To make a controlled emergency swimming ascent, simply swim upward with all your equipment in place, including your regulator. Look up, reach up and come up, swimming at 18 metres/60 feet per minute or slower. Exhale the entire time by making a continuous sound through your regulator as you ascend.

By saving, you exhale air at the right rate to prevent lung over expansion injury, but you don't exhale too much either The idea is to maintain a lung volume

Since you won't be 9 metres/30 feet deep during your confined water dive, you'll simulate the controlled emergency swimming ascent first horizontaly, then diagonally from deeper to shal lower water. You'll have enough air in your lungs to swim a long way horizontally while exhaling continuously, but 9 metres/30 feet will be ample for practice. After you do this horizontally, you can be more than sure that you can do it uerticallv assisted by air expanding in your BCD and lungs. After an actual controlled emergency swimming ascent, you don't feel out of breath-you still have air in your lungs. You'll get a chance to practice CESA vertically during your open water dives and may be surprised how much easier it is than simulating it horizontally.

Perhaps the greatest value of controlled emergency swimming ascent training is knowing you can do it. When you realize you can reach the surface without difficulty, even if you suddenly lose your air supply, you can relax and enjoy diving more. But watch your SPG and stay close to your buddy so you never need to.