What does nitrogen narcosis mean?

Gas narcosis in scuba diving

Narcosis in scuba diving is the change in thinking and awareness, sensory and motor function and behaviour that occurs at depth.  Breathing gas at depth leads to narcosis, often noticed around 30m it can be an issue from around 20m and below. What does nitrogen narcosis mean?

Narcosis: “a state of stupor, drowsiness, or unconsciousness produced by drugs.”

Oxford English Dictionary

Narcosis is not well understood

Divers get narked due to breathing gases, such as nitrogen, at depth.  The deeper we dive, the more nitrogen (and other gas) is taken into the body.  There are a few different theories about why this changes our mental and physical abilities, but no one really knows.  What is agreed is that the gases affect the nervous system including the brain.  They seem to affect the nerve cells in a way that interferes with how messages are sent around in the brain and to other parts of the nervous system. 

Narcosis or nitrogen narcosis?

Knowing the correct term is important, because the words that we use show a lot about our knowledge. That is due to the history of our discovery of narcosis:

In English, it was first referred to as “nitrogen narcosis” because it was believed that the effect was due nitrogen in the body causing interference. The nitrogen is in the air we breathe and is usually harmless, but when we dive the air we breathe gets “thicker” due to the pressure of breathing under heavy water. People used to think that narcosis happened because of the build up of nitrogen because, unlike oxygen, this is a gas we do not use up in the body.

But then it was realised that nitrogen is not the only gas that can cause the narcotic effect. So the term became “inert gas narcosis” to cover lots of different gases that we do not use in the body. (Inert means the gas does not have a chemical effect on us).

Recently, it has become clear that even the oxygen has a role in narcosis. So the “inert” has now been dropped and “gas narcosis” is often used, partly to not be confused with the non-diving meaning of narcosis due to drug intoxication.

As divers, speaking to other divers about scuba diving, we can simply say “narcosis” or talk of being “narked”. Better still, use the hand signal.