How to Understand Underwater Pressure in Scuba Diving

Almost all diving techniques and knowledge center around the principle of pressure. Here are a few basic concepts you should master.

Instructions

Difficulty: Challenging

Things You’ll Need:

• Scuba Gear

1. Know that air pressure decreases with altitude and water pressure increases with depth.
2. Understand that, because water is denser than air, pressure increases more rapidly as you descend.
3. Know that the human body is mostly water, and that in recreational diving, water pressure will be felt in the air spaces of the body (lungs, sinuses and ear canals).
4. Understand the meaning of 'atmosphere of pressure.' The air pressure at sea level is defined as one atmosphere of pressure (1 ATM).
5. Know that pressure increases at the rate of 1 ATM every 33 feet of water depth. A diver at 33 feet of depth is at 2 ATM, 3 ATM at 66 feet, and so on.
6. Understand that air volume in a flexible space (such as your lungs and sinuses) is reduced proportionate to pressure. At 2 ATM the volume is halved, at 3 ATM it is a third of surface volume, and so on.
7. Know that air density (such as in your lungs and scuba tank) is proportionate to pressure. At 2 ATM the density is doubled, at 3 ATM it is tripled.
8. Realize that air within an air space will expand proportionally as pressure is reduced. For example, moving from 2 ATM to 1 ATM (33 feet underwater to the surface), air in a closed container will double. Keep this in mind when surfacing.

Tips & Warnings

• Understanding these concepts shows how important it is to ascend slowly while scuba diving. It's extremely dangerous for air to expand too rapidly inside your lungs.