Simon M
 

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Discussion Starter #16
I have looked at the micropore website and there appear to be some units with them available. I believe that their products are also used on submarines.

Clearly micropore have a cracking product which addresses alot of issues. I don't really have reason to doubt that their duration is what it claims to be - I guess the key here is to have the correct gas flow entering the EAC since it is made up of channels and once gas enters one channel it can't move between them easily. (hence the need for flow cones)

Personally I would rather use an EAC in a heart beat - it is just the high cost that is the issue especially on some of the 25metre dives I do mid week.
 

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Hi Wol,

I have been confused by all the claims and counter-claims on the performance of these devices. Do you (or Brad / Alex) know of any military dive teams that use them in their rebreathers? I suppose that would suggest independent testing which has been interpreted favourably.

Thanks,

Simon M
Hi Simon,

I've seen so much bollocks posted here the last days, that I don't even care to reply...

it's just insane what we are reading here....

wait and see!

kind regards

Paul
 

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I have not seen the need to jump in here since nothing was shipping, but since the main loop parts are now available but the monitoring electronics are not yet shipping, I feel it important to remind people of the stated cartridge duration of this design.

I hope users of this system will remember that the upper end usage times quoted of 2+ hrs per micropore cartridge were for 2% loop CO2, with the justification for using that instead of .5% CO2 (the recognized standard) was that an active electronic CO2 monitor along with the automated loop shutoff would make increasing the top end loop CO2 figure tolerable. As the published OSEL duration tests showed, after the cartridges hit 2% CO2 passthrough, the ensuing climb to dangerous CO2 concentrations can occur quite quickly. Since none of these electronics are shipping at this time, I hope the company is stressing the lower limit time (55 min IIRC) to those who are making their own Mccr designs out of the parts which are now shipping, or diving the unit as an O2 ccr.

Stay safe!
 

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I have not seen the need to jump in here since nothing was shipping, but since the main loop parts are now available but the monitoring electronics are not yet shipping, I feel it important to remind people of the stated cartridge duration of this design.

I hope users of this system will remember that the upper end usage times quoted of 2+ hrs per micropore cartridge were for 2% loop CO2, with the justification for using that instead of .5% CO2 (the recognized standard) was that an active electronic CO2 monitor along with the automated loop shutoff would make increasing the top end loop CO2 figure tolerable. As the published OSEL duration tests showed, after the cartridges hit 2% CO2 passthrough, the ensuing climb to dangerous CO2 concentrations can occur quite quickly. Since none of these electronics are shipping at this time, I hope the company is stressing the lower limit time (55 min IIRC) to those who are making their own Mccr designs out of the parts which are now shipping, or diving the unit as an O2 ccr.

Stay safe!
We are not stressing the lower limits. We are giving both the 0.5% CO2 limit and 2% CO2 limit, and pointing out that the 2% CO2 limit has been used for open circuit for years (as Volume Weighted Average Inspired CO2), and is also the NORSOK rebreather limit. We provide the data to enable people to choose which of the two limits they wish to use.

We are not giving "out of the scrubber" figures, we are giving proper Volume Weighted Average Inspired CO2 figures, just like the standard says. Very few other companies indeed are doing that: they prefer to quote a longer duration by ignoring all residual CO2 in the mouthpiece.

've seen so much bollocks posted here the last days, that I don't even care to reply...

Paul
But you did reply. If I went onto the rEvo thread just to add noise, you would soon complain. Obviously the competition from the Apoc must worry you a lot, just as you expressed when you came to the stand at a DEMA and Boot.

Alex

NB: On Brad's comment above, all the test divers tried the Apoc fully flooded: we disconnect a pod, flood it totally, plug the pod back in, then go diving. It was their feedback that led to the snorkel tubes in the counterlungs, so whatever attitude the diver goes into, there is not a sudden surprise. The EACs perform very well in that test: the water from an EAC does not become caustic fast like a granular scrubber does. Brad has experienced another rebreather that developed a leak, using granules: Brad is fine to demo it with the EAC but I don't think all the money on earth would persuade him to do the same demo with granules.
 

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Obviously the competition from the Apoc must worry you a lot, just as you expressed when you came to the stand at a DEMA and Boot.

Alex
???? huh ???

it almost sounds like jneves on RBW with the little finger pointing :' yes, yes, you know you fear the competition of the XX...'

....well ALEX, i understand you fear the competition of the rEvo, as you have expressed so many times at all the shows where we met, at all the CE meetings, and you showed it even far more in the way you have always acted in a 'professional' way versus people/companies/organisations of wich you fear/feared competition!
and look how much better we, divers, are all now!
 
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