Evolution Scrubber Duration

abowie

Basic chemistry.

Fundamentally the respiratory exchange ratio is approximately 0.8, so if you use a litre of O2 you'll produce about 800ml of CO2.

This is an approximation because it fails to take anaerobic metabolism into account.

As to Graham's question.

The reason they quote on those numbers is because they think it's a reasonable safety margin.

There's nothing to stop you doing a 3 hour dive on your unit if you want, being cognisant of the risks and having some understanding of how the numbers are generated; that decision is entirely up to you. Using a condom wrapper for calculations is to me quite appropriate, because of course you're f***** if you get it wrong.

Can I suggest you have a bit of a search of the Rebreather world forums for some of the independant testing done on the Evo Temp Stick. They make interesting reading.

Happy dives

__________________
Andrew Bowie

Rebreather-friendly Buddy

caveseeker7

The protocol used for testing on the APD units (and others) is the one set forth in EN14143, required to get CE certification for a rebreather. Hence the high CO2 addition rate and low temperature.

One thing to consider is the influence of ambient pressure on the duration (more than temperature), the APD 3 hr/2 hr ratings are at 20 meters. At 50 meters that time will be reduced if the other parameters stay the same.

Take the Ouroborous for example: Same RMV/CO addition and temperature:
210 mins at 15 meters, 150 mins at 40 meters, 90 mins at 100 meters.

The APD units are 82 mins (I) and 55 mins (E) at 100 meters.

The absorbant manufacturers rating doesn't equal the actual duration because the numbers just give the total absorbtion capacity under ideal lab conditions. Different scrubber designs have different efficiencies and in the real world conditions are not ideal. The only importance in my opinion is that if a Rebreather manufacturer claims their scrubber absorbs more CO2 than the absorbant manufacturer does there is something fishy going on. And that's clearly not the case with APD.

APD actually gives pretty decent infrmation in regards to scrubber use, telling users two depth/durations as well as guidelines for deep/repetitive dives.

But I agree, there should be some more data available for say 40 meters (usual air dil limit) and 75 meters (seems to be the most frequent trimix depth). Especially considering that APD does have an ANSTI machine that has to pay off, rather than having someone to pay to perform the testing for them.

Hopefully once they have caught up with demand and sorted the software bugs will have and take the time to give some more data to their customers.

Dräger has done so in the past, and my hope is that other manufacturers will follow suit. We as divers should demand that from them.

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Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

grahamsp

Couldn't agree more. As long as there are CCR divers out there pushing their scrubbers past the limits set by the manufacturers (I feel a poll coming on!), then the CCR community should demand better data. Ideally, this should be in the form of a CCR-specific model in which you set all the parameters for the dive you are planning (including prior usage); in response the model would return the maximum duration allowable for the scrubber. Think V-Planner for scrubbers.

Graham

grahamsp

Have done and in particular the long running CO2 Detector Vs. Temp Stick thread - http://www.rebreatherworld.com/gener...stik#post6373). What a good thread should be - a vigorous debate based on data.

Graham

caveseeker7

Graham, I'm curious what was taught in your Evo class in Oz.
There is an intresting thread on Scubaboard about the Evo class taught by SDS and Jeff Bozanic. Taking place in warm Mexican waters, the Evos were used to four and more hours on a fill. APD endorses that practice on units equiped with the TempStick.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

grahamsp

Do it by the book, so 2 hours. As for APD, I thought they were consistent in saying not to go over 2 hours under any circumstances (and less for deep dives), hence my post in the first place. I've certainly never seen anything to the contrary. Can you remember where you saw the endorsement?

Graham.

caveseeker7

Yes, in an e-mail to me from Martin Parker.

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Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

Crazyduck

HEHEHEHEHE
You need to put on your flame suit Dude!
Can't say more.....

I am going to pour myself a Single Malt Scotch.
Four hour Kitty Litter on a scrubber that won't go together right! HA!

__________________
Howdy Senor- What’s Happening!
Rob Davie April 2005-

Presently in a state of transition from Open Circuit to Closed Circuit.

"You will not be punished for your anger; you will be punished by it." - Buddha.

Karlos

Graham - the way you packed your last scrubber you were lucky to get one hour out that fill without getting a CO2 hit.

Yep - I heard Martin Parker talking about the 4 hour limit as well. Personally I think -- that is the limit.

Steve Lonegan took his Inspiration to 7 hours on the South China Sea trip. I get edgy at 6 hours in Sydney. Dave Ash is a whole different kettle - I think he produces O2 instead of CO2 - I had 6.5hrs on my unit and he took it for another 1 hour out the front in shallow water...

Cheers,
Karl

or you could do a Dave H and repack and get hit.....

decoweenie

For what its worth...

Have done about 30 hours of 5-hour/pack in UAE warm water (22-25C) with TempStick. Mostly shallow training dives, but also interspersed with about 7 hours of 70m dives.

Only 1 time did the red HUD came on to indicate last heat-segment of the scrubber. The rest of the time, there were at least 2 segments left at 5-hour mark.

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"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM