Nitrogen narcosis, also known as inert gas narcosis, raptures of the deep, or the Martini effect, is a reversible alteration in consciousness, it mostly occurs when deep diving. It is caused by the anaesthetic effect of certain gases at high pressure. It can also occur during shallow dives but does not usually become noticeable at depths less than 30m (100ft).
Except for Helium (H) and Neon (Ne) all the gases that can be breathed have a narcotic effect. As depth increases the mental impairment may become hazardous, divers can learn to cope with some of the effects, but it is impossible to become tolerant. There are no long term effects from Nitrogen Narcosis, with the effects being able to be completely reversed within a few minutes by ascending to a shallower depth, as long as divers are aware of the symptoms, and are able to ascend to manage it, a serious diving problem will rarely occur.
By using mixed gases to breathe it is possible to go deeper without fear of narcosis. There are various heliumcontaining gas mixtures such as trimix or heliox. These mixtures prevent narcosis by replacing some of the breathing gas with non-narcotic helium.
What Does Nitrogen Narcosis Mean to Divers?
A deep-shipwreck diver breathing air confronts two preliminary dangers. First at depths greater than 66 feet, his judgement and motor sills become impaired, a condition known as nitrogen narcosis. As he decends farther, the effects of narcosis become more pronounced. Beyond 100 feet, where some of the best shipwrecks lie, he can be significantly handicapped, yet he must perform feats and make decisions upon which his life may depend.” (Shadow Divers, 2004)
Narcosis results in relief of anxiety a feeling of tranquillity even in a possibly hazardous or life threatening environment. The effects resemble that of the effect of alcohol or marijuana. Such effects are not harmful unless they put the diver in immediate danger such as in an overhead environment.
Effects generally stay the same at a given depth and only worsen when the diver ventures deeper. The most dangerous aspects of narcosis are the impairment of judgement, multitasking and coordination and the loss of decision making and focus. Other effects include vertigo and visual or auditory disturbances.
Many experience “jungle drums” the deafening sound of one’s pulse in one’s own ear; or they may simply hear a hum, like a buzzing alarm clock lost under a pillow”
The relation of depth to narcosis is informally known as ‘Martini’s law’ the idea that narcosis results in the feeling of having one Martini consumed for every 10m descended.
At 1-2 bar or 0-10m the effects of nitrogen narcosis result in unnoticeable minor symptoms or none at all.
2-4 bar or 10-30 m results in mild impairment of performance in unpractised tasks. Mild euphoria possible and mild impaired reasoning.
4-6 bar 30-50m causes a delayed response to visual and auditory stimuli. Reasoning and immediate memory affected. Calculation errors. Over confidence, sense of well-being and laughter.
6-8 bar or 50-70m results in sleepiness, confusion, hallucinations, severe delay in response to signals, instructions and other stimuli, occasional dizziness, uncontrolled laughter.
8-10 bar 70-90m leads to poor concentration and mental confusion, loss of memory and increase excitability.
10+ bar and 90+ m causes hallucinations, increase intensity of vision and hearing. Sense of impending blackout, euphoria, dizziness, levitation, manic or depressive states. Disorganisation of the sense of time, changes in facial appearances, unconsciousness. Death.
For more information on nitrogen and narcotics read here