Deco cylinders O2 over pressurized

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flymolo

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not sure that 80% and 100% are interchangeable. one has 20% inert gas and the other has ~none
 

broncobowsher

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not sure that 80% and 100% are interchangeable. one has 20% inert gas and the other has ~none
Play with it in a dive planner. The 80% lets you get on Deco sooner. Run it on a 30' stop and not have to wait for the 20' stop. A lot will also depend on the profile you are running. If the first stop is 20' then there isn't a benifit.
 

Charles2

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Nothing unstable about O2 above 2250. Perfectly safe at 3000 and even higher. Clean and slow and key. No slapping the valve open. Crack it slowly, let the pressure build over several seconds, once equalized then open the valve fully.

Someone put a little too much fear into you about O2. And gave some incorrect advice as well. O2 is not suddenly safe if under 2250. Just about every rebreather out there has one bottle filled with 100% O2 and if there is a booster involved, filled to 3000 PSI. Maybe more.

You are wrong on most of that.

Check this out: What happens to an aluminum scuba tank in an oxygen-fed fire?
 

boulderjohn

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I've never used 100% for deco. It's MUCH easier to use 80% which is 155bar/2250psi topped off with 53bar/770psi air to bring the pressure up to 208bar/3000psi. There's no difference in your deco times; it allows you to get on it at 9m/30ft; easier to get a full-pressure fill... what's not to like.
A couple years ago there was a thread on SB in which people advocating for 80% made their case, and I found it compelling. I myself use O2 for my final deco gas, but I see nothing wrong with using 80%. I think a lot of people were overwhelmed years ago by the bullying attitude displayed in George Irvine III's Baker's Dozen for not USing 80/20 and cannot allow themselves to have any kind thoughts in that direction. If you read that article, understand that it does not address the key benefits to 80/20 and it relies heavily on Irvine's mistaken belief in the oxygen window theory that emphasized doing deco with the highest possible PPO2. The 13th item shows the overall attitude.
 

rjack321

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3000psi in a 3000psi cylinder is not over pressurized...

The fatality in Tampa IIRC was suspected to be due to particle impingement. The serious injury in NC which was the year before was a 6351 cylinder that tipped over but the cause was likely the same issue.

O2 is highly unpredictable. 3000psi is "riskier" than 2000psi which is riskier than ambient pressure no doubt. Is 3000psi o2 too risky? Pretty much nobody says that.

There is some NASA data cited long long ago by the now retired Oxyhacker that anything >50% O2 was functionally equivalent to 100% from a fire/explosion perspective. His books don't have good enough citations to derive the original paper for that. Certainly mixing 80% certainly has far more opportunities to introduce oils or contaminants than boosting O2 to 3000psi.

At the tech 40/45 level you don't need 3000psi O2 anyway. A 2000psi fill in an al40 is enough to do all the deco you are certified to actually do.
 

PfcAJ

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3000psi in a 3000psi cylinder is not over pressurized...

The fatality in Tampa IIRC was suspected to be due to particle impingement. The serious injury in NC which was the year before was a 6351 cylinder that tipped over but the cause was likely the same issue.

O2 is highly unpredictable. 3000psi is "riskier" than 2000psi which is riskier than ambient pressure no doubt. Is 3000psi o2 too risky? Pretty much nobody says that.

There is some NASA data cited long long ago by the now retired Oxyhacker that anything >50% O2 was functionally equivalent to 100% from a fire/explosion perspective. His books don't have good enough citations to derive the original paper for that. Certainly mixing 80% certainly has far more opportunities to introduce oils or contaminants than boosting O2 to 3000psi.

At the tech 40/45 level you don't need 3000psi O2 anyway. A 2000psi fill in an al40 is enough to do all the deco you are certified to actually do.
Agreed on all counts. 2000psi in an al40 is quite a bit of time, especially when you factor in gas breaks.
 
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