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Hazards of Diving Deep Glossary ambient pressure: at sea level, the ambient (surrounding) pressure is 14.7 pounds per square inch, which is equal to one atmosphere of pressure; as one dives, the ambient pressure increases by one atmosphere with every 33 feet of descent; thus, ambient pressure at 33 feet is 29.4 pounds per square inch anoxia: a form of hypoxia (a deficiency of oxygen reaching body tissues) so severe that it can result in permanent damage, even death arterial gas embolism: potentially life-threatening condition that arises when gas bubbles forced out of the lungs during rapid ascent from depth become trapped in and block arteries the bends: see decompression sickness barotrauma: painful and potentially dangerous compression or decompression of gas-filled spaces during descent or ascent closed-circuit rebreather: diving apparatus that recirculates breathed air, removing its carbon dioxide and replenishing it with oxygen (compare open-circuit) decompression sickness: sometimes fatal disorder characterized by joint pain and paralysis, breathing difficulty, and collapse that is caused by the release of gas bubbles, usually nitrogen, from the tissues following a too-rapid ascent from depth decompression stops: pauses during an ascent to allow the release of dissolved nitrogen in the tissues without bubble formation; depth and duration of stops are determined by depth and length of dive and by type of breathing apparatus hypercapnia: excessive amounts of carbon dioxide in the blood, which can cause respiratory distress and unconsciousness hypothermia: subnormal body temperature, usually defined as under 95°F; severe hypothermia (below about 82.4°F) can cause shock and death lung burst: see arterial gas embolism mixed gas: the use in diving of any mixture of gases other than air; includes nitrogen-oxygen blends other than air (Nitrox) as well as combinations of oxygen with other inert gases nitrogen narcosis: dangerous intoxicating effect of nitrogen breathed at depth; symptoms include euphoria, impaired judgment, and a false sense of security open-circuit: refers to standard scuba (Self-Contained Underwater Breathing Apparatus) equipment, in which breathed air is released rather than recirculated (compare closed-circuit rebreather) oxygen toxicity: oxygen breathed at partial pressures higher than about 1.6 atmospheres (see ambient pressure)—which occurs at a depth of 218 feet for a diver breathing air—quickly becomes toxic and can lead to sudden convulsions and unconsciousness partial pressure: the part of the total pressure of gases in a mixture contributed by a particular gas; since air is composed of about 21 percent oxygen, at sea level (one atmosphere of pressure), the partial pressure of oxygen is 0.21, while at a depth of 33 feet (two atmospheres), the partial pressure of oxygen is 0.42. Tour U-869 | Sole Survivor | Hazards of Diving Deep 400 Years of Subs | Map of Lost U-Boats | Fire a Torpedo Resources | Transcript | Site Map | Hitler's Lost Sub Home Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated November 2000 |