Even during a Controlled Emergency Swimming Ascent (C.E.S.A.) a diver should attempt to swim up at a safe ascent rate. That is why the skill is called the Controlled Emergency Swimming Ascent. It would be unfortunate to safely reach the surface only to have suffered a nasty hit of decompression sickness from ascending too quickly. A diver maintains a safe ascent rate by venting expanding air from his buoyancy compensator (BCD) as he swims towards the surface. He lifts his deflator above his head so that he is ready to release small amounts of air from the BCD if he finds that he is ascending too quickly. (If you do not understand why you should release air from the BCD as you ascend, read more about buoyancy basics.)
Because you are practicing the C.E.S.A. horizontally, pretend that whatever object or wall that you set as your goal is the water's surface. Extend your BCD deflator towards the “surface” just as you would if you were using the skill in the open water. The only difference is that you will be extending the deflator horizontally in front of you instead of up, because you have turned the skill on its side. This allows you to maintain the same body position as you would if you were ascending vertically in the open water.
