How to keep your scuba diving experience safe and comfortable is among the first lessons taught in any good dive school. Early in those lessons is one which covers how to handle the effects of pressure. Water pressure compresses gas much more readily than liquid. As a result, your torso and arms and legs may feel only slight squeezing, but any part of the body that contains trapped air will experience a much greater net force.
The ears are a prime example. As you enter the water, a small amount of air is invariably trapped in the ear. Water quickly fills the canal, but the ear drum – up to a point – is impenetrable. Air behind the drum surface gets squeezed, as if you were pressing on an orchestra drum. With nowhere to go, as the volume is decreased the pressure increases. That’s an instance of a physics principle called Boyle’s Law, taught in all elementary scuba diving courses. All you want to do is get in the water and you get sent back to science class! However, this is important, so hang in there.
Boyle’s Law states PV = constant (for a given temperature).
That may look scary, but it’s really very simple. Measure the pressure and volume and multiply them together. As you increase one, the other goes down, to keep the final product constant. For example, if you squeeze a balloon, you’re decreasing the volume. The pressure inside goes up. That’s why if you let go it returns to normal. Halve the volume and the pressure doubles. In a same way, as the volume of air behind the ear drum is lowered, the pressure inside goes up. At a certain point, that can cause discomfort and ultimately serious ear damage.
Taking care of the problem is quite easy. Descend into the water. As you feel the pressure on your inner ear, pinch or hold your nose and swallow or blow gently against your closed nose. Swallowing moves air from the ear canal into other cavities where the volume is much greater and the small change isn’t noticed. Most of your body’s air system is connected in one way or another which enables for this effect to work. Repeat as needed as you descend. The water pressure will increase by 1 atm (one atmosphere) for every 33 feet (10 m) you descend, and any air still trapped will continue to be squeezed. Once the pressure inside equals that outside, you’ll no longer feel the discomfort.
Several factors can affect the severity of the pressure. Colds and other sinus problems can hinder the ability to move air around the system. It’s best to avoid diving under those conditions. Allergies, too, obviously play hell with your sinuses. But, beware of diving after taking any allergy medicine that can make you drowsy. Safe diving requires acute mental focus.
Don’t wait until your ears feel an uncomfortable amount of pressure before equalizing. Make it a habit to perform the technique as you descend and ascend, whether you feel the need to or not.
There are other areas that trap air as well. Your face mask for example. As you descend, your face mask is subject to the same pressure. The glass plate is rigid, so it resists well. But, the pressure on the skirt (the ‘rubber part’) of your face mask will experience additional pressure and compress the air in front of your eyes slightly. A good mask will counteract that, but you can help it along by slight exhalations through the nose when needed. Do so slowly, to avoid fogging the mask, though.
Equalizing the pressure in other cavities that trap air, such as the lungs, is taken care of automatically by the regulator.
Equalizing air pressure as you dive will help you stay safe and allow you to enjoy your dive to the fullest.