Rebreather Discussion from Brockville Incident

[gianaameri]

I flatly reject that you can do absolutely everything right and still die. You just can't. You have to screw something, forget to do something up, cut corners or act negligent up to end up dead.

Dr. Mitchell and before him Dr. Lucarini took the time to explain in simple terms how CO2 Retention kills a diver even though the diver has done everything right.

It takes high WOB for that to happen, which means the manufacturer has in the first instance screwed up big time releasing to the general public a rebreather which has excessive WOB.

It does not take for the diver to go deep.

Excessive WOB can occur in a poorly designed rebreathers at 40 meters using Air Diluent as well as at 100 meters using Heliox.

Due to an error by a military lab, rebreathers with excessive WOB were released to the general public (and some may still be in use).

It cannot be ruled out that of some of the earlier fatalities on the earlier units a number could be attributed to excessive WOB.

We will never know for sure because post-mortem an autopsy cannot test for CO2 Retention (brain tissue will have died no matter what of O2 starvation and CO2 increase).

Luckily, modern rebreathers which have been properly tested by good civilian labs should not have excessive WOB, but some still do (so better check the test results for WOB, Hydrostatic Imbalance, and Elastance before buying).

There are still rebreathers being sold which are untested or whose WOB numbers are not known - which is a big risk for the user.

User error can also increase WOB significantlly:

1. Diving too deep
2. Poor diluent gas selection (gas too dense)
3. Fighting a current
4. Working hard
5. Allowing your counterlung to lift from your back or shoulders even a small amount
6. Maybe more, some instructor could fill in the list

...not to mentions that electronics in a caustic or salty wet environment do not perform very well over time, and no rebreather electronics and software available to the general public meets the Functional Safety (Clause 5.13.1 of EN14143:2003) required of "life-support" equipment (i.e. they fail miserably far too often and dangerously).

Russian roulette whichever way you look at it!

---------- Post added July 25th, 2013 at 08:11 AM ----------

At 100ft we will live for eight minutes, shallow we live for two minutes.

I believe that is incorrect in an eCCR or mCCR.

The time to unconsciousness ("TTU") is the same irrespective of depth for the same rebreather (eCCR or mCCR) used in the same manner - specifically with the same Setpoint at constant depth.

So, all other things being equal, my TTU with a Setpoint of 1.0 will be the same at 10 meters as it is at 100 meters on eCCR or mCCR (i.e. if I were or the unit were to stop injecting O2).

On the other hand, in SCR Bail-out rebreather mode (or pSCR or SCR rebreathers) the TTU would vary with depth (spreadsheet here http://www.rebreathermallorca.com/video/scubaboard/SCR modev1.xls ) due to the Oxygen Drop effect.

 

[HIGHwing]

I believe that is incorrect in an eCCR or mCCR.

I'm diving a ziplock bag in my example. There are admittedly problems diving using only a ziplock baggie.

Are you saying a rebreather, O2 turned off, loop at a stable SP, is capable of supporting life for the same duration irrespective of depth?

 

[gianaameri]

I'm diving a ziplock bag in my example. There are admittedly problems diving using only a ziplock baggie.

Are you saying a rebreather, O2 turned off, loop at a stable SP, is capable of supporting life for the same duration irrespective of depth?

The math shows that given the same starting pPO2 (ï.e. 1.0), constant depth (ï.e. not ascending or descending), same rebreather (ï.e. same loop volume), same VO2 (ï.e. 1.2 ltr./min. metabolised O2), the TTU is the same at 10 meters as it is at 100 meters if no more gas is introduced.

Same applies to a ziplok bag.

Sent from my HTC Desire C using Tapatalk 2

 

[gianaameri]

So, HIGHwing, have you been able to figure out the math, or do you need some help?

I have been absent for a while because I was solo rebreather cave diving the last 10 days covering on average Km. 5/day and na na na na na - the rebreather did not kill me either.

However, it does not mean it is not incredibly dangerous. Very useful tool, but incredibly dangerous. Glad it did not get me this time around!

 

[Superlyte27]

And he's back.

 

[tridacna]

And he's back.

You sound disappointed!

 

[Tortuga68]

...and boy is he tired!

 

[gianaameri]

...and boy is he tired!

One more dive OC (much safer ) tomorrow to remove all the jump lines... tiring, but soooo beautiful and rejuvenating!

Can't wait to do it again.

---------- Post added August 9th, 2013 at 03:55 PM ----------

From the link:
"Sensors of this type don't wear out so they were hard wired into the circuit. Unlike galvanic sensors they don't use oxygen but rather just respond to its presence. They work equally well submerged so the effect of any condensation is negligible. A drop of water fully covering the end of the sensor would only slow the response time."

So the designer and maker of the Electolung states that the Electrolung O2 sensors were not galvanic, which is in contrast with your statement.

*edit* the link was quite interesting.

Some more interesting stuff:

"History: The oxygen sensor was invented in the 1960's.
The first use in a rebreather was by Walter Stark in the Electrolung.
Development of the Electrolung came about through a chance meeting of
John Kanwisher and Walter Stark aboard Ed Link's diving research vessel in
the Bahamas in early 1968. Ed was trying out his new diver lock-out
submarine ‘Deep Diver’ and had invited along several researchers with
relevant interests. Walter was there to do some deep biological collecting and
John was there to do heart rate/respiration measurements on divers using
some new acoustical telemetry equipment he had developed. It turned out
they had both been considering the feasibility of a mixed gas Closed Circuit
rebreather (CCRB) using electronic sensors to control the Partial Pressure of
Oxygen (PPO2). Hence the Electrolung was born."

From another interesting paper: http://rebreatherpro.typepad.com/Oxygen Sensors for use in rebreathers - release V1.pdf

 

[lanta]

I have been absent for a while because I was solo rebreather cave diving the last 10 days covering on average Km. 5/day and na na na na na - the rebreather did not kill me either.

Would you be willing to repeat that test a few hundred times to improve its statistical accuracy? If you find you are about to die, would you kindly jot your thoughts down in your wet notes, preferably before losing consciousness?

 

[gianaameri]

Would you be willing to repeat that test a few hundred times to improve its statistical accuracy? If you find you are about to die, would you kindly jot your thoughts down in your wet notes, preferably before losing consciousness?

Done that more than a few 100 times already... but don't kid myself - if and when it is going to happen it will be a mild sensation of something wrong and then it will be the end of my life as I know it.

I suspect the Probability of Death is independent between one dive and the next (all other things being equal)... so repeating the experiment 1000 times won't change a thing.

No time to write my experience for posterity (no other dead rebreather diver had that time... pass out, roll on your back, gurgle gurgle gurgle...).