Rebreather "Round Up"

[Mark Y]

I know . . .

********

I've marked my calendar for all dates . . .

As for the Spring get together, I like the 'Rebreather-a-go-go', just the place for my paisley mini-dry suit! Yeah baby!

'Silent Spring': I could dive my hazmat-dry suit!

[Chuck_Northrup]

I thought that I was the only one to make that grim connection. Better living through Chemistry Maybe Silent Summer would be better?

Jon, the Dive Rite RB is going to be CCR. I have not seen nor dove it yet, but it sounds promising. It uses the KISS OC/DSV and Hammerhead electronics. Front mounted counterlungs, and here is the kicker, retail price around $5k.

The difference between Santa Claus, the Easter Bunny, and the Dive Rite RB is that I still believe in Santa Claus and the Easter Bunny So many manufacturers have over promised and under delivered before that I always take these "rumors" with a grain of salt.

CN3

[Mark Y]

Chuck, do you know anything else about it? Does it have CO2 monitoring? Etc.

Dear Santa Claus, please leave one under the tree!

[Chuck_Northrup]

I am not sure if it has as CO2 monitor or not, but it makes no difference to me one way or the other. :

I think CO2 monitors are a BAD IDEA! Most are incapable of determining the most critical problems (loose o-rings/poor packing/dead scrubber material/etc) instead they focus on temperature and time. I think that a CO2 monitor will give divers a false sense of security about scrubber life and the abuse of the "3 hour" limit will increase. >

Pack your scrubber properly, dump it after 3 hours, perform all of your pre-dive checks, and IF IN DOUBT BAIL OUT! That is all the CO2 warning a good RB diver should need. ;D

Just my .02

CN3

[ghosch]

I think CO2 monitors are a BAD IDEA! Most are incapable of determining the most critical problems (loose o-rings/poor packing/dead scrubber material/etc) instead they focus on temperature and time. I think that a CO2 monitor will give divers a false sense of security about scrubber life and the abuse of the "3 hour" limit will increase. >


[/quote]

The same could be said about OxyGauges on an SCR

What I don't understand is why it is so difficult to make a CO2 sensor. Portable CO2 detection systems are comercially available for confined space work. They have been available for years. They do require some calibration and maintenance.

Whether or not they should be on the unit is a different question.

[Chuck_Northrup]

I understand your point on the OxyGauge, but have to disagree

More RB incidents resulting in fatalities have been linked to hypoxia than hypercapnia. The big difference is that during even a mild hypercapnia hit you "know something is wrong". As long as you acknowledge your body's warning signs and get "off the loop" you will be fine.

Hypoxia is a rather blissfull journey into the void. Granted if a diver is diving SCR 'according to Hoyle' the need for O2 analysis can be debated. Most Europeans dive without O2 analysis. The Azimuth does not have a ready-made port for O2 analysis and on the Dolphin and Ray it is seen as an "upgrade" not a standard feature.

On an SCR the situations which can lead to hypoxia include (as you know) running out of gas, blocked orifice, or improper gas use. The first two would have intrinsic warning signs (pressure gauge reading zero/excessive cycling of the ADV) and the third should not be done. ;D So if you don't want an OxyGauge fine, but for me it is nice for peace of mind.

Hypercapnia on the other hand can currently be detected only by "bio-feedback" so to speak. Other than exceeding the time limit (don't do it), or catastrophic scrubber failure (which would cause bubbles/increased resistance/etc), the remaining causes are those I listed earlier (poor packing/loose o-ring/using dead scrubber material) and NONE of these can be detected by modern CO2 "analyzers" in an RB. So you have the potential of a diver who "feels something is wrong" but checks his CO2-meter that says everything is hunky-dory and suffers an event. :'(

Mass spectrometry is the most reliable means of CO2 detection but is not possible in the humid environment of an RB loop. The need for a "robust" system which can handle the stress of a dive environment (bumpy boat ride/giant stride/etc) eliminates the use of most "surface" CO2 analyzers. :-\

The CO2 analyzer on the Evolution uses heat/moisture/and time to estimate "usable" scrubber time. The possible "false positives" related to this system make it unreliable in several instances. Like I said earlier, it makes ignoring common sense and proven protocal much to easy. :o

If and when a GOOD and RELIABLE CO2 monitor comes out I will be all for it. ;D

CN3

[ghosch]

CN3

Oxygauges are a crutch.

When I die, I want it to be a blissfull journey.

[Mark Y]

Hey guys, this thread is about:

[glow=red,2,300]the 'round-up'[/glow]

If you want to talk about CO2 monitors, start another thread. And if you want to discuss death, take it to the DIR section.

[Freedive WI]

While I, obviously, don't have the time in on a rebreather that you guys do, I thought you might be interested in this:

There's a couple of well know freediving instructors in Europe who use the Drager Dolphin to teach about shallow water black out. They hook up the unit with a properly filled scrubber, but don't attach the drive bottle. Then, they have the student breath off of the unit, in a classroom, until they pass out. The scrubber keeps them from ever feeling the painful effects of hypercapnia, and the body doesn't sense lowering 02, so they simply pass out- probably not something our insurance companies in the US would let us do to prospective students.

I can tell you from freediving that we train for high C02 levels all the time- and it hurts! C02 in much more intuitive, read "pain", and I can see why one wouldn't need a C02 monitor in your breathing loop.

02 is a real problem and I know that the unit I learned on didn't have an Oxygauge, and scared the crap out of me as a result- I really like to know what I am breathing. Math problems and gas consumptions rates are nice, but I really like to know what I am breathing at any given time.

Jon

[Chuck_Northrup]

A few years back I was on the Nautilus Explorer for the annual "Pseudo Tech" trip and we conducted a hypoxia experiment. I usually share the results with my RB students to show the importance of monitoring PO2.

We used the same set-up you describe with a couple of differences. We had a PO2 monitor (which the "guinea pig" could not see) and also an oximeter to read the 02 in the bloodstream. A mask ensured the test subject could not "cheat" by breathing through the nose.

The experiment began with about 50% in the loop and within 8 minutes it had been breathed down to 8% when the subject "blacked out". The interesting thing was his blood was still 98% saturated with 02. :o

The subject "felt fine" and was more or less lucid up until the point of passing out. The moral of the story is "ALWAYS KNOW YOUR PO2"

There are some people in the RB circles who advocate not only hypoxia exercises with students but hypercapnia exercises as well. :-\

As far as I know there are no training agencies that endorse this. ;D