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LogoKeyPointsBox.pngThe usual principles and caveats to writing letters certifying fitness to dive apply.

Diving is an activity, undertaken recreationally, or professionally, which imposes certain physiological challenges relating to pressure per se, and to its effect on the volume and solubility of gases. With every ten metre (30 feet) increase in depth, the pressure increases by one "atmosphere" (the atmospheric pressure at sea level).

As pressure increases:

  • Gases become more soluble in water. As a consequence nitrogen can be dissolved in the blood stream. Rapid decompression leads to bubbles forming, which can cause gaseous microemboli and a clinical syndrome known as decompression illness or "the bends".
  • The volume of a gas decreases according to Boyle's law. Descending by ten metres doubles the pressure, thus halving the volume of the gases in the lungs and airways, sinuses, ear, bowel, or elsewhere in the body. Ascending has the opposite effect (hence the need to exhale when ascending after breathing compressed air at depth).


"Fit to dive" certificates

See Get a note from your doctor.

Be careful.[1]

See also

  • Flying and diving page (Flying further decreases the pressure, and can increase the odds of a diver getting the bends.)

External links


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