50% O2 and and O2 for deco...........WHY? also labelling tanks........WHY?

[TTPaws]

AJ does not equal Trey.

I also don't find it that hard to hold a stop within a foot or so. I think a tech diver SHOULD be able to hold a stop within a foot or so with ease.

The problem with this is you are assuming that your gauge or computer is accurate.That may not be the case: see "Not All are Created Equal: Operational Variability in 49 Models of Diving Computer Azzopardi Elaine*, Martin D.J. Sayer"

I was surprised how far off the different computers were, and if you're throwing the dice with your life on the accuracy of gauges, I think I'll probably take the extra margin of 80%.

 

[GrimSleeper]

Studies have shown the off gas gradients between O2 and 80% are not that much different. On a sidenote,how many people test the oxygen? Very rarely does anybody get 100% from suppliers,and I have seen numbers as low as 92% Which,yikes,what is the other 8%? Which inspite of the variance of oxygen %s from suppliers,this minute difference doesn't seem to cause wholesale problems.

What was the analyser calibrated against? Air? Setting it up to be accurate at 21% is no guarantee that an analyser will read correctly at high fO2. Cell performance can vary quite dramatically from low to high output. I've seen O2 come out at 104%, straight off the supply cylinder… And the divers concerned recorded that as the analysis.

If you're buying medical O2, you have to assume the supplier is in fact giving you medical O2 and it's better than 99.9% Oxygen, because you have no meaningful way of testing it to be sure.

 

[PfcAJ]

The problem with this is you are assuming that your gauge or computer is accurate.That may not be the case: see "Not All are Created Equal: Operational Variability in 49 Models of Diving Computer Azzopardi Elaine*, Martin D.J. Sayer"

I was surprised how far off the different computers were, and if you're throwing the dice with your life on the accuracy of gauges, I think I'll probably take the extra margin of 80%.

I was in the water 2 weeks ago with a Xen, Uwatec puck, a tec2g and I think a person had a suunto. They were all within a ft. Even a few ft isnt really enough to make me raise an eyebrow. None of this stuff is that perfect (biology, analyzers, depth gauges).

 

[Michael Guerrero]

my two computers from different manufacturers are within a foot all the time. And there's a reason you don't see much difference between a last stop and 20' or 10' from a deco obligation perspective.

 

[nadwidny]

Studies have shown the off gas gradients between O2 and 80% are not that much different. On a sidenote,how many people test the oxygen?

I do. For a living. Pretty much all medical grade stuff. Not a lot but some. We also test for contaminants in the O2, not just percentage.

Very rarely does anybody get 100% from suppliers,and I have seen numbers as low as 92%

Very possible with a membrane system. If it was medical or even welding grade O2, with those results I would first suspect a sampling or methods issue (ie equipment used for the analysis). Then a supply issue.

Which,yikes,what is the other 8%?

Assuming the analysis was correct, probably nitrogen. Maybe some argon. After that the most common contaminant we see in medical O2 samples is methane.

 

[NAM001]

ALTHOUGH THE STANDARDS FOR 02 vary for ech type (industrial, medical,avation) 99.9 meets all the content standards. Ther rest of the differnences is dewpoint, and fill proceedures. When all is said and done that bulk tank fills everything. Medical has its own filling proceedures. So to get a true 92% tank is scarry. Either the bulk tank was contaminated or you filled on top of other than an o2 tank.