Nitrogen narcosis

Nitrogen narcosis, also called "rapture of the deep," is a condition that occurs in divers breathing compressed air from a tank. The condition becomes noticeable when divers go below about 100 ft. At that point, they experience analtered mental state similar to alcohol intoxication. Nitrogen narcosis has also been called "the martini effect" because for every 50 ft of depth beyondthe initial 100 ft, the effect is something like drinking one martini on an empty stomach. At 300 ft, the effect becomes disabling, causing stupor, blindness, unconsciousness, and even death.

Nitrogen narcosis occurs because gases in the body behave according to Dalton's Law of partial pressures. The law states that the total pressure of a gasmixture is equal to the sum of the partial pressures of gases in the mixture.Partial pressure is the pressure exerted by any one of the gases in the mixture. The greater the concentration of a gas in the mixture, the greater its partial pressure. As a diver goes deeper into the water, total gas pressure increases. As total gas pressure increases, the partial pressure of each individual gas also increases, in proportion to its concentration in the mixture. As the partial pressure of nitrogen increases, more nitrogen becomes dissolvedin the blood. This high nitrogen concentration slows the nervous system andmimics the effects of alcohol or narcotics.

Symptoms of nitrogen narcosis include: wooziness; giddiness; euphoria (an exaggerated feeling of happiness or well-being); disorientation; loss of balance; clumsiness; slowing of reaction time; and fuzzy thinking. Cold, stress, andrapid changes in depth make the effects worse.

Except for death, the effects of nitrogen narcosis are completely reversed asthe gas pressure decreases. They are typically gone by the time the diver returns to a water depth of 60 ft. Nitrogen narcosis has no hangover or lastingeffects requiring further treatment. However, a doctor should be consulted whenever a diver has lost consciousness.

Some experienced divers seem to become accustomed to the effects of increasednitrogen. The more often they dive, the less it affects them. Nitrogen narcosis can be prevented by using helium instead of nitrogen to mix with oxygen for deep water diving. Helium is colorless, odorless, and tasteless. However,it is more expensive than nitrogen, and it drains body heat from a diver. Insome situations, the helium-oxygen mixture may produce nausea, dizziness, andtrembling, but these reactions are not as severe than nitrogen narcosis. Another way to avoid nitrogen narcosis is by limiting the depth of dives. The risk may also be minimized by following safe diving practices, including properequipment maintenance, low work effort, proper buoyancy, maintenance of visual cues, and focused thinking. In addition, no alcohol should be consumed within 24 hours of diving.

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