CESA (Controlled Emergency Swimming Ascent)

A self-rescue technique for an out-of-air emergency in shallow water: swim to the surface at a safe rate exhaling continuously, regulator kept in the mouth.

A CESA, controlled emergency swimming ascent, is the self-rescue option when you run out of air in relatively shallow water and no buddy is close enough to share gas. You look up, keep the regulator in your mouth, swim toward the surface at a normal, safe ascent rate, and exhale a continuous stream of bubbles the entire way, classically while making a steady aaah sound. The continuous exhalation is the life-critical part: the air in your lungs expands as pressure drops, and venting it prevents a lung overexpansion injury.

The word controlled is doing real work. This is not a bolt for the surface but a swim at roughly the standard ascent limit, no faster than 18 m per minute, with the BCD deflator in hand to dump expanding air. The regulator stays in because as ambient pressure falls, a tank that felt empty at depth will often yield another breath or two on the way up. On reaching the surface, you establish buoyancy orally or by dropping weights, then signal the boat.

CESA sits in a hierarchy taught in every open water course: a normal ascent breathing your own gas beats everything, a buddy's alternate air source comes next, CESA is for shallow depths within a comfortable swim, and a buoyant emergency ascent is the last resort. It is trained horizontally in the pool and vertically from around 6 to 9 m in open water. The best CESA, of course, is the one your gas planning made unnecessary.