Time to recover SAC after CO2 hit

[matt]

I've seen the presentation before at a difference workshop.

In the Q&A he was asked what was the best thing to do if you had high CO2, the answer he gave being that you can reduce depth, work-load or lower your WOB. He also said:

...but there is no point in changing from a perfectly good closed circuit loop which has got a high work of breathing to a BOV which has an even higher work of breathing...

Matt.

 

[AlexBerger]

I can edit that if its not to your liking l:hehehm:

my liking lol no worrys as long as everybody els is still onboard

 

[Mark Chase]

I've seen the presentation before at a difference workshop.

In the Q&A he was asked what was the best thing to do if you had high CO2, the answer he gave being that you can reduce depth, work-load or lower your WOB. He also said:

...but there is no point in changing from a perfectly good closed circuit loop which has got a high work of breathing to a BOV which has an even higher work of breathing...

Matt.

No personaly id never do that which is why all my BOVs have a lower work of breathing than the loop they are on.

Only BOV I have had which had poor OC WOB were the JJ origional and the KISS origional. The KISS was particularly bad.

The Golum MK1 was massivly lower WOB on OC than it was on CCR

The Shrimp feels about the same as my standard OC bailout regs

I also had a Tec4 which was bassed on the Apex TX50 which was a superb OC breath but a heavy old lump

The Arora Blue BOV and Apoc BOVs I tested was also a very good OC breath I tested the AB one down at 70m but the Apoc only shalow on air.



I think BOV designers went a little silly in their serch for smaller and smaller BOVs. A bit like miniture mobile phones they became unusable. The Apex ATX type BOVs seem the happy medium but I have to say even the large BOVs I used in the past like the MK1 Golum & Tec4 did their job fine and I never realy considered the size / weight a serious issue

 

[Brad_Horn]

In the Q&A he was asked what was the best thing to do if you had high CO2, the answer he gave being that you can reduce depth, work-load or lower your WOB. He also said:

and only one of those you have control over pre-planning the dive. It means there is just as much need to know and have optimised your WOB for the dive as there is your PPO2 during the dive!

No personaly id never do that which is why all my BOVs have a lower work of breathing than the loop they are on.
The Shrimp feels about the same as my standard OC bailout regs

What is the actual WOB of your Shrimp in OC? Based on the single sample of testing by a third party that I am aware of, it is significantly higher than that of your loop and can't supply at >50L/min... happy to be corrected!

I think BOV designers went a little silly in their serch for smaller and smaller BOVs. A bit like miniture mobile phones they became unusable. The Apex ATX type BOVs seem the happy medium but I have to say even the large BOVs I used in the past like the MK1 Golum & Tec4 did their job fine and I never realy considered the size / weight a serious issue

As long as the BOV is neutral in the water, doesn't need hose weights and is out of the divers sight, your in a position to know any arguments based on size/weight are irrelevant. It is solely the breathing performance that matters at the end of the day if needed to be used in anger. Scant evidence of testing for those smaller and smaller BOVs is also telling: but they do look pretty in the marketing images.

 

[matt]

What is the actual WOB of your Shrimp in OC? Based on the single sample of testing by a third party that I am aware of, it is significantly higher than that of your loop and can't supply at >50L/min... happy to be corrected!

I have 2.07 J/l at 50m 49.5LPM. I don't see the gas in the report but assume it is air? Do you know, Brad?

Looks like it was tested on a meg and the WOB result for CC was 1.5 J/l. Also at 50m but at 62.5LPM. Again the gas is missing from the report.

For the JJ in CC I have 1.06 J/l air, 41.3m, 74.8LPM.

Matt.

 

[Mark Chase]

I have 2.07 J/l at 50m 49.5LPM. I don't see the gas in the report but assume it is air? Do you know, Brad?

Looks like it was tested on a meg and the WOB result for CC was 1.5 J/l. Also at 50m but at 62.5LPM. Again the gas is missing from the report.

For the JJ in CC I have 1.06 J/l air, 41.3m, 74.8LPM.

Matt.

I am prety sure the Meg testing was on the GG MK1 BOV in 2008 not the Shrimp

The MK1 was prety awfull untill the braught out the Low WOB kit which made it useable but still a bit naff. I was told by someone in the know that the Mk1 Golums WOB was 100% worse than the JJ BOV in CCR mode


The JJ BOV was hailed as the bench mark in CC BOV units and I can confirm that as a CC breath it was fantastic. However as an OC reg it was bloody awfull at depth

I am not an Ansti macheen but I cant tell the diferance between my Shrimp BOV as an OC reg and my bailout OC ATX40s. I never felt "wanting" for gas

I CAN tell the diferance with the old JJ and MK1 KISS units, which is why I got rid of both.

Back in the day when I dived OC id tune my APex to the point it would free flow if you took it out of your mouth underwater without inverting it. I loved the way it dived like that. However back up regs were always "detuned" to avoid the free flow issue

Same problem with my OC bailouts on CCR. I run them a bit "heavy" on the cracking presure to avoid accidental free flows.

This makes the whole WOB on bailout thing a bit mute for me.

 

[garethingham]

Retained C02 is why scooters make so much sense for rebreather diving, especially deeper dives where the consequences are greater and ability to carry bailout in realistic volumes are limited.

My advice to people on the boats asking about the scooter and the rebreather is buy the scooter 1st. Easier to maintain, more fun and a genuine safety feature for deeper dives.

Reinhard Buchaly used to respond to people who asked "should I buy and Rb80" with his own question. His question was, how many scooters do your have? If the answer was less than 2 he would say buy another scooter. Admittedly he was a cave diver in the days of cheap helium but there is a good lesson in his point.

 

[garethingham]

and only one of those you have control over pre-planning the dive. It means there is just as much need to know and have optimised your WOB for the dive as there is your PPO2 during the dive!


What is the actual WOB of your Shrimp in OC? Based on the single sample of testing by a third party that I am aware of, it is significantly higher than that of your loop and can't supply at >50L/min... happy to be corrected!


As long as the BOV is neutral in the water, doesn't need hose weights and is out of the divers sight, your in a position to know any arguments based on size/weight are irrelevant. It is solely the breathing performance that matters at the end of the day if needed to be used in anger. Scant evidence of testing for those smaller and smaller BOVs is also telling: but they do look pretty in the marketing images.

To the points earlier Brad. Even if a BOV can supply an unlimited amount of OC gas at any depth can you actually carry the gas that you may need.

I agree that a better BOV is better than a shit BOV but if neither of us can carry the adequate bailout gas then we both drown.

The lesson really has to be about avoiding the problem in the 1st place with good packing techniques and proper lung ventilation with limited exertion. As per my point above, scooters become a safety device.

 

[matt]

I am prety sure the Meg testing was on the GG MK1 BOV in 2008 not the Shrimp

The MK1 was prety awfull untill the braught out the Low WOB kit which made it useable but still a bit naff. I was told by someone in the know that the Mk1 Golums WOB was 100% worse than the JJ BOV in CCR mode

It just says "Golem Gear DSV with Regulator" and the serial number "Innerspace Systems". 14th December 2007.

I found another labeled Shrimp that has Average WOB is 0.41 J/l (40LPM, 40m, unknown gas). Doesn't say if this is CC or OC though.

Matt.

 

[Wol]

Thanks for reposting the video by Simon Mitchell - I had not fully appreciated the retained CO2 issue prior to that.

Key take aways seem to be:- keep a constant breathing rate, avoid work at depth, use more helium to reduce density of gas and use a rebreather with low wob. The video seemed to also imply that the exhale wob may be more relavent than the inhale wob in relation to preventing the collapse of alveoli at high breathing rates? _ or have I got the wrong end of the stick here?

Be good to get a view on what theoretical breathing rates should be maintained to avoid CO2 retention for a given gas mix and work rate - wonder if there is a study on this?

 

[Mr fish]

Thanks for reposting the video by Simon Mitchell - I had not fully appreciated the retained CO2 issue prior to that.

Key take aways seem to be:- keep a constant breathing rate, avoid work at depth, use more helium to reduce density of gas and use a rebreather with low wob. The video seemed to also imply that the exhale wob may be more relavent than the inhale wob in relation to preventing the collapse of alveoli at high breathing rates? _ or have I got the wrong end of the stick here?

Be good to get a view on what theoretical breathing rates should be maintained to avoid CO2 retention for a given gas mix and work rate - wonder if there is a study on this?

there will have been but ist going to be for hard hat diver,s. Deep Diving And Submarine Operations has some good reading on how the old hard hat / mix gas ccr diver went to grate lenth to keep co2 as low as possible , ventilation rates and standard operating procedure,s all sorted way back in the 30,s lol

 

[Mark Chase]

It just says "Golem Gear DSV with Regulator" and the serial number "Innerspace Systems". 14th December 2007.

I found another labeled Shrimp that has Average WOB is 0.41 J/l (40LPM, 40m, unknown gas). Doesn't say if this is CC or OC though.

Matt.

The clue is in the date.

I am prety sure the Shrimp didn't exist in 2007

The Shrimp WOB figure of 0.41J/L is off the golem gear web site but I beleive thats for the unit in CCR mode, not as an OC reg


Just checked and I got my Shrimp in 2010. I am prety sure thats about when they were launched

 

[Mark Chase]

Retained C02 is why scooters make so much sense for rebreather diving, especially deeper dives where the consequences are greater and ability to carry bailout in realistic volumes are limited.

My advice to people on the boats asking about the scooter and the rebreather is buy the scooter 1st. Easier to maintain, more fun and a genuine safety feature for deeper dives.

Reinhard Buchaly used to respond to people who asked "should I buy and Rb80" with his own question. His question was, how many scooters do your have? If the answer was less than 2 he would say buy another scooter. Admittedly he was a cave diver in the days of cheap helium but there is a good lesson in his point.

I own a scooter but in the UK the chances to use one are prety limited by the vizabuility.

Deepest I have dived with one is 70m which is a comfortable depth for me.

Planning a 80m+ dive I leave scooters cameras etc on the boat as I dont want the task loading

Possably if I dived a scooter more i'd be comfortable at depth with one. When I go properly deep I want the simplest rig and minial kit.

I have read many times about scooters and depth and always wonderd why? Caves scooters are all about getting there fast and possably back fast, but deep OW? I mean properly deep like around 100m+ we are doing such short run times for the dive part and traveling such short distances from the up line (like 10mins out 10mins back) that I never felt the advantage outweighed the task loading.

I did one dive where the scooter was "required" which was the Justicia (65m ish)where they always shot the bow and I wanted to see the stern.

Big wreck, so hit the scooter on full and get to the engin room area ASAP. The journy there is over a virtualy flat wreck

All my other scooter dives were just for the fun of it

ATB

 

[matt]

The clue is in the date.

I am prety sure the Shrimp didn't exist in 2007

The Shrimp WOB figure of 0.41J/L is off the golem gear web site but I beleive thats for the unit in CCR mode, not as an OC reg


Just checked and I got my Shrimp in 2010. I am prety sure thats about when they were launched

Yup, agree with that. Seems likely then that the OC WOB will be higher than the CC; ALVBOV is 0.87J/l OC.

Matt.

 

[Mark Chase]

Yup, agree with that. Seems likely then that the OC WOB will be higher than the CC; ALVBOV is 0.87J/l OC.

Matt.

Yes but hears where the confusion starts

Is this WOB of the BOV its self? OK great whats the WOB of this BOV on a JJ? or a KISS?

This is the problem because the BOV has an impact on the WOB of a CCR but you cant test the BOV as a stand alone unit, then say thats the WOB for the loop.

I am prety sure my Shrimp breathes easier in OC than it does as part of my JJ loop?

Could be wrong but thats how it feels as an end user.

ATB

 

[matt]

This is the problem because the BOV has an impact on the WOB of a CCR but you cant test the BOV as a stand alone unit, then say thats the WOB for the loop.

Yes, it's very difficult to actually compare anything, isn't it. Exactly as you say, needs testing as a system to be meaningful.

Matt.

 

[Brad_Horn]

I have 2.07 J/l at 50m 49.5LPM. I don't see the gas in the report but assume it is air? Do you know, Brad?

I have 3.24J/L for OC WOB, on a test report from a different independent 3rd party on a Shrimp optimised for best OC performance.... albeit it still requiring an inhalation effort of -57.33mbar or twice that allowed in EN250 and crapping out above 50lpm.

As no standard (NOAA?) that I am aware of requires testing at 49.5LPM (50LPM) I am guess they couldn't get it to go to 62.5LPM. Gas would be Air.

Looks like it was tested on a meg and the WOB result for CC was 1.5 J/l. Also at 50m but at 62.5LPM. Again the gas is missing from the report.

If it is at 50m at 62.5LPM that is the EN250 OC criteria so would be Air.
As the Meg WOB exceeds 1.5J/L, and is something like 2.2-2.5J/L (CL dependent) at 40m at 75lpm on Air, that will be the WOB of the Shrimp in isolation. Very very close to the 1.44J/L that I had extrapolated for it from the 0.41J/L at 40lpm. Can you share a link to that test report Matt?

For the JJ in CC I have 1.06 J/l air, 41.3m, 74.8LPM.

Yup. This is what DeepLife tested it for JJ at.
or nearly twice that of the ALVBOV in CC mode.

The JJ BOV was hailed as the bench mark in CC BOV units and I can confirm that as a CC breath it was fantastic.

A BOV with half it's WOB is even better. Why settle for 2nd best.

I am not an Ansti macheen but I cant tell the diferance between my Shrimp BOV as an OC reg and my bailout OC ATX40s. I never felt "wanting" for gas

And Mark at RMVs less than 40LPM your never likely knowing to know the difference; however, as per the HSE report that they just complied bailout RMVs start at 50lpm and go to over 100lpm..... At which point both the ALVBOV (and others such as the Poseidon BOV can be assumed to but without test data are an unknown) and your ATX40's continue to perform for bailout but the Shrimp (and others) simply don't work. AND you know they won't work before you even get in the water, thanks to the unmanned testing data.

I CAN tell the diferance with the old JJ and MK1 KISS units, which is why I got rid of both.

Which tells you just how high their WOB was....

Same problem with my OC bailouts on CCR. I run them a bit "heavy" on the cracking presure to avoid accidental free flows.

Did the ALVBOV you dive with free flow? With the cracking pressure set right, a well designed BOV won't, no matter the orientation or water flow over it.

To the points earlier Brad. Even if a BOV can supply an unlimited amount of OC gas at any depth can you actually carry the gas that you may need.

Yes, because if you can get off the loop onto a low WOB bailout option sooner you most probably won't have needed as much gas in the long run.... as your RMV will be lower. If you start on a low WOB CCR option then your much much less likely to have an issue in the first place.

I agree that a better BOV is better than a shit BOV but if neither of us can carry the adequate bailout gas then we both drown.

So I take it that you don't carry bailout gas?
If you do carry it, why not optimise your kit selection before you even get in the water, so your maximum needed is less to begin with! Still means you end up carrying the same amount, just there is less likelihood that you will drain it in anger. Lower WOB, less work = less gas needed though lower RMV.

The lesson really has to be about avoiding the problem in the 1st place with good packing techniques and proper lung ventilation with limited exertion. As per my point above, scooters become a safety device.

Having a low WOB CCR will then cover the niche times when the scooter won't save your butt.
Good packing is real easy with the right low WOB scrubber media. Noting that the WOB of granular sorb goes through the roof as it gets wet....

I found another labeled Shrimp that has Average WOB is 0.41 J/l (40LPM, 40m, unknown gas). Doesn't say if this is CC or OC though.

That Air as that is the default criteria for the CE scrubber test. Though why an earth they used 40lpm as opposed to the 75lpm required for EN14143 is an unknown: I assume they just didn't have a clue.
As per your other reporting its actually closer to 1.5J/L in comparison to other makes of CE tested BOV when you match test criteria.

Yes but hears where the confusion starts
Is this WOB of the BOV its self? OK great whats the WOB of this BOV on a JJ? or a KISS?

Where is the confusion? If you know that WOB of the BOV it remains a constant no matter what CCR it is fitted to. What then changes is the WOB of the CCR itself.
KISS CCR with KISS (Gordon era) BOV = Highest CC WOB or 5+J/L
KISS CCR with Shrimp (1.44-1.5J/L) = High CC WOB
KISS CCR with JJ-BOV (1.06J/L) = Lower CC WOB
KISS CCR with ALVBOV (0.57J/L) = Lowest CC WOB possible without improving something else in the loop. As the Apoc shows, with the right engineering and design, a CC total unit WOB of 1.44J/L is perfectly possible for the KISS. All it would need a bucket load of R&D $$$ to match the Apoc.
The USN proved this by changing out the DSV and hoses on the Mk15 and seriously lowered its WOB in incremental stages.

This is the problem because the BOV has an impact on the WOB of a CCR but you cant test the BOV as a stand alone unit, then say thats the WOB for the loop.

You don't need to test the BOV as a standalone unit. This should as Randy says be something supplied by the manufacturer.
As an end user, all you really need to know, is if it lowers or raises the total WOB of your unit. The DSV/BOV is such a contributor to the total WOB that it will have a significant effect either way. The JJ has quite good WOB so you have a reasonable starting point, allowing you much more flexibility than say that of an Inspo diver who has a much higher WOB to start from: but as a result more to benefit.

In your case Mark, you know that you have raised the total loop WOB by a fair chunk by fitting a Shrimp over the JJ-BOV.
Whereas an Inspo diver would know from the published testing that they have lowered their units WOB by a fair chunk by fitting a Shrimp over the stock APD DSV/OCB.
Fit an ALVBOV to ANY rebreather and it will lower its WOB. Which is why its such a perfect match for the rEvo.

I am prety sure my Shrimp breathes easier in OC than it does as part of my JJ loop?
Could be wrong but thats how it feels as an end user.

Which would indicate to me that you have increased your JJ-CCR's WOB to something closer to the Shrimps OC WOB.
Now what would interest me is if you did a back to back dive with an identical JJ but one that is fitted with a Hollis BOV and then one fitted with a Poseidon BOV. Both apparently offering near as good OC WOB as the ALVBOV but with unknown though reportedly good CC WOBs. I think you may be surprised by the result if you (we as humans) can feel a <0.5J/L difference in WOB.

Yes, it's very difficult to actually compare anything, isn't it. Exactly as you say, needs testing as a system to be meaningful.

I think you would agree it would be a piece of cake if everyone published as much testing openly as DL have done.... Why haven't they!

The system is already there: EN14143 for CC and EN250 for OC.
We should have the WOBs for all CCRs.
We should have the WOBs for CC mode of all BOVs/DSVs.
We should have the WOBs for OC modes for all BOVs and Regs
it would be good to have WOBs for mix and match units but that will come I am sure. The ALVBOV on the rEvo for example, as its stock DSV has quite a high WOB, is something that OSEL will publish down the track to support the number of ALVBOVs that they are selling to rEvo divers.

Manufacturers attempting to fudge things by giving WOB for anything other than Air or the test criteria for CE immediately red flags that something is off. The Hollis P2 is a classic for this as the Apoc offers the same WOB at 200m on heliox as the P2 does at 100m: yet no 40m/Air/75lpm test results for the P2 have been published by Hollis.

Comparing rebreathers on WOB should be no different to say comparing the colour of a car or its fuel consumption: you just pick what works for you!

 

[jturner]

A BOV with half it's WOB is even better. Why settle for 2nd best.

Because the "first best" you are hinting at is not designed for use with most recreational rebreathers due to having the gas flow direction arse about face. So this is like comparing the finest jump race horse with the finest racing camel - they can't be compared in much of any meaningful way as they won't ever be competing against each other.

Comparing rebreathers on WOB should be no different to say comparing the colour of a car or its fuel consumption: you just pick what works for you!

Oh I agree entirely. Only we should discount rebreathers that are designed for an entirely different market (like yours) as out of scope as they are no more relevant to the vast majority of recreational rebreather users than the air recycling systems on a submarine. It could have such the best work of breathing physically possible... but as it stands today, if you cannot use it, it is useless.

 

[WFO]

Yes, it's very difficult to actually compare anything, isn't it. Exactly as you say, needs testing as a system to be meaningful.

Matt.

I would suspect that the work of breathing of the BOV, being essentially head loss in a flow is simply additive to the rest of the loop and thus relatively easy to use results like that for comparison purposes.

i.e WOB of "bare unit" + WOB of DSV = total.

 

[matt]

I would suspect that the work of breathing of the BOV, being essentially head loss in a flow is simply additive to the rest of the loop and thus relatively easy to use results like that for comparison purposes.

i.e WOB of "bare unit" + WOB of DSV = total.

Me too - and would it not be useful if those figures were published?