Mailing List Archive

Mailing List: techdiver

Message Display

> When I first heard of blending nitrox using the partial pressure
> method, I was told that this leads to stratification in the tank. My
> experience in chemistry tells me that this is impossible,

Well, I was a Doubter, too, until I actually *saw* it happen. The
particular incident occurred with a tank that I mixed *myself* (I am
an IANTD Nitrox Instructor and Gas Blender). The tank was a Genesis
80, which started out with a couple hundred PSI of a standard mix (32
or 36, can't remember which).

At any rate, I did the math and added however much pure O2 I needed
for the mix I wanted, topped with air to the tank's rated pressure
(3500 PSI), and then checked the mix with a Mini-Ox. To my surprise,
the FO2 read significantly lower than I expected, so I checked the
FO2 with another analyzer - same result. I then re-did the math, but
all the numbers checked out.

The owner of the dive shop happened to be standing there while I was
doing all this, and suggested that the mix might have stratified, and
said I should roll the tank back and forth for a few minutes to see
if the FO2 changed. I was skeptical, but decided to try it anyway,
rather than blow a whole fill and have to start over.

Well, I rolled the tank for a few minutes, re-checked with the
Mini-Ox, and sure enough, the FO2 had gone up by a few percentage
points. After a few more minutes of rolling, the FO2 had risen to
what my "target" was, after which it leveled off (note that I did not
adjust the calibration on the Mini-Ox at any point).

I have only observed this phenomenon just the one time with that one
tank, but since I could not come up with any other explanation for
what I observed, then I assume it must have been the result of
stratification.

So now I am a Believer. Any Doubters out there care to shoot holes in
what I saw?

-JimG

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]