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
- Flying and diving page (Flying further decreases the pressure, and can increase the odds of a diver getting the bends.)
- Professional Association of Diving Instructors (PADI) website
- British Sub Aqua Club (BSAC) web site - and the BSAC "medical matters" page (with links to forms for medical examinations etc.) is here).
- UK Sports Diving Medical Committee web site (with links to e.g. self-declaration form)
- Guy de Lisle Dear. Asthma & Diving (article at the Divers Alert Network web site)
- Database of approved medical examiners of divers
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