How does nitrogen narcosis work?
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The effects of various gases on your body is all about partial pressure.
Partial pressure is the percentage concentration of a particular gas component times the bar pressure that gas is under. So, for example, air is 21% oxygen – the partial pressure of oxygen (ppO2) at sea level (1 bar) is 0.21. At a depth of 10m (2 bar) the ppO2 is 0.42.
Different gases will have different effects at different pp levels. Oxygen, for example, starts to become toxic to your central nervous system at a ppO2 of about 1.6.
This is what nitrogen narcosis is – as the partial pressure of nitrogen (ppN) goes up, you begin experiencing different neurological and physiological effects. At lower ppN levels, these can be as mild as confusion or delayed reaction to stimuli; at higher ppN levels, this can include hallucinations, euphoria, unconsciousness, and even death.
Almost every gas will cause some degree of narcosis at a high enough pp – we just typically only discuss nitrogen and oxygen as those are 99% of what air is made of. Only people breathing _really_ eclectic gas mixes need to worry about the pp of other gases and thus potential narcosis effects.
This is **different** than nitrogen saturation, which can cause decompression sickness (aka the bends).
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