COPIS

I was asked why we moved away from the Constant Oxygen Pressure Injection System (COPIS) in the MX Series. I thought I addressed this is the video blog but because someone asked me the question again, I thought I would clarify it here.

First off, a little background. The COPIS system is designed to slowly bleed O2 into the system at a constant flow rate of 0.7 L per minute. This is a community standard of an estimated value needed by the diver to replenish the metabolized O2 during the dive. This 0.7 l per min is much like the predicted SAC in open circuit in that it is an "estimated" value. Of course that metabolic rate changes throughout the dive, both because the divers' needs might/will change based on their workload, and second, because of depth changes.

As you descend, PPO2 increases (volume decreases) and so you need less O2 on the way down, sometimes to a point of having to add diluant into your loop with the back gas. This is why we descend using our back gas. If you are ascending, then the PPO2 is decreasing (and the volume increasing) so you need to add more O2, and of course you first need to get rid of the over-volumed low PPO2 gas first. Then you can manually add O2 to keep the constant PPO2 during the ascent. So with the parameter of keeping the PPO2 above a 1.0 during the various phases of the dive you need to have a by-pass manual injection value that allows you to manually add the O2 to adjust the PPO2.

With that in mind, after diving the COPIS for a year and applying our DIR background, we have came to the conclusion that the COPIS was unnecessary for a couple of reasons. First, your awareness is such that you are always on top of keeping the PPO2 above 1.0 which requires constant manual adjustments throughout the dive and therefore the COPIS was simply unnecessary or unable to keep up. The diver was doing all the work. Secondly, because you need a constant flow of 0.7 l per minute even at depth, this flow rate was subject to a constant Intermediate Pressure (IP) from the first stage. That means you needed a fixed IP first stage set to 135psi or 9.5 bars. That means the COPIS had a depth
restriction of 280' / 85 m. Thirdly the COPIS needed an isolator to ensure that you could turn it off it was failing somehow, which added a failure point. Fourth, by elimination we can stay within our foundational principle that only WE can add O2 to the system. No auto-add to the system such as solenoids or ADV's. The diver is the only one who can add O2 to the system.

As you can imagine, as we transitioned from our Open Circuit DIR system to the pSCR we had a learning curve to make it a DIR system. (The original Halcyon pSCR, called "the fridge," was way more complicated than the RB2000/orRB80) Now, as we transition to closed circuit rebreathers (CCR's), there is and will be a learning curve to make it DIR; albeit, much smaller learning curve but still a learning curve. As UTD forges ahead bringing DIR to the CCR world and bridges that gap, we have kept in mind some of the original principles of DIR, that we must maintain an open mindset, work through all the issues with the end in mind, maintain consistency and eliminate anything unnecessary to the dive and/or anything that adds RISKS. It is all about risk vs benefit.

Well, I hope this helps clarify some small points.

AG

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Replies to This Discussion

Permalink Reply by Maciej Arkuszewski on August 9, 2010 at 10:29pm

bloody impostor

Permalink Reply by Marc Blackwood on August 10, 2010 at 8:16am

I guess I've misunderstood. I've always thought that relying on sensors to tell you in real time what you're breathing was a big issue (and I've always found it a little weird since most of us OC guys rely on electronics on the surface to tell us beforehand what we will be breathing).

Permalink Reply by Nick Ambrose on August 10, 2010 at 10:31am

Marc,

Sensor use I think has been controversial.
That said, it's basically impossible to drive a CCR without sensors.
We can do sanity checks (i.e. if I do a 100 foot dive on 32%, I should know my bottom PPO2 as I only inject diluent on descent), monitoring how often you have to inject O2, monitoring how the PO2 drops on ascent so you try to rely on them as little as possible. Also, the HUD gives you a readout of each sensor so you can hopefully tell if one cell is starting to give erroneous readings

There has been at least one case of serious injury on a pSCR due to a bigger than planned-for PO2 drop, and one case of an unconscious diver due to entanglement shallow with a hypoxic mix.

For OC, yes you rely on a cell but it's in a dry environment and you have plenty of time to get it right before the dive.

For CCR, it seems that better sensors and better ways to prevent them from experiencing moisture may help. Sadly, due to lawsuits, one major vendor of sensors is no longer selling them for RB use, given that a single lawsuit could easily consume multiple years of their sensor sales...

Maybe someone more cleverer than I can come up with a way to avoid the sensors ...

Marc Blackwood said:

I guess I've misunderstood. I've always thought that relying on sensors to tell you in real time what you're breathing was a big issue (and I've always found it a little weird since most of us OC guys rely on electronics on the surface to tell us beforehand what we will be breathing).

Permalink Reply by Tymek Podgorczyk on August 10, 2010 at 4:03pm

Thanks. That makes it clear.

Tym

Unified Team Diving said:

Tym

To answer this precisely is impossible because you have different metabolic rates at different work loads, assuming a constant depth. So, to keep a consistent PPO2, it would require the same amount of monitoring and adjustments to the PPO2 with or without COPIS. This is one of the reasons we decided not to use COPIS anymore, is it was unable to ever be a accurate predictor of our metabolic needs. The COPIS would be constantly adding too little or too much O2 during depth changes, therefore not only creating unnecessary buoyancy issues, but but the potential to spike O2 levels at depth. It also required constant monitoring at depth – if your workload caused your O2 metabolic rate to drop below the .7 liters of the COPIS, O2 would creep up. If your workload caused your O2 metabolic rate to go over .7, the the COPIS would not add enough. So looking at the pros vs. cons, we decided against it.

Interestingly enough, some people made the argument to me that it is safer with COPIS because if you as the diver forget to add O2 or adjust the PPO2 because you are distracted you may go hypoxic or whatever. However, I was doing a series of tests with this idea and wanted to find out the PPO2 drop in 5 minute increments without adding any additional O2 or Diluent. Just simply go to a specific depth and set the PPO2 to 1.0 or 1.2 or 1.4 and then just stay either stationary at that depth or kick lightly or even work hard. The idea was to simulate what would happen, assuming a constant depth, if the diver was to be distracted and did not add O2 or adjust PPO2. How much would the PPO2 and how long would it take to become hypoxic?

So in my test I found that if I am stationary the PPO2 will drop 0.2 every minutes, for light work load I found a PPO2 drop of 0.25, a heavy work load a drop of 0.3. If I am at a constant depth and the PPO2 is set at 1.0 or above and I become distracted and am working hard we would get this:

1.0. @. 0 mins
0.7. @ 5 mins
0.4. @ 10 mins
0.1 @ 15 mins or potential hypoxia

The interesting part is that I was unable to sustain a workload for 5 minutes to get it to drop more than 0.35. What I found was that after 5 mins, without adding any additional O2 or Diluent, the breathing loop volume had become so dimenished due to the O2 metabolism that it become very difficult to breath, and by 7 minutes into the test it was impossible to breath and by 8 mins I had to bailout to open circuit because I could not breath the loop. In other words, I would run out of loop volume before significant or dangerous levels of PPO2 drop. This volume depletion is essentially an "alarm" of sorts that warns the diver that additional gas is needed. Adding O2 would both return the loop volume and the PPO2. Keep in mind we do dive standardized gases on the diluent side, so if the diver simply added dil at depth the PPO2 would still be very close to 1.0 or above, since the standard backgases have a PPO2 of approximately 1.2 at depth. Hence the advantage of using standardized mixes as diluent.

I hope this makes sense and explains the MX better. We have being diving it now for a while, since the project in Mexico in November, and much prefer it over the COPIS system. Not only because it is truly a fully manual addition system (true mCCR) and therefore we feel much safer, the real advantage is being able to easily control your PPO2 keeping it above 1.0 or what ever you choose, and ultimately not having a machine or solenoid or COPIS add gas that messes with your buoyancy and has the potential to very rapidly spike O2.

Andrew
.

Tymek Podgorczyk said:
Hi Nick,

In the bottom phase, keeping one deepth, how often you need do add O2 when using MX comparing to MC?

Tym