Rebreather Comparison Chart

I don't think they set out to make the optima look bad, they set out to test it using similair parameters that CE units are tested at.. The test data Kevin released is fairly close to what I have heard in the past..

The test shows that the extendair does not do well at high flow rates with high co2 production..

If you are comparing scrubbers the worse case is a good starting point, high flow rates quickly show flaws in a scrubber.. Anyone can choose test parameters that make their units look good..

We all knew ahead of time that the sport kiss did not do well at high flow rates due to its shape but had reasonable performance when flow rates were kept in usual dive parameters.. The all out tests have their uses, since it is possible to reeach these flow rates for short periods of time.. Scrubbers with longer beds will do better at high flow rates but will usually also have a higher wob (unless the diameter is increased as well)

That would indeed be interesting but how can you compare ECCR to MCCR in that catergory, other than discounting them?

I assume that a correctly setup KISS and rEvo breathing off a machine could be setup to perform almost identically?

Also the results imply the test is run at the same rate for the entire period, an ECCR's trump is surely that it can respond to different breathing rates without the PPO2 changing dramatically, MCCR's would of course suffer in a variable rate test unless some kind of universal method was used for deciding when and for how long the MAV is operated.

How long will the C02 Filter Last?
Once upon a time 17 years ago a LEBA scrubber design was tested to breakthrough using a breathing simulator a total of 12 times, each to 0.5% surface equivalent. Test were conducted in 0C degree water (not 4 deg C ) with a C02 injection rate or 1.6 SLM (surface litres per minute) The mean endurance time (average of all 12 tests) was 189 minutes, the minimum test run was 183mins and the best test run was 193mins.
I would assume if we were to repeat the test in 4deg C water endurance would exceed 200mins with the 2.5 kg load of absorbent (Sofnolime) used.
Point 1. Mean average over 12 tests is better than a single one off test.

How easy is it to breathe?
The breathing characteristics are measure as Work of Breathing (WOB) and are measured in both mouthpiece pressure normally in inches water gauge or kilopascals dependant on your location (4.01 inches is 1 Kp) and in the total work of breathing measured as Joules per litre.
Two factors effect breathing, the depth and the respiritive minute volume (RMV) measured in litres per minute. As the depth increases and as the breath per minute BPM and volume increases so does the WOB.
Again 17 years ago the self same canister was tested at 1.8 joules per litre at 40 msw with the breathing rate at 75 l/min.
Point 2. The WOB is a trade off between canister loading (how may Kg) volume, surface area, loop volume and passage design.

Conclusion.
17 years ago the canister design above was better at 1.8 joules with a rated canister life of 189 minutes in zero degree water than what is presently available for recreational divers.

Suggestion.
Although the above LEBA test was neither the Prism or the 15.5 it would be a simple matter for Kevin to shift all his results down a couple of pegs when the Prism and the 15.5/16 units are included.

Personally I dont care so much about the scrubber durations or their effciency (amount of sorb/min duration) as I do for WOB results

So to me the best unit is one that has the best WOB and a reasonable scrubber life (30 mins difference in scrubber duration means nothing in the real world where we best guess when to change based on usage or next dive requirements)


A high WOB will contribute a lot to things accelerating to becoming pair shaped when the sh1t hits the fan.

Another point is if I want to make the dive safer (from a scrubber expiry viewpoint) I can put in a fresh fill, but I cant do anything to change the WOB.....

I have been emphasizing the importance of low WOB to safety for a long time and I doubt I could have done some of the divng I have done, or would have even attempted it, if I was diving on a unit with high WOB.

A unit that has OK WOB at 30M and a low RMV will breathe like a straw at 60M when you are finning at your maximum exertion level, trying not to be blown any further down in a nasty current, something which has happened to me many times. If I understand my physiology correctly, a CO2 hit starts with the diver retaining CO2 and not being able to vent it out of the body fast enough and a high WOB, especially at depth, is certainly the last thing you want when the "s" hits the fan.

do u still see an OpTima as a valid choice with these #'s?

Ian i have long since wondered but do you have WOB figures for the mk15.5?

I have been emphasizing the importance of low WOB to safety for a long time and I doubt I could have done some of the divng I have done, or would have even attempted it, if I was diving on a unit with high WOB.

A unit that has OK WOB at 30M and a low RMV will breathe like a straw at 60M when you are finning at your maximum exertion level, trying not to be blown any further down in a nasty current, something which has happened to me many times. If I understand my physiology correctly, a CO2 hit starts with the diver retaining CO2 and not being able to vent it out of the body fast enough and a high WOB, especially at depth, is certainly the last thing you want when the "s" hits the fan.

have things that should be fixed like ... only 2 sensors displayed on each display (rEvo and Palagian),