Scuba Source

Pressure Basics in Scuba Diving

Air pressure and water pressure play a very important role in scuba diving. Most of your body is made up of liquid, but there are a few airspaces in your body, including your ears, sinuses, and lungs, that will be sensitive to changes in pressure. When the pressure outside is greater than the pressure in these airspaces, the air inside shrinks. When the pressure outside is less than the pressure in these airspaces, the air inside expands. Anyone who has been on an airplane will be familiar with these feelings.

Pressure becomes even more important underwater because water is much denser and heavier than air, so small changes in pressure underwater can have a big effect on the pressure within the airspaces in your body. When you descend 10m/33ft underwater, the air in your airspaces will have twice the density and half the volume. Think of a full-size balloon at the surface. At 10m/33ft underwater, the balloon will be half its original size and the air inside it will be twice as dense.

The opposite is true when ascending. If you are underwater at a depth of 10m/33ft and you rise to the surface, the air in your airspaces will expand to twice its size as the density is halved. Think of a full-size balloon at this depth. If you took the balloon to the surface, the air would expand to the point where the balloon bursts before you even get to the surface.

Likewise, your lungs always have a certain volume of air in them. If you are 10m/33ft underwater and you ascend to the surface, the air in your lungs will double in size if you do not exhale and let some of the air out on the way up. If you do not exhale on the way up, you could cause your lungs to overexpand, which is a very serious health program. Because of this, you should never hold your breath if you are ascending even a few feet. If your mouthpiece is out, you should exhale a small stream of bubbles constantly, even if you are not ascending. When you are ascending and you have your mouthpiece in, you should be fine as long as you breath in and out smoothly and continuously.

NOTE: The information on this page is for educational purposes only. You should receive proper training, such as a certification program, before attempting to dive.