Controlled Emergency Swimming Ascent (CESA) — What It Is and Why It Matters
A controlled emergency swimming ascent (CESA) is an emergency procedure used when a diver runs out of air and cannot obtain air from a buddy. The diver ascends to the surface under their own power while continuously exhaling — producing a continuous stream of bubbles — to prevent lung overexpansion. The ascent must be slow and controlled, not panicked.
CESA is taught as a last-resort skill in Open Water courses, typically practiced from 9 meters (30 feet) or shallower. The key elements are: look up, exhale continuously (say "ahhhh" into the regulator), swim at a normal ascent rate, and do not hold your breath at any point. Having a buddy with an alternate air source available prevents the need for a CESA.
Frequently Asked Questions
How deep can I do a CESA from?
Training typically limits CESA practice to 9 meters (30 feet). In a real emergency, it is physically possible from deeper, but the risk increases significantly. Beyond about 18 to 20 meters, the ascent time is long enough that running out of exhaled air becomes a concern. Buddy air sharing or an alternate air source is strongly preferred over CESA from any depth.
Why do I need to exhale during a CESA?
As you ascend, the air in your lungs expands per Boyle's law. If you hold your breath, the expanding air can rupture lung tissue, causing life-threatening pulmonary barotrauma. Continuous exhalation allows the expanding gas to escape safely. Even a slow, steady exhalation produces surprisingly long-lasting airflow as the gas expands.
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