Optima ExtendAir Duration Experiences?

dreamdive

All very interesting but what happened to monitoring your O2 consumption and discard the cartridge after 240 L scrubbed?

Claudia

otterinaround

Apparently you guys are getting a MASSIVE DEAL!!! Out here in the WILDS of BEIRUT LEBANON we pay a wonderful $65 PER EAC!!! We change after three 1 hour dives. Usually covers about 2 days and never more than a week. Dives hit about 40m and are multilevel with minimal deco commitment. I know that deep dives increase ppCO2 and that the EAC would burn faster so I don't double up on deep deep dives. I'm sure I could get more out of the cartridge but in order to preserve the reputation of rebreathers and of the club with which I dive... I prefer to keep a spotless record.

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• Started as a free diver .Moved on to scuba and advanced at Penn State Uni. 1998.
• Took up Nitrox while I got evacuated from the War in Beirut Summer of 2005.
• Began training in tech, advanced Nitrox and Trimix/HELIOX summer 2007...
• Starting Rebreathing on an Optima....Ouroboros...whenever I find someone to buy my other kidney.

AD_ward9

The metabolic rates are unrealistically low.

Gene Hobbs very kindly mounted onto the Rubicon site yesterday the study by NEDU on O2 metabolism of clearance divers doing gentle swimming: Knafelc, ME, "Oxygen consumption rate of operational underwater swimmers", NEDU Report TR 1-89 1989, now online at Rubicon Research Repository: Item 123456789/7406

The study finds that an average diver swimming at their own pace consumes 1.5 litres of O2 per minute, and resting about 0.65 litres. This is where the 1.78 litres of O2, and 1.6 litres of CO2 comes from in EN14143: it is the 99% percentile for very fit clearance divers doing gentle swimming at their own pace.

The O2 consumption rates in the plot you posted are too low: lower than that for an average fit diver. However, there is an even bigger hazard:

Sports divers tend to be a lot bigger than clearance divers. Some are 50% heavier and have a metabolism that is proportionally higher. This means that if you are planning on safe exposures, the EN14143 figure is the minimum you should be using, and should have test results for up to 4 litres per minute: that is what some people can achieve.

The stuff being published that divers can only do 1.35 litres per minute of O2 for short periods is a dangerous load of nonsense

Alex

NB: If you find this information useful, contribute to Rubicon online. They are doing a great service, but reading between the lines, hardly anyone is paying for it. If dive companies paid even a 100 Euro a year for it, they could save a fortune on research. If they do not contribute, what are they saying: they are not interested in safety, or science, or just cheapskates? If all of us on Rebreather World paid just $10 a year, they would be able to do so much more. This could be the best subscription ever for rebreather divers with an interest in safety. There is a lot of scientific testing that has been done by reputable organisations, reported well, to make our diving safer. Rubicon are almost alone in making this accessible so we can use it, rather than work on guesses, redesign the wheel or repeat experiments done already.

jiseson

the real time usage experiences of divers on the Extendairs seem to agree with the published data by micropore fyi.!

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Jonathan D Iseson

AD_ward9

The fatal accident list has a much larger number of big divers on it than one would expect.
This problem of people underestimating their metabolism is not unique to those using EACs: it applies to all scrubber duration figures. People get a benefit over published figures from using helium, warm water, and decos where they are virtually sleeping but these factors are not a sound foundation on which to plan a dive.


Alex

jiseson

i will state again-the cartridges have proven with a decent varied user base to perform as described. tk u for your global observations tho.

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Jonathan D Iseson

diverreb

Alex,
Does the C.O.D. of the 'larger people' on the list correlate directly to a CO2 hit?

Could it be that the this group may be more prone to Heart failure or some other non Rebreather C.O.D.?

It would seem that if the metabolism rates are as high as suggested that there would be a lot more incidents.

Empirically divers are getting three to four hours out of their EAC's, on a regular basis, without incident, many of them 'larger divers.'

Richie

AD_ward9

Large divers suffer all round. More on CO2 hits, more on hypoxia hits (less time to respond I guess), more on heart attacks.

The warm water factor, and that deco is the lowest RMV so the best dwell time, means that people are getting more time. However, it is not the way to plan a dive. Better to look at your metabolism, look at the capacity of the scrubber, then when you have used 2/3 *1.2 times that much O2, get out.

I emphasise this is nothing specific to EACs, it applies to all scrubbers. Indicators are people are pushing them, so when the muck hits the fan there is not a lot of slack about to accommodate things. We should think in thirds, just like trimix gas management. Get out with a third left, even though trimix costs more than EACs or granules.
Alex

AD_ward9

The real life experience fits the metabolism model we have been building. Some very interesting things here. Just start with the public information:

1. CCR Ltd publish a chart showing scrubber life, and for the Optima it is 60 mins. This is for the EN14143 test conditions, with 1.6lpm of CO2, (from 1.78lpm of O2).
   
2. Micropore and DL each separately state figures of around 2 hours 30 mins. This is for the EN14143 test conditions, with 1.6lpm of CO2. The rebreather configurations used for these tests are very different to those for the Optima.
   
3. Users report getting 4 hours on the Optima, even 5 hours.

How does this stack up? The simple answer is all the above are correct, and it is because metabolism changes over a 10:1 range during the dive. We have been doing tests steadily, this is what we are finding:

1. First, during the initial few minutes of a dive, the diving reflex has not set in, the diver is finning, may be a little bit stressed from the boat, so we find metabolisms up around 1.8lpm of O2 for an average sized man (70kg to 80kg, if you are bigger than that, scale it up proportionally). Divers then usually slowdown a bit, but if the diver is one of those who swim like clockwork at their comfortable pace, he can do this 1.8lpm for the whole dive. Doing very hard work, such as finning in a strong current, a fit big diver can achieve 4.5lpm of O2 consumption, and 3 to 3.5 lpm is pretty easy to achieve.
   
2. Sports dives more usually hang out a lot, especially on deco. This means we get an average for the whole dive of between 0.8 and 1.0 lpm of O2, for normal sized men, experienced divers. We have not done any testing on women at all.
   
3. During the deco part of the dive, metabolism is almost the same as the basal rate. This is what we found so surprising, because basal rate is measured with the person laying down, lots of rest, empty guts, etc. It seems in water, the base level of our body has to do less work than on land.

After getting results, we did more work to compare with what other people were finding, and low and behold, we discover that all this is known and well documented. There are 3 key papers on this:

1. Donald KW and Davidson WM (1954) "Oxygen update of booted and fin swimming divers", Journal of Applied Physiology V7:31-37
   
2. Morrison JB (1973) "Oxygen update studies of divers when fin swimming with maximum efforts at depths of 6-176 feet". Aerospace Medicine. V44:1120-1129.
   
3. Knafelc, ME (1989) "Oxygen consumption rate of operational underwater swimmers", NEDU Report TR 1-89, which Gene Hobbs has very kindly mounted on request on the Rubicon site at : Rubicon Research Repository: Item 123456789/7406

The latter two I obtained electronically, with the help of Gene Hobbs which I assume will be available on the Rubicon site soon: a refreshing change as the librarian in the Edinburgh Medical Library is very strict on copyright by applying a blanket rule their journals and they have no scanner. Gene has a nice electronic copy .

What the two earlier papers report is that a clearance diver (who are usually very fit and nearer 70kg than 80kg - diver training screens out fat guys), uses 1.6 lpm of O2 when fining at their own pace: some need more 1.96 lpm for example, others have things sussed out do a slower own pace at 1.3 lpm. Working hard they can get to 3.4lpm. Just waiting with minimal effort, and they achieve pretty well their basal metabolism (around 0.28lpm). This is why some dive attendants can achieve such incredibly low gas consumption: they just hang out. The NEDU 1989 study is where the European 1.78lpm of O2 figure comes from: NEDU got an average of 1.35lpm for their small group of clearance divers, and the 1.78lpm is the 99% percentile from that - this figure does not have the diver finning around all the time. At 1.78lpm of O2 being metabolised, then 1.6lpm of CO2 is generated.

At low metabolism rates, the scrubbers work much more efficiently, because the dwell time is much longer: typically 6.4 times longer! The deco is shallow, which helps, the water is warmer, which helps a bit on EACs and a lot on granular scrubbers. So scrubber efficiencies increase, a lot.

How does this affect our use of the scrubber as divers? It means yes all the duration figures I mentioned were correct. However, if you try and exercise after doing say 3 hours on an Optima, you will get breakthrough almost immediately. It means regardless of what someone else can do, the manufacturer's figures are the ones to use.

I do emphasise, this applies to all scrubbers of all types. It is not unique to EACs or Optimas: the advantages of EACS in this context are the scrubbers are consistent, and you don't have to worry about other problems such as channelling or increase in WOB as the scrubber is used, etc. With granular scrubbers one has to use wider margins.

If you use a KISS Sport, you will get roughly the same durations as I mentioned for the Optima. Use a larger scrubber such as on the Inspo or Meg, and at 1.8lpm of O2 it will last around 2 hours, if you do the average metabolism profile I describe it will last 5 to 6 hours. However, as soon as you try and exercise near the end of the dive, you will get very rapid breakthrough. The thermal mass of the scrubber is such that the scrubber stick won't help you. Try and get your metabolism right down, and you can on occasion do 9 hours on a Meg or Inspo scrubber, but as soon as you are active, you have the same fast breakthrough. The "chuck the scrubber after 3 hour" rule seems to be the safest one to follow on these two units.

Cheers,

Alex

NB: I cannot emphasise enough how valuable the work Gene Hobbs and his wife are doing with Rubicon. If each instructor got the student to go and donate just $10 to them through their site, the students would want to get value for money by learning, going to the Rubicon site and finding out more and more. It would be a lasting legacy of their training, keeping the students aware. I am not affiliated or related to Rubicon or Gene in any way, but think it is a shame that the only donations he is getting for his work are a small number of appreciative people in the USA, when what is being done at Rubicon is probably the best thing for the whole industry.

NB2: The above is a quick easy to read synopsis. Get the papers I quoted for the exact figures, and look carefully at the test conditions, size of the divers etc.

jiseson

on same line of thought-typical profile is deep firts and then deco-so large mass of gas early on then as majority of time on deco soent at shallower depts the mass of gas greatly drops....as does diver work rate hanging on the line (in theory!)

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Jonathan D Iseson