According to Boyle's law, flexible gas spaces will compress
as pressure is applied to them externally. Put a face mask on and go down
in the water. The pressure of the water will try to make the face mask smaller.
Because it is rather rigid other things will happen first. The pressure inside
the body is also greater than the pressure inside the mask. So, the face
is "pushed" into the mask. Possible results: The eyes bulge, the nose bleeds,
blood vessels break under the skin and in the whites of the eyes, the vision
narrows, and there may be swelling. Depending on the difference in the pressure
results in the variety of results. The diver may not notice the squeeze or
damage because there is not that much pain connected with it. To avoid it
simply gently exhale through the nose as you descend. This will keep the
pressure differential to a minimum so no facial damage can occur. As the
divers comes up the expanding air in the mask will simply bubble out without
notice. When it happens some divers have left the water looking like they
were involved in a serious domestic encounter. Usually the appearance of
a face mask squeeze barotrauma is worse than it really is. It usually does
not require treatment and will go away in about a week.
If you were to wear goggles in scuba diving serious
barotrauma to the eyes may result. There is no provision for adding air to
the inside of the goggles as descent is made because the nose is not in it.
Dry suits contain air. That air will compress as the
diver descends. The suit will feel like a total body blood pressure cuff
as the outside pressure increases. The skin may be pushed into the natural
folds in the suit. Blood vessels may burst in the skin causing lines of blood
blisters and bruises. As with any other air space that is connected to the
body, air must be added to the dry suit when going down to prevent the squeeze.
And, most importantly, the air must be removed as the diver ascends to avoid
an out-of-control ascent because of the expanding air in the suit.
Dry suits require an extra measure of training that
is way beyond the training needed for a wet suit!