Safety of radial vs axial scrubber

[gianaameri]

[
Experience alone does not cut it (sadly). Totally agree

All we have is Experiance,Trainiing and a big part of confidence in the kit we use .Initial Confidence in our kit comes in many forms wether its ,homebuild and knowing every nut and bolt,advise from industry respected individuals,or dare i say CE marked kit .

Neil

We need numbers and facts to start (on top of training, experience...).

Without numbers you cannot risk manage and make an informed purchase/use decision, and without the true facts any plan will fail miserably insofar it will be predicated on hope and false information.

This applies for sure to scrubber selection (i.e. "Know your WOB" and "Know your scrubber Duration").

 

[emmbee]

Diving experience has nothing to do the construction and design of closed circuits

What nonsense! History is full of nifty engineering that failed the "can this actually be used" test. If you want to pretend to design a rebreather, you'd better start with getting an experienced user on board. Besides, any experienced rebreather diver will start getting ideas about how to do things better. Good and bad, sure, but worth listening to.

In any case, the question was "is axial safer than radial". And in that context the word of someone who's got loads of experience with diving (Dave) or designing and testing (Paul) both is very relevant.

Cheers,

Matthieu

 

[gianaameri]

In any case, the question was "is axial safer than radial". And in that context the word of someone who's got loads of experience with diving (Dave) or designing and testing (Paul) both is very relevant

It is incredibly relevant, but if they cannot substantiate their opinion with numbers, on the specific subject, it is kind of like neither here or there.

Dave says it makes no difference in terms of safety (Axial vs. Radial).

But why?

The numbers do show that Radial is safer than Axial all other things being equal because it delivers lower WOB and longer Duration.

Paul from rEVO talks about some conceptual radial scrubbers holding Kg. 1.5 of absorbent... well, they do not exist and no one is planning to make them...

Equally irrelevant is a Patent which has no application. I can write a Patent document now, pay a fee to the Patent Office, and hold a Patent and claim I am Scientist Inventor, but I am neither. I am just the holder of a useless Patent.

So, if we have 10 "experts" who say Axial and Radial scrubbers are equally safe, but cannot substantiate why, are they to be taken seriously (when actual numbers suggest the contrary and they cannot provide any numbers)?

 

[WFO]

For me it would depend on the type of diving.

Two factors in favour of axial,

If they are easier to pack you're more likely to do it more often when you might be tempted to risk it, and more likely to do a more thorough job.

If it is a pain in the *rse, you might be tempted to be lazy.



Any testing data takes the near perfect case. I think reality is a bit different to test lab.

 

[opheim]

It is incredibly relevant, but if they cannot substantiate their opinion with numbers, on the specific subject, it is kind of like neither here or there.

Gian, I think you may be missing the point here. "Safety" is a very relative term. Your "WOB-crusade" has its value, absolutely, but WOB is just one of many aspects that sums up to a units relative safety. You can have the best WOB in the world, but still have a crazy dangerous unit...

Radial scrubbers will *normally* have a better WOB than axial, this is probably well documented in your numbers as well. But it's a fact that the gas travels less distance through scrubber material in a radial, thereby increasing the risk of a CO2 breakthrough. This is common sense. If both are packed 100% correctly this is less likely to happen, but still it is obviously more likely to have a breakthrough through 5-6cm of scrubber material than through 20-25cm of scrubber material.

So if you define safety as one of the two;
Looking at WOB only - radial is "safer"
Looking at risk for CO2 breakthrough only - axial is "safer"

Why do you only want to look at WOB and not the risk that the others are talking about? After all, WOB is more or less "constant" while the packing is done by the user every single time, and can't possibly be done 100% identically every time, do you still think that risk is not worth evaluating?

And how do you suppose one can quantify the safety element in the two aspects against eachother?

 

[emmbee]

Gian,

That's because from the perspective of a beginner, as in mine, and the OP's, the key things when it comes to scrubbers are:

Once correctly packed

only use good sorb that is recommended by the manufacturer, and stick to the recommended durations

Or, to quote my instructor "be anal about scrubber".

And, sadly, judging by the amount of threads about people trying to find ways and justifications to save 5 euro worth of sofnolime, this is not a trivial point.

WOB and duration may become relevant for more advanced diving - although seeing the crazy dives done on standard inspos, maybe not, and see opheim above - but not at this level.

Cheers,

Matthieu

 

[gianaameri]

For me it would depend on the type of diving.

Two factors in favour of axial,

If they are easier to pack you're more likely to do it more often when you might be tempted to risk it, and more likely to do a more thorough job.

If it is a pain in the *rse, you might be tempted to be lazy.



Any testing data takes the near perfect case. I think reality is a bit different to test lab.

Are they easier to pack?

I do not think so.

If you pack the Axial lose, the WOB will be better, but they could channel, or the WOB gets worse when the spring takes up the slack.

If you pack them tight, they may last longer, but the WOB may go outside the test results.

The Radials there is only one way to pack them - tight (my understanding).

There is benefit to Axial Micropore (no need to pack), but they do not last very long relative to Radials and do not offer WOB advantages to Radials (so not safer, but definitely more convenient than packable Axials).

 

[gianaameri]

Gian, I think you may be missing the point here. "Safety" is a very relative term. Your "WOB-crusade" has its value, absolutely, but WOB is just one of many aspects that sums up to a units relative safety. You can have the best WOB in the world, but still have a crazy dangerous unit...

Radial scrubbers will *normally* have a better WOB than axial, this is probably well documented in your numbers as well. But it's a fact that the gas travels less distance through scrubber material in a radial, thereby increasing the risk of a CO2 breakthrough. This is common sense. If both are packed 100% correctly this is less likely to happen, but still it is obviously more likely to have a breakthrough through 5-6cm of scrubber material than through 20-25cm of scrubber material.

So if you define safety as one of the two;
Looking at WOB only - radial is "safer"
Looking at risk for CO2 breakthrough only - axial is "safer"

Why do you only want to look at WOB and not the risk that the others are talking about? After all, WOB is more or less "constant" while the packing is done by the user every single time, and can't possibly be done 100% identically every time, do you still think that risk is not worth evaluating?

And how do you suppose one can quantify the safety element in the two aspects against eachother?

When you talk scrubber (this thread) you need to look at WOB and Duration, at minimum, and look at the numbers.

As to "a fact that the gas travels less distance through scrubber material in a radial, thereby increasing the risk of a CO2 breakthrough" - I am not sure that is fact.

Fact is that gas travels less distance, but over a much larger surface area, possibly for a greater dwell time, hence it may very well reduce the risk of CO2 breakthrough.

The numbers prove that Radial reduces the risk of CO2 breakthrough relative to Axial because they have lower WOB and higher Duration.

The risk I see is in clumping, that is break-through due to clumping.

BUT provided you remove the dust when you pack the scrubber (using a fan and thereafter hoovering the outside of the Radial), I have not observed any clumping in a Radial (including a well used one).

Reduced or no clumping and reduced dust (provided it is removed at the time of packing) I perceive another advantage of the Radial over the Axial.

 

[opheim]

The numbers prove that Radial reduces the risk of CO2 breakthrough relative to Axial because they have lower WOB and higher Duration.

What kind of documentation do you have that lower WOB in itself reduces the risk of CO2 breakthrough?

What kind of documentation do you have that higher scrubber duration in itself reduces the risk of CO2 breakthrough?

The risk of packing a radial "wrong" is larger than the risk of packing an axial wrong, agreed? So if that risk is higher, it would also mean that the risk of channeling, and thereby gas going through without being "cleaned", is increased? So how do you quantify that risk up against the WOB argument and conclude on a safety factor of radial vs axial?

 

[paulraymaekers]

Radial scrubbers will *normally* have a better WOB than axial, this is probably well documented in your numbers as well. But it's a fact that the gas travels less distance through scrubber material in a radial, thereby increasing the risk of a CO2 breakthrough. This is common sense. If both are packed 100% correctly this is less likely to happen, but still it is obviously more likely to have a breakthrough through 5-6cm of scrubber material than through 20-25cm of scrubber material.

well, people seem to forget that a radial is nothing more then a very wide, square shaped, limited hight axial that is bent in a curve so it becomes a tube

for the same volume of sorb, there is no difference in dwell time between the flat square and the curved square: shape does not change the dwell time, only volume does (that should be clear: if you double the surface, so half the hight, the speed of gas will be half (double surface), but the path to travel is also half (hight is half), so total travel time (= dwell time) is the same)

now everybody understands that if you compare 2 axials with the same total volume, but one less wide and higher, and the other one very wide, but not high, the first will have a bit higher WOB, the second will have a bit higher risk of preferential break-trough

there is no data that shows that, for the same volume of sorb, the duration of a radial is longer then the duration of an axial (I would even think the inverse, but no statistical data available either)

so all this fuss about what is better... it is not black and white

 

[gianaameri]

What kind of documentation do you have that lower WOB in itself reduces the risk of CO2 breakthrough?

What kind of documentation do you have that higher scrubber duration in itself reduces the risk of CO2 breakthrough?

The risk of packing a radial "wrong" is larger than the risk of packing an axial wrong, agreed? So if that risk is higher, it would also mean that the risk of channeling, and thereby gas going through without being "cleaned", is increased? So how do you quantify that risk up against the WOB argument and conclude on a safety factor of radial vs axial?

All I am saying is that it is a fact of life that the numbers show that the currently available Radial scrubber outperform in terms of WOB and Duration the currently available Axial scrubber - hence they are safer.

I am not trying to prove why.

As a matter of fact, I can care or less "why" when I buy/use a rebreather.

All I care is that it is fact, and I plan accordingly and make my purchase decision accordingly.

I have packed both Radial and Axial scrubber and I do not agree that the risk of packing it wrong is greater for Radial scrubbers relative to Axial scrubbers.

Both, if packing is not done carefully, and if you rush it, is very risky. I do think though, and know, that it does take longer to pack my Meg 8 lbs. Radial than it took me to pack my former Axial scrubbers.

 

[Casperlad]

We need numbers and facts to start (on top of training, experience...).

Without numbers you cannot risk manage and make an informed purchase/use decision, and without the true facts any plan will fail miserably insofar it will be predicated on hope and false information.

This applies for sure to scrubber selection (i.e. "Know your WOB" and "Know your scrubber Duration").

I agree but in risk management you look at Risk and the hazared
the risk to a newcomer if just looking at the scrubber is in the packing.
reduce the risk by diving a scrubber which is more forgiving to a poorly packed scrubber.

Risk to a more experianced person diving extended run times
would be reduced to risk of incorrect packing through there experiance but possibly increase the risk of over running the scrubber

2 divers 2 units the risk is not the same for both one size does not fit all.

Neil

 

[gianaameri]

I agree but in risk management you look at Risk and the hazared
the risk to a newcomer if just looking at the scrubber is in the packing.
reduce the risk by diving a scrubber which is more forgiving to a poorly packed scrubber.

Risk to a more experianced person diving extended run times
would be reduced to risk of incorrect packing through there experiance but possibly increase the risk of over running the scrubber

2 divers 2 units the risk is not the same for both one size does not fit all.

Neil

The risk in use is WOB and Duration.

Packing is just something we have to do if we use loose absorbent material.

Radial takes longer to pack in my experience, but it is not more risky than Axial, from a packing perspective.

 

[Casperlad]

The risk in use is WOB and Duration.

Packing is just something we have to do if we use loose absorbent material.

Radial takes longer to pack in my experience, but it is not more risky than Axial, from a packing perspective.

Why does it take longer ive never packed one.

 

[gianaameri]

Why does it take longer ive never packed one.

Because I take more care than I used to, I think.

Plus in my opinion it needs to be packed tighter, so there is more tapping and bumping... and it takes a lot more absorbent.

I weight it at the end of packing to check for consistency from one fill to another.

 

[Casperlad]

because i take more care than i used to, i think.

Plus in my opinion it needs to be packed tighter, so there is more tapping and bumping... And it takes a lot more absorbent.

I weight it at the end of packing to check for consistency from one fill to another.

thanks

 

[Paul Haynes]

After thinking for a long time, I have decided that I should go over to dive ccr.
I am very cautious by nature, and now it just before I'm about to order a unit.

I wonder:
I currently live in northern Norway, and the water temperature is usual between 4 and 12 degrees Celsius.

Is axial scrubber safer than radial scrubber?

- Gerhard

Hello Gerhard

When it comes to selecting life support you are right to be cautious and suggest you review a paper on CCR survival available from the downloads section at Haynes Marine. Although this paper represents only personal thinking on a variety of CCR related issues, it is based upon nearly 25 years of rebreather diving, development & testing and CCR instruction so will provide you with some broader considerations regarding CCR selection and use. However please remember it is just my opinion and you will encounter a range of differing opinions so consider them all carefully. However try to avoid being led ‘over the top’ by the ‘loudest trumpet’.

With regards to your specific question, at this stage I recommend you do not get too caught up on this single issue. There are numerous key considerations when selecting a rebreather and the canister is just one of them. However due to the significant variability in radial and axial designs, test parameters, conditions of use, CO2 absorbent type and critically, the actual CCR breathing loop in which these varying canister designs may be imbedded, discussion over the alleged ‘safety’ of one compared to another can be somewhat academic. Instead, what is of greater importance in my opinion is that the whole life support system has been independently subjected to un-manned and manned testing in accordance with the current internationally recognised rebreather standard EN14143. Whilst in no way do I propose that this standard represents the pinnacle in rebreather standards nor does it guarantee you will get a ‘great performing’ rebreather, it is the only civilian rebreather standard in the world at present and as such does provide a certain level of confidence that your life support has been appropriately tested and is considered fit for purpose against a minimum standard, which of course includes the performance of the canister.

Good luck.

Rgds Paul

 

[gianaameri]

Hello Gerhard

When it comes to selecting life support you are right to be cautious and suggest you review a paper on CCR survival available from the downloads section at Haynes Marine. Although this paper represents only personal thinking on a variety of CCR related issues, it is based upon nearly 25 years of rebreather diving, development & testing and CCR instruction so will provide you with some broader considerations regarding CCR selection and use. However please remember it is just my opinion and you will encounter a range of differing opinions so consider them all carefully. However try to avoid being led ***8216;over the top***8217; by the ***8216;loudest trumpet***8217;.

With regards to your specific question, at this stage I recommend you do not get too caught up on this single issue. There are numerous key considerations when selecting a rebreather and the canister is just one of them. However due to the significant variability in radial and axial designs, test parameters, conditions of use, CO2 absorbent type and critically, the actual CCR breathing loop in which these varying canister designs may be imbedded, discussion over the alleged ***8216;safety***8217; of one compared to another can be somewhat academic. Instead, what is of greater importance in my opinion is that the whole life support system has been independently subjected to un-manned and manned testing in accordance with the current internationally recognised rebreather standard EN14143. Whilst in no way do I propose that this standard represents the pinnacle in rebreather standards nor does it guarantee you will get a ***8216;great performing***8217; rebreather, it is the only civilian rebreather standard in the world at present and as such does provide a certain level of confidence that your life support has been appropriately tested and is considered fit for purpose against a minimum standard, which of course includes the performance of the canister.

Good luck.

Rgds Paul

In reference to "Instead, what is of greater importance in my opinion is that the whole life support system has been independently subjected to un-manned and manned testing in accordance with the current internationally recognised rebreather standard EN14143" - that is the best way to purchase a ticket to heaven!

...just read this about "CE" and Notified Bodies (EN14143 is no different from other standards for other devices):

Faulty medical implants investigation: Patients treated 'like guinea pigs’ - Telegraph

Video: Undercover investigation exposes EU licencing for faulty medical implants - Telegraph

Faulty medical implants investigation: 'Sometimes we cross the line' - Telegraph

Faulty medical implants investigation: How the scandal was uncovered - Telegraph

Video: Faulty hip implants have ruined lives says Orthopaedic Professor - Telegraph

Check the numbers for yourself and take nothing on face value when it comes to rebreathers (buying a tooth-brush is another story).

That is why I place so much emphasis on actual numbers... it is the actual performance figures which make the difference between a Yamaha FZR 1000 and a Piaggio Vespa or a Ferrari and a Fiat (all are "CE" but one is very different from another).

Current Radials are by far superior to current Axials and safer, based on available data.

 

[GO..]

Thank Paul for that article, I have a 19 our boat journey home for christmas tomorrow, and this article will fill som of that time with meaning.

I've decided to go for a radial scrubber. It's easyest for a beginner to not pack wrong, and I don't need the duration of a radial. I'm probably not going to be near the limit of the axial scrubber on a dive during my first year.

As for unit I've read alot on the forums and asked other divers in the area, and desided to go for a JJ.

 

[gianaameri]

Thank Paul for that article, I have a 19 our boat journey home for christmas tomorrow, and this article will fill som of that time with meaning.

I've decided to go for a radial scrubber. It's easyest for a beginner to not pack wrong, and I don't need the duration of a radial. I'm probably not going to be near the limit of the axial scrubber on a dive during my first year.

As for unit I've read alot on the forums and asked other divers in the area, and desided to go for a JJ.

There is an interesting document here:

http://www.jj-ccr.com/media/4950/test_report.pdf

I am not sure if the test result numbers are for the radial or axial scrubber. Some are for the back-mounted counterlung and other numbers are for the front-mounted ones.

Reports/numbers can be confusing at times.