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Dear tech divers,

Dennis pointed out the following 
> tim, i think you are on-it in your theory above; there is a cave that we
> visit on oahu that is about the size of a small school bus, after making
> your way thru a "tube" for about 125feet you end up in the room that
> is back at the surface (the opening is at 55fsw against a crater wall).
> five divers can easily stand in waist deep water and remove their masks.
> when the surge comes in the cave fills with a thick fog for about five
> seconds, then it's gone, i expect due to those pressure changes...
> 

	The surge is easy to explain- same effect as a compressor or a
cloud chamber.  When the surge comes in, the (water saturated) air is
compressed, the excess water comes out as fog.  That's why compressors
have drains on them and our compressed air is so dry when we breath it
at lower pressures.

	On a possibly related fogging topic.  We have noticed that
after diving here (52F), we often see fog from our breathing at the
surface on cold, damp days.  I had thought that the effect was due to
the N2 offgassing into small alveoli, where the air is saturated in
water, thereby flushing water saturated or water super-saturated air
out into the open.  In support of this idea, several quick, deep
inhalations will cause the misting to stop for a minute or two.  Mask
fogging as described by Rich and others would also then only be seen
on ascent, as the N2 offgasses.  I would guess that most warm water
divers would not see this effect at the surface as it is too warm, but
most divers would see it towards the end of longer cold water dives,
if they exhale into their masks.

	Safe diving,

		Peter David
		david@la*.st*.ed*

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