Chemistry and Physics in sealed part-used scrubbers

**PhilSiswick** · 4th October 2007, 08:30

Quote: (Originally Posted by Molecular Products Ltd)

Ben when we say it is not safe I must clarify that we mean it is compromised and any further use of the material could have very umpredictable performance, splashing round in the shallows is probably OK but pushing it, taking it deep or expecting it to perform to manufacturers guidlines is not advisable.

Many thanks for the clarification.

The question is - what does this do to our calculation of scrubber life over multiple dives on a day or multiple day trip? I was taught what seems to be the common practice - keep track of the time on each dive (I add some padding for pre-breathing) and, as long as that time, plus the planned time for the coming dive are less than the manufacturer's recommended scrubber time, then you're good to go.

Do we need to calculate some kind of factor in to reduce the scrubber time with each repeated use of the same lime? Something like:

- First dive = 100% of mrst (manufacturer recommended scrubber time)
- Second dive = 75% of remaining mrst
- Third dive = 50% of remaining mrst
- etc

Does the time on each dive in the series affect the decay in performance, or is that simply a function of the fact that it has been used?

On the subject of longer storage - personally, I bin used scrubber if it is more than 14 days since I first used it, which seems in line with what others seem to do.

Cheers,

Molecular Products Ltd · 15th October 2007, 14:50

Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away.

The answer is you need to use your experience and common sense as their are to many variables to take into account, time left, temp, RH, heat cold all can have some effect. I even heard of one guy who microwaved it, 'don't'!!

OK I am going to sign off before I put any more crazy ideas out there.

Regards

Stephen

Quote: (Originally Posted by PhilSiswick)

Many thanks for the clarification.

The question is - what does this do to our calculation of scrubber life over multiple dives on a day or multiple day trip? I was taught what seems to be the common practice - keep track of the time on each dive (I add some padding for pre-breathing) and, as long as that time, plus the planned time for the coming dive are less than the manufacturer's recommended scrubber time, then you're good to go.

Do we need to calculate some kind of factor in to reduce the scrubber time with each repeated use of the same lime? Something like:

- First dive = 100% of mrst (manufacturer recommended scrubber time)
- Second dive = 75% of remaining mrst
- Third dive = 50% of remaining mrst
- etc

Does the time on each dive in the series affect the decay in performance, or is that simply a function of the fact that it has been used?

On the subject of longer storage - personally, I bin used scrubber if it is more than 14 days since I first used it, which seems in line with what others seem to do.

Cheers,

Ben Field · 15th October 2007, 15:22

Quote: (Originally Posted by Molecular Products Ltd)

Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away.

The answer is you need to use your experience and common sense as their are to many variables to take into account, time left, temp, RH, heat cold all can have some effect. I even heard of one guy who microwaved it, 'don't'!!

OK I am going to sign off before I put any more crazy ideas out there.

Regards

Stephen

ARGH! No don't so that, tell us more?

I don't think I'm at all unique in what I've been doing. For example, if I'm doing a trip and I have say a 50mtr dive on day one and a 50mtrs dive on day 2, both will have 1 hour run times and my scrubber is nominally rated to 3hours. I will do both on the same fill with a 24hr gap then dispose of it.

I had assumed this was conservative from what I've seen and heard others do.

I can understand why you would say don't do it, because you have no test data, I'm more than alittle surprised this is the First time I've heard of this at all.

Sutty · 18th October 2007, 14:30

Quote: (Originally Posted by Molecular Products Ltd)

Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away.

Apart from every hospital I have ever worked in!

Anaesthetic scrubbers are routinely unused in many theatres over weekends or longer, and then used for the next list.

A bit different of course as we have CO2 monitoring, a bit of breakthrough is not a big problem should it occur, and the "user" is not doing the monitoring!

Abbo · 10th January 2008, 23:52

Quote: (Originally Posted by Molecular Products Ltd)

The reaction sequence shown in your note is an oversimplification of the actual chemical reaction sequence that occurs. Sodium carbonate is not formed at the pH of the reactions, it is sodium bicarbonate that acts as the carrier molecule. A better description is:

Overall: CO2 + Ca(OH)2 => Ca(CO3) + H2O made up of the individual stages:

CO2 + H2O <=> CO2 in solution (it just dissolves - it does not form carbonic acid)

CO2 + NaOH => NaHCO2

NaHCO3 + Ca(OH)2 => Ca(CO3)2 + NaOH + H2O

I'm not a chemist, but these equations appear to be wrong - not least because they don't balance. Correct me if I'm wrong, but shouldn't the equations be:

CO2 + NaOH => NaHCO3 (otherwise you have 3 oxygen on the left and only 2 on the right - plus you don't have a bicarbonate ion).
NaHCO3 + Ca(OH)2 => CaCO3 + NaOH + H2O
Otherwise the Cs and Os don't balance and you have the wrong formula for chalk.

Hanssing · 11th January 2008, 08:17

Quote: (Originally Posted by Molecular Products Ltd)

Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away.

No but there's is an old navy-test (1995), about leaving partly used scrubbers for a week.
Their conclusion: No difference in performance-ratio.

See: Rubicon Research Repository: Item 123456789/3871

Regards
Nicolai

**wedivebc** · 11th January 2008, 12:59

Quote: (Originally Posted by Hanssing)

No but there's is an old navy-test (1995), about leaving partly used scrubbers for a week.
Their conclusion: No difference in performance-ratio.

See: Rubicon Research Repository: Item 123456789/3871

Regards
Nicolai

Thanks for posting that.

Nad · 29th January 2008, 10:14

Quote: (Originally Posted by Molecular Products Ltd)

Once soda lime has been left open or part used the water balance in the material is changed and the performance will be affected. Soda lime that is too dry or too wet will reduce the CO2 removal rate and place the diver at risk.

I was just wondering. during the use, because of the heath, some water go away in form of condensation. And it should lower (at some level) the performance of CO2 filtering.
What's if we leave some water to go in the filter to umidificate it a little bit ? I kind of give back some of the lost water?

Note: I just asking something about chemistry, I'm aware of the danger of a caustic cocktail...

Nad

4th October 2007, 08:30	#11 (permalink)
PhilSiswick WSKD 0001 Current Rebreather/s: Evolution Other Rebreather/s: Inspiration Vision Join Date: Apr 2006 Location: Oxford, UK Posts: 884	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) Ben when we say it is not safe I must clarify that we mean it is compromised and any further use of the material could have very umpredictable performance, splashing round in the shallows is probably OK but pushing it, taking it deep or expecting it to perform to manufacturers guidlines is not advisable. Many thanks for the clarification. The question is - what does this do to our calculation of scrubber life over multiple dives on a day or multiple day trip? I was taught what seems to be the common practice - keep track of the time on each dive (I add some padding for pre-breathing) and, as long as that time, plus the planned time for the coming dive are less than the manufacturer's recommended scrubber time, then you're good to go. Do we need to calculate some kind of factor in to reduce the scrubber time with each repeated use of the same lime? Something like: - First dive = 100% of mrst (manufacturer recommended scrubber time) - Second dive = 75% of remaining mrst - Third dive = 50% of remaining mrst - etc Does the time on each dive in the series affect the decay in performance, or is that simply a function of the fact that it has been used? On the subject of longer storage - personally, I bin used scrubber if it is more than 14 days since I first used it, which seems in line with what others seem to do. Cheers, __________________ Phil No comment on open circuit... it's an evolutionary dead end not really worth discussing here. Dave Sutton, 2007 I have always felt that the dive I am on is not nearly important as the dives I plan to be on the rest of my life. Tom Rose, 2007 www.hugsac.org.uk
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15th October 2007, 14:50	#12 (permalink)
Molecular Products Ltd New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Oct 2006 Location: UK Posts: 53	Re: Chemistry and Physics in sealed part-used scrubbers Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away. The answer is you need to use your experience and common sense as their are to many variables to take into account, time left, temp, RH, heat cold all can have some effect. I even heard of one guy who microwaved it, 'don't'!! OK I am going to sign off before I put any more crazy ideas out there. Regards Stephen Quote: (Originally Posted by PhilSiswick) Many thanks for the clarification. The question is - what does this do to our calculation of scrubber life over multiple dives on a day or multiple day trip? I was taught what seems to be the common practice - keep track of the time on each dive (I add some padding for pre-breathing) and, as long as that time, plus the planned time for the coming dive are less than the manufacturer's recommended scrubber time, then you're good to go. Do we need to calculate some kind of factor in to reduce the scrubber time with each repeated use of the same lime? Something like: - First dive = 100% of mrst (manufacturer recommended scrubber time) - Second dive = 75% of remaining mrst - Third dive = 50% of remaining mrst - etc Does the time on each dive in the series affect the decay in performance, or is that simply a function of the fact that it has been used? On the subject of longer storage - personally, I bin used scrubber if it is more than 14 days since I first used it, which seems in line with what others seem to do. Cheers,
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15th October 2007, 15:22	#13 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,482	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away. The answer is you need to use your experience and common sense as their are to many variables to take into account, time left, temp, RH, heat cold all can have some effect. I even heard of one guy who microwaved it, 'don't'!! OK I am going to sign off before I put any more crazy ideas out there. Regards Stephen ARGH! No don't so that, tell us more? I don't think I'm at all unique in what I've been doing. For example, if I'm doing a trip and I have say a 50mtr dive on day one and a 50mtrs dive on day 2, both will have 1 hour run times and my scrubber is nominally rated to 3hours. I will do both on the same fill with a 24hr gap then dispose of it. I had assumed this was conservative from what I've seen and heard others do. I can understand why you would say don't do it, because you have no test data, I'm more than alittle surprised this is the First time I've heard of this at all. __________________ www.hugsac.org.uk Beware Fridge Suck
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18th October 2007, 14:30	#14 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 775	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away. Apart from every hospital I have ever worked in! Anaesthetic scrubbers are routinely unused in many theatres over weekends or longer, and then used for the next list. A bit different of course as we have CO2 monitoring, a bit of breakthrough is not a big problem should it occur, and the "user" is not doing the monitoring! __________________ Never forget that life is a finite resource.
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10th January 2008, 23:52	#15 (permalink)
Abbo Going down on Meg Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 389	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) The reaction sequence shown in your note is an oversimplification of the actual chemical reaction sequence that occurs. Sodium carbonate is not formed at the pH of the reactions, it is sodium bicarbonate that acts as the carrier molecule. A better description is: Overall: CO2 + Ca(OH)2 => Ca(CO3) + H2O made up of the individual stages: CO2 + H2O <=> CO2 in solution (it just dissolves - it does not form carbonic acid) CO2 + NaOH => NaHCO2 NaHCO3 + Ca(OH)2 => Ca(CO3)2 + NaOH + H2O I'm not a chemist, but these equations appear to be wrong - not least because they don't balance. Correct me if I'm wrong, but shouldn't the equations be: CO2 + NaOH => NaHCO3 (otherwise you have 3 oxygen on the left and only 2 on the right - plus you don't have a bicarbonate ion). NaHCO3 + Ca(OH)2 => CaCO3 + NaOH + H2O Otherwise the Cs and Os don't balance and you have the wrong formula for chalk.
(Offline)

11th January 2008, 08:17	#16 (permalink)
Hanssing flap-flop ..... flap-flop Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Denmark Posts: 348	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) Unfortunately this is not a body of work we have done as diving is the only industry that leaves sodalime for any length of time without just throughing it away. No but there's is an old navy-test (1995), about leaving partly used scrubbers for a week. Their conclusion: No difference in performance-ratio. See: Rubicon Research Repository: Item 123456789/3871 Regards Nicolai __________________ Woohooo - I can change my rEvo! Its going to be bitchin' tricked out piece of gear
(Online)

11th January 2008, 12:59	#17 (permalink)
wedivebc FIGJAM Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,358	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Hanssing) No but there's is an old navy-test (1995), about leaving partly used scrubbers for a week. Their conclusion: No difference in performance-ratio. See: Rubicon Research Repository: Item 123456789/3871 Regards Nicolai Thanks for posting that. __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
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29th January 2008, 10:14	#18 (permalink)
Nad Rebel to the Bone Current Rebreather/s: Ouroboros Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Mar 2005 Location: Europe Posts: 941	Re: Chemistry and Physics in sealed part-used scrubbers Quote: (Originally Posted by Molecular Products Ltd) Once soda lime has been left open or part used the water balance in the material is changed and the performance will be affected. Soda lime that is too dry or too wet will reduce the CO2 removal rate and place the diver at risk. I was just wondering. during the use, because of the heath, some water go away in form of condensation. And it should lower (at some level) the performance of CO2 filtering. What's if we leave some water to go in the filter to umidificate it a little bit ? I kind of give back some of the lost water? Note: I just asking something about chemistry, I'm aware of the danger of a caustic cocktail... Nad __________________ The Impossible is often the Untried
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