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 George K. Watson on July 8, 2010 at 10:03am

I would add that since I have begun contemplating/executing dives that are beyond the range of the COPIS's fixed IP, I have quit using it entirely for any dive. The main reason is that we teach and dive under the principal of 'equipment consistency' both within a team and across our diving careers. Diving the COPIS for shallower dives then having to completely switch it out and alter my equipment for deeper dives starkly violates the consistency principal. Learning how to dive with the COPIS, then dumping it for more aggressive profiles could, of course, lead to mistakes due to the inconsistency of equipment.

Permalink Reply by Lynne Flaherty on July 8, 2010 at 10:19am

Good explanation, Andrew. Thank you. Many of my friends who dive Megs do it without the COPIS for the same reasons.

Permalink Reply by Dave Woodward on July 14, 2010 at 10:16am

I am not sure I fully understand how the issues with the constant feed justify removing it?

Permalink Reply by Andrew Georgitsis on July 14, 2010 at 1:40pm

Dave

I am traveling but I thought I would try to put it another way. I hope this helps and answers some questions.

ALL rebreathers, regardless if they are eCCR, cCCR (copis) or strict mCCR (like mx series) require that the operator must develop excellent PPO2 awareness and O2 management. This is simply a skill an operator must learn through proper training and practice and of course proper configuration of the equipment such as HUD placement and so on. DIR/UTD philosophy is such that at no time should the operator of a rebreather "rely" on either the electronics or COPIS or whatever other primary or "backup" mechanisms to manage the PPO2 or O2 addition. It is my belief that if the operator does not have the proper skill or awareness to dive a rebreather and manage their PPO2's then they should not be certified to do so or should steer clear of rebreathers. Diving a rebreather requires "situational awareness" and in that, your awareness of the PPO2's. It is simply another item in your "scan", just like your depth or time or deco or whatever other "awareness" items you must manage. One cannot simply neglect your depth or buoyancy or PPO2 because you are distracted. That is what and why we train so hard in open circuit and in rebreathers. Situational awareness needs to be managed at all times even during emergencies.

Now as a side note: PPO2 changes are not nearly as sensitive if you take out buoyancy issues. With good buoyancy skills, PPO2's do not change that dramatically and the only thing that changes PPO2 is the diver metabolisms, which is negligible. There is no massive a drop of PPO2 from metabolism and even if one did not scan within 10 mins, it would not drop enough to become life threatening. In fact this a a test we do during the class. How long does it take to drop the PPO2 while diving. You would be surprised. None the less, good situational awareness negates this issue.

So essentially when implementing a primary or "backup " auto O2 injection system such as a solenoid or COPIS, one should make the evaluation of benefit vs risk.

A quick look at the COPIS benefits vs risks shows us...

Benefits: mmmmmm none

I actually see none as the COPIS is incapable of keeping up with the volume needed or o2 replenishment needed due to metabolism during descents, ascents and or dive operations. The O2 volume or metabolism replacement needed is simply to unpredictable to assign it a COPIS flow rate of 0.7l per min.

Risks and negatives:
- Additional failure points. 5 extras places to leak or o-rings to replace and so on.
- Needs a diver operated isolator to prevent the COPIS from adding unwanted O2 when rebreather not in use. Such as surface or at depth or during an airsharing or any other time the diver is on the open circuit. If the O2 COPIS is not isolated it will add unwanted or needed O2 to the loop without divers' knowledge and when the diver switches back will have a huge O2 spike.
Clogging due to water, or dirt intrusion and therefore not adding.
Not turned on.
Not a high enough IP.
Not correct flow rate for most situations.
Still requires manual bypass for constant adjustments by diver.
Still requires high level of awareness from dive, as it is not capable of predicting O2 requirements.
May give the diver a false sense of a backup system when in reality it is not functioning.
Depth restriction of 280'/85m

I can go on and on but you get the point.

Anyway, the bottom line is that we found it didn't add anything to the system, so we eliminated it.

Hope this further explains things.

Andrew

Permalink Reply by Nick Ambrose on July 14, 2010 at 7:59pm

I agree (in my very very limited experience)

in the dives I did with no COPIS, I used less O2, had no trouble keeping PO2 up, and everything just seemed a lot easier to manage. Less clutter, less crap and easy to use.

Permalink Reply by Tymek Podgorczyk on August 8, 2010 at 3:00pm

Hi Nick,

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

Tym

Permalink Reply by Unified Team Diving on August 9, 2010 at 9:41am

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

Permalink Reply by Nick Ambrose on August 9, 2010 at 10:53am

Tymek, my results seem to match Andrews pretty close.
I used the MX for 6 dives recently and had to add O2 only every few minutes to keep within the 1.1-1.2/3 range (at recreational depths)

As an aside, another diver was on the trip, using the COPIS, and used significantly more O2 than I for essentially the same dives (taking into account he did 1-2 dives more than me)

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

Permalink Reply by Marc Blackwood on August 9, 2010 at 1:55pm

Unified Team Diving said:

Tym
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

Andrew - With this type data in mind, is there ever a plan to drive the unit without the oxygen sensors (a major point of contention in the DIR vs. CCR history)?

Permalink Reply by Unified Team Diving on August 9, 2010 at 3:48pm

Marc

That is what got the manufacturer who promotes "NO O2 sensors required" in the proverbial hot-water. So, if you notice, within UTD, to take a rebreather class, including the PSCR or RB2000 style, we require at minimum of at least 1 O2 sensor on the unit. We will ever move away from requiring O2 sensors on rebreathers. As far as the "point of contention" in DIR, this is more in my mind the fact that a computer would try to fire a solenoid to adjust PPO2 and when that system breaks down is when we have the issues. Not so much the O2 sensor failure.

Andrew.

Andrew

Marc Blackwood said:

Unified Team Diving said:
Tym
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

Andrew - With this type data in mind, is there ever a plan to drive the unit without the oxygen sensors (a major point of contention in the DIR vs. CCR history)?

Permalink Reply by Maciej Arkuszewski on August 9, 2010 at 9:45pm

I agree here. I have no PSCR experience but I dont see any possibility to dive the CCRs with no sensor.
Maybe there will be better ways to protect the sensor from floods/moisture and/or better sensors but I really cannot see getting away from them ... the system is too dynamic and your needs change too much during each portion of the dive (descent, bottom, deco etc)

Permalink Reply by Nick Ambrose on August 9, 2010 at 9:47pm

haha apparently Mr Maciek logged into Nicks UTD account last night :)
This was nick and not maciek :)

Maciej Arkuszewski said:

I agree here. I have no PSCR experience but I dont see any possibility to dive the CCRs with no sensor.
Maybe there will be better ways to protect the sensor from floods/moisture and/or better sensors but I really cannot see getting away from them ... the system is too dynamic and your needs change too much during each portion of the dive (descent, bottom, deco etc)