Reusing a scrubber?

[davehicks]

I don't get your point about the risk of channeling. That makes no sense to me at all, but I'm eager to learn from your point of view.

The scrubber material (not the canister) is being placed in a ziplock bag and then later poured and "repacked" per normal procedures. Obviously if the used scrubber (75 minutes in this case) were clumpy, wet, or otherwise visibly degraded I would not use it. We know from multiple studies that the remaining runtime on "re-used" scrubber is not impaired by this practice of storing it safely in a sealed container.

 

[Gareth J]

I am extremely cautious with Scrubber time.

One of the big advantage of the temp stick over the original Inspiration I learnt on, is that you can monitor the Scrubber. Watching the active front, and the dead scrubber area.
For recreational diving, I can easily do a weekends diving, often as much as three days. If I have any doubts, I ditch the scrubber. Certainly over two days, I would use the same scrubber for recreational diving, unless I see anything adverse on the temp stick.
On the occasions the scrubber has only done a days recreational diving. I can take the scrubber cartridge out and store it in a 'dry bag', when I'm stripping and cleaning the rebreather, prior to reassembly.

If I have any doubts, then I ditch the old scrubber material and replace with new. It's just not worth the risk.

Certainly If I'm diving beyond 50m and accruing any significant decompression time I will change the scrubber.

NOTE - I never remove the sofnolime from the cartridge, once its in use. If I disturb the sofnolime, once it's in use, it goes straight in the bin. NEVER reuse sofnolime. Repack with fresh lime.

This last season has mainly been dives shallower than 40m, and no decompression requirements exceeding 30minute, so basic recreational dives.

There is no reason I can see to push a scrubber. It's significantly better to ditch a scrubber which has 'life' in it, than find yourself in the water with a scrubber that has no life in it. Much the same as when I was on open circuit, better to exit the water with plenty of gas left, than find myself in the water without gas!

 

[jgttrey]

I don't get your point about the risk of channeling. That makes no sense to me at all, but I'm eager to learn from your point of view.

The scrubber material (not the canister) is being placed in a ziplock bag and then later poured and "repacked" per normal procedures. Obviously if the used scrubber (75 minutes in this case) were clumpy, wet, or otherwise visibly degraded I would not use it. We know from multiple studies that the remaining runtime on "re-used" scrubber is not impaired by this practice of storing it safely in a sealed container.

The risk is this (& apologies if I say a bunch of stuff you already know).

The sorb in your canister is not equally/uniformly used during a dive. As the exhaled gas goes through the scrubber, the CO2 reacts with pretty much the first unused sorb it encounters, creating a "reaction front." That reaction front generates heat, which is the basis for the temp sticks some units use to estimate remaining time. In an axial can, it's generally sort of cone shaped. In a radial it's, well, radial. And it progresses from through the scrubber bed from where the gas enters to where it leaves.

Upstream of the reaction front, the sorb is used, downstream it is not, at least within reason.

The danger of dumping and repacking is that you've mixed fully exhausted grains of sorb with fresh grains. When you use that repacked can, you no longer have a uniform reaction front and if it so happens that a bunch of used sorb ends up in one area, you now have a channel where CO2 can make it all the way through the canister without encountering any fresh sorb. That's a problem and is what happened to the guy in the video, which is worth a watch.

 

[_Ralph]

For me, 2.4kg axial ~ 4hrs runtime 4-9C waters

Tech dive (i.e. deeper than 45m) = new sorb

2nd/3rd recreational dive = <3hrs scrubber time



Storrage ... overnight/same day .. unit is built and closed loop.

Anything longer, scrubber goes into a vacuum packer.



Warmer waters? Don't know, the RB hasn't been that lucky in my hands


_R

 

[cathal]

I don't get your point about the risk of channeling. That makes no sense to me at all, but I'm eager to learn from your point of view.

The scrubber material (not the canister) is being placed in a ziplock bag and then later poured and "repacked" per normal procedures.
We know from multiple studies that the remaining runtime on "re-used" scrubber is not impaired by this practice of storing it safely in a sealed container.

Just wondering do you have the course material from your CCR courses that advocates this repackaging of used scrubber practice or is this just a practice that you have developed over time?

Cheers

 

[davehicks]

Just wondering do you have the course material from your CCR courses that advocates this repackaging of used scrubber practice or is this just a practice that you have developed over time?

Cheers

This is a forum for sharing experience and learning from each other. I feel like a learned something from this exchange, how about you? If we could learn everything there was to know from a manual, there would be no need for a forum such as this.

 

[CptTightPants21]

This is a forum for sharing experience and learning from each other. I feel like a learned something from this exchange, how about you? If we could learn everything there was to know from a manual, there would be no need for a forum such as this.

I think you are taking the (very legitimate) question a little too harshly. Jgttrey's explantion was excellent and I think the question was more just to see if your practice had been actively endorsed or taught somewhere or if it was developed organically by yourself. So it sounds like this was a practice that you started doing yourself and now it has been explained how this practice could result in some very dangerous circumstances.

 

[cathal]

This is a forum for sharing experience and learning from each other. I feel like a learned something from this exchange, how about you? If we could learn everything there was to know from a manual, there would be no need for a forum such as this.

This is just a simple query as to where you got this practice from, nothing more other than that.
If it’s on course material that would be extremely relevant.

 

[jgttrey]

My sense - and others will be able to weigh in with far more knowledge - is that some of these "operational" aspects of CCR diving don't get good attention the materials.

Agency materials are pretty generic and unit agnostic, so they focus on theory, physiology and sort of generic descriptions of emergency procedures. It's up to manufacturers to supply information about the unit itself and "operational" stuff and specifics -- and those materials are very uneven. I think important stuff falls through the gaps and is left up to the instructor.

This particular issue of course is one that is common to any unit and should be in the written materials from both the agency and manufacturer. IIRC, in my case the risk of repacking was something covered by my instructor. I don't recall it in the materials one way or another, but I could easily be wrong about that.

 

[jgttrey]

There is a good representation of the reaction front in a scrubber canister here:

A Look Inside Rebreather Scrubber Canisters, Part 1

and

A Look Inside Rebreather Scrubber Canisters, Part 2

If you watch the videos you can get a feel for how having mixed up old and new sorb granules could lead to problems.