Controlled Emergency Swimming Ascent
Encyclopedia
Controlled Emergency Swimming Ascent (CESA) (aka "blow and go") is a technique used by scuba
divers as a safety measure when a diver has run out of breathing gas
in shallow water and must return to the surface.
The technique involves simply ascending at a controlled pace, while exhaling slowly or vocalizing a continuous sound. As the diver ascends, the pressure in the lungs increases relative to surrounding water pressure. Exhaling serves to equalize this difference. Hence, the diver can continue exhaling throughout the ascent, and still have air in their lungs at the surface. For the same reason, if the diver fails to exhale during the ascent, lung over expansion injury
is likely to occur. As the diver swims to the surface (making the ahhhhh sound) they will feel as if they are not running out of breath; this is because the compressed air they inhaled at depth is expanding as they ascend.
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
divers as a safety measure when a diver has run out of breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
in shallow water and must return to the surface.
The technique involves simply ascending at a controlled pace, while exhaling slowly or vocalizing a continuous sound. As the diver ascends, the pressure in the lungs increases relative to surrounding water pressure. Exhaling serves to equalize this difference. Hence, the diver can continue exhaling throughout the ascent, and still have air in their lungs at the surface. For the same reason, if the diver fails to exhale during the ascent, lung over expansion injury
Barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...
is likely to occur. As the diver swims to the surface (making the ahhhhh sound) they will feel as if they are not running out of breath; this is because the compressed air they inhaled at depth is expanding as they ascend.