Why You Must Equalize
If you dive without equalizing your ears, you can experience painful and damaging middle-ear barotrauma. Step-by-step, here’s what happens:
At one foot below the surface
Water pressure against the outside of your eardrums is 0.445 psi more than on the surface air pressure on the inside. They flex inward and you feel pressure in your ears.
At four feet
The pressure difference increases to 1.78 psi. Your eardrums bulge into your middle ears. So do the “round windows” and “oval windows” between your middle and inner ears. Mucus begins to fill your Eustachian tubes, making it difficult to equalize your ears if you try. Nerve endings in your eardrum are stretched. You begin to feel pain.
At six feet
2.67 psi difference. Your eardrum stretches further. Its tissues begin to tear, causing inflammation that will last up to a week. Small blood vessels in your eardrums may expand or break, causing bruising which will last up to three weeks. Your Eustachian tubes are now locked shut by pressure, making equalization impossible. Pain increases.
At eight feet
3.56 psi difference. If you are lucky, blood and mucus is sucked from surrounding tissues and begins to fill your middle ear. This is called middle-ear barotrauma. Fluid, not air, now equalizes pressure on your eardrums. Pain subsides, replaced by a feeling of fullness in your ears which will remain for a week or more until the fluid is reabsorbed by your body.
At 10 feet
4.45 psi difference. If you aren’t so lucky—if your descent is very fast, for example—your eardrums may break. Water will flood your middle ear. The sudden sensation of cold against your balance mechanism, your vestibular canals, may cause vertigo, especially if only one eardrum breaks. Suddenly, the world is spinning around you, though the sensation will probably stop when your body warms up the water in your middle ear. Or, if you try to equalize by blowing hard and long against pinched nostrils, you may rupture the “round window” membrane between your middle and inner ears. This is called inner-ear barotrauma. Perilymph fluid drains from the cochlea into the middle ear. Temporary, even permanent, hearing loss may result.