In training for scuba diving, they tell you that when you\'re bellow 100 ft or s

Question

In training for scuba diving, they tell you that when you're bellow 100 ft or so you have to watch out for changes in mental state that resemble drunkenness. The cause of these mental disturbances is called nitrogen narcosis, and it has something to do with the increased pressure on the nitrogen component of the gas that you're breathing out of your tank. I just read this article from the what-if section of XKCD (halfway down the page, under the header about Michael Phelps) that mentioned a very similar sounding disorder called high pressure nervous syndrome. Are nitrogen narcosis and high pressure nervous syndrome related, or are the effects of high pressure nitrogen and high pressure by itself separable?

Explanation / Answer

These are different things.

Nitrogen Narcosis or more commonly Gas Narcosis is the narcotic effect of gasses like Oxygen and Nitrogen under pressure. The effects are most prominent under 30m and commercial/technical dives doing dives to 40/50m on air tend to experience the effects most. (Narcosis is managed by adding an inert gas - in most gases Helium - to air to form a mixture referred to as Trimix (Helium/Oxygen/Nitrogen) this then produces an effect as if the diver is diving to a shallower depth and is referred to as Equivalent Narcotic Depth, in some cases Heliox (Helium & Oxygen) was also used)

High Pressure Nervous Syndrome is an interesting aspect of deep diving and used to be called Helium Jitters/Tremors as the accepted standard was that it was caused by breathing Helium mixtures under 150m. Some people hold this to be true and others claim that it has nothing to do with Helium but rather the pressure disrupting the flow of electric signals thru the nervous system.

What is interesting is that they found that if you used Trimix (Helium/Nitrogen/Oxygen) rather than Heliox (Helium/Oxygen) the onset happened later or not as severe. And teh slower your descent is the slower the onset of the symptoms.

Some Docs to Read:

Narcosis - Relatively simple document on Narcosis

Narcosis - "Narcosis is not unique to nitrogen; however, it can occur with many of the so-called

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