Rebreather Discussion from Brockville Incident

[gianaameri]

Every dive, every flight.

On checklists, something does not add up.

First, I took flying lessons, gone through the checks on the plane on the ground, the pre-flight procedure, pre-take off procedure, pre-landing procedure, taxied, taken-off, and landed planes - no mention of check-list by my instructor and neither he or I ever used one.

Are there planes where a check-list is in practice not required and why?

Second, Dr. Concannon concludes at RF 3.0 that given a checklist was not found where a diver died on rebreather, that the use of checklist would prevent the death and rebreathers require no change or further improvements.

In contrast instead, Dr. Mitchell at RF 3.0 says "CO2 Retention" is the silent killer (my words for short) in rebreathers and an End-Tidal CO2 Monitor (i.e. monitoring CO2 on the exhale side) would be a very important addition to a rebreather to protect the diver.

My experience with check-lists is that they do not prevent me from making an error on rebreather.

The cause of error in pre-dive procedures is lack of proper procedures, wilful lack of adherence to proper procedure, and distractions.

Which means there has to be a pre-dive system, procedure, and control which works, but also the environment has to be such that you can give your pre-dive rebreather preparation your undivided attention.

Checklists with distractions to me give a false sense of having achieved something correctly when in reality I did something terribly wrong and I don't know it.

Like for some planes (or maybe I just had a bad instructor), if the tasks to be performed are few and simple (i.e. the rebreather is designed in the first instance so that the risk of bad assembly is eliminated... meaning you can't forget or misplace an o-ring or a spacer or a scrubber...), would not that go to much greater length to reduce human error (than asking the human to follow a lengthy check-list to assemble a more complex than necessary machine)?

An End-tidal CO2 Monitor like Dr. Mitchell proposes, would not that enhance safety in rebreather diving (as opposed to the "it's fine as it is" [my words] conclusion of Dr. Concannon)?

 

[Larry7895]

Doesn't the Hollis Explorer have such a CO2 monitor? As I understand it, the Explorer has also been fully CE certified to the standard you have been quoting. How close does this unit go to making rebreather diving safer?

 

[gianaameri]

Doesn't the Hollis Explorer have such a CO2 monitor? As I understand it, the Explorer has also been fully CE certified to the standard you have been quoting. How close does this unit go to making rebreather diving safer?

No, the Hollis Explorer has an inhale side CO2 Monitor (same as the Sentinel).

I also developed an inhale side CO2 monitor specific for my rebreather and an entrepreneur has taken my research and experience and has added some of his and there is now a Patent Application pending (he intends to roll out the inhale CO2 monitor as a plug-and-play kit for many rebreathers).

An inhale side CO2 Monitor is a basic GO/NO GO device which measures inspired CO2. On a rebreather, inspired CO2 is initially 0 (zero), less than the CO2 found in air, and then as the scrubber nears its end progressively the measured inspired CO2 increases.

A GO/NO GO inspired CO2 Monitor would basically allow you to bail-out if the Monitor were to indicate say a level of 0.5% inspired pCO2.

As explained by Dr. Mitchell at RF 3.0 (and Dr. Luca Luccarini article prior to Dr. Mitchell's RF 3.0 presentation), rebreathers have an insidious failure mode.

Even if the inspired pCO2 is 0 (zero), which means the scrubber has been properly fitted, packed, and functioning (and the rebreather is 100% working, no faults, no user error), you can still pass out and drown due to excess ("retained") CO2.

See Dr. Mitchell's RF 3.0 presentation for a clear/detailed explanation here: https://www.youtube.com/watch?v=GW1yVFF_FK4

An exhale side (downstream of the rebreather DSV or mouthpiece) CO2 monitor (a.k.a. "End-tidal CO2 Monitor") is currently unavailable to the general public.

I am toying with developing one (I no longer use an inhale side CO2 Monitor), and so are others, but none is available.

Before buying a rebreather, ask the manufacturer if the rebreather meets Clause 5.13.1 of EN14143:2003. So, ask Hollis if this new rebreather does.

If your rebreather bears the marks on the case as "CE" and no more - IT DOES NOT!!!

If your rebreather bears on the case the marks "EN14143:2003" it does, except for some rebreathers which were falsely marked "EN14143:2003" (either because of an innocent blunder or outright fraud).

Be safe and ask the manufacturer in writing before committing to such large investment and risking your life.

 

[Tortuga68]

People greatly overestimate the level of "complexity" in a rebreather

That perception probably isn't helped by people who refer to themselves as 'rebreather pilots'

I posit that it's entirely more likely that a diver would swap to the wrong gas on open circuit than that a rebreather diver would sufficiently screw up their PO2 and tox

Swapping to the wrong gas is also a danger on a RB e.g. Jim Miller

 

[Larry7895]

No, the Hollis Explorer has an inhale side CO2 Monitor (same as the Sentinel).

I also developed an inhale side CO2 monitor specific for my rebreather and an entrepreneur has taken my research and experience and has added some of his and there is now a Patent Application pending (he intends to roll out the inhale CO2 monitor as a plug-and-play kit for many rebreathers).

An inhale side CO2 Monitor is a basic GO/NO GO device which measures inspired CO2. On a rebreather, inspired CO2 is initially 0 (zero), less than the CO2 found in air, and then as the scrubber nears its end progressively the measured inspired CO2 increases.

A GO/NO GO inspired CO2 Monitor would basically allow you to bail-out if the Monitor were to indicate say a level of 0.5% inspired pCO2.

As explained by Dr. Mitchell at RF 3.0 (and Dr. Luca Luccarini article prior to Dr. Mitchell's RF 3.0 presentation), rebreathers have an insidious failure mode.

Even if the inspired pCO2 is 0 (zero), which means the scrubber has been properly fitted, packed, and functioning (and the rebreather is 100% working, no faults, no user error), you can still pass out and drown due to excess ("retained") CO2.

See Dr. Mitchell's RF 3.0 presentation for a clear/detailed explanation here: https://www.youtube.com/watch?v=GW1yVFF_FK4

An exhale side (downstream of the rebreather DSV or mouthpiece) CO2 monitor (a.k.a. "End-tidal CO2 Monitor") is currently unavailable to the general public.

I am toying with developing one (I no longer use an inhale side CO2 Monitor), and so are others, but none is available.

Before buying a rebreather, ask the manufacturer if the rebreather meets Clause 5.13.1 of EN14143:2003. So, ask Hollis if this new rebreather does.

If your rebreather bears the marks on the case as "CE" and no more - IT DOES NOT!!!

If your rebreather bears on the case the marks "EN14143:2003" it does, except for some rebreathers which were falsely marked "EN14143:2003" (either because of an innocent blunder or outright fraud).

Be safe and ask the manufacturer in writing before committing to such large investment and risking your life.

Hmmm, very interesting presentation. Why is measuring end tidal CO2 so difficult? What rebreather do you make/design?

 

[gianaameri]

Hmmm, very interesting presentation. Why is measuring end tidal CO2 so difficult? What rebreather do you make/design?

I do not make/design rebreathers. I modify existing ones for my own use to reduce risk to an acceptable level to myself (i.e. as low as reasonably practicable). In the process it is fun and I learn a lot of interesting things.

The problem is the sensing technology which is designed to work on land at ambient pressure, but not in a rebreather.

Same thing with galvanic O2 Sensors.

Galvanic O2 Sensor as a technology is effective on the surface in ambient air, but less effective and reliable in a rebreather (with tragic consequences).

The problem with the CO2 Sensors is that a. some tend more than others to go off calibration even on normal use on land and require recalibration. These are unsuitable for rebreather use (i.e. you do not want a sensor which drifts off of its own volition in use, at least not easily and frequently), and b. all use infrared and a tiny mirror and require pre-heating and heating.

So, no CO2 sensor likes humidity...

The one I have used in the inhale counterlung works fine provided it is not stored while not used in a rebreather. So, if you insert before the beginning of the dive and remove it at the end of the dive, it is stable.

If you leave it in a rebreather after the dive, you will need to let it dry before using it again for about 24 hours, and it will work fine again. You cannot accelerate the drying process by blowing dry air over it (not even blowing dry air for 12 hours will accelerate the drying process). No re-calibration is necessary because it is stable (on occasion you need to make sure it is still accurate by blowing on it a known gas mix like 1% CO2 and 99% N).

Different brand of absorbents seem to affect the mirror surface destroying it (which makes you wander what absorbents do to your lungs). It works with Sofnolime.

That is on the inhale side, in the counterlung, which is one of the drier and more stable temperature wise and least aggressive environment.

On the exhale side it is not dry. The closer you get to the mouthpiece, the worst it gets. You need to measure the very last portion of the breath to measure the end-tidal arterial CO2 (which is what matters), so the further away you place it from the mouth, the least accurate the measurement it gets.

Basically, it is a technology which won't work reliably inside a rebreather loop on the exhale side.

On the inhale side, when it fails, it fails reading high, which is fail-safe, because say instead of bailng out at 0.5% pCO2, you'd be bailing out at 0.3% pCO2 (which is safer).

In any event, if zero CO2 is what you want in a rebreather, 0.3% pCO2 you are already heading towards the beginning of a slippery slope.

So, my solution (for fun, I am not in the rebreather business nor ever care to be) is not to place it inside the rebreather, but on the body where it is a less aggressive environment.

I suspect the break-through will come when you can swallow a pill and this will measure various physiological parameters and transmit them wirelessly to a wrist display.

The reality though is that no one has been able to design and build one such device ("End-tidal CO2 Monitor") and make it available to the general public, which means that rebreathers cannot protect the end-user from CO2 retention (and a host of other risks) - users can pass-out and drown without warning.

For recreational diving, go sidemount on OC - safer and good fun (more fun than rebreathers)!

 

[HIGHwing]

No, the Hollis Explorer has an inhale side CO2 Monitor (same as the Sentinel).

Rumors abound the CO2 detection is no longer standard on the Hollis Explorer and Hollis has not been precise about exactly what the consumer is going to get for the $4,995 (MSRP) price point.

 

[Superlyte27]

No, the Hollis Explorer has an inhale side CO2 Monitor (same as the Sentinel).

I also developed an inhale side CO2 monitor specific for my rebreather and an entrepreneur has taken my research and experience and has added some of his and there is now a Patent Application pending (he intends to roll out the inhale CO2 monitor as a plug-and-play kit for many rebreathers).



Be safe and ask the manufacturer in writing before committing to such large investment and risking your life.

I think we just found out why you're so passionate about your stance, albeit with a flawed approach within your ability to illicit proponents for what you're selling.

 

[fishb0y]

I was thinking the same thing... Kinda like the "Music Man" of rebreathers.

 

[Superlyte27]

I was thinking the same thing... Kinda like the "Music Man" of rebreathers.

I was thinking he's more like the "Rain Man" of rebreathers. You know, kinda like an idiot savant minus the savant.