Nitrogen narcosis
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| Divers breathe a mixture of oxygen, helium and nitrogen for deep dives to avoid the effects of narcosis. A cylinder label shows the maximum operating depth and mixture (oxygen/helium). | |
| Classification and external resources | |
| DiseasesDB | 30088 |
| MeSH | C21.613.455.571 |
| Some components of breathing gases and their relative narcotic potencies: | |
| Gas | Relative narcotic potency |
|---|---|
| He | 0.045 |
| Ne | 0.3 |
| H2 | 0.6 |
| N2 | 1.0 |
| O2 | 1.7 |
| Ar | 2.3 |
| Kr | 7.1 |
| CO2 | 20.0 |
| Xe | 25.6 |
Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect), is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gases at high pressure. The Greek word ναρκωσις (narcosis) is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates. Narcosis produces a state similar to drunkenness (alcohol intoxication), or nitrous oxide inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than 30 meters (100 ft).
Except for helium and probably neon, all gases that can be breathed have a narcotic effect, although widely varying in degree. The effect is consistently greater for gases with a higher lipid solubility, and there is good evidence that the two properties are mechanistically related. As depth increases, the mental impairment may become hazardous. Divers can learn to cope with some of the effects of narcosis, but it is impossible to develop a tolerance. Narcosis affects all divers, although susceptibility varies widely from dive to dive, and between individuals.
Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. Thus narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving beyond 40 m (130 ft) is generally considered outside the scope of recreational diving. Below these depths, as narcosis and oxygen toxicity become critical risk factors, specialist training is required in the use of various helium-containing gas mixtures such as trimix or heliox. These mixtures prevent narcosis by replacing some of the breathing gas with non-narcotic helium.
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