Controlled emergency swimming ascent

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.^[1]

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.

References

1. ^ Samson RL, Miller JW (eds.) (1979). "Emergency Ascent Training.". 15th Undersea and Hyperbaric Medical Society Workshop. UHMS Publication Number 32WS(EAT)10-31-79. http://archive.rubicon-foundation.org/4260. Retrieved 2008-08-07. 

Additional reading

• Walker, D (1978). "Emergency Ascents: some background information.". South Pacific Underwater Medicine Society Journal 8 (2). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6175. Retrieved 2008-08-07. 
• Knight, J (1978). "Free Ascent Training.". South Pacific Underwater Medicine Society Journal 8 (2). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6180. Retrieved 2008-08-07. 
• Egstrom, GH (1978). "Ascents.". South Pacific Underwater Medicine Society Journal 8 (2). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6181. Retrieved 2008-08-07. 
• Curtis, ASG (1978). "Free Ascents: A view from the Scottish Sub-Aqua Club.". South Pacific Underwater Medicine Society Journal 8 (2). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6179. Retrieved 2008-08-07. 
• Graver, DK (1978). "In support of emergency ascent training.". South Pacific Underwater Medicine Society Journal 8 (3). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6186. Retrieved 2008-08-07. 

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