More than 1000 diving-related injuries occur annually in the US; > 10% are fatal. Similar injuries can befall workers in tunnels or caissons (watertight retaining structures used for construction), in which pressurized air is used to exclude water from work sites.
Many injuries are related to high pressure, which, at depth or in a caisson, results from the water weight above plus the atmospheric pressure at the surface. At a depth of 10 m (33 ft), seawater exerts a pressure equivalent to standard sea level atmospheric pressure, which is 1.03 kg/sq cm (14.7 lb/sq in), 760 mm Hg, or 1 atmosphere absolute (atm abs); thus, the total pressure at that depth is 2 atm abs. Every additional 10 m of descent adds 1 atm.
The volume of gases in body compartments is inversely related to external pressure; an increase or a decrease in gas volume due to pressure change exerts direct physical forces that can disrupt various body tissues (barotrauma). The amount of gas dissolved in the bloodstream increases as ambient pressure increases. Increased gas content can cause injury directly (eg, nitrogen narcosis, oxygen toxicity) or indirectly during ascent when decompression of the supersaturated blood or tissues releases nitrogen bubbles (decompression sickness). Arterial gas embolism can result from barotrauma or decompression.
Some medical disorders, if they cause symptoms at depth, may be disabling or disorienting and thus lead to drowning (see table Specific Medical Contraindications to Diving).
Physicians caring for patients with diving or compressed air injuries may contact the Divers Alert Network: 919-684-9111 for emergencies and 919-684-2948 for other information (www.diversalertnetwork.org). Physician-to-physician consultation can be obtained through Duke Dive Medicine: 919-684-8111.