Rebreather Discussion from Brockville Incident

[Larry7895]

All this WOB conversation is interesting. I remember thinking about it yesterday during my 3:20hr dive in a high flow cave.

I remember thinking how effortless the dive was even at depth and in high flow. Swimming or scootering each breath took as much effort as each breath I take now sitting at this laptop. And then came the 2hr ride home. My wife who was tagging along with me yesterday asked if she needed to drive home. It was nearly 11pm after a long day of diving, but the effort spent diving a rebreather with a perfect mix of gas (combined with the 60 minute scooter ride) was minimal. I've found that even after very long days of diving, you have more energy on CCR than you do on OC at the end of the day, and this time was no different. Add in the fact that I did a 30 minutes less deco than my OC buddy on this dive, and I carried 70lbs instead of 140lbs to the car, and it's a no brainer for me.

Rebreathers can kill the lazy, ignorant or complacent
Rebreathers can change your diving for the better in ways you couldn't possibly imagine.
Don't believe ANY of the hype... dive one for yourself and see.

Thanks Superlyte27, I fully intend to try one, but as a newbie, this thread has been really interesting. My own view as I sit here is that for the type of diving I do (photography and wreck, max depth of 60m, though most in 40m range) there is more complexity and potential failure points in CCR. Your comment above ("Rebreathers can kill the lazy, ignorant or complacent") has certainly hit home from yours and a number of other posts. However, while the residual risk on CCR is never likely to be as low as OC, from where I have got to to date, with the controls, safety features, training, appropriate maintenance and discipline, I believe the residual risk can be quite close for my type of diving. The one area that controls in CCR don't seem to be mature yet is measurement of CO2 in the diver and hence my interest in it. Given feedback from experts and my reading, though, this risk does not seem to be significantly higher than OC at the depths I dive. Appropriately managing work effort, WOB etc is clearly important on both. Net result, next step try it, speak with more practitioners in my neck of the woods and then decide if I'm disciplined enough after I've had some practical experience. Really appreciate everyone's contribution of their knowledge and experience. Regards.

 

[lv2dive]

All this WOB conversation is interesting. I remember thinking about it yesterday during my 3:20hr dive in a high flow cave.

I remember thinking how effortless the dive was even at depth and in high flow. Swimming or scootering each ... Add in the fact that I did a 30 minutes less deco than my OC buddy on this dive, and I carried 70lbs instead of 140lbs to the car, and it's a no brainer for me....
Rebreathers can change your diving for the better in ways you couldn't possibly imagine.
Don't believe ANY of the hype... dive one for yourself and see.

You HAD 30 minutes less deco or you DID thirty minutes less deco than your buddy? ;-)

Anyhoo...sounds like you had a really nice dive Pete! I might have heard something similar from your buddy. And I have to admit you paint an intriguing picture of the RB! <G>

 

[Superlyte27]

Kate:

When I had 10 minutes left on my 10 minute stop, James had I think 47 TTS showing on his Petrels. I had an awesome dive. Thanks for lending me your boyfriend. He shows me all the cool places.

Larry:
Take a real close look at the rEvo. Because the scrubbers are SO easy to pack, and there's two of them, I truly believe it would take a very large moron mistake twice in a row in exactly the same fashion to result in a serious CO2 event. The scrubbers are redundant, and super simple to pack. Honestly, WOB is a non-issue. I was told during class that if breathing my rEvo was any different than how I was breathing right now, there was an issue. Well, truthfully, the unit breathed like crap. So there was an issue. Placement, crotchstraps, waist straps, etc played into it. We fixed it and now the rebreather breathes just like you are breathing right now. Truthfully, that doesn't happen over night. But it does happen over month

Today, I can't imagine giving up diving with my rebreather. I miss it when I'm on OC.

 

[gianaameri]

Given feedback from experts and my reading, though, this risk does not seem to be significantly higher than OC at the depths I dive.

WOB: The math proves that at 40 meters on Air a rebreather is more risky than the same rebreather at 100 meters on Heliox and that at either depth a rebreather is more risky than OC.

pPO2: All it takes is a software bug or hardware problem or an intermittent fault with the O2 Sensors (O2 Sensors can fail at any time, they even come faulty out-of-the-packet when new) and a rebreather can make you unconscious at any depth.

 

[Larry7895]

WOB: The math proves that at 40 meters on Air a rebreather is more risky than the same rebreather at 100 meters on Heliox and that at either depth a rebreather is more risky than OC.

pPO2: All it takes is a software bug or hardware problem or an intermittent fault with the O2 Sensors (O2 Sensors can fail at any time, they even come faulty out-of-the-packet when new) and a rebreather can make you unconscious at any depth.

Hi Gianaameri
Thank you for all of the info you have provided, it has been been really useful. I appreciate you are passionate about this topic and you have certainly emphasized issues skipped over in other forums. However, as I understand it, you dive a rebreather and regardless of logistics or any other consideration, by definition must have made a decision that it is safe enough. Otherwise you would be putting yourself and your family at an unjustifiable risk. Surely no dive can be worth it if you truly believe that the outcome is a matter of random chance with a significant probability that you will die having done nothing wrong? Yet you still do it?

In any event, at a broader level, I think the argument as to whether CCR is more or less dangerous than OC is moot. Both have inherent dangers that can be reduced but not eliminated. More importantly, both are here to stay, that is the nature of progress (be it good or bad in your opinion). History proves a number of things, not least of which is that putting your head in the sand does not make things better.

I firmly believe everyone is responsible for their own decisions and must take appropriate steps to be adequately informed, no question and hence I believe the info you have put forward has been very valuable. But I believe the focus of any conversation on this topic, given CCR's are not going away, must be about how to make it safer, how to develop new approaches, to recognize and value those manufacturers who are trying to make it safer, to recognize and support those experts, particularly in the medical profession, who give of their time to do just that. YES some manufacturers and others may have a profit motive, but that is the nature of a free market. We need smart people to not only point out the problems, but to suggest solutions or encourage those who are genuinely trying to do so. If it was not for the past efforts of such people (profit driven or altruistic) we would not be diving at all or a good many other things for that matter.

Apologies everyone, sermon over.

 

[gianaameri]

Hi Gianaameri
Thank you for all of the info you have provided, it has been been really useful. I appreciate you are passionate about this topic and you have certainly emphasized issues skipped over in other forums. However, as I understand it, you dive a rebreather and regardless of logistics or any other consideration, by definition must have made a decision that it is safe enough. Otherwise you would be putting yourself and your family at an unjustifiable risk. Surely no dive can be worth it if you truly believe that the outcome is a matter of random chance with a significant probability that you will die having done nothing wrong? Yet you still do it?

In any event, at a broader level, I think the argument as to whether CCR is more or less dangerous than OC is moot. Both have inherent dangers that can be reduced but not eliminated. More importantly, both are here to stay, that is the nature of progress (be it good or bad in your opinion). History proves a number of things, not least of which is that putting your head in the sand does not make things better.

I firmly believe everyone is responsible for their own decisions and must take appropriate steps to be adequately informed, no question and hence I believe the info you have put forward has been very valuable. But I believe the focus of any conversation on this topic, given CCR's are not going away, must be about how to make it safer, how to develop new approaches, to recognize and value those manufacturers who are trying to make it safer, to recognize and support those experts, particularly in the medical profession, who give of their time to do just that. YES some manufacturers and others may have a profit motive, but that is the nature of a free market. We need smart people to not only point out the problems, but to suggest solutions or encourage those who are genuinely trying to do so. If it was not for the past efforts of such people (profit driven or altruistic) we would not be diving at all or a good many other things for that matter.

Apologies everyone, sermon over.

Once a person if fully informed of the risks and he/she can assess them, up to them if they want to engage in the activity or not.

Informed consent, however, can only be given once the person has been properly and fully informed.

To claim that a rebreather is suitable and appropriate for recreational diving, for example, would be obscuring some of the things that we know which makes a rebreather less than suitable and appropriate for recreational diving.

To summarise:

1. WOB: A rebreather WOB is higher than that of an OC regulator. Beyond a certain level of WOB we know this is likely to cause CO2 Retention. We have no means of measuring arterial CO2 on a diver on rebreather and there may also be individual variabilities to CO2 Retention.
2. pPO2 Monitoring system: regretfully, due to technological constraints, the electronics and software on rebreathers have a high Probability of a Dangerous Failure. By high, I mean higher than that which is mandated in the rebreather standard EN14143:2003 (which references the internationally recognised standard IEC61508).

So, once informed, the diver can make his own choice.

Personally:

1. I do not dive rebreathers other than when it is absolutely unavoidable (i.e. no rebreather for me on dives which can be done with one bottle of Nitrox or Air, for example, but also on a dive which I could logistically do on OC).
2. I do not dive rebreathers at depths which exceed the WOB NEDU limits (i.e my rebreather exceeds such limit on Air at 40 meters, so I set a max. depth of 30 meters for my rebreather on Air).
3. I do not dive rebreathers whose software and electronics are ill conceived or do not minimise risk to ALARP limits (i.e. I modify my rebreather for my own use to increase reliability and dependability).
4. When I use a rebreather for long dives, I use a DPV and back-up DPV to keep WOB at minimum.
5. I do not dive a rebreather in a current, especially and including on the surface (i.e. to swim from the stern of the boat to the anchor at the bow against a strong current).
6. Whenever possible, I reduce in the design and configuration the possibility of human error (i.e. if I can forget to hook on the eCCR O2 Feed QC, I remove the O2 QC, wherever possible so that I cannot forget to hook it on...).
7. ...there is a lot more.

Nonetheless, diving a rebreather, the outcome is ALSO a matter of random chance with a significant probability that I will die having done nothing wrong, no more and no less like many other divers better than me in every respect have already died.

There is not escaping that because rebreathers have a "SIL Level of less than 1" and technology is not available yet to reduce the Probability of Failure to a level which we are accustomed in other activities (i.e. flying, boating, driving...).

No one has delivered to the general public an electronic rebreather properly assessed and certified to meet "Functional Safety" to at least a SIL 1 level (anybody know of one, please let me know).

It is a game of Russian Roulette.

I play it to achieve cave penetrations on consecutive days which logistically I could not otherwise achieve (otherwise I don't play it).

Are you ready to join in the game and is the risk worth the dive you are going to undertake?

One word of caution on second-hand rebreathers.

The release of rebreather technology to civilian use was rubber stamped by a military research lab likely after consultation with senior political figures.

The military research lab then marketed and sold rebreather countermeasures for profit as a private entity (the technology would detect a rebreather diver miles away, identify the number of divers, and even type of rebreather. A directional wave of energy, or other more conventional measures, could then be used to disable the diver making it impossible for the diver to breathe underwater, hence the diver has to surface dead or alive).

The early generation of rebreathers released to the general public had a WOB which far exceeds the USN limits. The electronics were far less than dependable than they are now (and yet after many years and improvements no electronic rebreather we can buy and use has reached a "SIL 1 or better" level.

So, don't buy second-hand especially the older generation of rebreathers.

Check the WOB, Elastance, and Hydrostatic Imbalance of the unit before you buy. Avoid those which exceed the USN limits. Reduce your depth max limit (i.e. 30 meter in air, instead of 40 meters in Air) for those rebreathers who are just over the USN limit (and avoid altogether those for whom you cannot get figures or are more than 10% over the USN limits).

Look at how many Firmware updates they had since release. Frequent firmware updates are an indication of attempts to fix hardware problems with software solutions or lack of Functional Safety systems, procedures, and controls at the design stage (i.e. you are the guinea pig).

Your life, your choice - dive safe!

 

[Larry7895]

Once a person if fully informed of the risks and he/she can assess them, up to them if they want to engage in the activity or not.

Informed consent, however, can only be given once the person has been properly and fully informed.

To claim that a rebreather is suitable and appropriate for recreational diving, for example, would be obscuring some of the things that we know which makes a rebreather less than suitable and appropriate for recreational diving.

To summarise:

1. WOB: A rebreather WOB is higher than that of an OC regulator. Beyond a certain level of WOB we know this is likely to cause CO2 Retention. We have no means of measuring arterial CO2 on a diver on rebreather and there may also be individual variabilities to CO2 Retention.
2. pPO2 Monitoring system: regretfully, due to technological constraints, the electronics and software on rebreathers have a high Probability of a Dangerous Failure. By high, I mean higher than that which is mandated in the rebreather standard EN14143:2003 (which references the internationally recognised standard IEC61508).

So, once informed, the diver can make his own choice.

Personally:

1. I do not dive rebreathers other than when it is absolutely unavoidable (i.e. no rebreather for me on dives which can be done with one bottle of Nitrox or Air, for example, but also on a dive which I could logistically do on OC).
2. I do not dive rebreathers at depths which exceed the WOB NEDU limits (i.e my rebreather exceeds such limit on Air at 40 meters, so I set a max. depth of 30 meters for my rebreather on Air).
3. I do not dive rebreathers whose software and electronics are ill conceived or do not minimise risk to ALARP limits (i.e. I modify my rebreather for my own use to increase reliability and dependability).
4. When I use a rebreather for long dives, I use a DPV and back-up DPV to keep WOB at minimum.
5. I do not dive a rebreather in a current, especially and including on the surface (i.e. to swim from the stern of the boat to the anchor at the bow against a strong current).
6. Whenever possible, I reduce in the design and configuration the possibility of human error (i.e. if I can forget to hook on the eCCR O2 Feed QC, I remove the O2 QC, wherever possible so that I cannot forget to hook it on...).
7. ...there is a lot more.

Nonetheless, diving a rebreather, the outcome is ALSO a matter of random chance with a significant probability that I will die having done nothing wrong, no more and no less like many other divers better than me in every respect have already died.

There is not escaping that because rebreathers have a "SIL Level of less than 1" and technology is not available yet to reduce the Probability of Failure to a level which we are accustomed in other activities (i.e. flying, boating, driving...).

No one has delivered to the general public an electronic rebreather properly assessed and certified to meet "Functional Safety" to at least a SIL 1 level (anybody know of one, please let me know).

It is a game of Russian Roulette.

I play it to achieve cave penetrations on consecutive days which logistically I could not otherwise achieve (otherwise I don't play it).

Are you ready to join in the game and is the risk worth the dive you are going to undertake?

One word of caution on second-hand rebreathers.

The release of rebreather technology to civilian use was rubber stamped by a military research lab likely after consultation with senior political figures.

The military research lab then marketed and sold rebreather countermeasures for profit as a private entity (the technology would detect a rebreather diver miles away, identify the number of divers, and even type of rebreather. A directional wave of energy, or other more conventional measures, could then be used to disable the diver making it impossible for the diver to breathe underwater, hence the diver has to surface dead or alive).

The early generation of rebreathers released to the general public had a WOB which far exceeds the USN limits. The electronics were far less than dependable than they are now (and yet after many years and improvements no electronic rebreather we can buy and use has reached a "SIL 1 or better" level.

So, don't buy second-hand especially the older generation of rebreathers.

Check the WOB, Elastance, and Hydrostatic Imbalance of the unit before you buy. Avoid those which exceed the USN limits. Reduce your depth max limit (i.e. 30 meter in air, instead of 40 meters in Air) for those rebreathers who are just over the USN limit (and avoid altogether those for whom you cannot get figures or are more than 10% over the USN limits).

Look at how many Firmware updates they had since release. Frequent firmware updates are an indication of attempts to fix hardware problems with software solutions or lack of Functional Safety systems, procedures, and controls at the design stage (i.e. you are the guinea pig).

Your life, your choice - dive safe!

Thanks Gianaameri. Your points on WOB, Elastance, and Hydrostatic Imbalance, together with software are noted and already on my list of questions along with quite a few others. It is personal informed choice, but if you truly believe it is Russian Roulette, can ANY cave dive be worth it? Why not restrict yourself to those cave dives you can do on OC? BTW what is your point about max depth of 30m rather than 40?

 

[Doppler]

... Frequent firmware updates are an indication of attempts to fix hardware problems with software solutions or lack of Functional Safety systems, procedures, and controls at the design stage (i.e. you are the guinea pig).

I would question the definition of "Frequent" but perhaps more germane is that ANY system -- especially a piece of software/firmware -- SHOULD be re-assessed on a regular basis. As a v-p and owner of a company that produced brand management software, my task included connecting the propeller-heads in back of the shop with the punters using the tools those "software engineers" produced. We tested the crap out of what we built but our customers always found creative and devious ways to "break it" but more importantly, often came up with requests for solutions to "challenges" that we had never even thought of... I believe that process is called progress.

 

[gianaameri]

I would question the definition of "Frequent" but perhaps more germane is that ANY system -- especially a piece of software/firmware -- SHOULD be re-assessed on a regular basis. As a v-p and owner of a company that produced brand management software, my task included connecting the propeller-heads in back of the shop with the punters using the tools those "software engineers" produced. We tested the crap out of what we built but our customers always found creative and devious ways to "break it" but more importantly, often came up with requests for solutions to "challenges" that we had never even thought of... I believe that process is called progress.

My pPO2 monitor never required a software update. I cannot interact with it other than turning it ON by removing a rubber band around the case which also removes a magnet which triggers an ON/OFF switch internally to the case. It is waterproof to 120 meters without oil filling and it is oil filled (so any leak will be easily detectable). No matter how creative I can be, there is no room for me to mess it up (I got 2 for good measure and rotate them between dive series).

I also have another "life-support" system which never required a software update (just a change of battery every few years). It is Always ON. It runs of its own volition self-tests. It alerts me if the self-tests fail.

70 or 50 firmware "updates" is a bad sign in "life-support" equipment... and 10 within a short-space of product release is also a bad sign.

Is your work experience with "life-support" equipment (or non life-support products)?

 

[Dr Simon Mitchell]

Simon: can you point me towards any information you have that helps to qualify the statement that high CO2 worsens narcosis, and predisposes to cerebral oxygen toxicity? Thanks, mate. Hope all is well.

Hello Steve,

I seem to be having trouble sending you a pm. None of them appear in my sent items. Not sure if you are getting them. Can you send me an email address please.

Simon