Safety of radial vs axial scrubber

[opheim]

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

Keyword here is "minimum", whereas you seem to _only_ look at WOB and duration. Hence my former (and so far unanswered) question - how do you quantify the safety / risk of uncomparable values. For instance WOB vs. risk of faulty packing.

It's not all as black and white as you try to make it.

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.

Risk of channeling increases when you reduce the "thikness" of material, that's just common sense. This is, as far as I can understand, the reason why all manufacturers I have heard of emphasize the importance of correct packing of radials. Whereas the axials are more forgiving because the distance from gas intake to outlet is in itself a safety margin against channeling / breakthrough.

And since we know that we are all just humans, bound to make mistakes, one could easily argue that axials are safer since they are more forgiving of "sloppy packing" than radials. Hence providing a larger safety margin for errors.

It's not all as black and white as you try to make it.

And as Paul (who likely posesses more knowledge and for sure more testing equipment / experience than yourself) says:

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)

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.

How does duration in itself increase safety? If you have a BMW with a 60 litre petrol tank (filled up), and the same BMW with a 80 litre petrol tank (filled up). Why would the 80 litre be safer if you're only travelling 10 kilometres in the car? It's not. So if you're diving well within the limits of an axial with 180 minutes duration (say doing a 120 minute dive), a 240 minute radial would - based purely on duration - bring you absolutely no extra safety.

One could even take that argument to the extreme and say - with a 120 minute dive, you'd ditch the "remaining 60 minutes" of the axial and refill to do your second 120 minute dive, whereas you could be within the testing limits doing another 120 minute dive on the 240 minute radial. Which is safer now? The axial where you had plenty of margin to spare or the radial where you max out the limits of testing?

It's not all as black and white as you try to make it.

Now, based on the available standards and testing methodology, I tried to answer the question raised:
The available numbers to date show that Radial is safer than Axial.

No, at best you could say that the testing of larger volume radials in most cases have better WOB and longer duration than smaller volume axials. I have yet to see documentation that states that radials are per definition _safer_ than axials. That would be very hard, as those making the actual documentation probably look at a "broader picture" than your "WOB&Duration numbers give the only correct answer" philosophy, and would not jump to conclusions as you do.

It's not all as black and white as you try to make it. (can you spot the pattern here?)

 

[gianaameri]

Keyword here is "minimum", whereas you seem to _only_ look at WOB and duration. Hence my former (and so far unanswered) question - how do you quantify the safety / risk of uncomparable values. For instance WOB vs. risk of faulty packing.

It's not all as black and white as you try to make it.




Risk of channeling increases when you reduce the "thikness" of material, that's just common sense. This is, as far as I can understand, the reason why all manufacturers I have heard of emphasize the importance of correct packing of radials. Whereas the axials are more forgiving because the distance from gas intake to outlet is in itself a safety margin against channeling / breakthrough.

And since we know that we are all just humans, bound to make mistakes, one could easily argue that axials are safer since they are more forgiving of "sloppy packing" than radials. Hence providing a larger safety margin for errors.

It's not all as black and white as you try to make it.

And as Paul (who likely posesses more knowledge and for sure more testing equipment / experience than yourself) says:





How does duration in itself increase safety? If you have a BMW with a 60 litre petrol tank (filled up), and the same BMW with a 80 litre petrol tank (filled up). Why would the 80 litre be safer if you're only travelling 10 kilometres in the car? It's not. So if you're diving well within the limits of an axial with 180 minutes duration (say doing a 120 minute dive), a 240 minute radial would - based purely on duration - bring you absolutely no extra safety.

One could even take that argument to the extreme and say - with a 120 minute dive, you'd ditch the "remaining 60 minutes" of the axial and refill to do your second 120 minute dive, whereas you could be within the testing limits doing another 120 minute dive on the 240 minute radial. Which is safer now? The axial where you had plenty of margin to spare or the radial where you max out the limits of testing?

It's not all as black and white as you try to make it.




No, at best you could say that the testing of larger volume radials in most cases have better WOB and longer duration than smaller volume axials. I have yet to see documentation that states that radials are per definition _safer_ than axials. That would be very hard, as those making the actual documentation probably look at a "broader picture" than your "WOB&Duration numbers give the only correct answer" philosophy, and would not jump to conclusions as you do.

It's not all as black and white as you try to make it. (can you spot the pattern here?)

I agree it is not all black and white insofar some scrubber design may be poor relative to others, raising packing risk or user error, but that is an additional factor to take into account.

As to your logic, it is flawed in many ways.

RC in his broken English has taught us that experience does not make a person a competent rebreather design and engineer.

I can shoot a rifle, but I cannot build one.

A U.S. Navy Seal can tell you from experience on the field why the M4s keep on jamming and what simple modification he has devised to stop them jamming... but he cannot build an M4.

Paul with all his experience cannot even tell us the performance numbers of his designs, like Hydrostatic Imbalance.

He is not obliged to of course, but we make purchase and usage decisions for cars, computers, tablets, mobile phones... based on performance numbers, and it is at odds with being a rational thinking consumer to make a decision on rebreathers based on a manufacturer charisma alone, and no performance numbers.

It is a free world though!

 

[opheim]

I agree it is not all black and white insofar some scrubber design may be poor relative to others, raising packing risk or user error, but that is an additional factor to take into account.

Excellent, then we can agree that stating that radials per definition are safer than axials to a guy who's looking to buy his first rebreather is not necessarily the correct answer.

The right answer seems to be (in particular as he's buying the JJ-CCR as stated earlier in the thread) - the radial and axial according to published test reports carry the same WOB, so there is no difference there. There is a difference in duration, as the radial packs ~3kg sofnolime vs the axials ~2.3kg (~4 vs ~3 hours dive profile). In reality, it's more than likely that the axials duration will be more than sufficient for all Mod1 and Mod2 diving, even a lot of Mod3 diving. And according to the manufacturer, the radial requires more precise packing [1]. So for a beginner, it might be safer to go for the axial as that's easier to pack and leaves less room for mistakes to be made at the same time as it provides more than sufficient duration and equally low WOB as the radial.

I'd say that's a pretty short, precise and correct answer in one single post, without all the black&white mumbojumbo.

[1]

The radial soda lime canister must be filled extremely carefully and it is essential to ensure that the soda lime is correctly compacted.

 

[opheim]

we make purchase and usage decisions for cars, computers, tablets, mobile phones... based on performance numbers

That's where we disagree. There are other aspects to consider than pure performance numbers. To do a more fitting analogy - I use mostly Apeks regs on my OC equipment. There may for all I know be (even) better performing regs out there, but the ones I use perform more than sufficient for all the dives I have done to date (including both warm water caves and cold water 100m ocean dives). My reasoning for not choosing other regs is simply that;

1. the performance is excellent (even though there may exist better regs)
2. the servicing is quite simple (I service all my own regs, so that's important to me) and last but not least
3. most of the regs in our team is Apeks, so there's always spare parts, exchange parts and plenty of experience available whenever we need it, even though every diver might not have or bring everything on their own.

Those last two points in my mind adds to safety, even though it is not possible to quantify it up against possible increased safety on a reg delivering slightly better performance in a given environment.

The same goes for choice of scrubber - WOB, and even duration, may not be the single most important aspect to consider, even though you may choose to base your personal choices on those alone. And to measure a vague term such as "safety" on those two alone does not make sense.

 

[gianaameri]

I re-affirm that Radial is safer than Axial, based on available numbers.

In no way I suggested the purchase of a JJ.

I did suggest the purchase of an Apecs ISC 8 lbs. Radial Meg with no complex electronics (i.e. Shearwater).

Still, I would not dive it without modifications, my life, my choice.

This to answer the below posts.

 

[opheim]

I re-affirm that Radial is safer than Axial, based on available numbers.

I take note of that, but since it doesn't make sense I'll simply disregard it, and will be happy to encourage others to do the same.

In no way I suggested the purchase of a JJ.

No you didn't, but if you had been paying attention to the original question / topic, you might have caught that more than 200 posts ago, as the OP stated in this post that's the unit he's buying. Disregard his small typo, he meant the axial.

I did suggest the purchase of an Apecs ISC 8 lbs. Radial Meg with no complex electronics (i.e. Shearwater).

Wouldn't really fit in the OPs unit of choice now would it...

I'm sorry, do you mean to imply that a Shearwater is too complex? If so I'm pretty sure we have food for a new 300+ post topic on our hands...

 

[gianaameri]

I take note of that, but since it doesn't make sense I'll simply disregard it, and will be happy to encourage others to do the same.



No you didn't, but if you had been paying attention to the original question / topic, you might have caught that more than 200 posts ago, as the OP stated in this post that's the unit he's buying. Disregard his small typo, he meant the axial.



Wouldn't really fit in the OPs unit of choice now would it...

I'm sorry, do you mean to imply that a Shearwater is too complex? If so I'm pretty sure we have food for a new 300+ post topic on our hands...

I re-affirm that I did NOT suggest in any way, shape, or form the purchase of a JJ or any other rebreather other than:

Apecs ISC 8 lbs. Radial Meg with no complex electronics (i.e. Shearwater).

It was a choice of the OP to buy the JJ.

He is perfectly capable of choosing for himself what he wants (luckily).

I have explained in detail why Radial is safer than Axial, based on available numbers.

Feel free to disregard what I write, and reach you own conclusions based on whichever decision matrix you want to employ.

As I said, it is a free world (despite "CE")!

 

[matt]

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.

If I were to buy a JJ then I would buy the axial scrubber not the radial that is suggested here (perhaps axial was meant as that fits the description better as opheim suggests).

Axial is easier to deal with for a new rebreather diver and has a great deal more duration than is required to make no-stop air dives.

Wikipedia says this about ALARP:

It is more a best common practice of judgement of the balance of risk and societal benefit.

Doesn't sound like what is being described here.

Matt.

 

[Clare]

Do you all really still have some point which needs making here or are you all wielding pointy sticks?

 

[Wilbo]

On other fora they have the concept of introducing 'the cheeky girls' to defuse situations and stalemate. Would that work here?

 

[Clare]

Well something to lighten the mood would be good.

Personally I'd prefer

But I realise I'd be in a minority.

 

[anarchista]

The right answer seems to be (in particular as he's buying the JJ-CCR as stated earlier in the thread) - the radial and axial according to published test reports carry the same WOB,

Your view is inconsistent with:

December 19th, 2012, 02:24 PM #5 (permalink)

High volume scrubbers: there radial becomes more interesting because when going from low to high volume, with axials usually the WOB increases, where as for radials the WOB decreases.

greet rc

 

[Clare]

Enough please. He said, she said, he said, I said. I don't want to lock this thread in case there is anything NEW to add but it is getting to the state where I am getting as many complaints as new posts.

Take voluntary time out gentlemen.
Remember there is more to life than diving or arguing about it.

 

[Mike Ferguson]

Well something to lighten the mood would be good.

Personally I'd prefer

But I realise I'd be in a minority.

you are in a minority. I hope this doesn't become the CCRX equivalent of the cheeky girls on YD.

 

[tufty]

:chuckle::chuckle::chuckle:

Well something to lighten the mood would be good.

Personally I'd prefer

But I realise I'd be in a minority.

I don't remember giving approval to use my pic :chuckle:

 

[matt]

Personally I think this thread came to a natural conclusion sometime ago, but then I was simply accused of being narrow minded and wanting the thread closed as it didn't suit my needs. I have no needs so I have no clue what I'm being narrow minded about. I'd be very happy diving any of the mainstream units, with either type of scrubber, but obviously not a Sentinel oke:

Oh, and I received the number I was looking for (and a citation) by PM, so the thread was useful after all.

Regards
Mo.

 

[WFO]

Regards
Mo.

Something you're not telling us? :sface:

 

[matt]

Something you're not telling us? :sface:

:censored:

 

[PeterN]

Once upon a time in a far away place (Yorkshire) there was a popular forum that sustained a thread for thousands of posts about a re breather that never existed.

Occasionaly a news letter would come out and many posts would be generated. More often a news letter would not come out, and many posts would be generated.

There was 4,367 people who hated the re breather that never existed. There were three people who loved it. There were thousands who could care less, but read every post.

Of those thousands of posts, at first some good points were made. After a while only good insults were made.

Good fun.

So, time to decide. Do we aspire to the big leagues? Should we carry on a pointless, repeditive debate about relative merits of whatever it was we were discussing, or talk about diving.

Probably we should carry on. Then when we have generated some good numbers, (only numbers matter after all) Clare can sell off to some faceless Canadian multinational that is run by non divers and use the cash to build the worlds most complicated re breather.

:deadhorse

Peter

 

[anarchista]

en we have generated some good numbers, (only numbers matter after all) Clare can sell off to some faceless Canadian multinational that is run by non divers and use the cash to build the worlds most complicated re breather.

Espacenet - Bibliographic data

Espacenet - Bibliographic data

greet rc