What is Equalising?
Descending in water exerts greater pressure on your body’s air spaces than it would outside of water (eg. When using a lift or stairs). This is because water is denser than air, a theory known as Boyle’s Law. To protect your ears when diving you must counter the pressure. The most popular means of achieving this is the Valsalva Manoeuvre, the act of exhaling against a closed airway. This process is known as equalising.
What happens to your ears if you don’t equalise?
1ft (30cm) below the surface:
Water pressure increases to 0.445 psi more than on the surface. You feel the pressure on your ears as the eardrums flex inwards.
4ft (1.2 m) below the surface:
Water pressure increases to 1.78 psi causing your eardrums to bulge into your middle ears along with the membranes between each section of your ears. As your nerve endings stretch your ears become painful.
6ft (1.8 m) below the surface:
Water pressure increases to 2.67 psi. The tissues of your ear drum tear due to over-stretching. The resulting inflammation will last for up to a week. Small blood vessels in your eardrums can expand or even break causing bruising which can last for up to 3 weeks. Equalisation is now impossible as your Eustachian tubes have become locked shut. Your ears are becoming increasingly painful.
8ft (2.4 m) below the surface:
Water pressure increases to 3.56 psi. Middle ear barotrauma can occur where blood and mucus from surrounding tissues fill the middle ear. Fluid rather than air then equalises pressure on your eardrums. A feeling of fullness in your ears replaces pain and will remain for at least a week until the fluid is reabsorbed into your body.
10ft (3 m) below the surface:
Water pressure increases to 4.45 psi. Descending quickly to this level can cause your eardrums to break. If this happens the sudden rush of cold water into your ear can cause you to experience vertigo. Inner ear barotrauma can occur if the membrane between your middle and inner ears is ruptured, sometimes resulting in permanent hearing damage.
Otovent as a visual aid to equalising
How To Use Otovent
Pior to your dive connect the balloon to the nose piece. Hold the round part of the nose piece firmly against the right nostril with the right hand. Press the left nostril closed with the left hand.
Inhale deeply, close the mouth and inflate the balloon until it is the size of a grapefruit by blowing through the nostril. This will allow you to experience the sensation of equalisation so that you can recognise it during your dive.
Repeat the procedure with the left nostril. You will know that you have equalized successfully if you experience a pressure change and/or a “click” in the ear.