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Hi all,

Dennis Pierce & I were talking earlier today, and we discovered that we
had both independantly encountered an unusual phenomenon which neither of
us can really explain.  We thought we'd throw it out to the forum to see
if anyone has any ideas:

On mixed-gas dives, sometimes immediately after we switch gas mixtures
our masks fill up with some kind of fog-like stuff (sorry, can't think of
any better way to describe it).  I don't mean that our face-plates fog up,
I mean the gas inside the mask gets hazy (sort of bluish haze).  Each of
us originally thought that our eyes were causing an illusion of some sort
(perhaps from rapid off-gasing through the cornea or something), but on
closer inspection, we each realized that the haze was caused by some sort
of very fine mist within the mask itself.  I hadn't necessarily noticed
whether it was correlated with exhaling through my nose into my mask, but I
now suspect that it must be.

Both Dennis & I consistently have this happen immediately after switching
gas mixtures.  Dennis says it happens to him when he switches from trimix
to nitrox, and I notice it most when I switch from nitrox to my
surface-supplied oxygen. I think it has also happened on a couple of rare
occasions for me when I switch from nitrox to trimix on the descent, but
I'm not certain.

In any case, the mist only lasts for a few breaths, and then the mask
clears up.

I had always assumed that it had something to do with the gas in my 50-foot O2
hose, but Dennis' experience tend to suggest otherwise.  Some hypotheses
we've come up with include:  Water mist from a leaky hose/diaphragm (not
likely); condensation resulting from mixing gases of different
humidities/temperatures in the mask; condensation built up in the hose;
among others.

1) Has anyone else experienced this?
2) Anybody want to take a stab at explaining it?

Thanks and Aloha,

Rich (and Dennis)

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