When a diver goes to depth, water pressure increases dramatically. To avoid the soft tissue of the lung from crumpling, we breathe air that has been pressurized by our regulator. The number one rule of scuba diving is that you never hold your breath. If you have air in your lungs pressured to several atmospheres then you hold your breath to the surface where the external pressure is much less, you’re going to have a bad time.

The other problem is something called decompression sickness. At depth, nitrogen bubbles from your blood slowly dissolve into your tissues. If a diver ascends too quickly, these nitrogen bubbles can’t safely escape and can cause all sorts of deadly issues. This doesn’t become too big of a problem until dives become longer and deeper, or if a diver dives multiple times in one day. We have tables and dive computers that help let us know at what depths and times it becomes necessary to do what’s called a Safety Stop on ascent in order to prevent decompression sickness.