Introduction

People who engage in deep-sea or scuba diving are at risk of a number of injuries. Diving in cold water can rapidly lead to hypothermia (dangerously low body temperature), which causes clumsiness and poor judgment. Cold water can also trigger fatal heartbeat irregularities in people with coronary heart disease. Other potential diving hazards include drowning; bites and stings from various marine life; sunburn and heat disorders; cuts and bruises; and motion sickness. Drugs (both legal and illegal) and alcohol may have unanticipated, dangerous effects at depth.

Most diving-related disorders, however, are associated with changes in pressure. These disorders also can affect people who work in underwater tunnels or caissons (watertight enclosures used for construction work). Such structures contain air under high pressure to keep out water.

High pressure under water is caused by the weight of the water above, just as barometric (atmospheric) pressure on land is caused by the weight of the air above. In diving, underwater pressure is often expressed in units of depth (feet or meters) or atmospheres absolute. Pressure in atmospheres absolute includes the weight of the water, which at about 33 feet is 1 atmosphere (14.7 pounds per square inch), plus the atmospheric pressure at the surface, which is 1 atmosphere. So a diver at a depth of 33 feet is exposed to a total pressure of 2 atmospheres absolute, or twice the atmospheric pressure at the surface. With each additional 33 feet of depth, the pressure increases by 1 atmosphere.

Diving disorders can be divided into two categories: Those that result from expansion or compression of gas-filled spaces in the body (barotrauma) and those that result from dissolved nitrogen in the blood and tissues (decompression sickness).