People who engage in deep-sea or scuba diving are at risk of a number of injuries, most of which are caused by 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.
Underwater pressure
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 (10 meters) is 1 atmosphere (14.7 pounds per square inch [1.03 kilograms per square centimeter]), 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.
Pressure-related diving disorders can result from
Expansion or compression of gas-filled spaces in the body ( barotrauma Barotrauma Barotrauma is tissue injury caused by a change in pressure, which compresses or expands gas contained in various body structures. The lungs, gastrointestinal tract, part of the face covered... read more )
Release of dissolved nitrogen in the blood and tissues ( decompression sickness Decompression Sickness Decompression sickness is a disorder in which nitrogen dissolved in the blood and tissues by high pressure forms bubbles as pressure decreases. Symptoms can include fatigue and pain in muscles... read more )
Either process can cause bubbles in arteries to block blood flow to organs ( arterial gas embolism Arterial Gas Embolism Arterial gas embolism is blockage of blood supply to organs caused by bubbles in an artery. It is a leading cause of death among underwater divers, such as scuba divers, who breathe compressed... read more ). Gases such as oxygen and nitrogen can also cause disorders ( oxygen toxicity Oxygen toxicity Problems during diving can result from toxic effects of gases such as nitrogen, oxygen, carbon dioxide, and carbon monoxide. (See also Overview of Diving Injuries.) Air is a mixture of gases... read more and nitrogen narcosis Nitrogen narcosis Problems during diving can result from toxic effects of gases such as nitrogen, oxygen, carbon dioxide, and carbon monoxide. (See also Overview of Diving Injuries.) Air is a mixture of gases... read more ) when breathed at high pressures, such as when people dive to very deep depths.
Other diving-related disorders
Diving in cold water can rapidly lead to a dangerously low body temperature ( hypothermia Hypothermia Hypothermia is a dangerously low body temperature. Hypothermia is often regarded as a cold injury, because it can be caused or made worse by exposure to cold surroundings. Being in an environment... read more ), which causes clumsiness and poor judgment. Cold water can also rarely trigger fatal heartbeat irregularities Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more 
in people with coronary artery disease Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more 
. Other potential diving hazards include
Drowning
Bites and stings from various marine life
Sunburn and heat disorders
Cuts and bruises
Motion sickness
Immersion pulmonary edema
Drugs (prescribed, recreational, and some over-the-counter) and alcohol may have unanticipated, dangerous effects at depth, as can various medical conditions (see Medical Conditions That May Preclude Diving Medical Conditions That May Preclude Diving 
).
Impaired thinking or drowsiness
Unconsciousness, weakness
Panic
Loss of balance and disorientation
The Divers Alert Network (24-hour emergency hotline, 919-684-9111) is an important resource that addresses the needs of recreational scuba divers around the world in two important ways:
It helps doctors provide emergency medical assistance to divers in need.
It promotes dive safety through research initiatives, educational services, and diving-related products.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
Divers Alert Network: 24-hour emergency hotline, 919-684-9111
Duke Dive Medicine: 24-hour emergency consultation with a doctor, 919-684-8111
