co2 hits? bov or not

[Mark Chase]

Brad you say a Shrimp is 1.44Kj and the APOC BOV 0.56 I think?

To me that sounds a lot but I know from diveing both I personaly can't notice it under water

Breathing the old Paragon BOV was like breathing through a wet coth in comparison and the Golum MK1 wasn't much better before they put the low WOB kit on it.

However despite the fact I personaly coulden't feel much benifit on my dive, I'd be willing to invest in the lower work of breathing for my unit. But you dont make a BOV with the right direction of flow so why are you trying to promote it.

I dont think many would be up for changing the direction of flow their unit was designed with. I know i am not

You rightly promote this amazing bit of kit then say OK fine but if you want one you have to buy the whole CCR because we dont make one for you.

Then you say its not worth tooling up for a reversed flow unit? However many companies have found it worthwhile tooling up for after market BOVs so why can't you make a profit if its the market leader?

I am not an expert on CE but I reely cant see reversing the flow on the unit to be requireing a full retest on all componants?

Untill then its no use telling us everything else on the market is rubbish and dangling something in front of us as an alternative that we simply cant use.

ATB

Mark

 

[GLOC]

Brad, you make the following statement

Can the BOV OC mode be as high at 2.5J/L at 50m on Air at 62.5lpm (which is the worst case example of a CE marked OC reg) or must it be closer to a good OC reg at around 1J/L like an Apeks or Poseidon one?

For 50m on air on a CCR, there are going to be major issues, both from CO2 and N2 narcosis, therefore the easy (and most effective) solution is to kill two birds with one stone and add helium to the mix.

Using your own figures for WOB, what is the WOB for an 18/45 (or equivalent mix which you have tested for a 50m dive) compared to Air for the same dive? Yes, the non-ALBOV WOBs are going to be greater than yours, but are they less than your WOB figures when using air?

Regards

 

[mick4707]

To Mark's point about diving them and not noticing any difference it could be down to the fact the testing is down at such a high flow rate. When you get to a normal flow rate you probably won't be able to notice, this is always an issue when use an extreme test and not having any data for what is 'normal'. It would be good to see 2 data points maybe air at 50 m with 20 liters/min and 75 liters/min and then as GLOC asked a trimix at 50 m and 20 liters/min and 75 liters/min

 

[lof]

Jakub, I presume you did this deliberately and knowingly had the scrubber flooded for a significant point in time? See above video

No it was not deliberate. It was in the course of shooting a movie, so we did a lot of flips and tumbles, being blown up by compressed air cannons. It also stripped all anodizing from the can.

 

[Ben Field]

For 50m on air on a CCR, there are going to be major issues, both from CO2 and N2 narcosis, therefore the easy (and most effective) solution is to kill two birds with one stone and add helium to the mix.

Purely as an aside- that's the CE test criteria, not Brads recommendation of what to breath... FWIW I (and I suspect many others) have dove 50mtrs on air dil and can report no CO2 issues and negligible narcosis (but that's a personal parameter) although are both considerations they are not "Major" issues.

The standard stipulated testing with air because most OC divers dive air and 50mtrs is the general limit of recreational diving so it is a worst case scenario.

Who cares what the results are on helium? We know they are lower, we know lower is better so a low WOB BOV with a Lower WOB gas is Better + Better... until it freeflows in your face.

 

[Brad_Horn]

Brad you say a Shrimp is 1.44Kj and the APOC BOV 0.56 I think?

To me that sounds a lot but I know from diveing both I personaly can't notice it under water

Mark,
You have to consider a few more things in the direct comparison:
1) Your very likely breathing at less than 75lpm during your try dive.
2) Were you also breathing at the identical same rate on both dives? Impossible to answer unless your on an iCCR or were a lab rat at QinetiQ or NEDU etc.
3) The 1.44J/L for the Shrimp and 0.57J/L for the ALVBOV are at 40m on Air and are for the BOVs in isolation in CC mode.
4) During your try dive, your actually comparing the entire units WOB:
- for your JJ with Shrimp, that is what 1.6J/L plus the increase WOB of going from JJ-DSV to Shrimp.
- for the Apoc that is 1.44J/L plus the increase in WOB from your probably having dived with kitty litter instead of the EAC

The shallower you are and the less your breathing rate is, then the less the difference is going to be.

To give a fair comparison, you probably need to increase your workrate and be at 40m on Air in CC mode - which no one sane is going to ethically advise divers do. Hence the unmanned comparisons being the best means of identifying differences.

That is the CC side. On the OC side, no one appears to know what the OC WOB of the Shrimp is at 50m on Air at 62.5lpm. So you are comparing an unknown with a known, but again unless you breathed both with Air at 50m with a 62.5lpm work rate or higher/deeper, then you will have minimised the Delta between the two BOVs. Noting that when you need the BOV in anger is when you are working harder!

I'd be willing to invest in the lower work of breathing for my unit. But you dont make a BOV with the right direction of flow so why are you trying to promote it.

because the ALVBOV at the moment offers the ALARP http://www.hse.gov.uk/risk/theory/alarpglance.htm http://www.jakeman.com.au/media/alarp-as-low-as-reasonably-practicable for BOV choice. Therefore the ALVBOV is the gold standard that you have to choose from. Anything else is second rate. or unrateable because you have no idea what the WOB of it is in CC and OC modes.

Do I care if you buy an ALVBOV = not particularly.
Should it concern you that you do not have a comparable WOB for L-R flow, I would say so. So why do you not get your choice of rebreather manufacturer to supply a BOV of this standard to you; as you know it is physically possible. OSEL/DL have broken the ground and done the leg work to prove that it is possible and that you can get it CE in both CC and OC modes for use to 100m and breathable way deeper than that.

I dont think many would be up for changing the direction of flow their unit was designed with. I know i am not

Mark, again what proof do you have that the direction of flow for your unit is the better of the two?

You rightly promote this amazing bit of kit then say OK fine but if you want one you have to buy the whole CCR because we dont make one for you.

and? So what.

For everyone the purchase of a CCR is a balance of different competing priorities. Currently for most their priorities are subjective only; OSEL is just offering you the choice of adding physical facts to your decision loop, through the provision of actual performance data along with subjective considerations.

Then you say its not worth tooling up for a reversed flow unit? However many companies have found it worthwhile tooling up for after market BOVs so why can't you make a profit if its the market leader?

Mark, Where is the market for a L-R flow BOV? You say many companies have found it worthwhile tooling up for aftermarket BOVs, yet none of them can provide the WOB data for their BOVs, nor are they CE for bailing out deeper than 50m, if at all.

So what have those companies who have found it worthwhile not spent money on:
- any R&D to produce a low WOB BOV;
- any testing that is directly comparable to competitors products;
- any audits by notified bodies;
- any CE certification for use on other rebreathers (the ALVBOV has this as it is provably of lower WOB than any DSV or BOV);
- how much CO2 bypass occurs at 100m on the BOV;
- what their units scrubber duration actually is when measured at the mouth;
- any of those dreaded published reports in .pdf format directly comparing the performance against alternatives as part of the design verification process;
- and for some they are very cheaply (in comparison to high production injection moulding) CNCd out of a block of Delrin, despite this not being accepted by the likes of the USN for very good reasons for UBA (rebreather) use.

I am not an expert on CE but I reely cant see reversing the flow on the unit to be requireing a full retest on all componants?

For those that buy their certification from RINA, I am sure that is probably the case.

Other Notified Bodies appear to apply a little more rigour. This is a good thing for divers, if an expensive fact for the industry, for those who care about the subtle difference in end quality of product.

Untill then its no use telling us everything else on the market is rubbish and dangling something in front of us as an alternative that we simply cant use.

For those that dive R-L flow units, it is the best performing BOV option available by quite some margin. I doubt you are disputing that?
For those who choose to dive L-R units for other subjective reasons, you now know what is achievable and what you are missing out on. What is the issue of demanding equal performance from your manufacturer of choice before you shell out your hard earned cash on their BOV. They will either tell you that you do not need to know the performance of your rebreather, that sorry what you have is as good as they can provide or potentially, that yes it would be good to provide a better product and they are working on it.

If you get the later feedback then you will know that the smartest manufacturer will have approached OSEL with a PO for a L-R BOV with or without ALV feature; so saving themselves a significant amount of R&D and testing costs over attempting to replicate the high OC and CC performance themselves. Now this last point does make this somewhat commercial; but, can you honestly see this happening? As I would be quite surprised if it did occur. As you have said yourself, a fair number already supply BOVs to the market and can do so without having to spend anything on the above listed points.

For 50m on air on a CCR, there are going to be major issues, both from CO2 and N2 narcosis, therefore the easy (and most effective) solution is to kill two birds with one stone and add helium to the mix.

Using your own figures for WOB, what is the WOB for an 18/45 (or equivalent mix which you have tested for a 50m dive) compared to Air for the same dive? Yes, the non-ALBOV WOBs are going to be greater than yours, but are they less than your WOB figures when using air?

Gareth, Think about it. As Ben has pointed out, your argument is irrelevant. Yes, you will lower the WOB by adding He, but in directly comparing two competing products, you lower the WOB by the same amount with each.

The real question you should be asking, as posed to Simon, is what is the maximum safe WOB to bailout onto a BOV. Now if once we know this, you could potentially mitigate the risk from diving a mediocre BOV by running it with a tweaked He mix to get it under that WOB drop dead line. This just becomes another element to add into the dive planning pre-dive and assumes you know yours BOVs WOB in the first place.

In regards to your mis-interpretation of what I said with regards deep diving on Air on CCR, which as someone pointed out is the regulator comparison WOB depth at 62.5lpm. Have a look at the RN whose maximum Air CCR dive depth is 30m due to end-tidal CO2 issues AND they dive known LOW WOB rebreathers with LOW WOB dual mode masks; and not unknown WOB civvie jobbies.

To Mark's point about diving them and not noticing any difference it could be down to the fact the testing is down at such a high flow rate. When you get to a normal flow rate you probably won't be able to notice, this is always an issue when use an extreme test and not having any data for what is 'normal'. It would be good to see 2 data points maybe air at 50 m with 20 liters/min and 75 liters/min and then as GLOC asked a trimix at 50 m and 20 liters/min and 75 liters/min

Mick, your getting ahead of yourself. The ONLY BOV that the OC and CC WOB is known for is the ALVBOV. Perhaps this is a nut to crack, when you know the WOB for a few more!

No it was not deliberate. It was in the course of shooting a movie, so we did a lot of flips and tumbles, being blown up by compressed air cannons. It also stripped all anodizing from the can.

That sounds pretty deliberate for me. Based on the units design that you aware of in advance of the dive! Where did you expect the water to go if the design of the unit pools it in the can that the EAC is sitting in? As per the above video I linked to where the guy drinks the water after EAC has been sitting in it. If you pour water into an EAC in a scrubber you can purge it out and you have no caustic cocktail (and zero WOB issues). If you pour as little as a cupful into kitty litter you have an immediate caustic cocktail risk and not to mention a significant WOB problem.

 

[Ben Field]

Mark, again what proof do you have that the direction of flow for your unit is the better of the two?

Brad, I do not think its wise for anyone to recommend reversing the flow direction of an existing rebreather- alot of "consumers" will struggle to swap one BOV for another, let alone reversing their entire loop!

If I think only of my own unit, to accept a current back-to-front ALVBOV I would need to- make new counterlungs, remove the ADV and plumbing, reverse the position of the Scrubber to keep the hoses tidy, re-rig the high pressure plumbing as all hoses lengths are optimised or swap the Dil and O2 over (Very dangerous IMO as a decade of experience would need unlearning), invent some suitable connectors to join OSEL hoses to APD T-pieces, modify breathing hose lengths to suit connecting to shoulder T-pieces rather than back mounted unit... the list goes on to some more trivial items.

The point is you can't "just" change the loop direction to make use of a better BOV. We didn't choose to have our loops that way and since OSEL is the latest manufacturer to the party you could have chosen either (or both) ways to make BOV's but you choose to be different... so we loose the chance of a better BOV and you lose lots of potential customers, shame as we've all lost out.

 

[Brad_Horn]

Brad, I do not think its wise for anyone to recommend reversing the flow direction of an existing rebreather- alot of "consumers" will struggle to swap one BOV for another, let alone reversing their entire loop!

Ben, you have missed my point and I understand what you raise. At some point though folk need to think for themselves and to do this they need to ask hard questions and do their own research. What I asked Mark, is what proof does he have that the "as sold" direction of flow for his unit is the better of the two and not just arbitrary?

Will changing the flow cause any alteration to:
- scrubber duration at the mouth? = unknown anyway
- PPO2 at the mouth vs that displayed and recorded by the monitoring or dive computers? = unknown anyway
- Breathed PPO2 from the loop during rapid ascent? = unknown anyway
- anything else that anyone can think of?
the answer is almost certainly highly probably, but for better or worse?

As you have homebuilt your unit and it is completely untested; it is - in concept - irrelevant which way the flow is. You do not know which direction - if any - is safer.

If I think only of my own unit, to accept a current back-to-front ALVBOV I would need to- make new counterlungs, remove the ADV and plumbing, reverse the position of the Scrubber to keep the hoses tidy, re-rig the high pressure plumbing as all hoses lengths are optimised or swap the Dil and O2 over (Very dangerous IMO as a decade of experience would need unlearning), invent some suitable connectors to join OSEL hoses to APD T-pieces, modify breathing hose lengths to suit connecting to shoulder T-pieces rather than back mounted unit... the list goes on to some more trivial items.

Why do you need new CLs - other than to blank off the ADV, which you can now remove for a better performing one? Hose just plugs off and this may also remove that heavy manifold; if you fit Apollo A320 O2 regs you may also have better inverted cylinder hose routing.
If you need a better OPV get an Apollo one as fitted to the Apoc.
Your O2 cylinder and O2 add is already on the right hand side, yes.
What OD are your DSV end tee pieces? Likely they are too narrow, but curious.
ALVBOV breathing hoses can be significantly shortened by sliding them down the rigid elbows to fit FMCLs. This is a design feature.

All seems somewhat minor to me and will likely save you some weight, reduce your hoses and smooth your CLs. As you make your own CLs, it also potentially even allows you to copy the better PRISM style design (if you can acquire the fittings from Hollis) which is in and out, so offers much better water trapping and potentially even lower WOB through use of wider bore CL fittings.

The point is you can't "just" change the loop direction to make use of a better BOV.

Ben, Again, ask yourself why. What evidence do you have indicating that it is less safe?

and if you do have evidence, then if you want better WOB or a BOV that you know the WOB of when you bailout, perhaps you may just have to buy a CCR complete with BOV that has better documented performance!

 

[Ben Field]

is what proof does he have that the "as sold" direction of flow for his unit is the better of the two and not just arbitrary?

This is an issue, perhaps a linguistic one- you say reverse, I say reverse and might mean different things.

Some people reading this might be thinking we both mean using the scrubber in the wrong direction!! (clearly locating sensors before the scrubber and before the O2 addition is perilous)

For clarity I mean reversing all components- hence new lungs as the OPV hole is on the wrong side. As you say- minor (although with cost) to a home builder but if you are a basic customer relying on off-the-shelf parts it impossible and/or highly expensive, in either case not a "just" activity. Same as you Just pop out in the car but you don't Just pop out in a Steam Traction Engine

 

[Mike Ferguson]

because the ALVBOV at the moment offers the ALARP http://www.hse.gov.uk/risk/theory/alarpglance.htm http://www.jakeman.com.au/media/alarp-as-low-as-reasonably-practicable for BOV choice. Therefore the ALVBOV is the gold standard that you have to choose from. Anything else is second rate. or unrateable because you have no idea what the WOB of it is in CC and OC modes.

.

ALARP = As Low as Reasonably Practicable not As Low As Reasonably Possible. Big difference. it's possible (according to OSEL's own testing) to fit a 'lower WOB' BOV but it's not practicable to fit it to the overwhelming majority of rebreathers that are in use. therefore the ALVBOV does not offer ALARP

from the website you link to

'Reasonably practicable’ is a narrower term than ‘physically possible’ … a computation must be made by the owner in which the quantum of risk is placed on one scale and the sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble) is placed in the other, and that, if it be shown that there is a gross disproportion between them – the risk being insignificant in relation to the sacrifice – the defendants discharge the onus on them.”

In essence, making sure a risk has been reduced ALARP is about weighing the risk against the sacrifice needed to further reduce it. The decision is weighted in favour of health and safety because the presumption is that the duty-holder should implement the risk reduction measure. To avoid having to make this sacrifice, the duty-holder must be able to show that it would be grossly disproportionate to the benefits of risk reduction that would be achieved. Thus, the process is not one of balancing the costs and benefits of measures but, rather, of adopting measures except where they are ruled out because they involve grossly disproportionate sacrifices. Extreme examples might be:

To spend £1m to prevent five staff suffering bruised knees is obviously grossly disproportionate; but
To spend £1m to prevent a major explosion capable of killing 150 people is obviously proportionate.
Of course, in reality many decisions about risk and the controls that achieve ALARP are not so obvious. Factors come into play such as ongoing costs set against remote chances of one-off events, or daily expense and supervision time required to ensure that, for example, employees wear ear defenders set against a chance of developing hearing loss at some time in the future. It requires judgment. There is no simple formula for computing what is ALARP.

 

[GLOC]

Gareth, Think about it. As Ben has pointed out, your argument is irrelevant. Yes, you will lower the WOB by adding He, but in directly comparing two competing products, you lower the WOB by the same amount with each.

The real question you should be asking, as posed to Simon, is what is the maximum safe WOB to bailout onto a BOV. Now if once we know this, you could potentially mitigate the risk from diving a mediocre BOV by running it with a tweaked He mix to get it under that WOB drop dead line. This just becomes another element to add into the dive planning pre-dive and assumes you know yours BOVs WOB in the first place.

Brad, the argument is completely relevant.

If you are arguing that your air WOB passes the mark using air at 50m, what is your WOB for a mix-based gas at 50m? Assuming (big assumption) that there is linear relationship between air and helium-based gases in terms of WOB, there should be a corresponding drop in WOB for the non-ALBOV BOV and if that is below what yours passes, why is the argument irrelevant?

Regards

 

[Brad_Horn]

ALARP = As Low as Reasonably Practicable not As Low As Reasonably Possible. Big difference. it's possible (according to OSEL's own testing) to fit a 'lower WOB' BOV but it's not practicable to fit it to the overwhelming majority of rebreathers that are in use. therefore the ALVBOV does not offer ALARP.

Mike, Agreed. Although I would argue that it has been proven by OSEL that it is both practicable and possible for L-R users to have a BOV of equivalent performance to the ALVBOV. After all R-L users have it as their sole option for ALARP.

With that debated, it is now the question of what currently available BOVs offers ALARP at this time for L-R users?

WOB:
APD OCB - bloody high, but CE and under the line just, if only for use to 50m. ALARP potentially for units that only just scrape through the EN14143 WOB limit for MOD1 use!
JJ-BOV - good in CC mode, not in OC so ALARP for diving but not bailout. As bailout is kind of important for a BOV that probably rules that one out.
Shrimp - high in CC mode, can not meet CE in OC so unlikely ALARP
Poseidon - unknown in either CC or OC modes, but CCR is CE and Poseidon has a strong pedigree for OC regs performance, so probably ALARP for use to 100-150m?
Hollis - unknown in either CC or OC modes, but CE for use only to 40m (Explorer). Possibly ALARP for MOD1?
?
?
?

it is about as clear as a bowl of custard to me.

More than happy to be better informed though.

If you are arguing that your air WOB passes the mark using air at 50m

Err Gareth, minor thing you have missed that Ben has already pointed out to you. The 50m bit has bollocks to do with me and comes from the EN250 standard for the testing of OC regs. About as close as is currently available for the testing of OC bailout kit for rebreather BOVs to provide a baseline of the worst that is available that is still CE markable.

As most CE standards are designed by committee so more resemble a plodding camel than a thoroughbred race horse, their suggested limits are worst case examples. i.e.. nobody should use if higher and not the point at which you should stop offering better.

In my question to Simon, "what is the safe maximum WOB to bailout from a rebreather to OC", I am asking what is the safe go or no go for WOB for bailout. I would be very highly surprised if it is 2.5J/L at 50m on Air at 62.5lpm, but I await the academic answer with interest.

what is your WOB for a mix-based gas at 50m?

Again totally irrelevant. You have the wrong end of the stick. Based on this if a BOV needs to be fed He mixes to pass the worst case Air WOB limit it in not CE able by a large margin!

Feel free to advise where I can source OC reg WOB data for mixed gas testing at 50m however. Sounds useful.
FYI DL also tested an Apeks reg in comparison http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf so if you have it for that, we should be able to compare like with near like.

Assuming (big assumption) that there is linear relationship between air and helium-based gases in terms of WOB, there should be a corresponding drop in WOB for the non-ALBOV BOV and if that is below what yours passes, why is the argument irrelevant?

Cause the ALVBOV passes the EN250 for OC and EN14143 for CC, WOB requirements down to 350m, if you can adjust the He in the gas. So no matter what gas you pick, the ALVBOV will - certainly based on what else is currently available - always be lower with your criteria. How far down do you want to chase the bouncing ball?

 

[MatthewA]

Hollis - unknown in either CC or OC modes, but CE for use only to 40m (Explorer). Possibly ALARP for MOD1?

http://www.ccrexplorers.com/showthread.php?t=17600&page=3

 

[Simon Mitchell]

Simon, put simply. At what specific point (line in the sand) does the WOB of a BOV/OC reg become unsafe to bailout from a rebreather, be it a CCR with a WOB of 1.44J/L, your Mk15.5s 2.1J/L or your current units ~2.99J/L?

Hello Brad,

As you have implied, I have been interested in the effect of work of breathing on ventilation and CO2 levels in divers for some time. It is a complex and nuanced area of physiology, which I fear is being "over-simplified" by trying to tie acceptibility / desirability of an underwater breathing appartus (UBA) to a single work-of-breathing (WOB) benchmark. Nevertheless, it would be disingenuous of me not to observe that, all other factors being equal, a low external WOB imposed by a UBA is good and desirable. I think we can all accept that. This does not, of course, mean that the UBA with the lowest WOB is the best UBA because "all other factors" are not necessarily equal. In addition I must say that in accepting your claims about WOB in the Apoc ALBOV and rebreather loop, I am assuming that these parameters have been formally measured and documented by someone in addition to the "Baltic Assessment Institute".

In answer to your specific question, the best researched external WOB "line in the sand" lies somewhere between 1.5 and 2 J/litre. This was published by:

Warkander DE et al. Physiologically and subjectively acceptable breathing resistance in divers' breathing gear. Undersea Biomed Res 1992;19:427-45

The paper is available on the Rubicon Foundation website. Their estimate was based on avoidance of both an end tidal CO2 of 55mmHg and high shortness of breath scores in their subject divers who were exposed to a variety of conditions including exercise sufficient to produce minute ventilation around 50 L/min during air breathing at 57msw. There are other recommendations which are actually less conservative, but I cite this one because I believe it is the best researched.

What is obviously unclear is whether a WOB higher than Warkander's recommended maximum of 2 J/L measured in a pre-market test (using your example) at 50m depth with air ventilating at 62L/min automatically implies a piece of equipment is unacceptable. Warkander's recommendation (and what is physiologically important) relates to what the diver is actually exposed to on a dive; not to result of a test protocol under completely different conditions (like deep air at high ventilation rates). With the Apoc you may be in the comfortable position of claiming it performs adequately (within Warkander's recommendation) even with deep air at high ventilation rates. But you can't assume that other units fail to meet the recommendation in real dives. As has been discussed elsewhere the use (for example) of helium will reduce the external WOB in any UBA significantly compared to air. Obviously not all items of equipment get tested using multiple combinations of gases at multiple depths over multiple breathing rates so there are unknowns which I am sure you will highlight as undesirable, but it is not quite as clear cut as you are portraying it.

There is little doubt (with the caveat I mentioned earlier) that the low WOB attributed to the Apoc BOV and loop is a good feature. A large part of that in respect of the loop arises from the use of the non-granular CO2 scrubber cartridges. There is substantial controversy over whether these perform as well (in terms of CO2 absorption) as granular sorb, and right there you have a reason why some divers might prefer to forego the better work of breathing of a non-granular canister for potentially greater duration from granular absorbent. We could discuss this sort of stuff at length and I must remind you that the rebreather you promised the community (indeed, claimed was about to ship over 7 years ago) has still not materialised. Most divers do not want a basic loop that they have to modify to make it work, and other manufacturers offer very capable platforms that come as going concerns. Again, this is another reason why divers might sacrifice some work of breathing for the utility of a working eCCR.

Finally, as I have often pointed out to you in the past, there are unfortunate elements of history revision and hypocritical behaviour in your enthusiastic promotion of what are now (clearly) your products. You say:

You can also buy it with out elecs to do with whatever you want.

Yet 6 years ago Alex said:

Deep Life will put safety first. I have said before, that when it comes to a question of commercial gain or safety, there is no contest: the latter wins. I am worried by the sheer numbers of people ordering plain O2-CCRs, with the obvious intent of building their own eCCR.....If people think we are going to spend a fortune developing safe rebreathers, only to see large numbers of people fit a quick controller on it, they are mistaken. Our objective is to improve safety, not reduce it. etc etc

I'm not sure which one of these is right, but it can't be both.

Simon M

 

[MatthewA]

I'm not sure which one of these is right, but it can't be both.
Simon M

You do know who you are talking too, right?

 

[barrygoss]

Elmi, there is simply not the real demand. At the moment rec/tec divers are only at the initial evolutionary stage of knowing that a BOV is a good thing to have.

If there is not the obvious demand, which there is not as evidenced by the "GG shrimp selling like hot cake", it is pointless OSEL spending the quite considerable cash on retooling the ALVBOV for left to right flow and having it re certified to EN14143 and EN250 by SGS. It is a non-core business to OSEL as they will never sell a left to right flow rebreather

It 'could' have been made to be left to right, but this is the opposite flow direction to what commercial and military rebreathers use. and there just isn't the demand for it.

So the golem sells like hot cakes, but there isn't the demand for a albov and the retooling costs of changing the slight routering of the mushroom spiders mountings is too much.
Methinks sir doth protest too much.
It's a change of cnc programme.
Tbh, I'm in the market to swap the kiss bov out. It's golem or Poseidon, but I'd like to have apoc put cock on block as well.


B

 

[MeRodent]

So the golem sells like hot cakes, but there isn't the demand for a albov and the retooling costs of changing the slight routering of the mushroom spiders mountings is too much.

To be fair. I believe the albov is injection moulded so it's a case of a new mould rather than a change in routing program.

No doubt brad will confirm or correct this in a mere 27 paragraphs.

 

[Brad_Horn]

To be fair. I believe the albov is injection moulded so it's a case of a new mould rather than a change in routing program.

Correct.

You can see a cutaway image of the number of injection molded parts that retooling would needed for in this simple image https://www.facebook.com/1512989548...1298954899613/174849205877921/?type=3&theater

An example of one of the tests that would need to be repeated amongst many others prior to sale of a L-R ALVBOV http://www.deeplife.co.uk/or_files/Fault_Study_CO2_Bypass_110314.pdf

You do know who you are talking too, right?

Matthew, some in the dive community are actually interested in elements that are attributable to improved safety.

That you at Hollis appear to have no idea what the WOB of your BOV is in CC mode and that it is apparently not CEable for deeper than 40m use, does not appear to help those who want a high performance BOV. Bit pointless having a good WOB to bailout to if the high CC mode WOB caused the need to bailout in the first place.

As you have implied, I have been interested in the effect of work of breathing on ventilation and CO2 levels in divers for some time. It is a complex and nuanced area of physiology, which I fear is being "over-simplified" by trying to tie acceptibility / desirability of an underwater breathing appartus (UBA) to a single work-of-breathing (WOB) benchmark.

Agreed.

There are obviously two very distinct factors at play here:
1) A safe maximum WOB level for UBA as you discuss below. That is exceeded by a fair amount of kit used by recreational rebreather divers.
2) The safe differential for bailout onto a BOV from a rebreather at different workrates or CO2 exposures. Which appears to be a complete unknown.

Nevertheless, it would be disingenuous of me not to observe that, all other factors being equal, a low external WOB imposed by a UBA is good and desirable. I think we can all accept that. This does not, of course, mean that the UBA with the lowest WOB is the best UBA because "all other factors" are not necessarily equal.

A fair point but one that as I pointed to earlier, means that you then let subjective ***8220;all other factors***8221; overrule a known desirable safety datapoint. To each their own.

In addition I must say that in accepting your claims about WOB in the Apoc ALBOV and rebreather loop, I am assuming that these parameters have been formally measured and documented by someone in addition to the "Baltic Assessment Institute***8221;.

Simon, I put to you that if ANY of those figures were wrong, even by the smallest of margins, Alex would have had it very publicly brought to his attention by any number of interested parties: of which, even you will likely agree with me that there are a few. There is a very good reason why you do not see the likes of any recreational rebreather manufacturer publishing a comparison chart of their products performance against the Apoc or any of its components like the ALVBOV. I actually think it was Hollis that put out some joke advertising saying their CCR had the lowest WOB at 100m; when amusingly the Apoc has the same low WOB; only at 200m.
Like this CC WOB design validation report http://www.deeplife.co.uk/or_files/DV_OR_WOB_Respiratory_C1_101111.pdf all of the test criteria, equipment used and calibration data is openly published. If that does not make it scientifically repeatable for comparison purposes and very easily independently verified by any interested third parties, I am not sure what does.

But I do agree you cannot always take what a manufacturer says at face value, especially when they have deliberately concealed any testing from customers. Just look where that got APD when NEDU tested your rebreather. pg16 https://www.google.com.au/url?sa=t&...vYXAYJzm6gORzuA&bvm=bv.98717601,d.dGY&cad=rja

In answer to your specific question, the best researched external WOB "line in the sand" lies somewhere between 1.5 and 2 J/litre. This was published by:
Warkander DE et al. Physiologically and subjectively acceptable breathing resistance in divers' breathing gear. Undersea Biomed Res 1992;19:427-45

The paper is available on the Rubicon Foundation website. Their estimate was based on avoidance of both an end tidal CO2 of 55mmHg and high shortness of breath scores in their subject divers who were exposed to a variety of conditions including exercise sufficient to produce minute ventilation around 50 L/min during air breathing at 57msw. There are other recommendations which are actually less conservative, but I cite this one because I believe it is the best researched.

Thanks Simon, and as you have said before, obviously having a BOV with a OC bailout WOB <1.5J/L is a good and desirable.

Does your own OCB meet this best researched ***8220;line in the sand"?

What is obviously unclear is whether a WOB higher than Warkander's recommended maximum of 2 J/L measured in a pre-market test (using your example) at 50m depth with air ventilating at 62L/min automatically implies a piece of equipment is unacceptable. Warkander's recommendation (and what is physiologically important) relates to what the diver is actually exposed to on a dive; not to result of a test protocol under completely different conditions (like deep air at high ventilation rates). With the Apoc you may be in the comfortable position of claiming it performs adequately (within Warkander's recommendation) even with deep air at high ventilation rates. But you can't assume that other units fail to meet the recommendation in real dives. As has been discussed elsewhere the use (for example) of helium will reduce the external WOB in any UBA significantly compared to air.

Simon, I am not assuming anything with regards what other products fail as far as that recommendation goes. But unless there is testing data clearly indicating that their performance is adequate, I assume most CCRs and BOVs do fail that basic requirement, unless the diver is using Heliox on every dive. And as per NEDUs testing, for some users like you, even that does not appear to be sufficient.

But it would obviously assist the diver pre-dive or even pre-purchase, if they knew that their kit was below this worst case 2J/L level?
and if it is below this 2J/L level on air, then it is also obviously under it to an even more desirable level on mixed-gas, yes!

Obviously not all items of equipment get tested using multiple combinations of gases at multiple depths over multiple breathing rates so there are unknowns which I am sure you will highlight as undesirable, but it is not quite as clear cut as you are portraying it.

Simon, do you even know the WOB of your own kit on two different gases? As NEDU point out in the above link, your rebreather is 2.98J/L at 100m on Heliox or 50% greater than the upper safe limit that you cite. If it is that high on Heliox, what is it on Air?

There is little doubt (with the caveat I mentioned earlier) that the low WOB attributed to the Apoc BOV and loop is a good feature.

Yes.

A large part of that in respect of the loop arises from the use of the non-granular CO2 scrubber cartridges.

With regards the loop, yes, a portion of the low WOB stems from the use of EACs. That amongst the other safety features is a major consideration for there use. Also means there is less chance of loosing divers from their use of medical sorb.

A larger majority of the difference is due to the engineering R&D put into the design in order to minimise the WOB throughout the entire loop. As far as the BOV goes, this means it is not just the bit in your mouth that is an important choice to minimise WOB but also the breathing hoses and how these connect to the counterlungs.

There is substantial controversy over whether these perform as well (in terms of CO2 absorption) as granular sorb, and right there you have a reason why some divers might prefer to forego the better work of breathing of a non-granular canister for potentially greater duration from granular absorbent.

There is absolutely no controversy at all if you stick to facts.
If you get the flow through an EAC wrong as ISC and APD did, and KISS do, then yes, you get very poor duration but that is obvious upfront. Get the engineering right and to do this you need to design the Rb around the EAC, then you get very good durations.
Yes, the quoted scrubber durations for the Apoc seem low, until you realise they are at the mouth and include the dead space in the BOV. No other unit has this data available.

Compare like with like testing and under the USN criteria 1.3lpm CO2 low flow rate, then the Apoc with EAC has a 5hr duration compared to the Hollis P2s 4hr duration. Over 20% better duration.

I must remind you that the rebreather you promised the community (indeed, claimed was about to ship over 7 years ago) has still not materialised.

We obviously have very different definitions as to what a "rebreather" is but OSEL has sold plenty and has a fair few currently in build https://www.facebook.com/pages/Open-Safety-Equipment-Ltd/151298954899613

Most divers do not want a basic loop that they have to modify to make it work, and other manufacturers offer very capable platforms that come as going concerns. Again, this is another reason why divers might sacrifice some work of breathing for the utility of a working eCCR.

Fully agree that most divers do not want to add aftermarket electronics to a fully functioning rebreather. For those that do not, OSEL offer a mCCR with the lowest WOB amongst one or two other features.

As to a "working eCCR" I note you specifically do not mention a functionally safe ***8220;eCCR***8221; or underwater life support equipment.

By not focusing on the BOV aspect of the thread, you have deliberately taken your response to misguide folk and mis-direct attention of the thread down the Apoc route, which I am sure those that make particularly poor performance BOVs (like that which you dive) will be very happy with you for. Is mitigating a products poor performance by having to use high he mixes through it really the solution or should you just get the manufacturers to provide low WOB kit upfront!

Finally, as I have often pointed out to you in the past, there are unfortunate elements of history revision and hypocritical behaviour in your enthusiastic promotion of what are now (clearly) your products. I'm not sure which one of these is right, but it can't be both.

Simon, both of your quotes are quite true. It is just something that you need to approach with an open mind.
1) You can buy an Apoc for a very low comparative cost and fit whatever elecs you want to it. Fact.
2) Alex knows that most eCCRs that are available, have design issues, so does not want Apocs sold as eCCRs with those electronics. Fact.
Not sure what is difficult to understand about that.
It is trivial to offer an Apoc from the factory as an eCCR, using the Incursion head and a 3rd party controller with 3 or 4 cells. OSEL do not do this as it is impossible to offer an eCCR with 3rd party elecs that meets EN61508 to any SIL.

Back on topic.
So Simon says, the recommendation is that - as guidance only - not locked in stone, as other subjective factors also play a part. Divers should only consider purchasing rebreathers and BOVs and regulators (aka UBA) if the WOB on Air is known to be below 1.5-2.0J/L, correct?

What should divers do if the equipments WOB in either CC or OC mode is totally unknown or untested?

 

[MatthewA]

That you at Hollis appear to have no idea what the WOB of your BOV is in CC mode and that it is apparently not CEable for deeper than 40m use, does not appear to help those who want a high performance BOV. Bit pointless having a good WOB to bailout to if the high CC mode WOB caused the need to bailout in the first place.

The CE tests were done at 50m as the published data shows. The CE'd Explorer it is attached to is rated to 40m because it uses a minimum nitrox gas of 32%.

 

[MatthewA]

Compare like with like testing and under the USN criteria 1.3lpm CO2 low flow rate, then the Apoc with EAC has a 5hr duration compared to the Hollis P2s 4hr duration. Over 20% better duration.

4:20 to 5mbar breakthrough according to the NEDU tests. Is your 5 hour quote @ 5mbar or 20mbar? IIRC yours is to 20mbar, so its not "like with like".