Sorb surprises

[northernone]

-voice of reason-
This kind of human testing can kill a diver and is not standard operating procedure.
----

Here's what I did attempting break-through:

Packed 812 sorb into a spare prism scubber (~2.5kg).

Three dives:
3hrs ~80ft ~40° vigorous river dive
1hr 45ft ° ~60° vigorous river dive
2 hrs 20ft ~68° lake dive, 1 km finned slowly

Put the scubber in a plastic grocery bag in a open shed in southern Canada.

Wait 12 months.

Three more dives:
2hrs ~35 ft ~55° 1km finned, photography dive
1hr ~20ft ~70° calm dive
1hr ~20ft ~70° Fin briskly until feet blistered. (My kingdom for nice booties)

No signs of break-through yet. I'm puzzled.

(Edit: back story: on my home builds I've tested 5 scrubbers twice each to break-through for establishing safety margins. Hypercapnia is serious and without fast bailout hyperventilating can get uncontrollable very quickly. Done dry land complete scrubber bypass tests to failure as well. It is hell on the body afterwards.)

Dive safe,
Cameron

 

[jgttrey]

I've heard that there is some not well quantified rebound you get if you give partially used sorb time to sit like that.

"Recharge" is the wrong word because it likely isn't shedding CO2, but I believe that the thinking is the sorb, given time to equalize through the grains, gains a little capacity over what it would have had compared to one long dive. At least, that's the explanation I gathered, but I too would be interested in a scientific explanation. I think rEvo folks looked at this, IIRC. But, it was poorly quantified and I, for one, intend to stick with the hard and fast guidelines. Sorb is cheap - at least relative to everything else - and I'm not looking to push that particular boundary.

 

[lv2dive]

That’s a lot of hours on one scrubber!

Here's what I did:

Packed 812 sorb into a spare prism scubber (~2.5kg).

Three dives:
3hrs ~80ft ~40° vigorous rive dive
1hr 45ft ° ~60° vigorous river dive
2 hrs 20ft ~68° lake dive, 1 km finned slowly

Put the scubber in a plastic grocery bag in a open shed in southern Canada.

Wait 12 months.

Three more dives:
2hrs ~35 ft ~55° 1km finned, photography dive
1hr ~20ft ~70° calm dive
1hr ~20ft ~70° Fin briskly until feet blistered. (My kingdom for nice booties)

No signs of break-through yet. I'm puzzled.

Cameron

 

[Wookie]

Can I have your rebreather when you off yourself with it?

I promise to go to Oahu for training.

 

[Gareth J]

I'm not brave enough to push a scrubber like that, even with a monitor in the unit.

An old RN clearance diver told me that on his course, they made them run round the parade ground breathing off their rebreather, no scrubber fitted, until they collapsed.
He said they all felt like **** for the rest of the day, the instructors said, that's the last time you should ever have a CO2 hit - don't f**k with the scrubber, you don't want that to happen in the water.

 

[JohnnyC]

10 hours on a 5lb scrubber is.....bold.

I wouldn't do it. My rule is about 1lb per hour to be on the safe side, and I don't know any manufacturer who would even think about recommending even that. Scrubber material is cheap.

I have friends that do long ass dives in Eagle's Nest on a stock SF2 2.2kg scrubbers with Intersorb and I think they're nuts. However, I think scrubber design does play a part in the ability to do this. Theoretically, an axial design (like the SF2) will be less prone to breakthrough due to the increased dwell time through the scrubber bed (gas has gotta go through 7 inches of sorb). However, it's still a loooooooong time to be on one can of kitty litter, especially one that small. While the WOB is nicer on a radial, I don't think I'd push it that hard. The dwell time is just too short (around 2 inches of sorb all the way around) and you can overbreathe it much easier. If you could guarantee perfectly symmetrical gas flow around a radial it would be a different story, but I'm not convinced that it is possible. Fluid dynamics is a funny thing.

TLDR: can I have your stuff? I know @Wookie already called dibs, but I work for a Canadian company. That's gotta count for something right? (I mean, they're quebecois bastards but still)

That all being said, I'm really looking forward to @Dr Simon Mitchell 's study on shelf life of partially used scrubbers.

 

[Wookie]

10 hours on a 5lb scrubber is.....bold.

I wouldn't do it. My rule is about 1lb per hour to be on the safe side, and I don't know any manufacturer who would even think about recommending even that. Scrubber material is cheap.

I have friends that do long ass dives in Eagle's Nest on a stock SF2 2.2kg scrubbers with Intersorb and I think they're nuts. However, I think scrubber design does play a part in the ability to do this. Theoretically, an axial design (like the SF2) will be less prone to breakthrough due to the increased dwell time through the scrubber bed (gas has gotta go through 7 inches of sorb). However, it's still a loooooooong time to be on one can of kitty litter, especially one that small. While the WOB is nicer on a radial, I don't think I'd push it that hard. The dwell time is just too short (around 2 inches of sorb all the way around) and you can overbreathe it much easier. If you could guarantee perfectly symmetrical gas flow around a radial it would be a different story, but I'm not convinced that it is possible. Fluid dynamics is a funny thing.

TLDR: can I have your stuff? I know @Wookie already called dibs, but I work for a Canadian company. That's gotta count for something right? (I mean, they're quebecois bastards but still)

That all being said, I'm really looking forward to @Dr Simon Mitchell 's study on shelf life of partially used scrubbers.

Hey, Now. What is this about working for the froggies? You mining asbestos or cheating hard working New Englanders out of their Maple Syrup? J/K, my step-dad was born and raised in Montreal and played for the Hab.

 

[JohnnyC]

One of my favorite ways to troll the quebecers is to have them bring back some maple syrup whenever they make a trip to the home land, and after having some saying, "hmm, it's ok, but the stuff from Vermont is definitely better...."

 

[northernone]

One of my favorite ways to troll the quebecers is to have them bring back some maple syrup whenever they make a trip to the home land, and after having some saying, "hmm, it's ok, but the stuff from Vermont is definitely better...."

...but wait till you taste the cocktail made with Quebec sorb aged in the fresh mountain air.

(Partially used sorb shelf life studies interest me. Particularly with the history of mine emergency rebreathers being stored charged for years and the unorthodox habits of some divers I know.)

 

[tbone1004]

@JohnnyC not a lot of CO2 production when you're using scooters...
797 is something like 150l/kg, so on those SF2 scrubbers, using our normal rule of thumb with an hour a pound you have 5 hours on that scrubber. It is able to theoretically absorb 330liters of CO2, knock off some efficiency, usually 70% for axials which is 230 liters. We usually use 1lpm for calculations of O2 for consumption which we know is high, but call it 230 minutes of burn time.

CO2 production for scrubber duration is calculated at .8lpm, 1.3lpm, and 2.5lpm ish during testing. .8lpm is kind of lazily swimming, 1.3lpm is something like that river dive, and 2.5lpm is basically sprinting and is not considered sustainable. IIRC NEDU uses 1.4lpm for their testing.

1lpm seems pretty conservative for a normal use case with the rebreathers, especially if for deep diving where a majority of the time may be spent on deco essentially not moving and the 1lb/hr is practical for that.

The 2.5kg can theoretically process ~375liters of CO2. Assuming maybe 80% efficiency is 300liters, and over 8 hours is .625lpm CO2 production. If most of it was that calm lake dive and/or dpv/deco type diving I'd say that's easily plausible