page_title: Human physiology of underwater diving
section_title: Inert gas narcosis
hierarchical_section_title: Human physiology of underwater diving / Breathing under pressure / Metabolically inert components of the breathing gas / Inert gas narcosis
caption_attribution_description: English: A gas blending system consisting of a blending panel with gas inputs from 3 bank cylinders, located and blown by an electric powered compressor in the room behind, 3 inputs, for cascading, of oxygen J cylinders (black) and 3 inputs of helium J cylinders (brown). Cropped by User:RexxS
context_page_description: Human physiology of underwater diving is the physiological influences of the underwater environment on the human diver, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes the range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus. Several factors influence the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety.
  Immersion affects fluid balance, circulation and work of breathing. Exposure to cold water can result in the harmful cold shock response, the helpful diving reflex and excessive loss of body heat. Breath-hold duration is limited by oxygen reserves, the response to raised carbon dioxide levels, and the risk of hypoxic blackout, which has a high associated risk of drowning.
context_section_description: Except for helium and possibly neon, all gases that can be breathed have a narcotic effect under pressure,although widely varying in degree.  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 about 30 meters (100 ft).
  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. Due to its perception-altering effects, the onset of narcosis may be hard to recognize. At its most benign, narcosis results in relief of anxiety – a feeling of tranquility and mastery of the environment. These effects are essentially identical to various concentrations of nitrous oxide. They also resemble (though not as closely) the effects of alcohol or cannabis and the familiar benzodiazepine drugs such as diazepam and alprazolam. Such effects are not harmful unless they cause some immediate danger to go unrecognized and unaddressed. Once stabilized, the effects generally remain the same at a given depth, only worsening if the diver ventures deeper.
  The most dangerous aspects of narcosis are the impairment of judgement, multi-tasking and coordination, and the loss of decision-making ability and focus. Other effects include vertigo and visual or auditory disturbances. The syndrome may cause exhilaration, giddiness, extreme anxiety, depression, or paranoia, depending on the individual diver and the diver's medical or personal history. When more serious, the diver may feel overconfident, disregarding normal safe diving practices. Slowed mental activity, as indicated by increased reaction time and increased errors in cognitive function, are effects which increase the risk of a diver mismanaging an incident. Narcosis reduces both the perception of cold discomfort and shivering and thereby affects the production of body heat and consequently allows a faster drop in the core temperature in cold water, with reduced awareness of the developing problem.
  The management of narcosis is simply to ascend to shallower depths; the effects then disappear within minutes. In the event of complications or other conditions being present, ascending is always the correct initial response. Should problems remain, then it is necessary to abort the dive. The decompression schedule can still be followed unless other conditions require emergency assistance.
  The most straightforward way to avoid nitrogen narcosis is for a diver to limit the depth of dives. Since narcosis becomes more severe as depth increases, a diver keeping to shallower depths can avoid serious narcosis. Most recreational diver certification agencies will only certify basic divers to depths of 18 m (60 ft), and at these depths narcosis does not present a significant risk. Further training is normally required for certification up to 30 m (100 ft) on air, and this training includes a discussion of narcosis, its effects, and management. Some diver training agencies offer specialized training to prepare recreational divers to go to depths of 40 m (130 ft), often consisting of further theory and some practice in deep dives under close supervision. Scuba organizations that train for diving beyond recreational depths, may forbid diving with gases that cause too much narcosis at depth in the average diver, and strongly encourage the use of other breathing gas mixes containing helium in place of some or all of the nitrogen
caption: Narcosis while deep diving is prevented by breathing a gas mixture containing helium. Helium is stored in brown cylinders.
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