Extreme heat and temporary scrubber storage

[rddvet]

I don't understand throwing it in a drybag immeidately after use. Scrubber likes heat and humididty. The scrubber actively produces heat due to its exothermic reaction. If you put a just used scrubber into a drybag straight from your unit, you're just sealing in moisture and heat. IMO the appropriate choice is keep it in the unit, get home and remove scrubber and let it dry. Then store it as you see fit. I personally put my entire scrubber in a vacuum sealer bag I have out all the time for sous vide cooking and seal it air tight once it's dry. I've got no clue if the airtight bag makes a difference, but it makes my brain hurt less. The reality is the tub the scrubber material comes in isn't air tight and it's fine in there.

 

[rjack321]

Weird logic that somehow removing the scrubber from the unit but then putting it into a sealed drybag is valuable. The CCR is humid, the drybag is humid, both are hot. I don't think there's any outright harm here but these conditions are so aligned I also don't see a benefit.

My concern is the ride in the truck and weakly packed shifting sorb. The "drybag ride" might be better (or worse) than the "CCR ride" version depending on how the scrubber is aligned and how much jostling there is.

 

[Dr Simon Mitchell]

Completely agree with @rddvet and @rjack321 above.

The idea that heat will damage the scrubber ignores the fact that they get extremely hot during use.

On page 95 of the attached paper we reported gas exiting the scrubber in a circuit operated to simulate moderate exercise to be at an average temperature of 47.6 degrees Celsius (117.7 F). A caveat is that the rebreather was not immersed in these experiments, but it was an inspo, and the canister is not in direct contact with the water even if immersed. Even if it was, tropical water at 30 degrees would not exert much of a cooling effect. Moreover, others have measured similar exiting gas temperatures in immersed experiments. The point is that scrubbers get hot during normal use so heat during storage is unlikely to be problematic in relation to future performance.

Simon M

 

[macado]

Weird logic that somehow removing the scrubber from the unit but then putting it into a sealed drybag is valuable. The CCR is humid, the drybag is humid, both are hot. I don't think there's any outright harm here but these conditions are so aligned I also don't see a benefit.

My concern is the ride in the truck and weakly packed shifting sorb. The "drybag ride" might be better (or worse) than the "CCR ride" version depending on how the scrubber is aligned and how much jostling there is.

I completely agree. The situation that prompted this thread happen many years ago. The person no longer dives but it turned into one of those procedures that was taught and copied over and over again by most regulars on the boat.

I firmly believe the reason for CO2 hit was mispacked scrubber combined with a rough / bouncy boat and car ride back home. They were insistent that the heat was somehow "bad" for the scrubber; I challenged them to find me scientific literature that proved their point but it all came down to "feeling."

It's all moot point now; they're not going to change their procedures. If it makes them psychologically feel better then who am I to argue?

My scrubber stays sealed in my rebreather until I get it home when I break anything down and then put my rebreather in a sealed drysuit bag for temporary or semi-long term storage. One of my pet peeves is opening a rebreather on a boat. Watched too many people do it for pieces to go falling onto the deck or scrubbers getting dropped and spilled. I understand it's different for liveaboards obviously but I really do not like opening my rebreather on day boat type trips.

I appreciate all the responses here. I can find no scientific reason for the practice although I don't think there is any harm in doing so.

 

[Herje8990]

I am an SF2 backmount diver, IANTD MOD 2 with about ~150 hours on the unit.
If you take out the scrubber right after the dive and put them in the dry back wouldn't the moisture still be trapped in the scrubber? I was told once the "clumping" of the sorb was a sign of the sorb going bad, which I questioned and did my own testing. I believe the clumping is a sign of moisture buildup within the scrubber canister.

A little test I did:

1. Finish a dive (~50M DT 2hr) and once I got home ~3 hours later I pulled the scrubber out and left it out in the room and let it air dry for couple of days.
2. When I dumped the sorb after drying it there was zero clump.
3. My conclusion is that the clumping is just a sign of moisture buildup in the scrubber.

This is what I normally do now post a dive.

1. Open the DSV and flush the system with Diluent to remove hot humid air trapped in the system with cool fresh air. The SF2 MAV and CL design will push trapped air through the scrubber out the DSV.
2. Get home, pull the scrubber out, and let it air dry at room temp in front of the fan for a few hours.
3. Store in dry bag for next use.

 

[rjack321]

I am an SF2 backmount diver, IANTD MOD 2 with about ~150 hours on the unit.
If you take out the scrubber right after the dive and put them in the dry back wouldn't the moisture still be trapped in the scrubber? I was told once the "clumping" of the sorb was a sign of the sorb going bad, which I questioned and did my own testing. I believe the clumping is a sign of moisture buildup within the scrubber canister.

A little test I did:

1. Finish a dive (~50M DT 2hr) and once I got home ~3 hours later I pulled the scrubber out and left it out in the room and let it air dry for couple of days.
2. When I dumped the sorb after drying it there was zero clump.
3. My conclusion is that the clumping is just a sign of moisture buildup in the scrubber.

This is what I normally do now post a dive.

1. Open the DSV and flush the system with Diluent to remove hot humid air trapped in the system with cool fresh air. The SF2 MAV and CL design will push trapped air through the scrubber out the DSV.
2. Get home, pull the scrubber out, and let it air dry at room temp in front of the fan for a few hours.
3. Store in dry bag for next use.

Do NOT dry out your scrubber. Yes there's more moisture in a used scrubber vs a new one. But its integral to the reaction. You are playing with the CO2 hit fire by drying out your scrubber, just put it in the drybag as is.

 

[Tracy]

If I am diving multiple days, locally that is 2-3 days in a row. When I go south, it could be everyday for a week or two. My scrubber stays in the unit until it needs changed based on use. I have never seen or found a reason to take something apart that works perfectly.

 

[Herje8990]

Do NOT dry out your scrubber. Yes there's more moisture in a used scrubber vs a new one. But its integral to the reaction. You are playing with the CO2 hit fire by drying out your scrubber, just put it in the drybag as is.

I am not "drying" the sorb. I let it sit in the open air for a bit and let it cool down before I put it away. I am sure leaving it out in the open for an hour or two to vent off the excess moisture is not going to "Kill" the scrubber.

Read the research article at link below.
Storage of partly used closed-circuit rebreather carbon dioxide absorbent canisters

Results​

We completed five trials in each of the 28-day-sealed and overnight-open conditions, and four experiments in the 28-day-open condition. Unfortunately, we exhausted our same-batch supply of Sofnolime 797 with one trial in the 28-day-open condition remaining to be done. We attempted to run the trial with Sofnolime from another batch and obtained an aberrant result. Given the confluence of the results obtained in the trials performed using Sofnolime from the common batch (see below) we considered it reasonable to stop the study one trial short in the 28-day-open condition, rather than repeat the entire study with a new batch of Sofnolime.

The elapsed times to reach the failure end-point in each scrubber trial arranged by storage condition, and the mean times to failure for each condition are shown in Table 1. The breakthrough curves for each scrubber trial are shown in (Figure 2). There was a substantial (> 50 min) difference in mean duration to failure between scrubbers stored for 28 days in the sealed condition (longer) compared to the open condition (shorter; P = 0.003). Scrubbers stored 'open' for the much shorter overnight period showed no difference in mean duration to failure when compared to the canisters sealed for 28 days.