GEM recreational rebreather

[Thalassamania]

Hi Everyone,

Kim here from KISS Rebreathers.

Hi Kim, thanks for joining in.

I was just chatting with Jay from Dive Tech today, and he mentioned that there were a few questions about GEM. So far i think Jay and also Rob Neto have answered the questions well.

As you can see, I have not found the answers that I was looking for, would you help out?

1. What is the actual measured FiO2 percentage drop in the GEM?
2. Is there normally a set of O2 sensors to provide FiO2 information?

... With regards to GEM and deep diving, so far we only have a recreational course. But we are actively working on the next level of training, and hope to have that available soon.

Yes, GEM as it stands right now, is designed for the recreational market. but yes, it did come from deep cave diving. We tweaked the unit to make it more appropriate for recreational diving; but in essence very little has changed.

Deep diving on the GEM involves gas switches and carrying various gases, as well as a true understanding of what happens when you dive a low nitrox mixture in a semi closed rebeather. this is why a training program is important. When this level of training is complete, we will have an annoucment.

If anyone has others questions for me, please let me know.

all the best,

Kim Mikusch
Kiss Rebreathers and Boosters

Am I missing something? Breathe in, breathe out, know your depth at all times, know how (and where) to purge and fill.

 

[Dive-aholic]

This link might help.

What is the drop?

3-5%.

Do you have actual measurements of it on your unit?

Yes, there is an O2 sensor on the unit and a ppO2 display.

So you are doing purges and gas switches? Do you have instrumentation built in?

I do things in a way they work for me. I prefer not to go into details on an open forum on how I am diving my unit.

With helium that makes sense, with EAN, it does not.

I can only relate my experience.

Using a rebreather in a manner it was not designed for is something I would be unlikely to do.

But the GEM was designed for the diving I'm doing. It's simply being introduced to the market in steps. As Kim has stated plans are in place for more training programs.

Anyone who can knows Dalton's Law of Partial Pressures can calculate what it SHOULD be, the question, however is not on of "should" but rather on of "is." What IS your FiO2 at 15 fsw using EAN-32? Do you have a way to measure it on board?

True. I can't respond with what his was, but at 15' that's the ppO2 I get on my unit. There is a sensor and ppO2 readout.

Here's the problem as I understand it: an SCCR that is designed for deep use will tend to have problems shallow because of the FiO2 drop. An SCCR that is designed for EAN, is, by definition, designed for shallow use and should not work well deep because of the ppO2. Perhaps your solution of shifting gasses is a reasonable solution to the problem, I don't know, it is not my area of expertise, but it flies in the face of what I have been lead to believe about rebreather design.

The key to the GEM is the mouthpiece. It is the unique attribute of this rebreather. You need to have nitrox in your cylinder to dive the GEM shallow. If you try to plumb air, you will get 16-18% in the loop and, as you know, that is dangerous. There are different ways to deal with this. The recommendation is to use mixes no lower than 36%. However, I'm pretty certain the next level of training will have a different recommendation, possibly what I am already doing, possibly a different method. Only time will tell.

Basically, what is happening is a certain amount of gas is escaping the loop from vents in the mouthpiece on every breath. The gas is being replaced with every breath with gas from the supplying cylinder. Because it is being mixed with exhaled gas that is lower in O2 content (because your body has used it) you get a lower percentage on the inhalation side of the loop. That's all that's happening.

Now how does that account for the differences in what is happening at depth v. in shallow waters? I'm not exactly certain, but here is my theory. The drop in O2 percentage is partially due to some residual CO2 making it through the scrubber as happens in all rebreathers. This remains a constant number as long as the scrubber is working properly. The difference between shallow and deep depths (and in this I'm putting the line at 4 ata or about 100') is the ratio of CO2 left in the loop in relation to the increased density of O2 in the loop. Bear with me because I'm simplifying this and likely not using the correct terms. At 2 ata if you have 4 parts CO2 compared to O2 and N2 you will get a 4% (averaging the 3-5% drop) drop in O2 from your supply gas. So if you are using 36%, you will have a ppO2 readout of .64 on your ppO2 display and .6 on your dive computer. (Most dive computers will present a ppO2 readout to the first decimal place, so there is some significant rounding occurring.) Breathing that same mix at 4 ata will increase the density of the O2 while the CO2 density remains the same, so now you have 2 parts CO2. This results in a drop equivalent to 2% or a ppO2 reading of 1.36 on the display or 1.4 on your dive computer, which is close enough to be inconsequential in your dive planning as far as a decompression schedule. Again, this is my theory and I may not be correct in this. If I'm not, I will gladly take any critiques.

I hope this answers your questions.

 

[divejay]

I now have a new dive buddy with his new GEM, David Sharp. David use to be the guy that always had to call the dive because of his air consumption. He would be the first to say that he was a air hog. Well, not any more. The GEM has changed him into a diving machine. He is so proud that his wife is now calling the dives.

 

[ajduplessis]

I have been pondering the jump to a rebreather for awhile. But was looking for a more idiot proof system. In addition for photography the lack of bubbles is key. I like the idea of this system but with a 30% exhaust I am not sure it is the answer. Anyone packing a camera have any experience with this system?

There are no idiot proof RB's!

 

[Mr.X]

This has been an interesting thread. As a CCR instructor and multiple RB user (including the KISS classic) I'd personally wish new users would just back off on the 'amazing' capabilities of the GEM, the marketing 'hype' of being 'born deep in a cave' and just get back to the basics of what this thing is - another gas extension device based on simple rebreather mechanics/physics. At the end of the day - like any rebreather it doesn't do anything special other than make it a bit easier to stay a little longer, dive a little lighter and reduce bubbles.

 

[Lobzilla]

This has been an interesting thread. As a CCR instructor and multiple RB user (including the KISS classic) I'd personally wish new users would just back off on the 'amazing' capabilities of the GEM, the marketing 'hype' of being 'born deep in a cave' and just get back to the basics of what this thing is - another gas extension device based on simple rebreather mechanics/physics.

Let's go a little further and contemplate why the GEM is even on the market. Could it be because PADI wants to push rebreathers into the hands of "recreational" divers and manufacturers like Jetsam and Poseidon are trying to cash in on this (IMO bad) idea of some marketing geniuses?

At the end of the day - like any rebreather it doesn't do anything special other than make it a bit easier to stay a little longer, dive a little lighter and reduce bubbles.

...at the expense of adding two more "H"s to your list of enemies - hypercapnia and hypoxia. (The third "H", hyperoxia, is already present in recreational OC diving.)

 

[Dive-aholic]

At the end of the day - like any rebreather it doesn't do anything special other than make it a bit easier to stay a little longer, dive a little lighter and reduce bubbles.

Actually, the GEM is a little different than previous SCRs. Do you even know anything about the design of the GEM?

Let's go a little further and contemplate why the GEM is even on the market. Could it be because PADI wants to push rebreathers into the hands of "recreational" divers and manufacturers like Jetsam and Poseidon are trying to cash in on this (IMO bad) idea of some marketing geniuses?

If that's the case then why does PADI not have a GEM training program? Why was IANTD to the first agency to provide a program and TDI the second? The GEM is not on the market because of PADI.

 

[divejay]

I have been pondering the jump to a rebreather for awhile. But was looking for a more idiot proof system. In addition for photography the lack of bubbles is key. I like the idea of this system but with a 30% exhaust I am not sure it is the answer. Anyone packing a camera have any experience with this system?

Me and David Sharp are both shooting Macro and wide angle while diving the GEM. The exhaust is very minimal and does not interfere with the macro marine life shoots, like open circuit does.

The GEM is very well thought out and after 70+ hours diving it since May 2011, simplicity's and a joy to make long dives is just grand. You can try out the GEM for a day at different places in Florida and Grand Cayman as an rebreather experience with a instructor.

 

[Thalassamania]

There are no idiot proof RB's!

This has been an interesting thread. As a CCR instructor and multiple RB user (including the KISS classic) I'd personally wish new users would just back off on the 'amazing' capabilities of the GEM, the marketing 'hype' of being 'born deep in a cave' and just get back to the basics of what this thing is - another gas extension device based on simple rebreather mechanics/physics. At the end of the day - like any rebreather it doesn't do anything special other than make it a bit easier to stay a little longer, dive a little lighter and reduce bubbles.

...

The GEM is very well thought out and after 70+ hours diving it since May 2011, simplicity's and a joy to make long dives is just grand. ...

As someone with well more than ten times seventy hours of rebreather time let me second ajduplessis and Mr. X. Underestimating the problems and complexities of diving a CCR (of whatever flavor) is suicidal, and it appears to me that there seems to be an alarming propensity amongst the advocates of the "lower end" consumer units to soft pedal the issues.

 

[wedivebc]

I'm not sure I understand this statement How does a computer influence your N2 uptake

I think what fishb0y was referring to was the fact that you need a computer to monitor the O2 cell for optimal decompression due to the changing fraction of N2.