Sorb surprises

[tomfcrist]

The question "over there" was asked about how you managed the sorb between day 2 and 3 and I didn't see an answer? Did the sorb just stay in the CCR overnight? Sealed up the whole time? Or what?

Removed from the unit and sealed in an airtight container.

 

[tbone1004]

Removed from the unit and sealed in an airtight container.

let it cool off and dry out first or straight in the container?

 

[tomfcrist]

let it cool off and dry out first or straight in the container?

Sat on the bench for about an hour before getting sealed

 

[Dr Simon Mitchell]

Hi Guys,

The storage study, which addresses the issue of overnight vs longer term storage and how to do it has just been published in the latest edition of Diving and Hyperbaric Medicine. Unfortunately the full paper is embargoed for a year, but the Eurotek research fund is going to pay the early release fee so that we can get it out to divers within the next week or so. As soon as there is a link to the full paper I will let you know.

POLLOCK NW, GANT N, HARVEY D, MESLEY P, HART, J, MITCHELL SJ. Storage of partly used closed-circuit rebreather carbon dioxide absorbent canisters. Diving Hyperbaric Med. 48, 96-101, 2018. doi: 10.28920/dhm48.2.96-101.

Simon M

 

[rjack321]

And I don't know why anyone would choose to dive 4-8 mesh.

To get absolute lowest WOB on the deepest dives (eg 150+m). Duration might be too short to complete all the deco, but that can be done on a second deco CCR.

 

[fsardone]

A new scrubber, a 1/3rd used scrubber and a 2/3rds used scrubber are all functionally equal. The efficiency does not decline linearly at all. It's even (and very close to 100%) until the reaction front starts to poke through and then declines precipitously.

Well I believe this is not correct or at least is slightly misleading. For simplicity I am going to refer to an axial one but the concept applies to radial as well.
A new scrubber has its entire length available for reaction.
A partially used one only has the unused sorb length as depth for reaction.

Now since the depth of the reaction front is proportional to gas density, the deeper you go the more "length" of unused sorb you need. Therefore I argue that a new scrubber is not functionally equal to a partially used one.

My understanding is also reflected in the limits on my rebreather (APD vision inspiration) which are:
1: Max 3 hours scrubber time @1.6lpm co2 (CO2production rate applies also below)
2: For dives below 20 mt diver must leave bottom after 140 minutes scrubber time
3: For Dives below 50 mt diver must leave bottom after 100 minutes scrubber time

Which means that if your first dive is 100 minutes the second must be shallower than 50 mt and after 40 minutes you must be at or above 20mt.

Which means, as I stated at the beginning, that a partially used one and a new one are not equivalent in respect to depth in which they are capable of scrubbing and avoid breakthrough.

Just saying ...

 

[Superlyte27]

Well I believe this is not correct or at least is slightly misleading. For simplicity I am going to refer to an axial one but the concept applies to radial as well.
A new scrubber has its entire length available for reaction.
A partially used one only has the unused sorb length as depth for reaction.

Now since the depth of the reaction front is proportional to gas density, the deeper you go the more "length" of unused sorb you need. Therefore I argue that a new scrubber is not functionally equal to a partially used one.

My understanding is also reflected in the limits on my rebreather (APD vision inspiration) which are:
1: Max 3 hours scrubber time @1.6lpm co2 (CO2production rate applies also below)
2: For dives below 20 mt diver must leave bottom after 140 minutes scrubber time
3: For Dives below 50 mt diver must leave bottom after 100 minutes scrubber time

Which means that if your first dive is 100 minutes the second must be shallower than 50 mt and after 40 minutes you must be at or above 20mt.

Which means, as I stated at the beginning, that a partially used one and a new one are not equivalent in respect to depth in which they are capable of scrubbing and avoid breakthrough.

Just saying ...

Coming into this late....
But you are not right. Lol

 

[fsardone]

But you are not right. Lol

I see. Care to elaborate?
Wording supporting what I have explained are not only in my rebreather manual but also in mastering rebreather by Jeff Bozanick chapter 6.
So I am wondering why you have a different opinion.

Cheers

 

[abnfrog]

people stand in front of trains eventually die .....nuff said

 

[rjack321]

Well I believe this is not correct or at least is slightly misleading. For simplicity I am going to refer to an axial one but the concept applies to radial as well.
A new scrubber has its entire length available for reaction.
A partially used one only has the unused sorb length as depth for reaction.

Now since the depth of the reaction front is proportional to gas density, the deeper you go the more "length" of unused sorb you need. Therefore I argue that a new scrubber is not functionally equal to a partially used one.

My understanding is also reflected in the limits on my rebreather (APD vision inspiration) which are:
1: Max 3 hours scrubber time @1.6lpm co2 (CO2production rate applies also below)
2: For dives below 20 mt diver must leave bottom after 140 minutes scrubber time
3: For Dives below 50 mt diver must leave bottom after 100 minutes scrubber time

Which means that if your first dive is 100 minutes the second must be shallower than 50 mt and after 40 minutes you must be at or above 20mt.

Which means, as I stated at the beginning, that a partially used one and a new one are not equivalent in respect to depth in which they are capable of scrubbing and avoid breakthrough.

Just saying ...

Perhaps you didn't see it or didn't look at the graphs. fCO2 is effectively zero for the majority of a scrubber's life. Once the reaction front reaches the inhale side of the loop (regardless of its an axial or radial) breakthrough occurs rapidly.
How Long Will Your Rebreather Scrubber Canister Last?
Lifespan is depth dependent but you are mixing variables here. For the purposes of the OP's dive, 90mins of use is not "spent" or contributing to breakthrough issues.

What I think you are arguing (hard to know exactly because you are mixing depth with time) is the fCO2 is 0 at the start, 0.01% after 20mins, 0.02% after 40mins, 0.03% after 60mins etc etc. That is not how a scrubber works.

Its ~0% fCO2 for hours then...
0.25% fCO2 hmmmm something is amiss for a short time
then >0.5% fCO2 wham sudden deep deep doo doo time.