Medical sorb versus Dive Sorb questions

Barrie Law

Hi Mark,

The Medical Sorb is not recommended by Molecular Products Ltd for use in a rebreather and that is the relevant fact here for whatever reason they have issued a declaration to that effect.

You are of course entitled to ignore the manufacturers recommendations but you must accept you then have no redress in the event of an incident and I personally do not think any minor cost saving is worth relinquishing that right.

Regards

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Barrie Law
Rebreather World Store
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Scuttle

Many thanks for posting the advice/ recommendation Stephen. I think I recall having read it before & I was not totally convinced then as I am now. It reads more like a waiver---not tested & you use it & do so at your own risk. I too would like to see it tested for diving applications by an independent body to disclose the finer details/ results one way or the other.

The cost of medical grade---to me is more bang for your buck.
With the infrequent dives I do here at home & long surface intervals between dives, I will continue to throw out unused sorb that has been exposed, despite what it initially cost with either grade.
But of course I'd much prefer to throw away $10 than say 15-20.

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Molecular Products Ltd

It is the time old tale of what is independant testing.

I think the only way for it to be independant is for someone or some recognised body to do the testing and manufacturers to supply the material FOC to submit to the testing. As you can tell from my reply I would be happy to see this done and will provide a sample for testing. This does not mean every rebreather diver now asks for for a 100kg sample and they will get back to me with results. I am daft but not stupid!!

There is a regocnised Stanag NATO testing proceedure (1411 of the top of my head) to test military grade diving sodalime which would seem like the best method to follow,

On the subject of medical grade, show me a medical manufacturer who will put in writing there lime is suitable for diving. I am no longer going to get dragged into that debate. Thanks for all your posts and interest on the matter.

Down to you now!!

Regards

wizbang

I remember a thread where Alex (adward) offered to do some testing if divers / manufacturers would supply the sorb or cover the cost of procuring the sorb.

I antied up for testing of medisorb at the time i would also like to help cover the cost of testing large grade sofnolime.

Alex, are you still up for some testing if we can get some samples.
We would need to agree on the test method and its relevance to diving.
No camels please.

My preference would be for a std test as mentioned above but also a deep dive test with realistic CO2 levels. eg 130m dive with a 25 min bottom time and 6 hour total runtime. approx 10C water temp.
If enough sorb then maybe 5 x 30m dives of an hour each with the scrubber head left off for 24hrs, once again with a realistic CO2 level and water temp of say 15c.

That would mean something to me.

I am not sure how we agree on what type/size of scrubber but it could be hasshed out.

AD_ward9

Perhaps Molecular can publish the figures, to save us all time: no-one questions their integrity and people seem to be simply requesting data, so as Molecular are the business of selling lime, it would make more sense for them to publish the data showing the benefits of their product. If nothing is published then we can do this: it would be interesting. Send us a tub of the medical grade and a tub of what you want to reference it to.

However, I would point out you are fixing too many variables.

First, the length of the test is the time it takes for the scrubber output to hit 4%. We stop our tests at 4%. It is not a fixed length test.

Second, water temperature is normally 4C for scrubber tests (we use the method in EN14143:2003 as the standard for evaluating scrubbers, not naval standards as they are not applicable to sports or commercial divers). Standard test conditions are exhaled gas 32C, 40l/min RMV, 2 litre stroke, 1.6l/min of CO2. This will give one data point, for one scrubber. Every scrubber is different, so you will not be able to extrapolate from the test data to the scrubber you use.

To get an apples to apples comparison, to evaluate granular material we use the Inspo cartridge positioned vertically to avoid tunnelling problems. We use the "baby bot" packing method, even though it has gone out of vogue.

Just as a general comment on this thread: the manner in which people change key components on a piece of equipment on which their life depends never ceases to astonish me. People who do this, are those who live in dreamland: i.e. they declare that they have no experience - by that I mean they have not tested much. If they had, they would be much more careful.

In theory, everything works, in testing things, very little does. The number of side effects you can get by changing sorb here will surprise most on this thread. Why are people taking this economy with their lives. Tight bunch of .... ? Lazy? To be different for the heck of it? If using sorb, then just buy the stuff meant for diving. Those using medical grade lime need to price their lives more highly: do something worthwhile.

Alex

NB: What is a camel, other than an animal that lives in desert regions, and a brand of fags?

wizbang

Hi Alex, people will be people and there will always be those willing and able to try out all the different options available. A human fact of life.

This testing could be used as a tool to help those that should know better to cease and desist from unsafe practices. It won't help everyone.

Who knows it may shed some light all round and maybe even spur some manufacturers into providing more rebreather friendly sorb.

The reason I gave the three options was.
First option to cover the std methods which would allow for comparitive testing and for comparison to the Rebreather/SORB manufacturers statements.
The second for those that are doing the deeper/longer dives on units with a relatively short duration scruber (or any duration for that matter).
The third for people to see what difference multiple use diving does for duration, especially if let standing to "dry out the head".
The last two would need to be in a "realistic dive" setting as apposed to
clinical presets. temp, CO2 levels.

The camel reference is to the horse designed by a committee. Sorry to be so obtuse.

wizbang

If changing the brand of sorb is something so death defying or remarkable then I can't help but wonder about all those people that have created their own scrubber, lungs and hoses/DSV let alone decide on its duration or its abilities at depth.

I am not saying that they aren't flying blind or ignorant but it would not seem to be the ultimate death wish either.

AD_ward9

Earlier in this thread, there is reference to a fatal accident where someone used medical grade lime instead of diving grade. I know of other deaths where the cause is almost certainly due to the diver pushing a scrubber too far. Warnings about packing methods were, I understand, the result of specific fatal accidents. What I am saying is there are enough dead bodies to illustrate the result of a lack of caution.

In many Rebreather accidents the cause is never known for sure, but when we measure the breathing resistance of a loop, and see things that cause it to quadruple, it is clear doing that will cause an accident sooner or later.

Thanks for filling me on the Camel referece. Sorry, brain not engaged in cross-word mode this morning .

I hope no-one takes offence at the blunt response to things that can cause a fatal accident. When it comes to safety, we should not cloud the issue of if someone does X, then they risk death. No personal insults intended, just divers should not encourage people to do things that they have not tested themselves and which are clearly hazardous, and I think the discussion on using medical grade sorb is in that area.

Alex

Faceless

My precaution against using Medical Sorb would be a higher probability of channeling at the "end" of scrubber life.

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Peoples risk perception is almost always focused on the most dramatic rather than the most probable. (c) Gordon Smith

Dutchy

This is NOT about sorb. This is about design. If your combination of loop (especially scrubber) and sorb works then it works.
Even Molecular Products has more than one grade (size) of lime with different characteristics.
There's nothing wrong with using a medical sorb in a rebreather designed to work with it. (e.g. Jetsam explicitly mentions Spherasorb as one of the recommended sorbs)
If it is not then it may or may not be good for you...
If a sorb is better in all aspects then it will perform better overall. That is only when a sorb has lower wob, higher capacity and faster reaction speed then it is a better sorb. If not then it can only be a better sorb for a SPECIFIC application...

I'd say that as a rule of thumb Sofnoline has a higher wob than Sperasorb. If that's acceptable then you'll have a sorb that packs denser and is capable of absorbing more CO2. That sentence could also be turned into Sperasorb allows for longer (bigger) scrubbers because of inherent lower wob.
You choose what you like...

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